The Origin of the Carolina Bays 9780231895996

Table of contents :
Acknowledgments
Contents
Tables
I. Introduction
II. Nature of the Bays
III. Scientific Studies of the Bays
IV. Hypotheses Based on Supposed Terrestrial Origin of the Bays
V. Hypothesis of Ancient Meteorite Scars
VI. Hypothesis of Recent Meteorite Scars
VII. Further Tests of the Meteoritic Hypothesis
VIII. Magnetic Tests of the Meteoritic Hypothesis
IX. The Hypothesis of Complex Origin
X. Competence of the Hypothesis of Complex Origin
XI. The Artesian Phase of the Hypothesis
XII. The Solution Phase of the Hypothesis
XIII. The Lacustrine Phase of the Hypothesis
XIV. The Aeolian Phase of the Hypothesis
XV. Possible Weaknesses of the Hypothesis
INDEX

Citation preview

The Origin of the CAROLINA NUMBER

IV O F

Columbia Geomorphic EDITED DOUGLAS

BAYS THE

Studies

BY

JOHNSON

F I G U R E I : Cotton Patch Bay near Myrtle Beach, S. C. Length of bay a little more than one mile. Arrow points N. Note that there is stronger curvature of NE side and greater accumulation of white sand about SE quadrant; also that parallel lighter and darker bands (beach ridges and swales) are cut off abruptly at border of bay. On left side of bay near its upper (NW) end a faint gray band (sandbar) continues curvature of outline across mouth of marshy embayment. Numerous "pimples" are trees. (From composite aerial photograph by Fairchild Aerial Surveys, Inc.)

The Origin of the CAROLINA

BAYS

By DOUGLAS JOHNSON PROFESSOR

O F GEOLOGY

COLUMBIA

NEW

IN

UNIVERSITY

YORK

COLUMBIA UNIVERSITY i 942

PRESS

COPYRIGHT C O L U M B I A

UNIVERSITY

1942 PRESS,

N E W

Y O R K

Foreign agents: O X F O R D U N I V E R S I T Y PRESS, Humphrey Milford, Amen House, London, E.C. 4, England, AN» B. I. Building, Nicol Road, Bombay, India. MANUFACTURED

IN

THF.

UNITED

STATES

OF

AMERICA

Acknowledgmen ts

W

H E N , as in the present case, the preparation of a book has extended over a number of years and help has been sought and received from many quarters, it becomes practically impossible to make proper acknowledgment to all those to whom credit is due. But this volume would be incomplete without some expression of gratitude to the administrative authorities of Columbia University who have so generously supported my geomorphic researches; to the Columbia University Press for making possible the Columbia Geomorphic Studies of which this volume forms a part; to my secretary Elizabeth Pinckney Torpats for invaluable aid throughout the preparation of the manuscript and publication of the book; to my former secretary Clara Rom Lougee for aid in connection with the early part of this study; to my present and former research assistants Margaret Cooper, J a n e Reger, Clementene Walker Wheeler, Anastasia Van Burkalow, Dorothy Wallace Irwin, and Dorothy Brauneck Vitaliano for innumerable tasks ably performed in connection with different stages of the investigation; T o Dr. Arthur Howard and Dr. Girard Wheeler for generous assistance in the field studies and for constructive criticisms which have much improved the manuscript; to Dr. William F. Prouty for valuable aid in the field and for many helpful suggestions throughout the whole progress of this study; to Professor Walter H. Bucher, Professor Frank J . Wright, Dr. C. Wythe Cooke, Dr. Frank A. Melton, Dr. M. King Hubbert, and Dr. Oscar E. Meinzer, for reading all or portions of the manuscript and contributing many valuable criticisms; to Professor J . Hoover Mackin for so critical a reading of the proof sheets that countless improvements in both the form and the substance of the text are due to his labors; T o officials of Fairchild Aerial Surveys, Incorporated, for many courtesies in connection with the study of aerial photographs in their collections; to officials of the U. S. Department of Agriculture for aid in connection with the study of soil survey reports, weather records, and aerial photographs; to officials of the Agricultural

vi

Acknowledgments

Adjustment Administration for opportunity to examine the large collection of aerial photographs of the Atlantic Coastal Plain on file in their laboratories; to officials of the U. S. Geological Survey for aid in connection with the study of geological and artesian water conditions in the Atlantic Coastal Plain and aerial photographs of the same region; to officials of the War Department for aid in connection with the study of craters formed by the impact of projectiles; and to the many public officials and private individuals who furnished needed data on shallow artesian wells in many parts of the Coastal Plain; T o Professor William H. Hobbs, Professor Charles P. Berkey, Professor Paul F. Kerr, Dr. Charles F. Brooks, Mr. Fletcher Watson, Jr., Professor Charles W. Brown, Dr. R . M. Harper, and Dr. Donald C. Barton for advice on specific problems arising in the course of the study; to Dr. Horace N. Coryell for determining the derivation of chert breccia and silicified shell rock from Tertiary foraminiferal limestone and shell marl; T o Mr. John M. P. Thatcher of New York City and the Ocean Forest Company of Myrtle Beach, South Carolina, for repeated use of the aerial mosaic of bays in the Myrtle Beach region; to Mr. Robert White, Mr. James Bryan, and Mr. Robert Montgomery of Myrtle Beach for providing guidance and facilities for examining the bays of that region; to Mr. E. R . Morris of Turbeville, South Carolina, for help in studying the bays of that district; to my sister Ellen Johnson Burt for assistance in the field; to Mr. J . E. Lockwood of the U. S. Weather Bureau at Charleston, South Carolina, for special data on weather conditions at that station; to Mr. Edgar Tobin of San Antonio, Texas, for aerial photographs of ''clamshell" lakes in that state; to Lieut. Col. Charles A. Walker, Office of the Chief of Ordnance, Washington, D.C., for data and photographs relating to the cratering action of shells; to Professor Donald M. Burmister and Mr. Bedrich Fruhauf of the Soil Mechanics Laboratory at Columbia University for advice on the behavior of artesian flow and groundwater flow through sand. Other acknowledgments will be found in the body of the text. DOUGLAS

Columbia University January, 1942

JOHNSON

Contents I . INTRODUCTION II.

N A T U R E OF T H E B A Y S

III.

S C I E N T I F I C STUDIES OF T H E B A Y S

IV.

H Y P O T H E S E S B A S E D ON SUPPOSED T E R R E S T R I A L

V. VI. VII. VIII. IX.

3 8 19 ORIGIN

OF T H E B A Y S

30

H Y P O T H E S I S OF A N C I E N T M E T E O R I T E SCARS

51

H Y P O T H E S I S OF R E C E N T M E T E O R I T E SCARS

62

F U R T H E R T E S T S OF M E T E O R I T I C H Y P O T H E S I S

97

M A G N E T I C T E S T S OF T H E M E T E O R I T I C H Y P O T H E S I S

130

T H E H Y P O T H E S I S OF C O M P L E X ORIGIN

151

X . C O M P E T E N C E OF T H E H Y P O T H E S I S OF C O M P L E X ORIGIN

195

X I . T H E A R T E S I A N P H A S E OF T H E H Y P O T H E S I S

221

X I I . T H E SOLUTION P H A S E OF T H E H Y P O T H E S I S

247

X I I I . T H E L A C U S T R I N E P H A S E OF T H E H Y P O T H E S I S

275

X I V . T H E A E O L I A N P H A S E OF T H E H Y P O T H E S I S

281

XV.

P O S S I B L E W E A K N E S S E S OF T H E H Y P O T H E S I S

318

INDEX

329

Illustrations i. Cotton Patch Bay near Myrtle Beach, S. C.

Frontispiece

x. Distribution of Principal Areas of Typical Oval Bays

9

3. Oval Bays 7 Miles S of Mullins, Marion Co., S. C., Showing Parallelism of Long Axes

13

4. South Barebone Bay near Myrtle Beach, S. C., Showing Double Sand Rim about SE Half

15

5. Watts Bay near Myrtle Beach, S. C., Showing Parts of Three Sand Rims about SE Quadrant

16

6. Closely Spaced Large and Small Bays near Silver, Clarendon Co., S. C.

17

7. Oval Bays Associated with Sandy Beach Ridges and Marshy Swales near Myrtle Beach

22

8. Stages in the Change of a Lagoon into a Chain of Lakes, According to Cooke's Hypothesis of Segmented Lagoons

37

9. Sand-Atoll and Group of Crescent-shaped Keys in Mosquito Lagoon, Fla.

42

0. Bays 2 Miles W of Lewis Ocean Bay, near Myrtle Beach

52

1. Well-developed Oval Bay with Irregular and Poorly Developed Bays near Myrtle Beach

53

2. Chain of Oval Bays Paralleling Sandy Beach Ridges and Marshy Swales in Myrtle Beach Area

57

3. Cluster of Bays Occupying Curving Band of Sand between Marshy Swales

59

4. Chain of Oval Bays Paralleling Beach Ridge and Topography in Myrtle Beach Area

76

Swale

5. SE Half of Big Bay 4 Miles SE of Wilmington, N. C., Showing Six or More Well-developed Sand Rims

84

6. T e n Mile Bay and Maidendown Bay near Smithboro, S. C., Bordered by Multiple Rims

86

7. Big Bay 4 Miles N of Pinewood, Sumter Co., S. C., Showing Multiple Rims

87

8. Typical Cross Profile of Sandy Rim from Inner Side Next Bay to Outer Side Bordering Plain 109

X

Illustrations

19. South Barebone Bay near Myrtle Beach, S. C., Showing Relations of Secondary Inner Rim as Interpreted by Prouty and by Johnson 111 20. Bays S of Makatoka, Brunswick Co., N. C., Showing Variations from Highly Irregular Form to More Perfect Ovals with Sand Rims 21. Sketch Map of Coastal Plain Showing the Probable Area of Bombardment by Meteorites According to Melton and Schriever 22. Comparison of Area of Abundant Meteorite Finds with Area of Abundant Bays 23. Magnetometer Observations around Singletary Lake, White Lake, and Large Bay NW from White Lake 24. Early Magnetic Survey and Later Magnetic Survey of Dial Bay Region 25. Lines of Flow of Water through Sand in Which a Lake Basin Has Been Excavated 26. Diagrams Showing Movements of Artesian Waters

115

122 124 132 135 157 160

27. Axial Trends of Basins in N and S Parts of Area of Abundant Oval Bays 167 28. Graphs Showing Regional Contrast in Axial Directions and Percent of Total Number of Oval Bays Measured Which Are Oriented in the Directions Indicated 169 29. Index Mosaic of Aerial Photographs Covering Part of Bladen Co., N. C. 172 30. Index Mosaic of Aerial Photographs Covering Part of Barnwell Co., S. C. 173 31. Effect of Artesian Flow Combined with Groundwater Flow

175

32. Salters Lake Bay, Bladen Co., N. C.

178

33. Suggs Mill Pond Bay, Bladen Co., N. C.

180

34. Complex Bay 7 Miles SW of Bishopville, Lee Co., S. C.

182

35. Open Bay W of Coward, Florence Co., S. C.

183

36. Ovoid Bays S of Elko, Barnwell Co., S. C.

184

37. Laboratory Demonstration of Behavior of Sand under Water 189 38. Hypothetical Distribution of Wind-drifted Sand Rims about Oval Bay with Dominant Winds from NW, W, and SW 206

Illustrations

xi

39. Elliptical and Ovoid Bays near Mullins, Marion Co., S. C., Showing Outer and Inner Rims Similarly Spaced in Adjacent Bays 210 40. Elliptical and Ovoid Bays 5 Miles SE of Marion, Marion Co., S. C., Showing Outer and Inner Rims Similarly Spaced in Neighboring Bays 212 41. Elliptical Bays Intimately Associated with Irregular Depressions Resembling Sinks 4I/2 Miles E of Center of Wilmington, N. C. 257 42. Blackville Bay, Barnwell Co., S. C. 43. SE End of Jones Lake, Bladen Co., N. C., Showing Rim of White Sand Bordering the SE Quadrant of Its Basin 44. Shallow Circular and Oval Basins E of Sarasota, Fla. 45. Circular or Oval Lakes in Coastal Marshes near Charleston, S. C.

265

46. Clamshell Lake in Vidauri District, Texas

323

276 320 322

Tables 1. Average Axial Trends of Oval Bays in Northern Part of Area 165 2. Average Axial Trends of Oval Bays in Southern Part of Area 166 3. Velocities and Duration of Winds from the Sectors NW-W-SW and NE-E-SE 292 4. Velocities and Duration of Winds from the Sectors W-SW-S and N-NE-E 294 5. Precipitation Records for the Four Driest Months at Stations in the Bay Country, Compared with Wind Records at the Nearest Stations for Which Satisfactory Data Are Available 297 6. Precipitation Records for the Summer Rainy Season at Stations in the Bay Country, Compared with Wind Records at the Nearest Stations for Which Satisfactory Data are Available 306

The Origin of the CAROLINA

BAYS

I Introduction

T

HE C U R I O U S oval craters of the Carolina coast have long been known to inhabitants of the Coastal Plain. T h e y called the marshy depressions "bays," but did not differentiate them from marshes of highly irregular form. Even geologists and soil surveyors gave them no special attention, until in 1895 Dr. L. C . Glenn observed that oval bays near Darlington, South Carolina, exhibited peculiarities which called for explanation, and published a brief account of them. This first discussion of the origin of the Carolina bays attracted little attention. T h e n three things happened. First, aerial photographs of various portions of the Atlantic Coastal Plain were made as a basis for the disposal of timber and timber lands, for military studies, and for other uses. Second, these photographs were examined by Dr. F. A . Melton and Dr. William Schriever of the University of Oklahoma, who discovered that they revealed the existence of hundreds of bays of beautifully oval outline, bordered by rims of sand usually heaped up most abundantly near the southeastern ends of the depressions, the long axes of the ovals being remarkably parallel to each other and oriented northwest-southeast. Third, after study of the photographs and examinations on the ground Melton and Schriever published a paper in 1933 in which they attributed the origin of the oval bays not to terrestrial causes but to bombardment of our planet by a great shower of meteorites, possibly forming the nucleus of a comet which collided with the earth, the direction of approach having been from the northwest. Immediately popular curiosity was aroused and world-wide publicity was given to the "meteorite scars." Aerial photographs of typical oval bays appeared in the daily press, in magazines, and later in books. Scientific curiosity was equally stimulated, and "the origin of the Carolina bays" began to be debated in scientific meetings and in technical magazines. T h e remarkable craters of

4

Introduction

the Carolina coast had at last been brought to popular and scientific attention, and efforts to solve the problem of their origin were in progress. A review of studies thus far made appears in an early chapter of this volume. Perusal of that review should convince the reader that no apology is needed for a further contribution to the subject. Competent opinion as to the origin of the curious oval craters or "bays" is still widely divergent. It must be confessed that tens or hundreds of thousands of oval craterlike depressions, many of them remarkably symmetrical, oriented in the same general direction, and bordered by rims of sand which may be multiple in places, present a problem of peculiar difficulty. N o matter what hypothesis of origin one prefers, he must admit that the features observed are novel and perplexing. T h e y confront the geologist with a mystery not easily solved. In more than forty years of geological study the writer has encountered no problem so difficult, unless it be that of submarine canyons. T h e Carolina craters represent a newly discovered type of landform and may require novel hypotheses to account for their origin. There are additional reasons for a more critical scrutiny of the problem of bay origin than has yet been attempted. Despite the fact that the forms in question are novel, having been brought prominently to public notice only recently, they are already known to occur in great numbers and to cover an enormous area. More than one authority has supported the meteoritic origin of these oval bays, and at least one treatise' on meteors and meteorites has as its frontispiece a photograph of several of the Carolina bays, with a caption definitely informing the reader that it is a picture of "meteor scars." A recent text on astronomy 2 discusses briefly Melton and Schriever's account of the supposed meteorite scars under the introductory statement: "Other meteor craters are being recognized or at least suspected." 3 It has been pointed out that one of the greatest known concentrations of meteorite falls in the world is found in the southeastern United States, covering an H. H. Nininger. Our Stone-pelted Planet. 237 pp., Boston and New York, 1933. Robert H. Baker. An Introduction to Astronomy. 31s pp., New York, 1935. 3 Successive editions of this text erroneously attribute to Melton and Schriever the excellent published aerial photographs of the bays. 1

2

Introduction

5

area so vast that it stretches from Virginia southward into northern Georgia and Alabama and westward over much of Tennessee and Kentucky. T h e meteoritic interpretation of the bays raises problems affecting a large and important section of the United States. Discussion of the bays necessarily carries us even farther afield. On the sandy Atlantic Coastal Plain we have to deal with oval basins which show a peculiar and systematically recurrent asymmetry of form (to be discussed later), remarkable uniformity of orientation over certain areas, and frequent bars or ridges of sand developed at their southeastern ends. On the sandy Gulf Coastal Plain of Texas are found groups of lake basins of somewhat different shape, which likewise show a peculiar and systematically recurrent asymmetry of form, remarkable uniformity of orientation, and at least occasional bars or ridges of sand developed at their southern ends. By some authorities both the shape and orientation of the two systems of basins have been attributed to winds operating upon lakes, and the accumulations of sandbars in both systems have been given a common explanation. Lakes and lagoons in still other regions are believed by some to throw light upon the origin of the Carolina bays. In short, we find ourselves face to face with a problem which is both novel and perplexing, of great popular and scientific interest, affecting vast expanses of territory, and inviting widely different interpretations. If conflicting hypotheses as to the origin of the oval bays are still entertained by different students of the problem, it may be in part because most of the studies published have been based on inadequate factual data. In the course of his field investigations the writer personally examined 127 bays with sufficient care to record some of their characteristic features, and saw many more. These bays were widely distributed, occurring in Burke and Screven Counties, Georgia; in Barnwell, Hampton, Allendale, Orangeburg, Bamberg, Dorchester, Sumter, Clarendon, Williamsburg, Florence, Marion, Horry, Darlington, and Marlboro Counties, South Carolina; and in Bladen County, North Carolina. All topographic maps of the Atlantic and Gulf Coastal Plain and all soil maps of the Carolinas and Georgia have been examined, and those showing bays have been studied in detail. In addition to the

6

Introduction

aerial photographic mosaic of bays near Myrtle Beach in Horry County, South Carolina, the writer has, thanks to the courtesy of the United States Geological Survey, the Agricultural Adjustment Administration, and the Fairchild Aerial Surveys, Incorporated, examined other mosaics and large collections of individual aerial photographs showing bays in various parts of the Coastal Plain. In these several ways it is believed that a comprehensive idea of the essential characteristics of the bays has been obtained. Another cause of present divergent views may well be that the process of testing different hypotheses has not been pushed far enough to eliminate those which are invalid. No one has as yet invented an explanation which will fully account for all of the facts observed. If by analyzing and testing the various hypotheses already offered we succeed in eliminating all hypotheses but one, and if that one is competent to explain all facts which the others sought to explain and can in addition explain new facts not previously brought to light, we may hope that solution of the problem of the bays is in sight. Otherwise, new hypotheses must be invented and tested until one competent to explain all the facts is found. In the following chapters the different explanations offered to account for the craterlike bays will be analyzed and tested in an effort to discover which hypotheses are clearly so inadequate that they may safely be eliminated from further consideration, and which hypotheses have sufficient merit to deserve further study. T h e order of treatment followed will be one determined by convenience rather than by the historical order in which the explanations were advanced. Most attention will be paid to those hypotheses which for one reason or another seem to deserve careful consideration. It is not deemed necessary to devote much space to hypotheses so clearly defective that today no one regards them as worthy of serious attention. THE

SETTING OF THE

PROBLEM

T h e ancient crystalline rocks of the Appalachian Mountains are bordered on the east and south by a relatively flat, sandy plain forming the low Atlantic and Gulf coasts. In the Carolinas this Coastal Plain attains a breadth which in places exceeds 125 miles. T h e waters of the Atlantic once covered the area of the present

Introduction

7

plain, and as the land emerged, the gradually retreating sea, through the action of waves and currents, left shoreline features upon the seabottom deposits which can still be recognized in many places. In other places rain wash or stream erosion has destroyed such features or river or wind-blown deposits have buried them. Deposits making u p the Coastal Plain are for the most part not yet compacted and hardened into solid rock; but certain layers of lime mud have been moderately hardened into marl or firmly consolidated into limestone, shell beds have been solidified into shell rock or coquina, and some layers of sand have been cemented by iron or other material to give fairly resistant sandstone. T h e ancient crystalline rocks, which in the eastern part of the Carolinas underlie the sedimentary deposits, come to the surface farther northwest in that part of the Appalachians called the Piedmont Belt. When fresh the crystalline rocks are very hard and resistant; but where they are deeply decayed (and this is the case over much of the Piedmont) the surface layer of decomposition products, sometimes a hundred feet or more in thickness, may be little if any more consolidated than are the Coastal Plain deposits. Surface soils of much of the Coastal Plain are sandy, and the loose sands are often extensively blown about by the wind. On the other hand, the surface soils of the Piedmont are usually more compact and clayey because of the presence of sticky decomposition products derived from the decay of crystalline rocks. Finally, the surface of the Coastal Plain, especially that part nearest the sea and hence most recently exposed above water and least dissected by stream erosion, is apt to be much flatter than the surface of the Piedmont. But the inner margin of the Coastal Plain is often as badly dissected as the adjoining portions of the Piedmont, so that a traveler passing from one province to the other would notice little change in the hill and valley topography, although he might observe contrasts in the soil and rock. Such is the geological setting of the problem to be discussed in the pages which follow. T h e curious Carolina bays are found on the sandy surface of the Atlantic Coastal Plain. In our effort to solve the problem of their origin we shall find that the geologic features emphasized above provide clues of significant value.

II Nature of the Bays

T

H R O U G H O U T the South Carolina portion of the Coastal Plain (Fig. 2) and extending into North Carolina and Georgia are low areas of flat and frequently more or less swampy ground, often highly irregular in outline, locally called "bays," "pocosons," or "swamps." T h e term bay is perhaps most widely used and may owe its origin to the fact that the bay tree is of common occurrence in the swampy depressions. T h e soil of the drier depressions, as determined by soil surveys of the Department of Agriculture, is apt to be a fine loam, dark gray to black in color, high in organic content, and frequently containing beds of partially decayed vegetation or peat. Beneath the loam, silty to sandy clay frequently is found; elsewhere a purer sand occurs, and sometimes a light incoherent sand locally called "quicksand." Beneath swamps and peat bogs, silts and clays are commonly encountered, then sands of the Coastal Plain series. Many of the bays have a remarkably oval outline (Fig. 1) and are shallow craterlike depressions bordered in whole or in part by rims of fairly coarse white or buff-colored sand. It is these curious oval craters which have confronted geologists with a problem peculiarly difficult to solve. Many of the craters are imperfectly drained and in wet weather may contain ponds or shallow lakes. Some marshy bays, although containing no open water, are named "ponds" or "lakes" on topographic and soil maps. Even when covered with dense vegetation the bays normally have stagnant water close below the surface, with the result that efforts to drain, clear, and cultivate them have often been unsuccessful. Many of the craters remain today, after the best timber has been removed, oval areas of dense young forest or of open forest in which scattered trees rise above a dense undergrowth. Shortleaf pine is abundant, while sweet gum, black gum, juniper, bay, water oak, and willow oak are found. Where water is abundant, cypress

Nature of the Bays

9

occurs. T h e thick undergrowth includes azalea, gallberry, huckleberry, and other shrubs, as well as numerous vines and ferns. T h e central part of a forested bay is often a pond or lake of open water.

F I G U R E 2 : Distribution of principal areas of typical oval bays so far as known at the time of this study.

Other bays contain lakes surrounded by open marsh or grassland; others are occupied wholly by marsh grasses; while some, especially small ones, may be dry and contain a central area of dark carbonaceous soil cultivated by the farmer. Where much water is present or dense undergrowth covers a peat bog, it is difficult to traverse the bays. From the slightly higher and drier rims of coarse sand, which often border the bays and which commonly support a growth of longleaf pine, one may look out over a dreary stretch of flat swampy lowland or into a dense swampy forest. But one usually hunts in vain for a path across either. As a rule, trails and roads make long detours around the sandy margins rather than traverse the treacherous surfaces of the depressions.

IO

Nature of the Bays D I S T R I B U T I O N OF O V A L B A Y S

T h e oval bays are distributed over an area of at least 25,000 square miles, typical examples being most abundant, so far as is now known, in a belt of territory (Fig. 2) roughly eighty miles wide extending from the southeastern portion of North Carolina across southeastern South Carolina into northeastern Georgia. Soil maps and aerial photographs show occasional areas of oval depressions similar to the Carolina bays as far southwest as southwestern Georgia. But these more distant ovals are often less symmetrical and more variable in orientation and appear to have sandy rims less well developed than is the case in the Carolinas. Nevertheless, they are often called "bays" locally, and soil reports sometimes mention the existence of sandy rims surrounding them. Some writers have extended the bay area to include northeastern North Carolina and southeastern Virginia and have estimated that the bays cover a territory at least 40,000 square miles in extent. Such topographic maps as exist for the two areas last mentioned do not show undoubted oval bays. It must be remembered, however, that most maps for these northern areas are old and highly generalized. T h e soil maps for these same areas fail to reveal undoubted indications of bay development. But here again we must remember that many soil maps fail to show bays even where they are abundant. Aerial photographs, the best source of information about bay distribution, show what appear to be oval bays in scattered localities in northeastern North Carolina. It is altogether probable that later information will extend the limits of the typical "bay country" outlined above, but, until satisfactory evidence is available, the writer prefers to adhere to the more conservative limits shown in Figure 2. These do not include certain areas near the inner edge of the Coastal Plain which exhibit depressions having rounded or irregular rather than oval outlines. O n purely theoretical grounds some students 1 of the bay problem have extended the limits of bay distribution to include a vast oval extending far northwestward into the Appalachian 1 F. A. Melton and William Schriever. T h e Carolina "Bays"—Are They Meteorite Scars? Jour. Geol., 41:52-66, 1933. See p. 59. Fig. 7-

Nature of the Bays

11

Mountains and southeastward into the Atlantic Ocean. T h e writer knows of no facts indicating that the bays ever had such wide distribution. SIZE OF

BAYS

T h e oval craters or bays vary in size from a few hundred feet in greatest diameter to examples three or four miles long by two or more miles wide. T h e proportion of length to breadth is quite variable, both large and small bays exhibiting such variability. T h e large bay (Fig. 17) north of Pinewood in Sumter County, South Carolina, is 3I/6 miles long by 214 broad, whereas another large example, Hilson Bay in Marlboro County of the same state, is 4 miles long, but little more than 1 i/2 miles in breadth. S H A P E OF

BAYS

Outlines of the so-called "oval bays" or "oval craters" are of two general types. In one type the outline is more or less elliptical but, as will later appear, with one side usually more strongly curved than the other. For the sake of simplicity, bays or craters having this form will be referred to as elliptical bays or elliptical craters, despite the departure from ellipticity just mentioned. In the second type the outline is distinctly more egg-shaped, with one end somewhat more pointed than the other. Since the term "oval" is defined by some authorities as "roughly elliptical," while the term "ellipse" is defined as "an oval," it is not appropriate to specify the egg-shaped bays by the term "oval." T h e term "ovoid," on the other hand, is usually defined simply as "eggshaped." For this reason bays or craters having outlines broadly rounded at one end and somewhat more pointed at the other will be called ovoid bays or ovoid craters. A general term is needed to distinguish all bays or craters having regular outlines, whether elliptical or ovoid, from those of highly irregular shape. T h e term "regular" is open to the objection that it might imply "conforming to an established type," which in a sense is also true of bays or craters having irregular outlines. "Symmetrical" is objectionable when applied to forms having the systematic bilateral asymmetry described above. T h e expressions

Nature of the Bays "oval bays" and "oval craters" arc already widely in use as applied to both elliptical and ovoid types, previous writers not having distinguished between the two. The usage conforms to authoritative definitions of the term "oval," which is applied equally to elliptical and ovoid forms. Therefore, despite the fact that "oval" and "ovoid" come from the same Latin root and closely resemble each other in their English forms, it seems wise to follow established usage and designate all bays or craters of regular or more or less symmetrical outline as oval bays or oval craters. It is believed that the meaning of the text will be sufficiently clear in the discussions which follow and that readers will not encounter any practical difficulty in following the distinctions proposed. Bays of irregular outline will be referred to simply as irregular bays. For obvious reasons the irregular bays have never been called craters. Some writers, believing that the regular and irregular forms had distinctly different origins, have proposed that the term "bays" be restricted to the regular or oval type often called craters. The proposal is objectionable, both as prejudging the question of origin and as being in conflict with widespread popular usage. Under the terminology here suggested all "bays" are divided into two major classes: (I) oval bays and (II) irregular bays. Bays of Group I are often called "craters"; those of Group II are not so called. The oval bays or craters are further subdivided into (a) elliptical bays and (b) ovoid bays. Unless otherwise specified, in the pages which follow all discussions of bays refer to oval bays (either elliptical or ovoid, or both), and not to irregular bays. PARALLELISM

OF

BAYS

The most striking characteristic of the oval bays, aside from their peculiar form, is the degree of parallelism in orientation of their longer axes (Fig. 3). These most frequently trend somewhere between south and east, and so uniform is the orientation over certain areas that some investigators2 have determined the mean direction of major axes to be S 46° E, with an average of the deviations from the mean amounting to 3.08°. But when one extends his observations throughout the Coastal Plain, it becomes evident 'Ibid., p. 55.

F I G U R E 3 : Oval bays 7 miles S of Mullins, Marion Co., S.C., showing parallelism of long axes. N is at top, and largest bay is a little more than a mile long. White angular patches are cultivated fields. Three of bays apparently drain N W into a depressed wooded swale, while to N E what appear to be alternating sandy beach ridges (light bands) and wooded swales (dark bands) curve northeastward and then more nearly eastward beyond limits of this picture. (Fairchild Aerial Surveys, Inc.)

14

Nature of the Bays

that the parallelism of axial trends is far less perfect than one might infer from the figures just cited. This matter will be fully treated in a later chapter. Suffice it to say here that while there are wide deviations from the mean direction, the vast majority of the bays trend from S io° E t o S 5 5 ° E. SAND R I M S

OF

BAYS

On aerial photographs, ridgelike rims of sand partially or completely surrounding the oval depressions are very conspicuous features. This is because the dry sand forming the rims is nearly white or pale buff in color, and often the scattered pine trees and other vegetation do not conceal it as effectively as the dense cover of underbrush conceals the moist dark sandy loam of the bays and surrounding portions of the plain. A typical photograph (Fig. 4) of one of the bays taken from the air shows a dark gray oval area bordered by a white or light-gray rim, the whole lying on a mottled or banded plain of alternate lighter and darker gray. T h e sandy rim is apt to be broader and higher near the southeastern end of the oval; but it may completely surround a basin, may be lacking at any point, or may be entirely absent. T h e rims usually rise only a few feet (from 2 or 3 feet up to 5 or 6 feet) above the bay and the surrounding plain; but the writer has found a number of bays having rims 10 to 15 feet high. In width the rims vary from less than one hundred up to several hundred feet, rarely attaining a thousand feet or more. Frequently the rim is double or triple (Figs. 4 and 5) for a part or all of the distance, the extra ridges of sand in such cases being nearly or quite concentric with the main ridge. Occasionally (Figs. 15, 17, 33) the concentric ridges are present in larger numbers. Often the bays mutually intersect each other, and occasionally one or more small bays are found within a large one. DEPTH

OF

BAYS

The floors of the craterlike bays lie anywhere from 1 or 2 feet to as much as 30 or 40 feet below the surface of the surrounding plain. These figures do not necessarily represent the full depth qf the craters, since many of them contain accumulations of soil and vegetable matter. Well records and borings with a soil auger

4: South Barebone Bay near Myrtle Beach, S.C., showing double sand rim about SE half. Arrow points N, and bay is about s/4 mile long. Note stronger curvature of N E side, from near center of which an outlet channel apparently connects with small meandering valley to NE. Other outlet or inlet channels occur farther NW. White patch at NW end of bay (top of picture) is migrating dune sand. Light gray "pimples" are trees, and black specks are their shadows. (Fairchild Aerial Surveys, Inc.) FIGURE

have led different observers 3 to conclude that in bays of average size the craterlike depressions may have total depths below the general plain level of from 15 to 50 feet, the filling consisting of dark clayey carbonaceous sand or silt, sandy or clayey loam, and peat. ASSOCIATION

OF

BAYS

WITH

BEACH

RIDGES

Where the plain on which the oval bays are found is composed of alternate bands of lighter and darker gray (Fig. 7), examination on the ground shows that the banding is due to an alternation of sandy ridges and silty swales or linear depressions, the latter often marshy or boggy. T h e ridges are interpreted as beach ridges formed 3

L. C. Glenn. Some Notes on Darlington (S.C.) " B a y s . " Science, 2:472-475, 1H95. F. A. Melton and William Schriever. T h e Carolina " B a y s " — A r e T h e y Meteorite Scars? J o u r . Geol., 41:52-66, 1933. See p. 57.

5: Watts Bay near Myrtle Beach, S.C., showing parts of three sand rims about SE quadrant, where quantity of sand is greatest. Arrow points N, and larger bay is about y 4 mile long. Note outlet channel to N E and poorly developed pear-shaped bay in lower right corner of picture. "Pimples" are trees, angular white patches are cultivated fields, other white areas wind-drifted sand. (Fairchild Aerial Surveys, Inc.) FIGURE

Nature of the Bays

17

by the sea when the shoreline was farther inland than today, the swales representing the intervals between successive displacements of the shoreline. T h i s intimate association of some of the bays with beach ridges of a former seashore is, as we shall see, highly significant. ABUNDANCE

OF

BAYS

From field investigations and from inspection of maps and photographs the present writer has gained a strong conviction

FIGURE 6 : Closely spaced large and small bays near Silver, Clarendon Co., S.C., many largely or wholly obscured by cultivation of fields (light more or less rectangular areas). N is at top. Largest bay, with NW half obscured by cultivation, and in part beyond limit of picture, is nearly miles wide. (Fairchild Aerial Surveys, Inc.)

that the number of bays dotting the Coastal Plain is enormously larger than previous investigators have supposed. Field examinations reveal the presence of scores of such bays where a topographic map shows few or none. Aerial photographs of regions topographically mapped reveal hundreds where the map may show two or three, or at most eight or ten. Such aerial photographs (Fig. 6)

18

Nature of the Bays

demonstrate that considerable areas of the Coastal Plain are fairly peppered with countless ovals, close-set, overlapping, or intersecting, many of them shallow and dry and fast disappearing as towns are built over them or as cultivation of fields effaces the distinction between loamy center and sandy rim. Were the present writer to guess at the probable number of the oval bays, he would place the figure in the hundreds of thousands. T h e enormous number of these curious basins must duly be considered when attempting to solve the problem of their origin.

Ill Scientific Studies of the Bays A P P A R E N T L Y the first scientific account of the oval bays I % was that published by Dr. L. C. Glenn 1 more than forty1 m. five years ago. T h i s early study contained a very clear and accurate description of the characteristic features of oval bays found near Darlington, South Carolina, some seventy miles inland from the coastline. Glenn, keeping in mind the fact that the sea had covered the area of the Coastal Plain in comparatively recent geologic time, sought an explanation of the craterlike depressions in processes associated with the eastward retreat of the sea and its shore. He was commendably cautious in offering hypotheses but suggested that the peculiar oval basins might represent former stream valleys flooded by a readvance of the sea to give drowned valleys or bays, which latter were then blocked on the southeast with bay-mouth bars of sand built by the ocean waves. As an alternative solution he suggested the possibility that the depressions represented initial inequalities of the old seabottom revealed to view when the seabottom deposits were uplifted to form dry land. T h e question of the bays was not again brought to public notice until nearly forty years later, when Drs. Melton and Schriever 2 presented before the Cambridge meeting of the Geological Society of America, 1932, the results of their studies of aerial photographs and field examinations of oval depressions found between Conway and Myrtle Beach, South Carolina. In papers published soon thereafter they presented unusually full descriptions of the bays and noted for the first time many peculiarities L. C. Glenn. Some Notes on Darlington (S.C.) "Bays." Science, 2:472-475, 1895F. A. Melton and W i l l i a m Schriever. Meteorite Scars in the Carolinas (Abstract). Bull. Geol. Soc. Amer., 44:94, 1933. T h e Carolina " B a y s " — A r e T h e y Meteorite Scars? Jour. Geol., 41:52-66, 1933. F. A. Melton. T h e Origin of the Carolina "Bays." Discovery, 15:151-154, 1934. 1

2

20

Scientific Studies of Bays

of the bays which require explanation. After considering the hypotheses advanced by Glenn to account for the origin of the remarkable craterlike depressions, and a number of other possible explanations, they concluded that the bays could not be attributed to ordinary geological processes. They then set forth the meteoritic hypothesis of origin which immediately attracted world-wide attention. The details of this hypothesis will be discussed in subsequent chapters. Professor C. C. Wylie 3 in 1933 published two papers in which he appears to accept the meteoritic hypothesis of bay origin and suggests that the Carolina bays are oval rather than circular because the meteorites struck the earth at a low angle and penetrated far during the process of explosion. He accepts the view that the concentration of iron meteorites in the Appalachian Mountains is the result of a single meteorite shower, although he admits that "such a shower would be very different from any fall of meteorites which has been observed." C. Wythe Cooke4 later challenged the interpretation of Melton and Schriever and offered a new explanation. In Cooke's opinion the elliptical sand ridges are in part bars and beaches built up in shallow lagoons during a higher stand of the sea and in part crescent-shaped keys formed in shallow lakes. T h e lagoons, according to Cooke, were transformed into chains of oval lakes through the action of waves and currents set in motion by the wind. T h e observed parallelism of the oval forms is by Cooke ascribed to "a constancy in the direction of the wind while they were being shaped." Replying to Cooke, Melton 5 criticized the hypothesis of segmented lagoons and crescent-shaped keys and further defended the meteoritic hypothesis; but at the same time he admitted the possibility of a third interpretation: that the oval bays were the product of submarine scour. As none of the explanations offered seemed adequate to account 3 C . C. Wylie. On the Formation of Meteoric Craters. Pop. Astron., 4 1 : 2 1 1 - 2 1 4 , 1933. Iron Meteorites and the Carolina "Bays." Pop. Astron., 41:410-412, 1933. 4 C. Wythe Cooke. Discussion of the Origin of the Supposed Meteorite Scars of South Carolina. Jour. Geol., 42:88-96, 1934. 5 F. A. Melton. T h e Origin of the Supposed Meteorite Scars: Reply. Jour. Geol., 42:97-104, 1934.

Scientific Studies of Bays

21

for the origin of the forms described, the present writer visited the Conway-Myrtle Beach area of South Carolina in March, 1934, and examined a number of the more typical bays of varying size, including some with double and triple rims and others with mutually intersecting rims. Among the craterlike depressions studied at this time were the great Lewis Ocean Bay and associated forms (Fig. 7); the group including South Barebone Bay (Fig. 4), North Barebone Bay, and Watts Bay (Fig. 5), all shown in the northeast corner of Figure 7; the large and almost perfect Cotton Patch Bay (Figs. 1 and 7); and several smaller unnamed bays associated with the preceding groups. On this visit the writer profited not only by the excellent descriptions of Melton and Schriever and the criticisms of Cooke, but also by the generous cooperation of Mr. Robert White of the Ocean Forest Country Club and of Mr. James Bryan and Mr. Robert Montgomery of Myrtle Beach, who placed at his disposal their intimate knowledge of the country as well as material facilities for traversing it. Mr. Montgomery acted as guide on a long journey over the difficult woodland roads which afford access to the bays and beach ridges of this district. Mr. John M. P. Thatcher of New York City had previously made available the original copy of a large aerial photographic map of the region (partly shown in Fig. 7) prepared for the disposal of timber and timber lands. Thanks to the earlier work of Melton, Schriever, and Cooke and to some advance consideration of possibilities not mentioned by them, the present writer entered upon his field inspection of the oval bays with a number of alternative hypotheses in mind and with some idea of the tests which might enable one to discriminate between hypotheses which were entitled to further study and those which were manifestly invalid. As will appear in subsequent pages, these tests involved primarily the relation of the oval sand rims to the associated beach ridges and swales of the Myrtle Beach area, the mutual relations of double rims and intersecting rims, the loci of major sand accumulation, and the cross profiles of the rims. Field observation suggested one or two additional possibilities, which were duly explored. The results of this field study led the writer to advance the

Scientific Studies of Bays

23

hypothesis that the Carolina bays of the Myrtle Beach area represent earlier freshwater lakes formed on a beach plain approximately at the present level of the bays. According to this hypothesis the symmetrical form of the more perfect bays resulted f r o m exceptionally complete development of the normal mature lake shoreline in soft unconsolidated sands of uniform texture; elongation of the lake basins in a northwest-southeast direction and the tendency for sand to accumulate in maximum quantities about the southeastern shores of the lakes were attributed to winds of maximum velocity coming from the southeast and setting up an undertow along the shallow lake bottoms directed toward the southeast; the rims of sand were regarded as dune ridges due to the transportation by variable winds of dry sand exposed along the shores of the lakes. T h i s hypothesis was presented before the National Academy of Sciences at its April meeting in 1934. 0 Later that same year Dr. Erwin J . Raisz 7 published a paper in which he showed that lake basins in glacial outwash plains left by melting ice tend to acquire rounded or oval forms as a result of the normal development of the shoreline under wave attack. Dr. Raisz's paper was written without knowledge that the present writer had been applying the principles of shoreline development to the interpretation of the oval bays of Carolina, and he independently suggested that the observed rounding of lakes by wave 8 Douglas Johnson. Supposed Meteorite Scars of South Carolina. Nat. Acad. Sci., Abstracts of Papers Presented at the Scientific Sessions, April 23 and 24, 1931. See p. 30. See also Science, 79:461, 1934. 7 Erwin J . Raisz. Rounded Lakes and Lagoons of the Coastal Plains of Massachusetts. J o u r . Geol., 42:839-848, 1934.

F I G U R E 7 (on facing page): Oval bays associated with sandy beach ridges (parallel light bands) and marshy swales (dark bands) near Myrtle Beach, Horry Co., S.C. Arrow points N, and perfect bay (Cotton Patch Bay) near W-central border is slightly more than one mile long. Largest bay of imperfect outline near E-central border is Lewis Ocean Bay. Larger pictures of some of bays shown here are in Figures 1, 4, 5, 10, 12, 13, 14. Note that certain bays occur in elongated groups or chains trending parallel with beach ridges and swales, while long axes of individual bays trend approximately NW-SE. (Part of mosaic by Fairchild Aerial Surveys, Inc., for Ocean Forest Company, Myrtle Beach, S.C.)

24

Scientific Studies of Bays

action might have bearing on the origin of the supposed meteorite scars. A few months after the appearance of Raisz's paper Dr. William F. Prouty 8 published the results of magnetometer surveys of portions of the Carolina Coastal Plain where oval bays and elliptical lake basins are found. Because "most of the elliptical bays and elliptical lake basins [in the surveyed sections] show a decided high magnetic area to the southeast of the bay," Prouty attributed the magnetic highs to "buried meteoric bodies" and concluded that his results supported the meteoritic hypothesis of origin as propounded by Melton and Schriever. At the December, 1935, meeting of the Geological Society of America three papers dealing with the curious Carolina bays were presented orally or by title. Of these three papers, one by Dr. Prouty 9 (read by title) and one by Dr. Gerald R . MacCarthy 10 (presented orally) set forth additional arguments in favor of the meteoritic hypothesis of origin. The third paper, by the present writer 1 1 (read by title), questioned the sufficiency of evidence thus far secured by magnetometer surveys, stressed the difficulties confronting the meteoritic hypothesis, and concluded that the evidence thus far available accorded best with the interpretation that the oval bays are former freshwater lakes rounded by normal wave action and elongated in the direction of maximum wind velocity. In January, 1936, Mr. Fletcher Watson, Jr., 1 2 published an account of the features characteristic of undoubted meteorite craters and discussed the mechanics of their formation. According to Watson, true meteor craters are normally circular, not oval, 8

William F. Prouty. "Carolina Bays" and Elliptical Lake Basins. Jour. Geol., 43:200-207, 1935. 9 William F. Prouty. Further Evidence in Regard to the Origin of "Carolina Bays" and Elliptical Lake Basins. Geol. Soc. Amer., Preliminary List of Titles and Abstracts of Papers to Be Offered at the 48th Annual Meeting, December, 1935, p. 25, 1935. See also Geol. Soc. Amer., Proc. for 1935, 96-97, 1936. 10 Gerald R . MacCarthy. " T h e Carolina Bays." Geol. Soc. Amer., Preliminary List of Titles and Abstracts of Papers to Be Offered at the 48th Annual Meeting, December, 1935, p. 21, 1935- See also Geol. Soc. Amer., Proc. for 1935, 90-91, 1936. 11 Douglas Johnson. Origin of the Carolina Bays. Geol. Soc. Amer., Preliminary List of Titles and Abstracts of Papers to Be Offered at the 48th Annual Meeting, December, 1935, p. 16, 1935. See also Geol. Soc. Amer., Proc. for 1935, p. 84, 1936. 12 Fletcher Watson, J r . Meteor Craters. Pop. Astron., 44:2-17, 1936.

Scientific Studies of Bays

25

even when the angle of impact is very oblique. This author presented other objections to the meteoritic hypothesis of bay origin and concluded that the Carolina bays could not have been formed in the manner suggested by Melton and Schriever. In March, 1936, the present writer again had opportunity to study certain of the bays of the Coastal Plain. On this occasion he profited by the generous cooperation of Professor William F. Prouty of the University of North Carolina, who provided in adj vance certain important maps not available to the writer and sketches of other areas which greatly facilitated field work. Best of all, he conducted the writer on a field excursion to several bays in North Carolina which had been the object of special study by Professor Prouty and his associates. As a result of these 1936 studies the writer presented before the American Philosophical Society in April of that year a more complete working hypothesis of the origin of the oval bays than it had been possible to offer in 1934. The earlier views that the bays represent freshwater lake basins and the oval rims accumulations of wind-blown sand were confirmed. In addition, it was possible to present for the first time much evidence tending to show that the lake basins were in many places intimately associated with sinkholes and other solution phenomena over large areas and that in certain localities every gradation from typical sinkhole to typical oval bay could be found. It was accordingly suggested that the Carolina bays might represent in part a peculiar type of karst phenomenon, in which removal of underlying soluble beds permitted slumping of overlying sands or loam to give depressions of fairly symmetrical form in some localities, while uprising waters passing through the sandy cover elsewhere would remove finer material and thus contribute to the deepening of certain of the lake basins. Wave action along the lake shores would perfect the oval form, the elongation of which in a northwestsoutheast direction might be due either to wind control or to the direction of groundwater movement down the slope of the Coastal Plain beds. This "complex hypothesis" (solution-lacustrine-aeolian hypothesis) of bay origin was first published in outline in July,

26

Scientific Studies of Bays 13

1936. Early in 1937 a similar outline 14 of this hypothesis was published in France. While the two papers last referred to were still in press, Cooke 15 published his valuable report on the "Geology of the Coastal Plain of South Carolina," in which he briefly refers to the Carolina bays, states that there is little factual evidence to support the meteoritic hypothesis of bay origin, and interprets these forms in accordance with his theory as already outlined on an earlier page of this chapter. After another visit to the bay country and further studies of the problem of uprising waters referred to in the 1936 paper, the writer was able to expand that earlier statement of the hypothesis of complex origin. In an article 16 published in September, 1937, it was shown that artesian springs, fed by uprising shallow artesian waters before stream incision in the Coastal Plain had lowered the groundwater level, would produce basins or craters, similar to those observed, partly by solution and partly by removal of finer sediment. Lakes for a time occupied many of the developing basins, while lake waves smoothed the contours of the basins and built beach ridges about portions of their borders. Sand blown from beaches and beach ridges by the winds built more extensive dune ridges, some of these being superposed on preexisting beach ridges within the basins, others upon the Coastal Plain strata at their margins. Lowering of groundwater level consequent upon incision of Coastal Plain streams later extinguished most of the lakes and will in time extinguish the few that remain. In this statement the hypothesis of complex origin becomes in fact the artesian-solution-lacustrine-aeolian hypothesis of crater origin. Further studies led to the elaboration of this hypothesis presented on later pages. In the same month (September, 1937) there appeared a paper 13

Douglas Johnson. Origin of the Supposed Meteorite Scars of Carolina. Science, 84:15-18, 1936. 14 Douglas Johnson. "Cicatrices météoritiques" sur la côte des Carolines. Mélanges de Géographie et d'Orientalisme offerts à E. F. Gautier, 464 pp., Tours, 1937. See pp. 272-277. 1 5 C. Wythe Cooke. Geology of the Coastal Plain of South Carolina. U. S. Geol. Surv., Bull. No. 867, 196 pp., 1936. See p. 7 and Plate 17. 16 Douglas Johnson. Rôle of Artesian Waters in Forming the Carolina Bays. Science, 86:255-258, 1957.

Scientific Studies of Bays

27

by Gerald R . MacCarthy 17 reviewing briefly several hypotheses of bay origin and supporting the meteoritic hypothesis. This paper adds little factual data to that already presented by MacCarthy's associate, Professor Prouty, in 1935 but discusses more fully the theoretical aspects of the meteoritic interpretation. Developing a suggestion by Prouty, MacCarthy explains that the craterlike depressions were formed by shock-waves of air accompanying a shower of large meteorites and not directly by the impact of the meteorites upon the earth; that the bays are much larger than the meteorites that produced them; that the meteorites probably were largely or wholly volatilized by the heat developed when their motion was checked; that the magnetic highs associated with the bays are caused by the presence, under ground, of meteoritic material, but that this material may partially or wholly represent condensations from the vapor formed when the meteorites volatilized; and that the underground courses of the meteorites were not straight but curved toward the southwest, possibly as a result of the deflective effect of the earth's rotation. W. F. Prouty and H. W. Straley presented to the Geological Society of America at its December, 1937, meeting a report on further studies of the Carolina bays. The published abstract 18 of this report creates the impression that the authors are less confident than formerly was the senior author respecting the validity of the meteoritic hypothesis. They accept solution as an agent modifying some elliptical depressions and the role of wind action in modifying rims to give larger accumulations of sand about southeast quadrants. A new and detailed magnetometer survey near Syracuse, South Carolina, is reported to show "a spot high or spot highs . . . associated with each of the bays in the proper positions to support the meteoric theory"; but "there are, however, in the area two minor spot highs which have no present apparent connection with the bays." What final conclusion, if any, was reached in the light of this conflicting evidence is not stated. 17

Gerald R . MacCarthy. T h e Carolina Bays. Bull. Geol. Soc. Amer., 48:12111226. 1937. 18 William F. Prouty and H. W. Straley. Further Studies of "Carolina Bays." Geol. Soc. Amer., Preliminary List of Titles and Abstracts of Papers to Be Offered at the 50th Annual Meeting, December, 1937, 42-43, 1937. See also Geol. Soc. Amer., Proc. for 1937, 104-105, 1938.

28

Scientific Studies of Bays

At the meeting of the Geological Society of America just referred to, L. C. Glenn 19 presented a paper in which it was stated that no section of the banks of the Intracoastal Canal showed any disturbance of the strata such as a meteorite would have caused. T h e value of the statement is uncertain in view of the further statement that "the line of the canal unfortunately runs just seaward from the area thickly pitted with the so-called meteorite scars and gives no positive evidence of their origin." In April, 1938, John D. Boon and Claude C. Albritton, Jr., 2 0 reviewed the state of our knowledge respecting real and supposed meteorite craters. They place the Carolina bays in their group of "questionable meteoritic craters," and after discussing briefly and very incompletely 21 the conflicting arguments they conclude that "as the matter stands . . . the meteoritic hypothesis does not offer a satisfactory explanation for the Carolina Bays." In October, 1939, Murray F. Buell 22 discussed briefly the formation of peat in the Carolina bays. While Buell does not attempt to review evidence and arguments respecting the origin of the craterlike depressions, he does state his opinion that "all the phenomena described by these men [Melton, Schriever, and Prouty] seem to be adequately explained only by the meteorite hypothesis." T h e dissenting interpretations of Cooke and Johnson are cited but not discussed. Buell confirms the view that some of the bays at least are filled-in lake basins and demonstrates that in the several cases studied by him the lakes were encroached upon by peat deposits forming most rapidly from the northern and western borders of the basins. Open water thus remains longest in the southeastern parts of the basins, and an excellent aerial photograph shows two elliptical bays solidly filled with peat in their northern and western portions but with residual lakes of open 19 L . C. Glenn. Geology of the Intracoastal Canal near Myrtle Beach, South Carolina. Geol. Soc. Amer., Proc. for 1937, p. 83, 1938. 20 John D. Boon and Claude C. Albritton, J r . Established and Supposed Examples of Meteoritic Craters and Structures. Field and Laboratory, 6:44-56, 1938. 21 T h e authors cite almost exclusively those papers on the Carolina bays which support the meteoritic hypothesis and seemingly were not acquainted with the papers discussing alternative hypotheses. 22 Murray F. Buell. Peat Formation in the Carolina Bays. Bull. Torrey Bot. Club, 66:483-487, 1939.

Scientific Studies of Bays

29

water at the south and east. This distribution of peat development is attributed to the joint influence of prevailing southwest winds (which would develop major wave agitation toward the northeastern sides of the basins) and the shape of the lake basins, which are said to be shallower toward the north (northwest?) than toward the south (southeast?). In his textbook of geomorphology, published in 1939, Professor A. K. Lobeck 23 discusses briefly the character and origin of the Carolina bays. On the basis of field observations, he supports the solution hypothesis earlier advanced by the present writer, with modification of the solution forms by lake currents and wind action. In February of the following year, Dr. C. Wythe Cooke 24 published a paper in which he expresses doubt respecting his earlier view that uniform orientation of the bays is due to preponderance of wind from one direction, and explains both form and orientation as due to "the tendency of rotary currents in liquids to assume the shape of an ellipse whose major axis points N. 45 0 W. in the Northern Hemisphere, and N. 45 0 E. in the Southern Hemisphere." Objections to this new hypothesis were set forth by the writer in April, 1941. 2 5 In March, 1940, the writer discussed the origin of the bays in some detail in a lecture delivered at a number of American universities under auspices of the National Society of the Sigma Xi. This discussion, entitled "Mysterious Craters of the Carolina Coast," appeared in a volume of Sigma Xi lectures published by the Society in 1940.26 T h e foregoing review of the literature makes clear the urgent need for further study of the curious oval craters of the Carolina coast. Our first task is to analyze and evaluate the various hypotheses advanced to account for these remarkable forms. 23 A. K. Lobeck. Geomorphology, an Introduction to the Study of Landscapes. 731 pp., New York, 1939. See pp. 714-715. -* C. Wythe Cooke. Elliptical Bays in South Carolina and the Shape of Eddies. Jour. Geol., 48:205-211, 1940. - 5 Douglas Johnson. Rotary Currents and the Carolina Bays. Jour. Geomorph., 4:164-166, 1941. 26 Douglas Johnson. Mysterious Craters of the Carolina Coast. Science in Progress, Society of the Sigma Xi National Lectureships for 1939 and 1940, 317 pp., New Haven, 1940. See pp. 78-106.

IV Hypotheses Based on Supposed Terrestrial Origin of the Bays

I

N T H E present chapter we shall examine somewhat critically all but one of the various hypotheses of bay origin in which terrestrial forces alone are invoked to account for the phenomena observed. Critical analysis of the one remaining hypothesis of terrestrial origin, that proposed by the author, is reserved for treatment in later chapters. DROWNED-VALLEY

HYPOTHESIS

As already noted, L. C. Glenn cautiously offered, as one possible explanation of the oval bays, the hypothesis that they were former drowned valleys of an earlier coastline, blocked on the southeast by bay-mouth bars of sand cast up by the ocean waves. T h e hypothesis was invented primarily to explain the low basinlike areas and the sand ridges. Glenn pointed out that this interpretation is open to the objections that no remains of old stream channels entering the heads of the supposed drowned valleys have been found; no wave-eroded headlands are in evidence; the distribution of the ovals with respect to the present shore (and hence presumably with respect to earlier shores) is highly irregular; and the prevailing rounded or elliptical shape is not explained. It may be added that the presence of certain of the bays in the midst of a broad beach plain composed of successive beach ridges and swales and the fact that the sand ridges surrounding the bays are obviously distinct from and independent of the sandy ridges of the beach plain seem to render this hypothesis untenable. When Glenn wrote his account, sufficient facts regarding the bays were not available to make it feasible to formulate a satisfactory hypothesis of origin. No aerial photographs were yet at hand, while topographic and soil maps were few and unsatisfactory

Hypotheses of Terrestrial Origin

31

or wholly lacking. Field studies without these aids are difficult, and Glenn's observations were apparently limited to a few bays near Darlington. Under the circumstances his caution in formulating hypotheses was particularly justified. But while Glenn did not succeed in inventing a hypothesis of origin which fully satisfied him, it should be recorded that his description of the bays is remarkable for its accuracy. He observed and recorded, what many later writers overlooked, that the major locus of sand rim accumulation is "on the east and southeast and sometimes extends fairly well round toward the south." When the present writer visited the field, he did not have a copy of Glenn's paper with him and had forgotten his discussion of the precise location of the rims. Having in mind later published statements that the sand is chiefly piled up "at the southeastern ends" of the bays, he was much surprised to observe that the normal locus of accumulation was rather about the southeast quadrants of the ovals from the southeast end up the northeast side approximately to its middle point or somewhat beyond. When he returned from the field and read anew Glenn's paper, the writer found that what he had supposed to be an original discovery was merely an independent confirmation of the excellent description written by Glenn forty years before. AEOLIAN

HYPOTHESIS

It has long been known that wind can erode hollows or basins and deposit the eroded material in the form of ridges partially or wholly surrounding the depressions. Melton and Schriever considered the possibility that the oval bays of Carolina and their associated rims are of aeolian origin but rejected this hypothesis for the following reasons: (a) only prevailing northwesterly winds could have built the rims of sand around the southeastern ends of the bays, and the prevailing winds of this region are southwesterly or ninety degrees away from the chief direction of sand movement; (b) the formation of such regular and smooth depressions is not known to be characteristic of wind scour; (c) sand is not now being moved to any noticeable extent by the wind; (d) even if the prevailing winds were from the appropriate direc-

32

Hypotheses of Terrestrial Origin

tion, this hypothesis could not explain the formation of a rim completely encircling a bay, a condition sometimes observed. Analysis of these four tests of the aeolian hypothesis suggests that they are not in themselves adequate to exclude that hypothesis from further consideration: (a) If the origin of the oval bays dates back to the Pleistocene, or even earlier, as Melton and Schriever suggest, we cannot exclude the possibility that a shift of position of the wind belts, or even a modification of wind behavior within those belts, consequent upon the presence of the great continental ice sheets, may have given wind conditions in the Carolina region notably different from those existing today. Since the major sand accumulation is found not about the southeastern ends of the bays but about their southeast quadrants, and since sand transport depends on dominant rather than prevailing winds, the observed facts call for dominant winds from a westerly quarter. It will later appear that dominant winds in the bay country do blow from this direction, dominant winds being those having the greatest total force when both duration and velocity are considered, while prevailing winds are those which blow for the longest time. (b) In certain localities, as for example the El Oued district of the Algerian Sahara, are found more or less circular depressions partially or wholly surrounded by ridges of dune sand. It is true that the depressions near El Oued occur in a veritable sea of windblown sand rather than as more or less isolated features on a level plain of other origin, and that neither the depressions nor their rims are sufficiently symmetrical to make them really comparable to the Carolina bays. On the other hand, some possess a degree of symmetry which makes one hesitate to exclude the possibility that winds might, under suitable conditions, produce forms of as great symmetry as those observed in the Carolina bays, which are irregular in outline far more frequently than they are symmetrically oval. Small isolated depressions of circular form bordered by low rims are found on the Coastal Plain of Texas. Their origin is obscure, but excavation of the basins by wind erosion is one of the hypotheses advanced to account for them. (c) There are so many regions of dunes formerly active but

Hypotheses of Terrestrial Origin

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now fixed by a cover of vegetation that the absence of sand movement by winds today is not a safe indication of the non-aeolian origin of a given landform or deposit. Furthermore, the present writer found abundant evidence that wind-blown sand is still moving actively about many of the bays. (d) While prevailing winds may accumulate a larger sand ridge upon one side of a wind-formed basin or blowout, some sand may be moved in all directions so long as the winds blow for greater or less periods from all points of the compass. Dominant winds may differ in direction from prevailing winds and accumulate more sand than the prevailing winds. Because of the facts just stated, it seemed to the writer unsafe to exclude the aeolian hypothesis from among those to be considered during examination of the features on the ground. Melton and Schriever apparently assumed that the depressions and the encircling rims must have a common origin, for this assumption determines much of the reasoning set forth in their discussions. But such an assumption is clearly unsafe when one is investigating the origin of the earth's surface features. Landforms intimately associated in space may have originated at different times and in different ways. As will later appear, the present writer has discovered much evidence which seems to indicate that most of the oval rims are, in fact, of aeolian origin. On the other hand, the aeolian hypothesis seems wholly inadequate to account for the origin of the oval depressions. Many of these basins are devoid of sand rims, presenting no evidence that material abstracted from the depressions was transported by the wind to adjacent areas. Many details of basin morphology, to be fully described on subsequent pages, appear inexplicable on the hypothesis of aeolian excavation. We are forced to conclude that, while the rims of sand surrounding the oval bays may at least in part have been deposited by wind action, the bays themselves cannot satisfactorily be explained as the product of wind erosion. H Y P O T H E S I S OF R I P P L E U K E PITTINGS ON U P L I F T E D SEABOTTOM

Glenn tentatively suggested that the uplifted seabottom may have contained inequalities somewhat similar to ripple-mark

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Hypotheses of Terrestrial Origin

pittings, these constituting the basins of the bays. The form of the bays, their frequent sporadic distribution with many well isolated from their neighbors, and the oval pattern of the associated rims make it difficult to interpret the forms as giant ripple-marks. No features similar to ripple-marks and of such magnitude as the bays and their oval rims have been reported in geomorphic literature. No force competent to produce such symmetrical oval depressions on the seabottom is known. Another serious objection to the hypothesis that the bays represent ripplelike depressions on an uplifted seabottom is found in the fact that, before such depressions could reach their present position, they must pass through the shore zone and be subjected to the destructive action of the waves and currents there operating. In the Myrtle Beach case there is clear evidence that these shore forces completely reformed broad areas into parallel beach ridges and swales. Yet some of the most perfect oval bays and their delicate oval rims lie in the midst of these areas (Fig. 7) on ground repeatedly eroded and redeposited by ocean storm waves. We must conclude that the hypothesis here discussed cannot survive the tests applied to it. H Y P O T H E S I S O F S U B M A R I N E SCOUR

Closely related to the foregoing is the hypothesis of submarine scour by undertow, by oceanic eddies, or by other currents affecting the seabottom. This hypothesis was tested and rejected by Melton and Schriever1 in their initial paper on grounds which seem valid. Their conclusion was stated in the following words: "The authors are unable to conceive of the nature of a submarine activity which could produce such depressions on the ocean bottom." In a later paper, discussing Cooke's hypothesis of segmented lagoons, Melton2 returns to the hypothesis of submarine scour and apparently accords it greater favor. He recognizes submarine scour as a possible concurrent factor "operating upon pre-existing de1 F. A. Melton and William Schriever. T h e Carolina "Bays"—Are They Meteorite Scars? Jour. Geol., 41:52-66, 1953. 2 F . A. Melton. T h e Origin of the Supposed Meteorite Scars: Reply. Jour. Geol., 42:97-104, 1934.

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35

pressions in the weak sediments," reexcavating basins of some other origin which had become filled with loose sand, or otherwise contributing to the final form of the oval bays and their rims. If it becomes necessary to substitute for the meteoritic hypothesis some other, he believes "this would probably involve submarine scour." It is not necessary to repeat here all of the objections to the hypothesis of submarine scour which Melton and Schriever set forth in their earlier paper. There is an even greater obstacle to the acceptance of this hypothesis. The oval bays of the Myrtle Beach area, as will be more fully demonstrated below, are later in origin than the beach ridges among which they lie. Such beach ridges are formed with their upper parts above sealevel and are not normally subjected to submarine scour thereafter. It seems highly improbable that any series of beach ridges could be submerged by the ocean, subjected to submarine scour, and then emerge with the original ridge system beautifully preserved. Even if the double passage through the destructive shore zone did not remove every vestige of the original system, submarine scour sufficient to excavate basins estimated to be from fifteen to fifty feet deep and from one-fourth of a mile to three or four miles in length should destroy or bury the beach ridges. Yet the Myrtle Beach ridge system is beautifully preserved with its orderly alternation of sandy crests and silty swales undisturbed even in immediate contact with some of the largest basins. Most of the oval bays are not associated with beach ridges. In such cases it is equally clear that the passage of the bays and their oval rims of sand through the shore zone must, for reasons pointed out in connection with the hypothesis of ripplelike pittings, result in the destruction of both. Those familiar with the violent erosion, swift transportation, and abundant deposition which succeed each other endlessly along the ocean front must hesitate to accept any interpretation which requires delicate forms of loose sand and silt to pass through the destructive shore zone and still retain their essential characters. The hypothesis of submarine scour by ocean currents appears wholly inadequate to explain the bays. The same conclusion holds good with respect to submarine scour

36

Hypotheses of Terrestrial

Origin

by freshwater springs arising from the sea floor. Melton and Schriever rejected this hypothesis, stating that many bays now free from dense vegetation and therefore open to inspection show no evidence of springs. It will be seen later that some bays do have springs rising in them at the present time. T h e fact that many do not constitutes no objection to the hypothesis that seabottom springs formed the bays, for transformation of seabottom areas into dry land must be expected to alter radically the subterranean circulation of water. T h e hypothesis must be rejected for the same reason that caused us to reject the hypothesis of submarine scour by ocean currents. Bays and encircling rims, formed on the bottom of the sea by any method, could not survive passage through the destructive processes of the shore zone. HYPOTHESIS OF VOLCANISM

Craters of volcanic origin are very common on certain parts of our earth but do not show a persistently oval form nor parallelism in orientation over large areas. No volcanic materials are associated with the Carolina bays, and volcanic activity is practically unknown in this region during recent geologic time. For these reasons no one has seriously entertained the hypothesis that the mysterious craters of the Carolina coast are of volcanic or cryptovolcanic origin. HYPOTHESIS OF SEGMENTED LAGOONS AND CRESCENT-SHAPED

KEYS

In his study of the Myrtle Beach bays, Dr. C. Wythe Cooke observed that the oval depressions sometimes occur in chains, like beads placed obliquely upon a string, the chain as a whole being parallel to the associated beach ridges (Fig. 7). T o explain the oval bays and their encircling rims, the parallelism of bay axes in a direction approximately northwest-southeast, and the occurrence of chains of bays parallel to beach ridges trending more nearly east-west, Cooke 3 invented what may be termed "the segmented-lagoon hypothesis." According to this hypothesis, a long narrow lagoon with sandy shores across which winds blow domi3 C. W y t h e Cooke. Discussion of the Origin of the Supposed Meteorite Scars of South Carolina. Jour. Geol., 42:88-96, 1934. See pp. 90-91.

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37

nantly from one direction will be transformed into a chain of elliptical lakes in the following manner: " T h e wind would set up waves and currents that would scoop out hollows and build up points here and there along the shores. Each shore would thus become scalloped. T h e points on the windward side would continue

F I G U R E 8: Stages in the change of a lagoon into a chain of lakes, according to Cooke's hypothesis of segmented lagoons. Arrow indicates assumed direction of wind. (After Cooke.)

to grow outward under the influence of the wind-driven current and would gradually become bars extending into the lagoon in the direction of the wind. T h e return current would tend to carry sand away from the opposite shore and to build bars toward the wind. As the bars become longer and longer, the wind-driven currents would become more and more localized within their particular segments of the lagoon. If no strong tidal or river currents cross their ends, the bars eventually would cut the lagoon into a chain of lakes. Currents in a lake necessarily are rotary, for the water pushed constantly forward by the wind must flow back to its starting-point. Continued rotation of the water under the propulsion of the wind would fill in all re-entrant angles with sand and thus shape each lake into a more or less perfect ellipse or circle." Cooke's hypothesis is illustrated in Figure 8. Cooke's segmented-lagoon hypothesis deserves more careful consideration than has been given to the other hypotheses thus far discussed in this chapter. But before proceeding to test its validity, it is desirable to consider the supposed change of sealevel which Cooke made a part of his explanation. According to this author the lagoons, which were later subdivided into oval lakes, formed part of a system of tidal waterways which existed when the sea stood higher than now. T h e parallel sand ridges were correctly

38

Hypotheses of Terrestrial Origin

interpreted as beach ridges, and Cooke states that they were "evidently formed at a higher stage of the sea." T o the writer it does not appear evident, from the facts presented by Cooke, that the beach ridges in question were necessarily formed when the sea was higher than now. Waves normally build beach ridges well above sealevel, and both ridges and swales are usually further aggraded by wind-blown sand.4 Hence the mere presence of beach ridges in a given area does not of itself afford any proof of sealevel changes, relative or absolute. Uplift of the land or lowering of sealevel can be inferred only if the windaggraded portion of the ridges can be distinguished from the wavebuilt portions and if, further, the altitude of the wave-built portions can be shown to be higher than the highest storm waves of the region could possibly deposit the material composing the ridges. So far as the present writer knows, no attempt has been made to distinguish the true "beach ridge" from the "dune ridge" portions of the parallel crests of the Myrtle Beach plain. Elevations nearer the sea (22 to 36 feet above mean low water), where aggradation by wind-blown sand appears to be very marked, suggest that here at least no change of sealevel need be assumed to account for the facts observed. Even the higher figures given by Cooke 8 for the older northwestern part of the beach plain, namely 35 to 45 feet where crossed by the railroad, are not above the altitudes reached by dune ridges growing upward from present sealevel. Critical studies of the Myrtle Beach ridges, with which some of the oval bays are closely associated, may or may not support the conception of a change of sealevel after the ridges were formed. In any case it does not appear that such a problematical change of sealevel need be so closely linked with the segmented-lagoon hypothesis as has been done in Cooke's presentation. Freshwater lagoons originating above sealevel appear to be just as serviceable in the hypothesis as saltwater or brackish lagoons at sealevel. This 4 Douglas Johnson. Shore Processes and Shoreline Development. 584 pp., New York, 1919. See pp. 439 et seq. 8 C. Wythe Cooke. Geology of the Coastal Plain of South Carolina. U. S. Geol. Surv., Bull. No. 867, 196 pp., 1936. See p. 153.

Hypotheses of Terrestrial Origin

39

should be sufficiently apparent from two sentences in Cooke's article: "At just what stage in the development of the region the elliptical sand ridges came into being is not now apparent. They may have been formed before the withdrawal of the sea, or they may have been formed later, after fresh water had replaced the salt or brackish water in the tidal channels." If the oval sand rims could form in lagoons between beach ridges after uplift of the land or lowering of sealevel had caused freshening of the waters, they could form in similar lagoons which were always above sealevel and always fresh. In this connection it should be noted that whether or not the longitudinal depressions between beach ridges descend below sealevel, and hence whether or not they ever enclose salt or brackish water lagoons, depends upon the spacing of the beach ridges, which latter in turn is dependent on a variety of more or less fortuitous circumstances.6 Cooke 7 later concluded that the bays of the Myrtle Beach district, Horry County, South Carolina, occur on several different terraces instead of on one (the lowest) as he formerly believed. Whether or not this view be correct, the problem of sealevel changes does not necessarily affect the problem of bay origin. Bays occur at all levels of the Coastal Plain from the coastal border to the inner margin, associated with beach ridges and (more frequently) without any such association. If we omit from Cooke's hypothesis the apparently nonessential element of sealevel change and consider that hypothesis in its most favorable form, we find that it holds out promise of a possible explanation for certain important characteristics of the Carolina bays. Chief among these is the tendency of certain bays to occur as a chain of oval depressions. It should be noted that in this pattern of the bays there is a twofold parallelism to be explained: first, parallelism of the long axes of the oval bays to each other in a northwest-southeast direction; and second, parallelism of the chain of bays as a whole to the axes of the ridges and swales in a B Douglas Johnson. Shore Processes and Shoreline Development. 584 pp., New York, 1919. See Chapter I X . 7 C. Wythe Cooke. Elliptical Bays in South Carolina and the Shape of Eddies. Jour. Geol., 48:205-211, 1940.

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direction w h i c h varies from place to place but which in the Myrtle Beach area is in general more nearly east-west. T h u s a clear distinction must be made between the direction of elongation of individual bays and the direction of alignment of groups of bays

(Fig- 7)Cooke's hypothesis, by making the chains of bays form in l o n g narrow lagoons occupying swales between adjacent beach ridge6, offers a reasonable explanation for the latter type of parallelism. In Figure 8, if we consider the top and bottom borders of the figure as axes of beach ridges, it will be obvious that, if a chain of lakes forms between the ridges in the manner there illustrated, the axis of the chain as a whole must be parallel to the axes of the confining ridges. T h e parallelism of long axes of the individual bays is attributed to the influence of northwest or southeast winds which, b l o w i n g obliquely across the east-west lagoon, set u p currents which divide the lagoon into segments and form oval lakes elongated in the direction of the winds. W h y the lakes are ovals elongated with the winds, instead of ovals having long axes nearly parallel to the ridges (as might be the case if the lagoon of Figure 8 were narrowed, or if the sandy points developing along its scalloped margins were more widely spaced), Cooke does not make clear. B u t the reader can scarcely escape the intuitive feeling that elongation of lakes in the directions of winds which blow longest or winds which blow strongest is a phenomenon to be expected in nature, and that some reasonable explanation for the phenomenon can be found. H e n c e one may conclude the reading of Cooke's paper with the conviction that the author's hypothesis (I) offers a possible explanation of the parallelism between the chains of oval bays on the one hand and the associated ridges and swales o n the other, and (2) points the way toward an explanation of the observed parallelism in the long axes of the individual bays. W h e n tests are applied to the segmented-lagoon hypothesis in order to determine whether it fully explains all of the observed facts, it is f o u n d to present serious weaknesses. W e must note, in the first place, that the hypothesis does not include an adequate explanation of how the initial scallops, later to develop i n t o oval

Hypotheses of Terrestrial Origin

41

sandbars, are produced. T o say that "the wind would set up waves and currents that would scoop out hollows and build up points here and there along the shores" is merely to state what the author thinks would happen. The assertion carries no explanation as to why or how waves and currents would operate to produce the assumed result. For reasons which have been fully set forth elsewhere,8 the normal tendency of waves and currents is to straighten shores already irregular rather than to scallop in more or less regular pattern shores previously straight. Hence the production of the initial scallops, upon which further stages of the postulated sequence of events are necessarily dependent, requires a clear and convincing explanation before the hypothesis can be considered adequate. That there are exceptional conditions competent to produce a scalloped shore is fully recognized; 9 but whether a narrow lagoon of the type envisaged by Cooke could be thus scalloped and ultimately segmented to give a chain of lakes seems highly problematical. In the second place, it appears that, so far as is now known, very few of the Carolina bays occur in chains between parallel beach ridges. The conditions at Myrtle Beach, upon which Cooke based his hypothesis, appear to be exceptional. Elsewhere in South Carolina occasional chains of bays (Fig. 3) have been discovered, and in Brunswick County, North Carolina, the phenomenon is beautifully developed. But the vast majority of oval bays are scattered irregularly over the Coastal Plain of three states in localities where beach ridges are not found. Even in the Myrtle Beach area many of the bays are irregularly disposed. Thus the segmented-lagoon hypothesis leaves most of the oval bays unexplained. Cooke himself recognized that in the Myrtle Beach area the largest ellipses, instead of being strung out in chains parallel to the beach ridges, "lie in rather compact groups within larger irregular 'bays.' " (See Lewis Ocean Bay group, Fig. 7.) T o explain these he invented a second hypothesis, which we may call "the 8

Douglas Johnson. Shore Processes and Shoreline Development. 584 pp., New York, 1919. See pp. 74-76, 339 341. 9 Douglas Johnson. T h e New England-Acadian Shoreline. 608 pp., New York, 1925. See pp. 441-446.

4«

Hypotheses of Terrestrial Origin

crescent-shaped key hypothesis." H e presented this in the following words: " T h e incomplete elliptical ridges that lie within large 'bays' such as Lewis Ocean Bay and Cotton Patch Bay are probably also the work of waves and currents acting under somewhat different conditions. In this case, the hypothetical starting-point would be an irregular shallow lake or lagoon several miles in diameter. T h e winds and waves would build up piles of sand here

FIGURE 9: Sand-atoll and group of crescent-shaped keys in Mosquito Lagoon, Fla. Cited by C. Wythe Cooke to illustrate his conception of formation of oval bays from sand keys on floor of a shallow lake or lagoon. (Traced by Cooke from Sheet T-4440-B of U.S. Coast and Geodetic Survey.)

and there within it and would gradually curve them into crescentshaped keys, which were convex toward the wind. T h e water partly enclosed between a crescent-shaped key and an opposing shore or shoal would circulate under the force of the wind and might become completely enclosed by bars, thus forming a lake within a lake, like a lagoon within an atoll in the ocean." 1 0 (Fig. 9.) Cooke's hypothesis is based so largely on theoretical considerations and is so little subject to elucidation by concrete facts of field 1 0 C. W y t h e Cooke. Discussion of the Origin of the Supposed Meteorite Scars of South Carolina. Jour. Geol., 42:88-96, 1934-

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evidence that it is not easy to get a clear picture of all that the hypothesis implies. It seems certain, however, that in order to account for the oval bays of a single region Cooke was compelled to invent what some may consider as two hypotheses. As both involve the building of sandbars by waves and currents, in one case in long narrow lagoons or lakes, in the other case in irregular broad shallow lagoons or lakes, it is perhaps fairer to call it a double hypothesis, "the hypothesis of segmented lagoons and crescentshaped keys." T o explain a group of unusual and highly specialized features, which are identical in shape and in other characteristics, as the result of waves and currents operating in two distinct ways, places a severe strain on the explanation offered. How truly Cooke's hypothesis is a double explanation can be appreciated from the fact that in one case (segmented lagoons) the curved sandbars are in part built toward the wind, while in the other case (crescentshaped keys) they are uniformly extended in the general direction in which the wind is blowing. In one case the ovals originate in hypothetical scalloped sandy shores of a narrow lagoon, in the other in hypothetical isolated shoals on the floor of a broad shallow lagoon or lake. That waves and currents operating in such diverse ways under such diverse geographical conditions could produce identical results of highly specialized type seems most improbable. Cooke encountered one of the difficulties presented by his dual hypothesis when attempting to explain the fact that the oval sandy rims prevailingly have their maximum development toward the southeastern ends of the bays. In the case of oval rims developing from crescent keys, he seems to believe that winds coming from the southeast would cause waves to heap the sand highest on the windward part of the key, while the trailing horns of the crescent, being built chiefly under water, would be lower. Cooke then observes: "This explanation apparently would not apply to chains of ellipses formed by the segmentation of lagoons." He therefore suggests that in this latter case the space between the rounded ends of closely adjacent lakes and the original shore of the lagoon, being filled in with sand, would be more conspicuous, although not necessarily higher, than the rest of the oval rim. Field evidence

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Hypotheses of Terrestrial Origin

indicates, however, that in the case of closely adjacent bays of a chain, just as in isolated bays, the sandy rim is normally highest toward the southeast and not merely broader, and that it normally is a true rim and not merely the filling with sand of a triangular space between the rounded ends of adjacent ovals. Further tests of the segmented-lagoon and crescent-shaped keys hypothesis develop further weaknesses. Melton 11 has correctly observed that the hypothesis fails to account for the oval depressions within the sandy rims, which depressions lie well below the level of the plain upon which the sandy rims are built. Melton further observed (and the present writer's studies fully confirm the observation) that the bays do not occur prevailingly in lowlands, which once were waterways (as Cooke believed and as his theory requires), but are found for the most part on flat undissected uplands between drainage lines. In addition to these two points of capital importance, Melton lists eight other objections to Cooke's hypothesis; but, as none of these objections appears to the present writer to be valid, they need not be reviewed. A real objection is Cooke's failure to show that crescent-shaped sand keys can be transformed by waves and currents into such perfect ovals as the bays. The examples of keys and the atoll figured by him (Fig. 9), presumably the best he could find, are so incomplete or so irregular as to constitute an argument against, rather than in favor of, his hypothesis. On the other hand, the examples of elliptical lakes figured by Cooke (Figure 5 of Cooke's paper), while illustrating the fact that waves can simplify the contours of lakes, afford no satisfactory evidence as to the origin of the bays because the illustrative examples lack the highly specialized symmetry and the prominent sand rims which make the typical oval bays so difficult to explain. Nothing in Cooke's hypothesis accounts for the fact that the major locus of sand accumulation is toward one side (the southeast quadrant of the bays) instead of symmetrically about their southeastern ends. T o account for the smoothly elliptical form of the bays Cooke appealed to rotary currents generated by the wind. "Currents in 11

F. A. Melton. T h e Origin of the Supposed Meteorite Scars: Reply. J o u r . Geol.,

42:97-104.

1934.

Hypotheses of Terrestrial Origin

45

a lake necessarily are rotary, for the water pushed constantly forward by the wind must flow back to its starting-point. Continued rotation of the water under the propulsion of the wind would fill in all re-entrant angles with sand and thus shape each lake into a more or less perfect ellipse or circle." It is clear both from the context and from the requirements of Cooke's theory that this author visualized currents rotating in a horizontal plane. There is, however, no necessity for water in a lake to assume this form of rotation, and one may reasonably doubt whether under the conditions specified it could do so. Horizontal rotation would require that one side of the rotary current or eddy should flow against, while the opposite side flowed with, the wind. On a broad shallow lake, bay, or other body of water, all parts of which are fully exposed to the wind and no part of which is protected by high shores, the entire surface of the water commonly moves with the wind. Return to the starting point normally takes place as a subsurface current or undertow. There is rotation but it takes place in a vertical rather than in a horizontal plane. When the body of water has irregular shores, or is of such large size that wind action may differ notably over different parts of its surface, or has parts of its surface protected from certain winds by high shores, current action may become very complex. Studies of beach drifting and shore forms along the margins of lakes do not support the view that currents in such bodies of water must rotate in a horizontal plane. Studies of the Carolina bays do not support the view that their oval form is due in any notable degree to the filling in of reentrant angles by such currents, although, as we shall later see, they do indicate that lake shores initially more or less irregular in outline have had occasional embayments bridged by bay bars and the shoreline further smoothed by wave erosion or wave deposition. These changes are of such nature as to be reasonably explained as the product of ordinary wave and current action. In his 1940 paper 12 Cooke attributes not only the elliptical form of the bays but also their orientation to rotary currents. He pre12 C. W y l h e Cooke. Elliptical Bays in Soulh Carolina and the Shape of Eddies. J o u r . Geol., 48:205-211, 1940.

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sents a mathematical demonstration intended to show that a rotary current or whirlpool of water tends, because of the earth's rotation, to assume the form of an elliptical eddy with its major axis directed N 45 0 W in the northern hemisphere, N 45 0 E in the southern hemisphere. As evidence that "water in the lakes actually contained [rotary?] currents" Cooke cites a "curved spit" visible in an aerial photograph reproduced as Figure 1 of his paper. The evidence seems inconclusive for two reasons. First, interpretation of the form in question as a spit is not supported by critical data. Similar forms are abundant in the bay country and have been interpreted by the writer, on the basis of evidence set forth on later pages, as representing the junction of rims of sand deposited by wind action about two mutually intersecting bays. Second, a curved spit, even if present, affords no evidence of rotary currents since curved spits and bars commonly form in the absence of such currents.13 As an explanation for the oval form and northwest-southeast orientation of the Carolina bays, this revision of Cooke's earlier hypothesis has four notable weaknesses: (1) It assumes that there were horizontally rotating currents in the bays, an assumption which, as we have already seen, is of very doubtful validity. It is all the more doubtful in connection with Cooke's hypothesis, because the bodies of water postulated by him were not the lakes of limited size and more or less regular form inferred by the present writer, but greatly elongated lagoons representing old seaways, and irregular broad lagoons or lakes within the limits of each of which a number of the oval bays are believed frequently to have developed. This means that a number of highly regular elliptical eddies must have developed, for unknown reasons, in each such water body, instead of the very complicated systems of currents commonly observed in irregular lakes and lagoons. (2) Since the force appealed to by Cooke operates all over the world, northwest-southeast elliptical lake basins should be of widespread occurrence in the northern hemisphere, and northeastsouthwest elliptical lake basins in the southern hemisphere, wher13

Douglas Johnson. Shore Processes and Shoreline Development. 584 pp., New York, 1919. See pp. 335-339-

Hypotheses of Terrestrial Origin

47

ever shallow water bodies occur in loose sand, silt, loam, or other fine material easily eroded and transported. The widespread occurrence of systematically oriented elliptical lakes is not demonstrated by Cooke, nor does the writer know of such occurrence. It seems reasonable to conclude that the force appealed to, granting its existence, must be quantitatively incompetent in comparison with other factors affecting the development of the bays. (3) The elliptical eddies are invoked to explain elliptical bays with major axes trending N 45 0 W. While the average orientation of the bays in the Myrtle Beach area is probably somewhere near this figure, there is, as will later appear, a very great range in the axial trends of individual bays, those in the southern part of the bay country averaging S 20 0 E. Since large groups of bays covering vast areas diverge greatly from the direction required by the hypothesis of eddy current control, the strongest argument cited in favor of this interpretation (close accordance of observed axial trend of elliptical bays with theoretical axial trend of the hypothetical elliptical eddies) loses its force. (4) The dynamical reasoning on which the "elliptical eddies" phase of the hypothesis is founded appears to be of questionable validity. Cooke speaks of "the tendency of rotary currents in liquids to assume the shape of an ellipse whose major axis points N. 450 W. in the Northern Hemisphere and N. 45 0 E. in the Southern Hemisphere" as though this were an established law of terrestrial dynamics, and adds: "As this law is not generally known, the proof is here outlined." 14 Enquiry among colleagues competent in the field of dynamics has failed to develop knowledge of any such law, and the correctness of the reasoning adduced as proof has been challenged by those specialists to whom Cooke's paper was submitted. Even were the present writer competent (which he is not) to pass judgment on the merits of the issue thus joined by geologists and specialists in the field of dynamics, it is unnecessary to debate that issue here. We need only observe that in respect to this issue we find a very doubtful hypothesis of bay origin resting upon another hypothesis, the validity of which is challenged by competent critics. Until the supposed law of eddy 14

C. Wythe Cooke. Elliptical Bays in South Carolina and the Shape of Eddies. Jour. Geol., 48:205-211, 1940. See pp. 208-209.

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behavior is firmly established, it cannot lend support to a conception of bay origin which encounters other and formidable objections. We are forced to conclude that the hypothesis involving segmentation of narrow lagoons and the development of crescentshaped keys in irregular broad lagoons or lakes, offered specifically to explain the Myrtle Beach bays but not the many more later discovered, fails on analysis to account satisfactorily for all of the features found in the particular locality which inspired the hypothesis; and that it fails even more signally to account for essential characteristics of the tens of thousands or hundreds of thousands of bays scattered thickly over parts of the Coastal Plain from southeastern North Carolina to northeastern Georgia, where physical conditions are often significantly different from those existing in the Myrtle Beach area. In his latest paper, quoted above, Cooke states that in his earlier contribution to the bays problem he "interpreted some of the rims as beach ridges surrounding extinct-lake basins and others as sandy atolls built by winds and waves within larger bodies of shallow water." One might infer from this statement that Cooke visualized, for some of the depressions, the building of beach ridges about the margins of more or less oval moderate-sized lake basins to give the present bays, a process later invoked by the writer. MacCarthy, after citing Cooke's hypothesis, states that "a somewhat similar theory has been suggested by Johnson." It should be noted, however, that the lake basins postulated by Cooke were not the moderate-sized basins of more or less nearly oval form constituting the present bays, but large and irregular bodies of shallow water within which the oval bays were later developed. Cooke apparently was not even certain that the original water bodies were freshwater lakes, as he says "the hypothetical starting-point would be an irregular shallow lake or lagoon several miles in diameter." T h e sandy rims were not built as beach ridges about shores of the original water bodies but as "crescentshaped keys" out in the lake or lagoon, each of which ultimately developed, in connection with an opposing shoal or shore, into an oval bar enclosing "a lake within a lake, like the lagoon within

Hypotheses of Terrestrial Origin

49

an atoll in the ocean." It is clear from the context that under Cooke's hypothesis the oval basins and their contained lakes came into existence pari passu with, and as a direct consequence of, the development of keys and bars in the interior of a larger water body, the irregular outlines of which remain purely hypothetical. Under the writer's hypothesis, formation of the oval basins and their lakes antedates the building of the sand rims, which latter are chiefly dune ridges built of material carried up from the lake shores by wind action, but in part true beach ridges built by ordinary wave action about the lake margins and thus outlining, with minor exceptions, the immediate shore of the original water body. The two hypotheses are thus essentially distinct, and the processes involved are largely dissimilar. HYPOTHESIS OF SOLUTION

DEPRESSIONS

15

In 1931 Laurence L. Smith showed that descending waters charged with organic acids will dissolve and remove iron and alumina from sediments containing minerals rich in these elements, and that such removal of material from below will produce shallow depressions or sinkholes on the surface of the ground. Depressions due to this cause were reported from the inner margins of the Coastal Plain where arkosic and clayey sands are abundant. They have not been reported from the areas of siliceous sand where bays are most abundantly developed, although, as will later appear, sinkholes due to the solution of underlying limestone and other soluble beds are found in these latter areas. The depressions described by Smith are among those problematical forms which some may hesitate to class with oval bays, and that author did not apply his theory of solution to the bay problem. Nevertheless he deserves credit for elucidating one type of solution which may have played a significant role in the development of those bays located on the outcrop areas of arkosic sediments. Melton and Schriever,16 after stating that " L . L. Smith recently 15 Laurence L. Smith. -Solution Depressions in Sandy Sediments of the Coastal Plain ¡11 South Carolina. J o u r . Geol., 39:641-6^2, 1 9 3 1 . ,B I". A. Melton and William Schriever. T h e Carolina " B a y s " — A r e T h e y Meteorite Scars? J o u r . Geol., 41:52-66, 1933. See pp. 61-62.

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Hypotheses of Terrestrial Origin

has assigned the origin of the coastal plain depressions to the dissolving action of ground water," discuss briefly and reject the solution hypothesis of the bays. As noted above, Smith did not invoke his solution hypothesis to account for the Coastal Plain depressions in general nor did he mention the bays. In rejecting the solution hypothesis as an explanation of the bays, Melton and Schriever state that the process of solution does not account for the encircling rims of sand, for the uniform and regular ellipticity of the basins, or for the occasional existence of small bays almost entirely enclosed within larger ones. We have earlier pointed out that it is not necessary to attribute the same mode of origin to the oval depressions and to the encircling rims. T o invoke two distinct processes to explain identical peculiar forms, one process being responsible for some of the forms and another process for the remainder, places a severe strain on the interpretations offered. But to invoke two distinct processes to account for two distinctly different forms, even when the two forms are systematically associated, is amply justified by our experience with natural forces and their products. We must recognize the possibility that solution might form basinlike depressions, about which wind action or some other process could form ridges of sand. It will later be shown that solution is involved as a factor in the hypothesis of complex origin for the bays, mentioned briefly in the next section and fully discussed in a subsequent chapter. HYPOTHESIS OF C O M P L E X

ORIGIN

There is one more hypothesis involving a terrestrial origin for the curious oval craters of the Carolinas and adjacent regions to which we must give attention. This is the hypothesis of complex origin (the artesian-solution-lacustrine-aeolian hypothesis) advanced in incomplete form by the present writer in 1934 and further elaborated in later papers cited in Chapter III. Inasmuch as this was the latest hypothesis to be invented and is to be presented fully for the first time in this volume, it seems best to defer detailed consideration of its merits and defects until the far more spectacular hypothesis involving an extraterrestrial origin of the craters has been discussed.

V Hypothesis of Ancient Meteorite Scars

T

HE I N T E R P R E T A T I O N of the origin of oval bays which has most strongly challenged the imagination is that presented by Melton and Schriever. According to this hypothesis the peculiar oval basins and their enclosing rims were formed long ago by impact of a shower of meteorites upon dry land. T h e basins possibly were then partly filled by subaerial forces, were next submerged by the sea during a marine invasion, further filled by marine sand and silt, then again exposed on dry land by retreat of the sea, and finally occupied by peat bogs covered with vegetation as we see them today. It will be observed that this hypothesis not only requires the oval rims of loose sand to pass twice through the destructive shore zone and still preserve in a remarkable degree of perfection their delicate forms, but, as presented by Melton and Schriever, involves in the Myrtle Beach district the construction by storm waves of a great series of beach ridges without effacing the preexisting basins and their sandy rims. As the relative ages of the oval basins and their rims on the one hand, and the series of beach ridges and swales on the other, are a vital matter in the interpretation of these forms, we must definitely establish which first came into existence. Melton and Schriever correctly interpreted the origin of the parallel ridges and swales (beach ridges) which appear prominently in airplane photographs of the Myrtle Beach region. Their reasons for assigning the oval bays and their rims to an earlier date than the beach ridges are stated in the following terms: "In the area covered by the photographs the bays were once beneath the sea. Proof of this statement is found in the fact that beach ridges of an old shore intersect and obscure several of the depressions. . . . Not only have the depressions been obscured and their rims partially removed by wave and current action, but there are a few features visible on the mosaic to be explained

Bays 2 miles W of Lewis Ocean Bay (Fig. 7), near Myrtle Beach, S.C., two well formed and a larger one very imperfectly developed and associated with obscure beach ridges (parallel bands of darker and lighter shade). Arrow points N, and larger perfect bay is 1/2 mile long. Latter bay shows especially well the stronger curvature of NE side and major development of sand rim about SE quadrant. (Fairchild Aerial Surveys, Inc.) FIGURE 1 0 :

Ancient Meteorite Scars

53

only as basins w h i c h have been completely filled and buried by the beach material along this old shore." T h e s e authors give no further indication as to what features they interpret as "basins w h i c h have been completely filled and

FIGURE I 1 : Well-developed oval bay in upper right corner, associated with both larger and smaller irregular and poorly developed bays over rest of area and with obscure beach ridges and swales indicated by faint parallel lighter and darker bands. Near Myrtle Beach, S.C. Arrow points N, and perfect bay is 14 mile long. Note stronger curvature of NE side of oval bay and greater development of sand rim about SE quadrant. (Fairchild Aerial Surveys, Inc.)

buried by the beach material," but they publish an aerial photograph showing what they believe to be "bays partially obscured by beach ridges." T h e same area is shown here in Figure 11. Figure 10 represents another area which might be regarded as affording even stronger support for their interpretation. In both cases the original photographs show, rather vaguely to be sure,

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Ancient Meteorite Scars

alternate bands of lighter and darker shading, demonstrably continuous with undoubted beach ridges and swales; and encroaching upon, or even partially encircling these vague parallel bands, are what appear to be rims of sand decidedly imperfect as to both continuity and symmetry. It is difficult to get a picture which will adequately show such obscure features, but the reader may gain from Figures 10 and 11 some idea of the essential relations. While the vague and confused assemblage of imperfect ridges and swales and equally imperfect basins and rims are reasonably open to the interpretation given by Melton and Schriever—that the ovals and rims were formed first and later obscured by the process of beach ridge building—they are equally open to the opposite interpretation. Since certain theoretical considerations are strongly opposed to the interpretation that the oval bays and rims were formed before the beach ridges, one is impelled to scrutinize all the facts with special care. When this is done, both the original mosaic photograph of the region and field observations on the ground afford proofs that the oval bays and rims were developed on the sandy plain of beach ridges long after the latter had been completed. R E L A T I V E A C E OF B A Y S AND B E A C H

RIDGES

When an aerial photograph shows vague indications of parallel rectilinear ridges and swales in association with oval ridges and basins and both are imperfect, it is not easy to discriminate which set of forms is the older. Incompletely formed beach ridges might be obscuring older ovals, or imperfectly formed ovals might be obscuring older beach ridges. It should be observed, however, that so long as Melton and Schriever entertained the meteoritic hypothesis of origin for the oval forms, they were compelled to place the period of beach ridge formation later than that of the oval rims. For it is inconceivable that a meteorite could plunge into the earth, excavate a basin of considerable depth and of large areal extent, throw up the excavated sand in an encircling rim, and still leave the delicate tracery of loose sand ridges and swales within the area of impact. But if we postulate

Ancient Meteorite Scars

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some less violent mode of origin for the ovals, we must recognize that the vague association of forms described and pictured here is open to either of the two interpretations respecting relative age. When we consider the manner in which beach ridges originate, the correct interpretation becomes less doubtful. Plains of parallel beach ridges are common features of our present coasts, and the process of their formation is fairly well understood and sufficiently set forth in geomorphic treatises. It is known (a) that successive parallel ridges are added to a prograding coast by the action of storm waves which alternately erode and deposit, constantly cutting and filling in an effort to maintain a shore profile of equilibrium appropriate to the ever-changing size of the waves, direction of their impact, and quantity of sand in transport; (b) that the shore is again and again cut out many feet below sealevel and the products of erosion are heaped upon the land many feet above the sea, the vertical range involved in this cut and fill exceeding, on an open shore like the Atlantic, the observable depths of most of the oval basins and the maximum heights of their rims combined; and (c) that in this manner the whole mass of the shore zone is completely rewoiked many times with accompanying total destruction of earlier surface forms. There seems to be no escape from the conclusion that had oval basins and sandy rims existed in the Myrtle Beach area prior to construction of the beach ridges, the oval forms would not merely have been slightly modified or partially obscured: thev would have been annihilated. Study of the original aerial mosaic map of the Myrtle Beach region affords clear evidence in support of this conclusion. It is unfortunate that the only form of the mosaic map available in published discussions of the supposed meteorite scars is a greatly reduced copy of the original. I t was "a reduced copy" of the mosaic upon which Cooke based his studies, earlier cited. These reduced copies do not make sufficiently clear the important fact that the mosaic map is not a mere mosaic of aerial photographs but such a mosaic modified by draughtsmen for the purpose of delineating the distribution of different types of timber throughout the area. White broken lines drawn by hand not only ex-

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Ancient Meteorite Scars

aggerate the distinctness of the beach ridges and the perfection of some of the ovals but, in cases where the photographs making up the mosaic were obscure, they also introduce an element of personal interpretation. Such interpretation was essential to the purpose for which the map was made and will not mislead the student who carefully scrutinizes the original; but it does cause the reduced copy to misrepresent material bits of evidence, particularly by giving an appearance of distinct ridges about portions of certain ovals where no ridges are discernible on the original mosaic or on the ground. While cognizance must be taken of these alterations of the original photographic record on the mosaic and while, as will subsequently appear, they sometimes affect conclusions on vital points, their importance must not be exaggerated. T h e beach ridges and swales would usually be sufficiently distinct without the aid given by the draughtsman's pen; and enough of the ovals are in nature sufficiently perfect in form to excite our wonder, as witness the individual photographs reproduced by Melton and Schriever which are free from artificial retouching, and the similar photographs reproduced in this volume. When the original aerial mosaic map is studied, it is found that whereas there is not a single case in which one can be certain that the lack of continuity of an oval rim is genetically related to the subsequent construction of a beach ridge, there are (a) many cases in which the perfection of an oval rim is clearly related genetically to interruptions of the beach ridges, as well as (b) repeated cases in which the distribution of oval basins is clearly related to the control exerted by a preexisting pattern of the beach ridges. These relationships are less clear but are sometimes discernible on the reduced copies of the mosaic published in the articles by Melton and Schriever and by Cooke. In the case of Cotton Patch Bay (Fig. 1) beach ridges come to the very borders of the oval without affecting the integrity of its form. This fact seems sufficiently clear even on the composite photograph reproduced in the figure, but is even more apparent on the ground. T h e oval basin and its incomplete sandy rim appear to have occupied a depression where beach ridges were low and

Ancient Meteorite Scars

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inconspicuous or locally wanting, or else the production of the oval basin and its rim has locally destroyed the preëxisting ridges. In Figures 1, 3, and 10 it is the oval bays and their rims which are most perfect in form, the beach ridges and swales which are

12: Chain of oval bays paralleling sandy beach ridges (light bands) and marshy swales (dark bands) in Myrtle Beach area. N is at top. Bays are from 14 to 1/3 mile long. Part of mosaic shown in Figure 7. FIGURE

most vague or wholly obscured. Throughout the whole Myrtle Beach region this is the prevailing situation, a fact which forces one to conclude that the oval basins and their rims were formed last. Not only the greater integrity of the oval basins and rims but their distribution as well testifies to the prior formation of the beach ridges. T h e r e is a distinct tendency for many of the basins to be arranged along axes paralleling the trend of the beach ridges (Figs. 7, 12, and 13), as though they had occupied depressions already existing between certain of the ridges. Cooke recognized this arrangement as significant of the genesis of the oval basins. In replying to Cooke, Melton expressed the view that such arrangement might be due to chance. It seems difficult to accept this latter view when we note that the arrangement occurs

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Ancient Meteorite Scars

not once but repeatedly throughout the area represented in the original mosaic map. At least two of these "chains" of ovals are visible on that part of the mosaic reproduced in the paper by Melton and Schriever, while four may be seen in the larger section reproduced by Cooke. In other regions (Fig. 3) the parallelism of chains of bays and beach ridges is evident and testifies to the earlier formation of the ridges. Finally, it is apparent on the original Myrtle Beach mosaic that the irregular clusters of very large ovals, including Cotton Patch Bay and others (Fig. 7) in the western part of the area, and Lewis Ocean Bay and others in the eastern part, occupy depressions much more extensive and far more irregular than the oval bays themselves, and that throughout these larger depressions evidence of beach ridges is obscure or wanting. This situation cannot be interpreted to mean that the ovals are well preserved in these places because beach ridge formation did not take place there and hence did not obscure the ovals. These areas include some of the most poorly formed ovals and most incomplete rims in the district—a condition which should be associated with a particularly good display of beach ridges if formation of the latter were, as Melton and Schriever assume, the cause of obscuring preexisting ovals and removing their rims. In the second place, whether beach ridges are high and strongly developed, or low and inconspicuous, or wholly absent, the entire area must have passed through the zone of shore activity. In so doing it must have suffered the extensive reworking which is involved not only in the construction of beach ridges but equally in the shifting of their associated tidal inlets and other shore forms. We must conclude that the beach ridges, the parallel depressions between pairs of beach ridges, and the irregular depressions between different areas of beach ridges are fairly early features of this old shore zone; and that the ovals, developing later, were influenced by preexisting forms or structures of the region. This conclusion holds true for the tentative alternative suggestion of Melton and Schriever that the meteorites might have fallen on the bottom of a shallow ocean. Whether we imagine the oval bays and their sandy rims passing through the shore zone

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coincidence could occur as frequently as is required to explain the many observed (and doubtless very many more unobserved) examples of double and triple rims. T h e aerial photographs examined by Melton and Schriever showed only single, double, or triple rims. Fortunately there are now available photographs showing more than three concentric rims. The large bay (Fig. 15) near Wilmington, North Carolina, shows at least six well-developed concentric rims. Ten Mile Bay (Fig. 16), nearly three miles long and located three and one-half miles southwest of Smithboro in Marion County, South Carolina, is bordered on the southwest by belts of wooded country and cultivated fields in which parallel ridges are faintly visible on the aerial photograph. At the writer's request Dr. Girard Wheeler visited this area. His observations confirmed the existence of low parallel ridges or rims of sand which were easily traced in the open ground despite the leveling effects of clearing operations and cultivation of the soil, but which were too obscure in the forested area to permit definite conclusions. Dr. Wheeler counted four or five ridges, approximately two feet high, in the open ground and two obscure indications of ridges in the forest. T h e aerial photograph seems to show at least four ridges in the wooded area, so it appears probable that a total of eight or nine concentric rims border parts of this great bay. Maidendown Bay (Fig. 16), another great bay immediately to the south of T e n Mile Bay, appears to have four or five rims bordering its southeastern half, judging from the aerial photograph. It was not practicable to examine these ridges on the ground. That the great bay three miles long, located some four miles north of Pinewood in Sumter County, South Carolina, is bordered by a remarkable succession of concentric rims or sand ridges is apparent from the aerial photograph (Fig. 17), which seems to show a series of not less than six or eight in places. Dr. Wheeler examined this bay and found that multiple sand ridges were undoubtedly present. Some were not sufficiently accessible, because of swamps in the depressions between the ridges, to permit close examination. Those in cleared areas, while much obscured by attempted cultivation of the soil, are readily discernible. In height the ridges vary from

F I G U R E 1 6 : Ten Mile Bay (top) and Maidendown Bay (bottom) near Smithboro, S.C., bordered by multiple rims about their SE portions. SW of Ten Mile Bay sand rims and swales appear as parallel light and dark bands in wooded strip near bay and in cultivated fields farther out. Both bays are somewhat ovoid, with narrower end toward SE. Arrow points N, and Maidendown Bay is about 2 miles long. White lines are roads, white patches cultivated fields. (Fairchild Aerial Surveys, Inc.)

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half a foot up to two feet for those less obvious on the photograph, while portions showing pure white are reported by the natives to rise several feet higher. T h e photograph of Suggs Mill Pond (Fig. 33) shows parts of eight overlapping or coalescing ridges exclusive of the broad outer rim of more irregular form. It should be noted that the ridges bordering all these bays are composed of sand, are approximately but not exactly concentric, are separated from each other by low swales which are often marshy, are best developed toward the southeastern half or twothirds of the bays, are most widely spaced there, and usually coalesce or disappear on approaching the northwestern ends of the bays. There seems to be no reason to doubt that all these ridge forms are essentially identical in character except the outermost one, which is often higher and broader than the others and more irregular in form, and which suggests an independent origin (to be discussed later). If one may reasonably hesitate to accept an explanation of the rims which requires that in a number of instances two or three meteorites in succession shall strike nearly in the same spot, he must surely reject that explanation when it involves the necessity of six, eight, or possibly more meteorites striking so nearly in the same spot as to produce a succession of rims, each a little smaller in diameter than its predecessor, and each so systematically disposed with reference to its predecessors as to result in maximum preservation of rims in the southeastern portion of the resulting multiple bay. T h u s the meteoritic hypothesis, of doubtful utility when applied to bays having double and triple rims, becomes clearly incompetent when we consider bays possessing multiple rims in considerably higher number. INTERSECTING

BAYS

T h e writer's observations confirm those of Melton and Schriever to the effect that bays frequently intersect each other and that in such cases either the larger bay or the smaller bay may be the one to preserve complete integrity of outline. Furthermore, if one grants the competence of the meteoritic hypothesis in other respects, the deductions made by these two authors concerning

Recent Meteorite Scars

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intersecting craters appear to be valid. For it is obvious that if meteoritic impact can produce craters of the general type observed, either small or large meteorites, striking near or within the margins of craters previously produced, must form new and complete craters at the expense of those already existing. In this respect observed facts and the consequences deduced from the meteoritic hypothesis appear to be in agreement. Such agreement, however, does not add strength to the meteoritic hypothesis because it is not of discriminative value. Whatever the origin of the craters, those formed last should have the more perfect contours. S I M I L A R I T Y O F S A N D IN R I M S A N D IN B O T T O M S O F

BAYS

T h e reported similarity between material in the rims and material in the bottoms of the bays appears to be an inference based on occasional records of sand encountered in drilling through the bay deposits. If the inference were correct for the bays as a whole, it would not seem to be significant of the origin of either bays or rims since, no matter how these were formed, sand in the rims could slump or wash or be blown into the adjacent depressions. It should be fully understood, however, that there is no consistent similarity between material recently accumulated in the bottoms of the bays and material in the rims. Both types of deposit are abundantly described in many reports of soil surveys throughout the bay country, and the distinctions between them are made clear. T h e two are mapped independently, named and described as different soil types, and represented on maps by different colors. T h e differences observed are not merely those due to the presence of decaying vegetation within the marshy bays, although the presence of clay, freshwater shells, and other deposits does reflect the special conditions under which the bay deposits were formed. If Melton and Schriever meant to imply that the material underneath the peculiar deposits of the bays, the "bedrock" material in which the oval craters were excavated, is essentially similar to that found in the rims of the bays, then observations

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Recent Meteorite Scars

throughout the bay country as a whole indicate a situation altogether different from that reported by these authors for the Myrtle Beach area. Exposures in walls of many bays, in near-by road cuts or shallow wells, in the slopes of adjacent valleys cut below the levels of the bays, and in the walls of artificial ditches dug for the purpose of draining the bays14 almost invariably reveal a strong contrast between the material composing the Coastal Plain deposits in which the craters are found and the superficial sands of the bordering rims. Most frequently the Coastal Plain deposits consist of sandy or clayey loam, usually red but occasionally buff, pink, or purple, or a mottling of these colors, more rarely, of gravel, orange-colored sand, iron-cemented red or brown sands, marl, clay, and other beds. Even where the Coastal Plain surface deposits are of sand, one can usually distinguish readily between the slightly clayey, less perfectly sorted sands of the plain and the peculiar coarse, loose, white, gray, or faintly buff sands of the oval rims. Only when recently wind-blown sand forms a coating on the Coastal Plain sand is one in doubt, and then the doubt relates to the possible topographic development of a rim rather than to the distinction between rim and plain material when both are exposed in section. In the Myrtle Beach area, conditions are somewhat unusual because here the bays occur on a beach plain composed of sand 14 Bays showing red loam or other Coastal Plain beds exposed in their walls are too n u m e r o u s to record b u t not all of these possess rims. Examples possessing rims a n d showing contrasted Coastal Plain deposits exposed in bay walls are: several small bays near Shell Bluff village, center of Greens Cut q u a d r a n g l e , Ga.-S-C.; bay northeast of McBride C h u r c h , Hilltonia quadrangle, Ga.-S.C.; large bay east of Blackville and bay 3 miles south of Elko, Williston q u a d r a n g l e , S.C.; Swallow Savanna Bay, Peeples q u a d r a n g l e , Ga.-S.C.; Coles Bay, Dial Bay, a n d Woods Mill Bay, Mayesville q u a d r a n g l e , S.C. Examples of bays possessing white sand rims a n d k n o w n to be located in red loam or other contrasted Coastal Plain deposits revealed in neighboring Toad cuts, shallow wells, or valley walls are: the oval bays on either side of t h e Little Salkehatchie River, Olar q u a d r a n g l e , S.C.; Sand Hill Bay, z'/2 miles north of Elim, Florence County soil m a p , S.C.; Mossy Bay, southeast of Blenheim, Marlboro County soil m a p , S.C.; Dial Bay a n d associated bays previously mentioned, Mayesville q u a d r a n g l e , S.C.; small bay southwest of Sumter, o n road to Pinewood, S.C. Examples of bays in which the walls of recently cut drainage ditches reveal red loam o r other Coastal Plain deposits overlain by sharply contrasting white sand of rims are the bay northwest of McBride C h u r c h , Hilltonia q u a d r a n g l e , Ga.-S.C., and the Devil's Woodyard Bay near Springerville, n o r t h of Darlington, S.C.

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extensively reworked by wave action. But even here the parallel beach ridges of sand alternate with swales in which silt, clay, and marsh deposits are sufficiently abundant to cause marked contrasts in vegetation and to give muddy roads in which cars easily may be bogged. Yet the rims consist uniformly of clean white sand; and the silt and other material which should have been thrown out to help form the rims, were these the product of meteoritic impact, are not found in rim deposits. Prouty, 15 who supports the meteoritic hypothesis, has recognized the contrast between Coastal Plain deposits and the pure sand of the rims, and has suggested that rain wash may have removed finer material from the rims, thus bringing about a contrast in ejected rim deposits and underlying Coastal Plain deposits which did not originally exist. T h e r e can be no doubt that such separation does take place on the Coastal Plain surface, giving a superficial layer of sand quite unlike the underlying loam or similar material from which it was derived. Weathering could, furthermore, easily remove organic material from rims thrown up in such an area as the Myrtle Beach plain. But there are serious objections to applying Prouty's suggestion to the rims in general. If rims of red loam five, ten, and fifteen feet high could be leached of their finer material and otherwise altered to give white rims of pure coarse sand, adjacent Coastal Plain ridges or swells of the same material should similarly be leached; but these latter remain unaltered close to the surface. Commercial sand pits excavated deeply into the rims of white sand never, within the writer's experience, reveal an inner core of loam or other material differing from the true rim of sand. Drainage ditches cut through rims reveal not a gradation from white sand above to red loam below but a sharp contact, at the level of the adjacent plain, separating pure white sand above from distinctly different Coastal Plain deposits below. That the rims surrounding the oval craters are uniformly composed of coarse white, gray, or buff sand, regardless of what may be the color and composition of the Coastal Plain beds in 15

W i l l i a m F. P r o u t y , p e r s o n a l

communication.

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which these craters are formed, is a fact fully established by abundant field evidence. This fact seems to be fatal to any hypothesis which would explain the rims as portions of the Coastal Plain deposits ejected by the impact of meteorites. Melton and Schriever in some measure appreciated the force of this objection to the meteoritic hypothesis, for they wrote: "In at least one respect the authors are not convinced that the facts are adequate to substantiate theory. In the rims thus far examined there is a noteworthy absence of bed-rock fragments larger than sand grains." 10 But they pointed out that such fragments might be found in the rims of bays not yet examined, that perhaps such fragments should not be expected from the unconsolidated, watersaturated clastic sediments of the Coastal Plain, and that, even if they did occur, the time since formation of the bays might have been sufficiently long for weathering to reduce such fragments to their constituent elements. With respect to the first point, it may be noted that studies by Prouty and others, and the present writer's own extended examinations of bays in seventeen counties of three states, fully substantiate the observation of Melton and Schriever that "there is a noteworthy absence of bed-rock fragments" in the rims. Indian arrowheads and associated small fragments of flint and other materials used in making such arrowheads, evidently of recent human importation, are the only fragments larger than sand grains thus far reported. With respect to the second point, it should be noted that the Coastal Plain deposits include, close to the surface in many places as well as in depth, layers of well-consolidated, iron-cemented sandstone, beds of limestone, coquina, silicified limestone and shell rock, layers of chert, and other hard material. Large fragments of bedrock are found on the slopes of shallow valleys and ravines in areas where bays are present, and there appears to be no reason why they should not have been ejected with other rim materials if the rims were the product of meteoritic impact. With respect to the third point, the long period of weathering 1 6 F. A . Melton and William Schriever. T h e Carolina " B a y s " — A r e T h e y Meteorite Scars? Jour. Geol., 41:52-66, 1933. See p. 65.

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invoked by Melton and Schriever is based on their assumption that the bays are relatively ancient, antedating the period of Coastal Plain terracing and the formation of the Myrtle Beach plain with its parallel beach ridges and swales. In an earlier chapter we have demonstrated that this assumption of great age is invalid and that the bays are of later date than the surface on which they are found. Consequently, the opportunity for weathering has been more limited than was supposed. Furthermore, much of the material forming consolidated beds in the Coastal Plain is of a nature to resist weathering very effectively. Silicified shell rock found near the surface in valley walls and occasionally encountered in the marshes of baylike depressions is extremely resistant. Layers of even more resistant chert or of silicified foraminiferal limestone are found close to the surface in parts of the bay region, and the hard fragments are collected by the natives for use in stone walls or as decorations for flower gardens. All things considered, there seems to be no reason to doubt that, if the bay rims were thé product of meteoritic impact, there would be an abundance of bedrock fragments in the ejected material. Thus the meteoritic hypothesis fails to explain satisfactorily the striking contrast between the composition of the Coastal Plain beds and the composition of the rims, and the absence of bedrock fragments in the latter. A B S E N C E OF B A Y S IN

PIEDMONT

Since the publication of Melton and Schriever's paper, no evidence has been discovered to indicate that the peculiar oval craters, called bays on the Coastal Plain, are to be found in the adjacent Piedmont province. T h e inference of these authors that the bays are absent from that province appears to be correct. T h e meteoritic hypothesis, as presented by the authors cited, calls for the impact of numerous meteorites (from the supposed great shower) upon the surface of the Piedmont as well as upon the Coastal Plain. Thus the meteoritic hypothesis itself cannot account for the absence of bays in the Piedmont. Some other factor must be invoked either to prevent meteorites from forming craters in the Piedmont or to destroy the craters supposed

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to have been produced there. Apparently the authors rely chiefly upon more vigorous weathering and erosion in the hilly Piedmont with its stronger relief than in the Coastal Plain to account for destruction of the bays in one province and their preservation in the other. Geological conditions in the Piedmont appear to be sufficiently favorable for registering and preserving evidences of meteoritic impact. Large meteorites falling on hard crystalline rocks or on parts of the earth deeply covered with snow or ice might penetrate but slightly below the earth's surface and produce scarcely perceptible depressions, easily effaced or easily overlooked. 17 But the deep soil cover of the Piedmont upland appears to be as well adapted to the formation of conspicuous craters as are the Coastal Plain beds, and neither now, nor presumably even during the Glacial Epoch, do we have to reckon with a covering of snow or ice sufficiently deep to prevent effective penetration of such large bodies as would be required to form the Carolina bays. It is conceivable that the more sandy beds of the Coastal Plain might give larger craters than would develop in the more compact, tenacious decomposition products of crystalline rocks in the Piedmont; but it seems only reasonable to suppose that a shower of meteorites sufficiently large to produce many thousands of craters on the Coastal Plain, which are today from a quarter of a mile to three or four miles in longest diameter, must have produced in the deeply decayed mantle of the Piedmont many very conspicuous depressions. Differences in degree of erosion or weathering along the inner Coastal Plain border and the adjacent Piedmont do not seem competent to explain the apparent cessation of meteorite craters at the contact between the two provinces. Vigorous erosion in the immediate vicinity of major drainage channels might destroy near-by oval craters, just as it may have destroyed some of those close to stream valleys in the Coastal Plain. But despite the submature to mature dissection of the Piedmont surface, there are stretches of terrain so faintly undulating or so gently sloping 17

Charles P. Olivier. Meteors. 276 pp., Baltimore, 1925. See p. 247.

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that they should preserve from ready destruction by erosion and weathering deeply gouged or deeply blasted meteoritic craters. W e are forced to the conclusion that the meteoritic hypothesis not only fails of itself to account for the apparent absence of oval craters in the Piedmont province, but that the supplementary explanations, invoked to explain the absence of forms which under the meteoritic hypothesis should occur there, are of uncertain validity. SUMMARY

Melton and Schriever listed nine major "facts which any theory of origin must explain" and which in their opinion the meteoritic hypothesis did explain satisfactorily. In the light of our present fuller knowledge of the bays and after critical analysis of deductions which may properly be made from the meteoritic hypothesis, we have found that in eight out of nine cases the meteoritic hypothesis fails to provide a satisfactory explanation of the facts observed. T h e one fact satisfactorily accounted for by this hypothesis is not of discriminative value, for various hypotheses of origin will explain the fact that craters intersect and that the craters last formed, whether large or small, will be the more perfect in outline. T h e form of the craters, the wide range of their axial directions, the variability of ellipticity in both large and small craters, the rarity of completely encircling rims, the frequency of no rim development, the frequently erratic or asymmetrical distribution of such rims as do exist, the existence of multiple concentric rims systematically disposed in corresponding portions of various bays, the striking dissimilarity between material composing the rims and that composing the Coastal Plain beds in which the craters are excavated, as well as the absence of bedrock fragments from the rims, and the absence of similar craters and rims in the adjacent Piedmont province—all these are facts of major significance which appear incapable of rational explanation on the basis of the meteoritic hypothesis. We have been considering a modification of the original meteoritic hypothesis, a form of Melton and Schriever's explanation

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amended to bring it into harmony with the observed relationship of oval bays to earlier-formed beach ridges. It may occur to the reader that the original hypothesis of Melton and Schriever might be modified still further to bring it into harmony with the facts discussed in this chapter while still retaining the meteoritic explanation of the oval basins. T h u s we might explain the excavation of the craters by meteoritic impact but attribute the form and orientation of the craters to wave erosion on lakes occupying them and swept by winds prevailingly from one or more directions, the sand rims to the action of waves in building beach ridges or the action of wind in building dune ridges, and so on. It is sound scientific procedure to improve a proffered hypothesis in every possible way and then to test it in its most favorable form. W h e n this is done in the case of the meteoritic hypothesis two facts become apparent: (a) the meteoritic hypothesis is robbed of its support, since the critical facts supposed to indicate a meteoritic origin for the depressions (oval form, parallelism of axes, major sand accumulation about southeast ends of basins, and so on) are otherwise explained, and (b) there remain a large number of additional facts (such as enormous size of craters, highly irregular outline of many craters, undisturbed condition of Coastal Plain beds adjacent to craters, abundance of channels draining into or out of the craters) which cannot reasonably be explained on the basis of the meteoritic hypothesis modified in the manner suggested. T h i s last aspect of the problem will be made clear in the chapter which follows.

VII Further Tests of the Meteoritic Hypothesis

T

H U S F A R we have considered only those bay characteristics specifically listed by Melton and Schriever as requiring explanation. T h e r e are, however, other expectable consequences of the meteoritic hypothesis and other observed facts which should be compared in our effort to test fully the possibilities of this explanation of bay origin. W e may accordingly proceed to consideration of these additional points. ENORMOUS SIZE OF B A Y S

Were the Carolina bays produced by meteoritic impact we should expect them to be of moderate size. Known meteorite craters, even those produced by explosive impact, are relatively small. If we accept the meteoritic origin of Coon Butte or Meteor Crater in Arizona, we have one such crater 4,000 feet in diameter, "but all the other known [meteorite] craters are about 600 feet or less in diameter." 1 Many of the Carolina bays are from 2 to 3 miles in length, and several measure from 3 up to 4 miles; while many are one mile or more in breadth, some as much as 2 to 214 miles. T h e only large meteor crater known, the Arizona example, is obviously the product of a violent explosion and yet is less than a mile in greatest diameter. As already explained, an explosive origin for the Carolina craters is apparently excluded by their oval form (explosion craters being approximately circular), while such origin is certainly excluded by considerations discussed in other sections of this volume. W e are thus thrown back upon the theory of plowing impact, the theory apparently favored by Melton and Schriever. But craters thus produced without explosive impact are little wider than the masses which effected the plowing. T o explain the larger 1

Fletcher Watson, Jr. Meteor Craters. Pop. Astron., 44:2-17, 1936. See p. 15.

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Carolina craters as the product of plowing we would have to assume a violent dispersal of material not indicated, or meteoritic masses of an order of magnitude varying from 2,000 or 3,000 feet up to one or two miles in diameter—dimensions truly gigantic as compared with the sizes of known meteorites, the largest of which is less than 20 feet in diameter. "Even the largest meteorites known are insignificant when compared to the bodies required by the meteoritic theory to form the Carolina Bays." 2 It is not safe to "limit Nature" 3 by asserting that meteoritic masses of gigantic size, wholly unlike anything found on other parts of the earth's surface, could not in one particular instance strike in a given locality. All that can properly be said is that the enormous size of the Carolina craters, by requiring for their excavation meteorites of unheard-of dimensions, places upon the meteoritic hypothesis such a heavy burden as to cast doubt upon its validity. SHALLOWNESS OF B A Y S

Meteoritic impact, whether of the explosive or gouging type, should produce craters relatively deep. The reasonableness of this deduction from the meteoritic hypothesis is confirmed by conditions in known meteorite craters, which exhibit pronounced depressions. Meteor Crater, Arizona, 4,000 feet in diameter, has a visible depth of nearly 600 feet, while rock debris and meteoritic fragments are reported to a depth of nearly 1,300 feet below the level of the plain. The largest Wabar crater, only 330 feet across, has a visible depth of 40 feet. In the smallest Henbury crater, 30 feet in diameter, a meteoritic mass was found 10 feet below the ground level. In these cases the ratio of diameter to visible depth is approximately 7 to l and 8 to 1 in the two examples for which visible depth is given; and the ratio of diameter to depth of penetration below surface approximately 3 to 1 in the two examples for which depth of penetration is given. In the shallow Odessa crater, reported as ancient and weathered, the ratio of diameter to present visible depth is roughly 33 to 1. 2

Ibid., p. 17. Douglas Johnson. Role of Analysis in Scientific Investigation. Bull. Geol. Soc. Amer., 44:461-494, 1933. See p. 485. 3

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T h e Carolina craters, on the other hand, are remarkably shallow features. T h e visible depth of oval bays 1, 2, and even 3 miles in diameter may be only a few feet, often not over 2, 3, or 4 feet, more rarely 20, 30, or 40 feet. This means a ratio of maximum diameter to visible depth ranging from 125 or 150 to 1 up to more than 5,000 to 1. Borings through accumulated bay filling led Glenn, and later Melton and Schriever, to estimate that were this filling removed the total depth of the craters would be from 15 or 20 up to 50 feet (not over .25 feet, according to Glenn). This gives a ratio of diameter to estimated total depth varying from 25 to 1 up to 175 to 1, which must be compared with the ratio 3 to 1 for the meteorite craters cited above in which depth of penetration is reported. The foregoing figures are believed to be fairly typical for craters of the two types. Ratios of diameter to depth may be greater in some cases of meteorite craters and smaller in some of the bays. But there can be no doubt that in respect to relative depth there is a very remarkable contrast between known meteorite craters and the Carolina bays. Such contrast, resulting from the extreme shallowness of the bays, is distinctly unfavorable to the meteoritic hypothesis of bay origin. INSIGNIFICANT S I Z E OF R I M S

If the large Carolina craters were produced by the plowing action of gigantic meteorites or by the explosion of such meteorites, the volume of displaced material found in the rims should be enormous. In the words of Cooke 4 the rim around a crater a mile in diameter "would look like a mountain in the flat Carolina plain." Because the white sand of many rims, when but little obscured by vegetation, contrasts sharply with the dark foliage of dense forest and underbrush covering the floors of the oval bays and the adjacent plain, aerial photographs give a wholly false impression of notable ridges of sand surrounding the bays. As a matter of fact, the only conspicuous element of the rims is the white color * C. Wythe Cooke. Discussion of the Origin of the Supposed Meteorite Scars of South Carolina. Jour. Geol., 42:88-96, 1934. See p. 90.

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Tests of Meteoritic Hypothesis

of the sand as seen from the air. On the ground one could easily cross most of the rims without noticing them, were he not consciously alert to discover faint differences in slope, altitude, soil, and vegetation. Where the rims are poorly developed one must repeatedly cross and recross the borderland of the bays before he can decide whether or not a rim is present. In some places where the aerial photograph apparently shows the presence of a distinct rim, the observer on the ground is utterly unable to locate it even after painstaking efforts. T h e sensitive plate of the camera records a difference of vegetation, due perhaps to some faint difference in composition or moisture content of the soil, where the human eye, after long and detailed scrutiny on the ground, cannot find what the observer believes, from evidence of the aerial photograph, must be there. Even the best-developed rims are "ridges" only if we apply this latter term to broad swells of the ground usually 2, 3, or 5 feet high, more rarely 8, 10, or 15 feet, as compared with a breadth ranging from 100 feet up to 1,000 feet. Despite the misleading appearance of the aerial photographs, there is nothing in the bay region which in the remotest degree resembles the prominent ridges of sand one should expect to be cast out of depressions formed by the gouging or explosive action of large meteoritic masses. T h e small size of the rims cannot be an illusion produced by silting up of bays and adjacent plains until much of the rim lies buried, for no silting (except limited amounts in the bottoms of the craters) is in evidence about most of the bays, and the entire rim usually is exposed to observation. Even in the Myrtle Beach area, where silting occurs both within the bays and in low portions of the adjacent beach plain, the fact that the rims are really of small size is easily determined. Melton and Schriever were fully aware of the silting in this locality but were not deceived into thinking that such silting concealed all but the crests of really large rims. Melton estimated that the amount of material removed to form the craterlike depressions of this area must have been at least twenty-five times as great as the volume of material found in the rims. Observations of the present writer indicate that in the case of big bays with small rims the propor-

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tion must have been many hundreds, possibly thousands, to one. In addition there are, as already indicated, many bays, both large and small, without any rims. Melton and Schriever, by supposing that the bays were submerged under the ocean, could attribute to marine currents the removal of sand from formerly greater rims; and Melton himself, in his reply to Cooke, goes so far as to consider the possibility that marine planation was responsible for widespread reduction of the surface subjected to meteoritic bombardment, a process involving complete destruction of the original rims due to impact, and filling of the depressions with loose sand. On this assumption, the existing rims were interpreted, not as material ejected by the meteorites, but as loose sand washed out of the filled depressions by ocean currents moving southeastward. By thus admitting that "the rims may have been formed at various times long after the bays developed," instead of being the product of meteoritic impact, Melton removed much of the foundation upon which the meteoritic hypothesis was based; and it must be noted that the whole tenor of Melton's reply to Cooke indicates much less confidence in the meteoritic interpretation than characterized the original presentation by Melton and Schriever jointly. While ocean currents may be theoretically competent either to reduce or completely remove large rims due to meteoritic impact, the attempt to bring the meteoritic hypothesis into harmony with observed facts by invoking this submarine agency fails for reasons fully set forth on earlier pages. As was there made clear, no interpretation of bay history is tenable which would require delicate rims of loose sand to pass through the zone of destructive wave action and still maintain their integrity. We must conclude that the rims were built on dry land just as we observe them, with their nice adjustment of rims to depressions and of multiple concentric rims to each other and to systematic positions within the depressions; and that since these forms were developed the land on which they rest has not been beneath the surface of the sea. T h u s the insignificant volume of the rims, contrasting strangely with the enormous volume of ma-

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Tests of Meteoritic Hypothesis

terial removed from the oval depressions, remains, under the meteoritic hypothesis, an enigma for which there appears to be no satisfactory explanation. C O N V E R G E N C E OF M U L T I P L E

RIMS

Where multiple rims of the same bay converge to a single rim, the latter should be exceptionally high or exceptionally broad if it represents the product of repeated expulsions of material by meteoritic impact. Observed facts are not in accord with this reasonable deduction from the meteoritic hypothesis, as will be apparent from an inspection of those aerial photographs in this volume which show bays with multiple rims. For example. Watts Bay (Fig. 5) in the Myrtle Beach district shows three rims in its southeastern quadrant. Where these converge toward the northwest to form a single rim, the latter is not unusually large. It might, however, be held that in this direction all the rims are supposed, on the meteoritic interpretation, to thin progressively, so that their combined volume need not be large about the northwestern end of a bay. T h i s explanation will not apply to the southwestern quadrant of the bay, where the (supposedly) combined rim is even less conspicuous. Field studies of multiple rims failed to show any case in which variations in the volumes of sandy rims appeared to depend upon the superposition or coalescence of several independent rims. T h i s would seem to constitute an infirmity of the meteoritic hypothesis and to point to some other origin for the oval rims. C O N T A C T OF ADJACENT

RIMS

It is a reasonable deduction from the meteoritic hypothesis that, where oval rims of adjacent bays are in contact with each other, the portion of the rim common to both depressions should be abnormally high or abnormally broad because it is composed of material thrown out of both depressions by meteoritic impact. Observed facts are conspicuously in discordance with this expectation. Repeatedly the portion of the rim common to two intersecting ovals is abnormally narrow or abnormally low, or

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both. South Barebone Bay touches North Barebone Bay at the northwest, the line of contact being visible in the northwestern part of Figure 4. It will be noted that between the two the rim almost, and at one point apparently quite, disappears. T h e waterloving vegetation characteristic of the two bays seems at one point to continue right across the zone of intersection, the surfaces of the two depressed areas apparently merging just where a notable barrier of ejected earth should separate them. Watts Bay is in contact with a very perfect but much smaller bay at its southeastern end (Fig. 5). At the line of contact the rim of the larger bay, elsewhere notably conspicuous, becomes so low and so narrow as to be a very minor feature of the topography. Indeed, at one point it apparently disappears, and the writer noted in his field record: " A t the contact between this bay [the larger one shown in Figure 5] and the little one to the southeast, the sand ridge thins out to almost nothing and is very low. At one point the two bays seem to touch and there is a boggy place in the trail where it passes between the two. . . . T h e bog in the trail where the two bays meet seems to be a channel-way formerly connecting two lakes [in the two bays]." In other cases a continuous but relatively small sandy ridge separates adjacent bays. The prevailing absence of a notably conspicuous ridge between closely adjacent bays, and the frequent complete disappearance of such a ridge at the point of contact, call for explanation. Where two depressions profoundly intersect each other, so that their normal perimeters if protracted would extensively overlap, one might assume that two meteorites simultaneously falling close together had produced a double crater with only a low wall between its two parts. It will be noted, however, that in the cases here considered the two depressions are essentially distinct and touch each other for a short distance only. Under such conditions it seems reasonable, on the meteoritic hypothesis, to expect an unusually high or unusually broad rim at the place of contact. Failure to find facts conformable to this reasonable expectation imposes an infirmity on the meteoritic hypothesis.

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Tests of Meteoritic Hypothesis S I Z E OF R I M S U N R E L A T E D TO S I Z E OF

BAYS

If the Carolina bays are the product of meteoritic impact, there should be a definite correlation between size of bays and size of bordering rim. Large meteorites, excavating large craters, should pile u p large rims; small meteorites, excavating small craters, should form small rims. Cooke 5 observed that the facts in the Myrtle Beach area were not in accord with this reasonable expectation. Melton 6 replied that Cooke was in error, because of misinterpretation of the photographs upon which Cooke's observations were based, and stated: " I t is unquestionably true that the larger bays have the larger rims. T h e y are longer, higher, and in general broader than the rims of the small bays." A f t e r field studies of many bays, in the Myrtle Beach area and elsewhere, the present writer is convinced that there is no consistent relation between the size of bays and the size of their bordering rims. It repeatedly happens that large bays have inconspicuous rims or none, while small bays sometimes have remarkably prominent rims. Tony Hill Bay, Lodge quadrangle, South Carolina, is 1 ]/% miles long. Examination of its northern, eastern, and southern sides7 revealed only low and poorly formed rim development at its southeastern border. Elsewhere what looks like a rim on the topographic map proves to be the gently undulating Coastal Plain surface with only a coating of wind-blown sand. The great bay east and southeast of Rowesville, Orangeburg quadrangle, South Carolina, is nearly 3 miles long and should, according to the meteoritic theory, have a very impressive rim, especially at its southeastern end. Complete circling of this bay failed to discover any good rim development, although at one point on the southwest side a prominent but local undulation of the Coastal Plain, covered with wind-blown sand, presented some resemblance to a true rim. Wadboo Swamp, a great oval bay 2 miles long, on the same quadrangle, may have moderate rim development along part of its southwest border; but no rim was observed about its southeastern end, or up its eastern side, where rims are normally most prominent. Polk Swamp, 2 m > l e s long and located 5 C. Wythe Cooke. Discussion of the Origin of the Supposed Meteorite Scars of South Carolina. J o u r . Geol., 42:88-96, 1934. See p. 90. 6 1'". A. Melton. T h e Origin of the Supposed Meteorite Scars: Reply. Jour. Geol., 42:97-104. 1934. See p. 98. 7 In the following statements the omission of reference to parts of a bay's circumference means that those parts were not examined. Where the whole border could not be visited, a special effort was made to see the southeast quadrant where maximum rim development usually occurs.

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southwest of Wadboo Swamp, shows no true rim about its southeastern and southern borders where the theory calls for an exceptionally large rim. Buxton Flat, an imperfect bay over 2 miles long just northeast of the center of the Peeples quadrangle, South Carolina, appears on the map to have a prominent rim about its southern and eastern borders. But numerous sinkholes in this apparent rim reveal its true character, and a traverse showed normal Coastal Plain topography upon which no rim was superimposed, but only a moderate coating of wind-blown sand. Big Junkyard Bay, 1 m i l e s long, Manning quadrangle, South Carolina, lacks a distinct rim about its southeastern and southern sides where rim development should be at a maximum. T h e oval depression occupied by White Lake, Bladen County soil map, North Carolina, is 2 miles long. About its northern and western borders are large accumulations of sand which, on the soil map and aerial photograph (Fig. 29, southeast corner) and as seen on the ground, appear to be related to smaller bays to the north and west. But at the southeastern end of the lake and extending well up the eastern side is a very distinct and broad but low rim of white sand. T h e writer's field notes record that this rim, instead of being of a size appropriate to the great bay, "is never as large and impressive as many at the southeast borders of smaller bays." ¿¡ingletary Lake, in the same region, occupies an oval depression 1i/ 2 miles long located in a flat sandy plain the soil of which is here classed as "Norfolk Sand." Along the northern portion of its western side is a low rim of white sand, which southward gives place to the normal surface of the Coastal Plain covered with an unusually broad coating of wind-blown sand but no true rim. About the southeastern end of the oval is a true rim, roughly 5 feet high and 250 feet broad where measured, which continues northeastward. Its extension in this direction was not explored but the soil map indicates that the "St. Lucie Sand" composing the rim continues halfway up the eastern side of the lake. T h e following record appears in the writer's field notes: "This rim, considering the size of the lake, is insignificant as compared with good rims about smaller bays." Jones Lake, likewise in the same region and shown on the Bladen County soil map. North Carolina, and on Figure 2g, southwest of center, occupies an oval depression 1 1/3 miles long. At its southeastern border is a prominent low rim of white sand, moderately broad and not over 5 or 6 feet high. Westward this rim decreases to one foot in height and 50 feet in breadth, and then disappears in the marsh. Whether it reappears farther northwest is not known. What looks like a good rim in that direction on the soil map is labeled "Norfolk Sand," which in this region constitutes much of the surface of the Coastal Plain. T h e sand of the rims is usually called "St. Lucie Sand," but in the present case the rim just described extends westward into the area indicated as "Norfolk Sand." From the fire tower on the eastern side of Jones Lake the true rim appears to terminate about halfway up that side, but its course was not traced further on the ground. The writer's field notes record that "this rim is not comparable in size with rims about some of the smaller bays." It thus appears that while the rims about the three lakes examined in Bladen County, North Carolina, are much more prominent than those about

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Tests of Meteoritic Hypothesis

any of the bays previously described, they still fall far short of the dimensions appropriate to such large depressions. The greatest bay of which the writer has knowledge is Hilson Bay, Marlboro County soil map. South Carolina, a remarkably perfect example approximately 4 miles long and 1 m i l e s broad. According to the meteoritic hypothesis this bay should have a truly stupendous rim about its southeastern end as well as along its two sides. The yellow band which on the soil map encircles these portions of the bay and is marked "PI" suggests the possibility of such a rim. But this soil type is the "Portsmouth Sandy Loam" forming the floors and margins of certain bays but not rims. The rim-forming material in this region is "Norfolk Sand" (or "Norfolk Coarse Sand"), and two tiny patches only of this material are shown at the southeastern end of the bay. The natives of the region, usually familiar with all important sand deposits because of their commercial value, report no notable accumulation about any part of this bay. Hence, while the writer saw only the northwestern part of this depression, he believes it safe to say that the greatest bay of which he has any knowledge is bordered by a relatively insignificant rim. In contrast with the foregoing examples of large bays about which rims are imperceptible, inconspicuous, or of moderate magnitude only, we may cite a few cases of prominent rims about smaller bays. North Barebone Bay (Fig. 14) in the Myrtle Beach region, South Carolina, is only ^ of a mile in length but has a rim on the southeast 5 feet high and 650 feet or more in breadth.8 Watts Bay (Fig. 5), northeast of North Barebone Bay, only slightly larger than the latter, has a triple rim on the southeast which in places exceeds 860 feet in total breadth. If the fact that the rim is triple at this point makes it incomparable with simple rims, we may cite the bay northeast of McBride Church, Hilltonia quadrangle, Georgia and South Carolina, which, although but s/4 of a mile long, has a rim on the southeast 300 feet wide and 5 or 6 feet high. The bay just east of Blackville (Fig. 4s; see Williston quadrangle, South Carolina) is not quite 1 m i l e s long with an exceptionally prominent rim, twice as high (10 or is feet) as any of those cited above, and 1,000 feet broad in places, according to Cooke and as suggested by aerial photographs. Sand Bay near Kingstree, Williamsburg County soil map, South Carolina, about 1 miles long, has a remarkable rim is to 15 feet high and over 500 feet broad which is extensively worked for commercial supplies of sand. The three bays last mentioned and their prominent rims may be compared with the bays 2, 3, and 4 miles long which are devoid of noticeable rims. Hog Bay, Lodge quadrangle, South Carolina, i/4 of a mile long, has a rim 5 feet high and 150 to 300 feet wide about its southeast quadrant. The small bay near Atkinson's store at Springerville, north of Darlington, South Carolina, is only 1/2 mile long but has a more prominent rim than some bays 2 and 3 miles in length. In this same region the Devil's Woodyard Bay, a mile in length, has a very striking rim 6 feet high and 350 feet broad where measured. Swallow Savanna Bay, Peeples quadrangle, South Carolina, although but 2/3 8 All measurements are approximate, distances being paced, and elevations estimated by the height of a man standing at the bay margin, on the plain at the outer margin of the rim, or in the swales between double and triple rims.

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of a mile in length, possesses a remarkably prominent rim of snow-white sand 8 to 10 feet high and 400 feet broad where measured at the southeast border. These dimensions may be exceeded considerably farther up the east side, where the rim is the most spectacular of all those examined by the writer and where numerous but small commercial sand pits reveal the nature and extent of the imposing deposit. A wagon trail follows the rim, but cars are often deeply "bogged down" in the loose sand. Bostick Pond, just east of Swallow Savanna, occupies a bay which is not over 14 mile long, yet has a good rim of white sand on the southeast. Just southwest of Swallow Savanna is a small bay approximately i/2 mile long which is bordered on the southeast by a rim 200 to 300 feet wide and 6 or 8 feet high.

Emphasis has here been placed upon representative instances of large bays with comparatively small rims or none at all, and small bays bordered by large and prominent rims, in order to establish the truth respecting a disputed point of critical importance. It should be realized, however, that there are cases in which large bays have large rims, as well as cases in which small bays have small rims or none at all. T h e field evidence as a whole offers support neither for Melton's belief that the larger bays have the larger rims nor for Cooke's suggestion that, on the contrary, the smaller bays have broader and more conspicuous rims than do the larger bays. T h e evidence indicates rather that there is no systematic relationship between size of bay and size of bordering rim. T h i s conclusion is highly unfavorable to the meteoritic hypothesis, according to which large bays should have large rims, and small bays small rims. F O R M OF R I M S

If the Carolina bays are the product of meteoritic impact the rims bordering the craterlike depressions should be true ridges, high in their median portions and bordered by relatively steep slopes. Such a deduction from the meteoritic hypothesis seems justified by the observed form of debris rims resulting from largescale artificial explosions, from explosive volcanic eruptions, from the plowing action of inert projectiles striking at the grazing angle, and from undoubted meteoritic impact. T h e high median portion of the ridge is not necessarily along its central line but may be to one side of the center, with the result that one flank of the ridge is steeper than the other. Long-continued stream

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erosion of such a ridge may undermine and steepen the lateral slopes for a time, or may ultimately reduce them to slopes more gentle than those originally existing. Long-continued weathering may lower and round the ridge crest. In all these forms, however, there persists a high median portion which merges on either side into concave or convex lateral slopes. T h e r e is no tendency for the rim to be, or to become,

flat-topped

or nearly so, with

sudden transition to markedly steeper borders. T h e rims bordering the Carolina bays are peculiarly low and relatively flat and do not resemble in form any known rims composed of debris forcibly ejected from craters. T h e highest rims observed by the writer did not exceed fifteen feet in altitude. It is more usual for a rim hundreds of feet in breadth to have a m a x i m u m altitude of half a dozen feet or less, and to have this altitude persist over a large part of the rim surface, with abrupt transition to relatively steep marginal slopes. Lewis Ocean Bay in the Myrtle Beach area (Fig. 7) is bordered on its northeast side by a rim of almost snow-white sand which has a breadth of 450 feet where measured and a height of only 5 or 6 feet. T h e slope toward the inner bay is noticeably steep as compared with the broad surface of the rim. North Barebone Bay (Fig. 14) has at its southeastern corner a rim 650 feet broad, where traversed, and only about 5 feet high. T h e broad top is almost flat in average elevation but noticeably undulating in detail. Near its inner margin toward the bay, and again near its outer margin toward the adjacent plain, there abruptly begin perceptible downward slopes. These downward slopes of limited extent contrast strongly with the relative flatness of most of the rim. In the case of Watts Bay (Fig. 5) the rim on its northwest side is relatively narrow, only 225 feet wide where measured. But here again the rim is relatively low and flat, while the descent to the marshy land of the bay is short and relatively steep, resembling, as the writer recorded in his field notes, "a weathered wave-nipped cliff" cut in sand. Cotton Patch Bay (Fig. 1) has rims best developed on the northeastern and southwestern sides. Toward the northern end of the northeastern side the sandy rim is 220 feet broad, relatively flat, and not over 2 or 3 feet high, forming on the ground a very low and inconspicuous feature. Southward it increases in breadth. Both inward toward the bay and outward toward the adjacent plain, the marginal slopes of this rim are relatively gentle. A traverse across the rim on the southwest side of this bay, toward the northwestern end of the portion well developed, showed a breadth of 150 feet and an estimated height of 3 feet. T h e broad top was nearly flat but inclined faintly toward the bay. T h e marginal slopes were moderately steep, that toward the marshy plain being in this case slightly steeper than that toward the marshy floor of the

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109

bay. Farther southeast this rim is nearly goo feet wide, with the broad top notably flat, and is bordered by moderate slopes descending to the rear (plain) and the front (bay). Still farther south the rim becomes double, the outer rim being low, flat, 150 feet broad, and separated from the inner rim by a wet and boggy depression 75 feet wide. T h e inner rim where measured was only 65 feet broad and notably low and flat. A n ideal generalized cross section of the rims, showing their most typical characteristics, is represented in Figure 18. In this figure the vertical scale is necessarily grossly exaggerated because a natural scale would show a line which to the eye would appear almost straight.

Long-continued weathering, rain wash, and erosion might conceivably lower once-high ridges and dissipate their material over broader belts of territory. But these processes could not transBay

Plain

FIGURE 18: T y p i c a l cross profile of sandy rim f r o m inner side n e x t bay to outer

side

bordering

A l t i t u d e of broad

plain.

flat-topped

Vertical

scale

greatly

exaggerated.

rim usually v a r y i n g f r o m 2 or 3 u p to 5

or 6 feet; breadth f r o m 150 to 800 feet or more.

form such ridges into low, flat, sharply margined rims having cross profiles similar to that shown in Figure 18. W e are forced to conclude that the form of the rims bordering the Carolina craters is not favorable to the interpretation that these rims represent debris ejected from the craters by meteoritic impact. BILATERAL ASYMMETRY OF BAYS

T h e meteoritic hypothesis as propounded by Melton and Schriever calls for symmetrical craters of oval outline, and these authors apparently assumed the existence of such symmetry. Dr. Donald C. Barton, 9 who had been studying asymmetry in lakes of the Gulf Coastal Plain, first called the writer's attention to the fact that the Carolina bays as a rule show a notably stronger degree of curvature on their northeastern sides than on their southwestern sides. T o lakes exhibiting this type of asymmetry Barton tentatively applied the term "clamshell lakes," because in outline they bear some resemblance to the shells of certain clams. Once recognized, this asymmetry is readily detected in so many e

Donald C. Barton, personal communications, April, May, and October, 1934.

11 o

Tests of Meteoritic Hypothesis

of the ovals that it affords an easy means of orienting aerial photographs of the bays. Indeed, this feature of bay topography, the tendency of ovoid bays to have their narrower ends pointing southeast, and the tendency for major rim development to take place in the southeast quadrant, have constituted three valuable aids in speedily orienting aerial photographs preparatory to more accurate determinations of directions. Barton provisionally attributed the asymmetry of the clamshell lakes of the Gulf Coastal Plain to wind-generated water currents which deposited sand on one shore of the lake. T h e present writer discussed the asymmetry of the Carolina bays before the National Academy of Sciences in April, 1934, and suggested that erosion by waves driven by southwest winds might account for the phenomenon. T h i s suggestion will be more fully discussed in a subsequent chapter. Later Prouty, 10 in supporting the meteoritic origin of the bays, sought to explain their asymmetry by supposing that sand, drifted into the bay from the southwest by wind action, had reduced the originally greater curvature of that side. T h a t sand does occasionally encroach extensively upon bays in the manner suggested by Prouty is indicated by conditions in Big Bay (Fig. 17) four miles north of Pinewood, South Carolina. According to Dr. Girard Wheeler, who examined this bay, the somewhat irregular feature that destroys its symmetry on the west is a mantle of wind-drifted sand which has advanced eastward into the depression. A smaller advance of sand into the northwestern part of South Barebone Bay is visible in Figure 4, while encroaching wind-drifted sand appears to be partially filling and obscuring the marshy swales between multiple rims in Figure 15. Very frequently there is evidence that sand has moved outward in all directions from the rims, giving the notably irregular outer borders of many of them, a feature which contrasts strongly with the normally smooth curves of the inner borders next to the bays. Sand migration under the influence of variable winds is thus 1 0 William F. Prouty. "Carolina Bays" and Elliptical L a k e Basins. Jour. Geol., 43:200 207, 1935. See pp. »04, 207.

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111

a factor to be reckoned with in our study of the bays. But it is difficult to conceive how sand encroachment into bays could produce the perfectly curved borders characteristic of the type of asymmetry here under discussion. On the contrary, such encroachment must tend to destroy the regular outlines of any part of a bay thus affected. T h e present writer's observations of the bays extended to many excellent examples of the asymmetrical ovals. Those studied showed no evidence of appreciable encroachment

tions of secondary inner rim as interpreted by Prouty (A) and by Johnson (B). of wind-drifted sand into the bays from the southwest. In a few localities a little sand, derived from a sandy rim which already had the asymmetrical curvature fully developed,

a p p e a r e d to have

advanced inward over the surface of the bay. But the inner margin of the rim was prevailingly smooth and regularly curved, while outside the narrow rim there stretched marshy land providing no possible source for sand which might be drifted northeastward into the bay (see for example the southwestern side of Cotton Patch Bay, Figs. 1 and 7). In some of these cases, a partial secondary rim had formed, yet the marshy swale separating the two sandy rims remained clearly defined with smoothly curving margins, adequate evidence that here at least sand from the rims or from any other source had not been actively encroaching upon

112

Tests of Meteoritic Hypothesis

the oval basins. South Barebone Bay (Fig. 4) has such a partial secondary rim and was selected by Prouty to illustrate his conception that asymmetry results from encroachment of winddrifted sand which covers and conceals any secondary rims on the southwest sides of bays (see Fig. 19A). T h e present writer's interpretation of conditions in this bay is shown in Figure 19B. Examination of this figure, or of the aerial photograph (Fig. 4) from which it was traced, shows that the asymmetry in curvature of the two sides of the oval is quite obvious, whether one measures the inner or the outer margin of the accumulated sand. In other words, the total sand accumulation on the southwestern side of the bay is patterned on a larger radius of curvature than that on the northeastern side. Hence, movement of part of the sand into the bay or outward from its rim cannot account for the observed asymmetry. In the second place, there is no evidence that the inner rim continues practically in full strength to disappear under the outer rim at X , as shown in Figure 19A, or that the marshy swale between the two rims continues under the outer rim as shown by broken lines in this same figure. On the contrary, the aerial photograph (Fig. 4) shows that the inner rim, relatively broad and high at the southeastern end of the bay, becomes narrower and lower 1 1 toward the northwest, as though it were thinning out to disappear at X , Figure 19B, while the marshy swale curves toward this same point, ending in a line of trees (faintly discernible in the photograph) which grow in the moister soil of the depression. Field observations confirm the inferences based on the photograph, and the writer's field notes record that the inner rim "systematically thins out toward the northwest, like a tapering sandbar." The inner curve of this " b a r " prolongs the curvature of the bay border farther northwest, instead of meeting it at a marked angle; and the bay border in the area of supposed sand encroachment (y, Fig. 19B) is smoothly regular, instead of showing the irregular lobes of sand encroachment such as actually appear in the northwestern 11

T h e lowering is indicated by the color change from white to gray, due to greater dampness of sand nearer the level of water in the marshy bay and consequent denser cover of vegetation more effectually concealing the white sand.

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end of the bay (z, Fig. 19B), where sand invasion from the broad rim of North Barebone Bay is in progress. T h e present writer would interpret these field relations to mean that the southwestern border of South Barebone Bay had been cut back from the position of the broken line (y, Fig. 19B), instead of having been built forward by sand encroachment, and that this backward cutting at y was accompanied by the building of the "bar" which southeast of X forms the inner rim of the bay. The processes believed to be responsible for such changes in the bays will be described in a later chapter. Here we need only say that wave erosion along the margin of a former lake apparently cut back the shore northwest of X , while deposition to the southeast built a tangential curving beach ridge or bar. That minor transport of sand by wind action has occurred along this border of the bay is quite possible, but it is not believed to have been sufficient to account for those major features of the topography discussed above. T h e interpretations applicable to the asymmetrical curvature of South Barebone Bay hold good for all asymmetrical bays observed. The asymmetry extends to the pattern of sand accumulation as a whole, as well as to the curvature of the bay borders, and hence cannot be ascribed to local sand encroachment into one side of a bay. T h e less strongly curved southwestern borders of bays are normally as smooth and perfect as the more strongly curved northeastern sides, failing to show the irregular pattern characteristic of borders locally determined by sand encroachment. We are forced to conclude that the bays show a type of asymmetry not accounted for by meteoritic impact, and that sand encroachment into meteorite craters is equally unable to account for the facts observed. Wave erosion and deposition along the margins of lakes occupying meteorite craters might account for the observed asymmetry. I R R E G U L A R O U T L I N E OF M A N Y

BAYS

Depressions excavated by meteoritic impact should be (a) more or less nearly circular, according to the theory of explosive impact, the results of large-scale experiments with explosive shells

114

Tests of Meteoritic Hypothesis

and bombs, and the observations of known meteorite craters, or (b) elongated grooves or elliptical depressions, if we accept the plowing theory of impact as developed by Melton and Schriever. As a matter of fact, vast numbers of the Carolina bays are of highly irregular shape. Accounts of the bays have properly emphasized the remarkable oval forms revealed by aerial photographs, for it is the degree of perfection of these ovals and the degree of parallelism of their longer axes which arouse wonder and incite the observer to seek an explanation for their origin. T h e critical student must not, however, lose sight of the fact that perfect ovals, whether of the elliptical or ovoid type, are the exception, not the rule. He must guard against the well-known tendency of the human eye to seize upon a recurrent pattern in nature and concentrate attention upon it, to the exclusion of less symmetrical or wholly irregular forms. He must likewise guard against the tendency of the mind to project and complete imperfect figures in the likeness of those best formed and thus to gain an impression of perfect order which does not in fact exist. In the case of the Carolina bays as represented upon the mosaic of aerial photographs partially reproduced in previously published discussions of this problem, he must remember that the perfection of the ovals represented is in some degree the result of drawing, by hand, of white oval borders on the photographs where none exist in nature, the draughtsman being inevitably influenced by the repeated presence of the oval pattern elsewhere. That oval basins of remarkable perfection do exist has already been made clear. The photographs reproduced in this volume include a selection of the most perfect examples of both elliptical and ovoid outline, this selection involving the exclusion of a vastly greater number found less satisfactory. It is, in fact, a difficult matter to find a perfect oval basin nearly surrounded by a perfect sandy rim. Departures from the ideal type are almost infinite in variety. On the other hand, it is an easy matter to find many bays of such marked irregularity that they escape attention on the first casual inspection of the photographs. Examples of such irregular forms will be found on close inspection of

Tests of Meteoritic Hypothesis

115

Figures 5, 6, 7, 10, 1 1 , and 13. In Figure 5. to the southeast of the major bay having three very irregular rims along its southeastern border, is one that is rudely pear-shaped and without noticeable rim, although the contact between marshy bay and drier upland is well marked throughout much of its perimeter.

20: Bays S of Makatoka, Brunswick Co., N.C., showing variations from highly irregular form near center with what appears to be a wooded outlet channel to S, to more nearly oval forms on either side apparently draining NW, to more perfect ovals with sand rims (in lower left corner of picture) all trending NW-SE. N is at top, and largest bay, just NE of center, is about 2/3 mile in greatest diameter. (Fairchild Aerial Surveys, Inc.) FIGURE

From these imperfect forms every gradation can be traced to the most irregular bays imaginable (Fig. 20). It is this gradation of forms which is of prime importance in our attempt to solve the problem of the Carolina craters. If a shower of meteorites descended upon a plain the surface of which was already scarred by innumerable irregular marshy basins, we should then have two easily distinguishable types of depressions: regular craters of meteoritic origin and irregular basins of

116

Tests of Meteoritic Hypothesis

some other origin. T h e two types might frequently overlap or intersect, but there would not be imperceptible gradations between the two. In the case of the Carolina bays the gradation is so perfect that it is impossible to draw any distinct line between oval forms and irregular forms. Whether studying the bays on the ground, on topographic or soil maps, or on aerial photographs, the investigator is constantly at a loss to know whether to include this or that example among the "oval bays" or among the "irregular bays." Irregular forms with bordering rims may seem more closely akin to "the typical oval bay" than more regular examples wholly devoid of rims. T h e student is ultimately forced to the conclusion that nature has made no clear distinction between regular and irregular forms. T h e natives apply the term bay to both indiscriminately, and available evidence suggests no difference in origin of the two types. The meteoritic hypothesis was advanced with full appreciation of the fact that meteoritic impact produces a crater of regular form regardless of the particular shape of the meteoritic mass. Hence no attempt was made to explain irregular bays by the meteoritic hypothesis, it being assumed that the name bay was applied by the natives to two distinct types of depression, one regular in form and of celestial origin, the other irregular in form and due to one or more terrestrial causes. But when we realize that the regular bays grade imperceptibly into irregular forms, and that the latter have all the characteristics of the former except regularity of outline, it becomes apparent that the meteoritic hypothesis, aside from its many other deficiencies, fails to account for the irregularity of outline found in a vast majority of the bays. COASTAL P L A I N BEDS UNDISTURBED

Were the Carolina craters the product of meteoritic impact, the Coastal Plain beds exposed in the sides of the craters should show the effects of violent impact of a great meteoritic mass, or of violent explosion associated with such impact. It is scarcely conceivable that so catastrophic an event would leave sedimentary beds in the crater walls quite undisturbed. We should expect to

Tests of Meteoritic Hypothesis

117

find them badly shattered with fragments irregularly disposed, or turned upward as in Meteor Crater, Arizona, and the craters on the island of Osel. It appears to be well established, however, that the Coastal Plain beds are normally undisturbed about the Carolina bays. True, in a majority of bays the surrounding beds are not exposed at all; but exposures occur in so many that if disturbance were common the fact would be readily apparent. So far as the writer is aware not a single case of disturbance has thus far been reported. On the other hand, many instances of horizontal stratification or of horizontal plain surface have been observed beneath sand rims in the infacing walls of steep-sided bays, in road cuts trenching such walls, and in drainage ditches cut through bordering rims and several feet into the underlying Coastal Plain formations. 12 Melton noted that "beds of Coastal Plain sediments in a number of cases seem to lie flat beneath the bay rims." H e recognized that this fact imposed a burden on the meteoritic hypothesis, for he added: "Should this condition prove to be common it would be necessary, in order to retain the meteoritic hypothesis, to postulate widespread reduction of the original surface through marine planation." We have just seen that the condition is common; and we have earlier shown that the conception of widespread planation beneath the sea, with later elevation of the bays and their rims through the zone of destructive shore processes, is untenable. We can only conclude that the common occurrence of undisturbed Coastal Plain beds bordering the bays is a fact difficult to explain on the basis of the meteoritic hypothesis. C H A N N E L S D R A I N I N G INTO OR OUT OF B A Y S

If the Carolina bays are meteorite craters, they might well contain lakes, or might formerly have contained them. But such 13 Examples of bays revealing exposures of undisturbed Coastal Plain l>eds are: the bay northeast of McBride C h u r c h , Hilltonia q u a d r a n g l e , Ga.-S.C.; bay one mile northwest of Eureka Springs, Oliver quadrangle, Ga.; bay southeast of Reynold, and large bay just east of Blackville, b o t h on Williston q u a d r a n g l e , S.C. (in last case a p p a r e n t stratification of beds at one point dips faintly downward toward bay, as if slight s l u m p i n g might have occurred); c o m p o u n d bay with medial sand rim east of Govan, Olar quadrangle, S.C.; Dial Bay, Mayesville q u a d r a n g l e , S.C.; Devil's Woodyard Bay near Springerville, n o r t h of Darlington, S.C.

118

T e s t s of Meteoritic

Hypothesis

lakes should not commonly have surface outlets or form part of any integrated surface drainage system. T h e reasoning which underlies this deduction from the meteoritic hypothesis is simple. Prior to impact, the groundwater level and the surface drainage of the Coastal Plain must have been established. Wherever a meteoritic mass excavated a crater the bottom of which extended below groundwater level, water would stand in the depression to form a lake. But we should not expect the water to rise above groundwater level and overflow the crater rim. Normally the craters would have neither incoming nor outflowing surface streams. Even if a meteorite struck in a preexisting stream course, we should expect formation of the crater to deflect the stream. Crater lakes are relatively common phenomena in some volcanic regions, but surface streams draining such lakes are rare. We are accustomed to finding crater lakes, sinkhole lakes, kettlehole lakes of glacial regions, and similar water bodies without numerous integrated drainage connections. A remarkable feature of the Carolina bays, of which no account has previously been taken, is the frequency of channels affording ingress or egress to streams which now or formerly drained into or out of the bays. Such channels are beautifully shown in Figures 5, 15, 17, 32, 40, and 42, and less clearly in the case of many other bays figured in this volume. They are sometimes represented, although not always accurately, on soil maps. 13 Topographic maps show outlet streams in many cases and occasionally reveal a well-integrated drainage system draining into and out of a succession of bays.14 Although there is little surface drainage into White Lake and Suggs Mill Pond (see Bladen County soil map, North Carolina), both these bays have outlet channels carrying considerable volumes of water. In both cases the natives 1 3 See, for example, (he Bladen and Cumberland County soil maps, N.C.; Barnwell, Williamsburg, and Florence County soil maps, S.C. 14 See, for example: Alligator Bay and Doussoss Bay, Olar quadrangle, S.C.; Saint George Church bay, Rowesville bay, Black Bay, and others, Orangeburg quadrangle, S.C.; the bay east of West Middle School, Wadboo Swamp bay, Polk Swamp bay, and the bays drained by Sandy Creek, Bowman quadrangle, S.C.; B i g Junkyard Bay, Guys Branch Bay, Islanded Bay, and others. Manning quadrangle, S.C.

Tests of Meteoritic Hypothesis

119

report large springs "boiling" or "fountaining" on the lake floor due to strong upwelling of water from below. These two examples suggest that similar conditions formerly existed in many bays which do not now contain lakes, and that outflow of water supplied by bottom springs carved the channels so frequently observed leading outward from the craterlike depressions. T h e large bay north of Pinewood (Fig. 17) contains no large lake, but its outlet channel was long ago dammed to impound artificially the water entering the basin. Later the dam was destroyed, and at present a stream of sufficient volume to serve as the home of fish six or eight inches long flows freely from the great bay. 15 T h e channel traversing the rim of the large bay near Wilmington, North Carolina (Fig. 15), is particularly broad and sharply carved in places. In many cases outlet channels, while clearly visible, are partly or completely obstructed by accumulations of rim sand. Doubtless many former channels have thus been wholly obliterated. Many bays have two or more outlets, draining either into adjacent streams or into neighboring bays (Fig. 4). Whatever the cause of the Carolina craters, it evidently produced a vast number of basins into which or out of which water flowed freely through channels still visible and often still functioning. Because such drainage channels are not commonly found in known meteorite craters or, for that matter, in craters produced by volcanic eruptions, artillery fire, or other violent explosions or impacts, it seems doubtful whether the channeled craters of the Atlantic Coastal Plain can reasonably be attributed to meteoritic impact, whether of the gouging or explosive type. T o account for the observed facts by the meteoritic hypothesis we would have to assume that in every case where a crater now possesses, or formerly possessed, one or more outlet channels, the meteorite excavated a depression deep enough to tap artesian water under sufficient pressure to cause surface outflow. Where inlet channels are found, we would have to assume further that impact produced no rims which could impede the flow of surface water into the craters. 15

Girard Wheeler, manuscript report on observations made at the writer's request.

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Tests of Meteoritic Hypothesis

OUTLET CHANNELS

FREQUENTLY

TRAVERSE R I M

BARRIERS

If we admit, for the moment, that meteoritic impact could somehow produce the observed craters and their rims, and that peculiar geological conditions could cause waters to rise in these craters and overflow their borders, it is obvious that such outflow must take place where rims or crater borders were lowest. T h e water could not overflow where rim accumulation was at a maximum so long as other parts of the rim, or portions of the crater wall devoid of any rim, offered a lower outlet. Studies of aerial photographs (Figs. 4, 5, 15, and 17) suggest, and field examinations confirm, that outlet channels repeatedly traverse rim barriers. The writer was unable to run lines of level about the bays, so cannot offer definitive proof that the rim barriers where traversed by outlets are higher than other parts of bay borders. But the relations of bay borders and outlets to the marshy surfaces of the bays leave little doubt that, were the outlet channels filled to the surface level of the rim on either side, the position of the outlet would in a number of cases be materially higher than other parts of the bay borders. This indicates that the outlets are, in fact, antecedent streams, having begun to function before the rim came into existence, and having continued to flow while the rim on either side was built up to its present altitude. If this be true, the craters as well as their outlets are older than the rims, and the hypothesis which makes both craters and rims the simultaneous results of meteoritic impact appears incompetent to explain the relations actually observed. C H A I N S AND C L U S T E R S OF

BAYS

In an earlier chapter it was shown that in certain places elongated chains of oval bays occur paralleling beach ridges and their associated swales, and that distinct clusters of bays occur in low areas which interrupt the continuity of the beach ridge series; that these patterns in bay distribution are too peculiar, occur too often, and are too closely correlated with the surface topography and structure of the beach ridges to be explained as the result of mere chance; and that the evidence clearly indicates an

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earlier date of origin for the beach forms and structures and a later date for the oval bays. T h e sequence of events thus established relieved the meteoritic hypothesis of the heavy disability of requiring the bays to be carried through the zone of destructive wave activity and still survive the process of cut and fill incident to the development of a beach ridge plain. But in escaping the Scylla seemingly fatal to any hypothesis that assumes the oval bays to be older than the beach ridges, the hypothesis of recent meteorite scars encounters a Charybdis equally threatening. W e cannot admit that a shower of meteorites falling upon a beach plain could adjust itself in any measure to the preexisting pattern of the beach ridges and swales. Under the meteoritic hypothesis the observed correlation between bay distribution on the one hand and beach topography and structure on the other appears to find no satisfactory explanation. In a number of localities devoid of beach ridges and swales, chains of basins are so disposed as to suggest control by fracture lines, such as joints or faults. An example is found in the central part of the Greens Cut quadrangle, Georgia and South Carolina, where a number of oval and some circular depressions are aligned in an east-west direction. Farther east, Beaverdam Creek and some of its tributaries suggest similar control by east-west lines of weakness, one of which, prolonged, would easily pass through the chain of basins first mentioned. If, as is believed, these basins are to be classed with true bays, we have another type of adjustment of these forms to a preexisting structure. This places a further infirmity upon the meteoritic hypothesis. DISTRIBUTION

OF B A Y S AND M E T E O R I T E S

COMPARED

If the Carolina bays are the product of meteoritic impact, there should be a close correlation between the distribution of craters and the distribution of meteorites. Melton and Schriever cited Olivier's 18 emphasis on the large number of meteorites found in the southern Appalachians, extended their "probable area of bombardment" (Fig. 21) to include this district, and wrote: " T h u s " C h a r l e s P. Olivier. Meteors. 276 pp., Baltimore, 1925. See p. S40.

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Tests of Meteoritic

Hypothesis

the numerous meteorite discoveries in this region may be additional evidence of the reality of the shower which the authors [Melton and Schriever] have assumed."

F I G U R E 2 1 : Sketch map of Coastal Plain showing in large oval the probable area of bombardment by meteorites according to Melton and Schriever. (From paper by Melton and Schriever, Journal of Geology, 4 1 : 52-66, 1933.)

Students of meteorites are not agreed that the numerous examples found in the southern Appalachian region can safely be regarded as material falling upon the earth d u r i n g a single meteoritic bombardment. Nininger 1 7 and W y l i e 1 8 were willing to accept the evidence of these meteorites as suggesting a common origin for many of them. B u t Farrington's 1 0 study of each meteorite found in this region lends no support to the conception 1 7 H. H. Nininger. O u r Stone-pelted Planet. 237 pp., Boston and New Y o r k , 1933. See PP- 54-5618

C. C. Wylie. Iron Meteorites and the Carolina "Bays." Pop. Astron., 41:410-412,

>9331 9 O. C. Farrington. Catalogue of the Meteorites of North America to January 1, 1909. Mem. Nat. Acad. Sci., No. 13, 513 pp., 1915. See p. 11.

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123

of a single great shower. After reviewing the evidence and opinions on this point, Watson 20 was unable to accept "the available evidence as suggesting a common origin for many of these irons, or of any possible relationship between them and the region of Bays." Even were it known that the numerous meteorites of the southern Appalachian area represented, in whole or in considerable part, a single great meteoritic shower, it is difficult to see how that fact could be accepted as evidence favoring the meteoritic origin of the Carolina craters. Examination of Nininger's map 21 of all known meteorites found in the United States shows that the concentration in the southern Appalachian area is greatest in southwestern Virginia, western North Carolina, west-central South Carolina, northwestern Georgia, northern Alabama, central and eastern Tennessee, and central and southern Kentucky. These are almost exclusively areas where bays are unknown. O n the other hand, the area of abundant concentration of oval bays, comprising a belt extending from southeastern North Carolina across east-central South Carolina into northeastern Georgia, not only lies almost wholly outside the region of major concentration of meteorite finds but is for the most part quite free of such finds. T h e oval bays are known only in the Coastal Plain portion of the southeastern states, and in these portions meteorites have been found but rarely and, so far as yet known, never in association with the bays.22 Nininger's map shows but one or two iron meteorites and half a dozen or less stone meteorites in the whole Coastal Plain from Virginia to Georgia inclusive, an area considerably greater than that comprising the bay region. Prouty, 23 while supporting the meteoritic hypothesis, states: "As far as I am able to ascertain, there have been very few recorded discoveries of meteoric material in the Coastal Plain area"; and he notes that of twenty-four definite findings of meteorites in North Carolina Fletcher Watson, Jr. Meteor Craters. Pop. Astron., 44:2-17, 1936. See p. 14. H . H. Nininger. Our Stone-pelted Planet. 237 pp., Boston and New York, 1933. Map on p. 145. -- Prouty correctly points out that meteorite finds antedating the discussion of the bays presumably would not be correlated with these forms even if located near them. 23 William F. Prouty, personal communication. 21

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Tests of Meteoritic Hypothesis

recorded by F. P. Venable in 1890, only one was from a Coastal Plain county. T h e area of major concentration of meteoritic finds in the southeastern United States (based on the data plotted on Nininger's

FIGURE 22: Comparison of area of abundant meteorite finds (based on data collected by Nininger) with area of abundant bays (based on data collected by Johnson).

map, already cited) and the area of major concentration of oval bays are both shown in Figure 22. It would be difficult to imagine a much greater dissimilarity in the distribution of any two supposedly correctable features than is shown in this figure. Save for a possible overlapping in the vicinity of Columbia, South Carolina, the two areas are mutually exclusive. Not only is it true that the areas of most abundant meteorite finds and the areas of most abundant oval bays are mutually exclusive; even more significant is the fact that no meteoritic material of any kind has as yet been found in association with an oval bay. T h a t such material should be abundant about the bays were

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they of meteoritic origin is evident from observations made in the vicinity of known meteorite craters. These observations are summarized by Watson24 and by Boon and Albritton. 25 Watson gives data for twenty-seven craters, occurring in five separate clusters, which he regards as conclusively of meteoritic origin. One cluster of ten craters resulted from the great Siberian fall of 1908. In this case the meteorites descended upon an area of marsh and tundra into which the material would readily disappear. The region is difficult of access and had not been adequately explored when Watson wrote his paper; but Boon and Albritton report that in 1937 Kulik found silica glass and fused quartz aggregates containing globules of nickeliferous iron in association with two of the Siberian craters. In the case of the other seventeen craters the meteorites fell upon limestone, sandstone, desert sand and sand dunes, and glacial deposits three feet thick overlying dolomite. Meteoritic material was found associated with every group ("several thousand pieces of meteoritic iron"; "several pieces of meteoritic iron and numerous 'silica bombs' containing microscopic globules of meteoric iron"; "a large number of meteoritic irons"; "a siderite, four small pieces of meteoritic iron, much 'iron shale,' and over 1,500 pieces of magnetic material"; "abundance of nearly pure silica-glass clearly due to the fusion of clean desert sand," etc.). Boon and Albritton cite in addition the craters of Campo del Cielo, Argentina (number unknown), which have meteoritic material associated with them. In addition to the foregoing, Watson includes in his list one group of five craters and six smaller depressions possibly related to them, in the island of Osel, for which "several other possible origins [than the meteoritic] have been suggested." Watson was inclined to accept them as true meteorite craters, despite the fact that no meteoritic material had up to that time been found in their vicinity. He cites Reinwaldt as authority for the statement that "the apparent absence of meteoritic material from that region is not surprising, as the soil has been tilled for centuries and any 24

Fletcher Watson, Jr. Meteor Craters. Pop. Astron., 44:2-17, 1936. John D. Boon and Claude C. Albritton, J r . Established and Supposed Examples of Meteoritic Craters and Structures. Field and Laboratory, 6:44-56, 1938. 25

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iron would have long since been carried away." Boon and Albritton report that Reinwaldt in 1937 discovered meteoritic irons associated with two of the Estonian craters. Thus in the case of all the known meteorite craters, including those formed in the marshy tundra of Siberia and on the island of Osel, meteoritic material in greater or less abundance was found, even when evidence of extended erosion and weathering indicated a considerable antiquity for the craters. Repeated examinations of the oval bays of the Carolinas by various parties have not, up to the time of this writing, led to the discovery of any meteoritic fragments, fused silica glass, or other material suggesting a meteoritic fall. Melton and Schriever 20 state that they found "nothing definitely of cosmic origin." Prouty 27 writes: "As far as I know no meteorites have been discovered showing definite association with the 'bays.'" T h e bays occur in vast numbers, certainly tens of thousands and possibly hundreds of thousands. Some marshy examples have been drained and cultivated; many that are dry are fast being obliterated by repeated plowing (Figs. 6 and 34); some have been built over by villages or towns, and others occur in the immediate vicinity of large towns and cities. T h e borders of many have long been roamed over by countless hunters, farmers, surveyors, and other local inhabitants who would be quick to notice any hard material in a region where for the most part only loose sand appears on the surface of the ground. In recent decades soil surveyors, and geologists on the lookout for any unusual material, have examined the environs of great numbers of the bays. Within the last few years meteoritic material has been definitely searched for. T h e fact that such a history has not, up to the present writing, resulted in the discovery of a single fragment of meteoritic material in association with a bay can, on the basis of the meteoritic hypothesis, only be regarded as astounding. We may reasonably anticipate that in the region of the bays, just as in other regions, occasional meteorites will be discovered 26

F. A. Melton and William Schriever. T h e Carolina "Bays"—Are They Meteorite Scars? Jour. Geol., 41:52-66, 1933. See p. 65. 27 William F. Prouty, personal communication.

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in the future. Since the bays cover so vast an area and are so numerous in many localities as frequently to touch or overlap, some of these new finds may well be reported from bays or from their borders. But such occasional finds can offer no confirmation of the meteoritic hypothesis. So long as there is no obvious grouping of meteorite finds about specific bays, and so long as the region of abundant meteorite falls and the region of abundant bays ire mutually exclusive, these facts must frankly be accepted as throwing upon the meteoritic hypothesis one of the heaviest burdens it has been called upon to support. Both Melton and Schriever in their initial paper and Prouty two years later appealed to weathering to get rid of meteoritic material in the region of abundant bays, Prouty emphasizing the disintegrating effects of sodium chloride in sediments near the sea. In this case the authors apparently assumed that weathering sufficient to destroy meteorites would not destroy the craters. For the Piedmont and adjacent southern Appalachian areas Melton and Schriever suggested that weathering and erosion in a hilly region may have destroyed craters formerly present. Since these are areas of abundant meteorite finds, the assumption in this case must be that weathering and erosion sufficient to destroy craters would not destroy meteorites. Thus the meteoritic hypothesis, in the form which extends the area of meteoritic impact to include the southern Appalachians (so as to incorporate the nearest region of abundant meteorite finds), is confronted with a dilemma truly serious: In one area (that of abundant meteorite finds, Fig. 22), it must get rid of a vast number of craters without destroying many meteoritic masses which fell at the time of their production; while in an adjacent area (that of abundant oval bays, Fig. 22), it must get rid of vast quantities of meteoritic material without destroying the craters. This dilemma has not been fully faced by those supporting the meteoritic hypothesis. Olivier28 has shown that in the southern Appalachian Mountains conditions are highly favorable to rapid decay or disintegration of meteorites; yet this is the region of their most abundant occur28

Charles P. Olivier. Meteors. 276 pp., Baltimore, 1925. See p. 240.

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rence. Unusually rapid weathering due to the presence of sodium chloride in sediments near the sea will not account for the fact that numerous bays, devoid of meteoritic material, occur far inland and relatively near the Piedmont border, where weathering conditions cannot be greatly different from those areas where meteoritic material is frequently found. A l l things considered, it seems only reasonable to suppose, on the basis of the meteoritic hypothesis, that a vast shower of meteorites of the gigantic size required to form the bays must have been accompanied by a multitude of fragments of all dimensions and that many of these must have escaped complete destruction by the elements, to be found scattered about the bays just as they are commonly found about known meteorite craters. Even were weathering competent to explain the observed absence of meteoritic fragments from about the bays, it would not satisfactorily explain the absence of fused silica glass and other byproducts of meteoritic impact which are not readily affected by weathering. In considering what would happen if a huge meteoritic mass hit the earth, Prouty 29 raises the question: "Would not sand be hurled to a great distance from the area of impact, and might not the air cushion and the steam pressure prevent the actual contact of sand and meteor near the surface, so that we might not expect to find much, if any, fused quartz?" In answer to this question it may be observed that: (a) There is no evidence that sand was hurled to a great distance from the bays. T h e rims of sand are compact and local, usually only a few score or a few hundred feet broad, and very rarely attain a breadth of a thousand feet. T h e y are formed on the immediate borders of the depressions, and there is no indication of wide dispersal of sand beyond the rims, (b) Even were much sand expelled without fusing, the meteorites must have come in contact with sand eventually, and some of the resultant products of fusion should have been expelled from the point of such contact, (c) It seems only reasonable to suppose that the huge meteorites required to form the large bays, and the smaller meteorites forming the smaller 2 9 W i l l i a m F. Prouty. "Carolina Bays" and Elliptical Lake Basins. Jour. Geol., 43: 200-207, 1935. See p. «04.

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bays, were accompanied by countless fragments of still smaller size comparable to those constituting known meteorite finds. Whatever special theoretical explanations may be invoked to account for the absence of fused silica and other peculiar products of impact in the case of bays supposedly formed by meteorites of gigantic size, we must assume that the smaller fragments would behave normally. Observations in the vicinity of known meteorite craters show that meteoritic masses of the sizes actually known to exist will, when falling on loose sand or on sandstone, produce fused silica glass, silica bombs, and similar materials; and when falling on limestone, dolomite, and other formations will produce other types of burned or fused material. A vast area of sandy coastal plain, bombarded by a shower of literally countless meteoritic masses of all sizes, would seem to provide ideal conditions for the production of fused silica glass and similar material on a stupendous scale. We are forced to conclude that the absence of oval craters from the region of abundant meteorites in the southeastern United States, and the absence of meteoritic materials from the area of abundant oval craters, place upon the meteoritic hypothesis a double disability which seriously impairs its claim to confidence.

V i l i

Magnetic Tests of the Meteoritic Hypothesis

N

E X T T O the finding of actual meteorites, the best support of the meteoritic hypothesis would be satisfactory evidence that large meteoritic masses lie buried in or near the craters under discussion, even though such masses have not actually been found. SUPPOSED EVIDENCE OF BURIED

METEORITES

While no meteoritic material of any kind has thus far been observed in association with any oval bay, evidence supposed indirectly to indicate the occurrence of buried meteorites has been presented by Prouty and his associates.1 Magnetometer surveys in the vicinity of a number of oval bays showed the presence of magnetic highs to the southeast of most of the examples studied. These magnetometer observations were believed to "point very strongly to the presence of buried meteoric bodies." T h e nature and extent of the evidence are made plain in part by illustrations accompanying the articles cited and more fully by further data which Professor Prouty generously placed at the writer's disposal. Some who previously doubted the meteoritic interpretation of bay origin have been convinced of its validity by published results of the magnetometer surveys. It should be noted, however, that 1 William F. Prouty. " C a r o l i n a Bays" and Elliptical L a k e Basins. Jour. Geol., 43: 200-207, 1935. Further Evidence in Regard to the O r i g i n of " C a r o l i n a Bays" and Elliptical L a k e Basins. Geol. Soc. Amer., Preliminary List of T i t l e s and Abstracts of Papers to B e Offered at the 48th A n n u a l Meeting, December, 1935, p. 25, 1935. See also Geol. Soc. Amer., Proc. for 1935, 96-97. 1936. Gerald R . MacCarthy. " T h e Carolina Bays." Geol. Soc. Amer., Preliminary List of T i t l e s and Abstracts of Papers to Be Offered at the 48th A n n u a l Meeting, December, 1935, p. s i , 1935. See also Geol. Soc. Amer., Proc. for 1935, 90-91, 1936. T h e Carolina Bays. Bull. Geol. Soc. Amer., 48:1211-1226, 1937. William F. Prouty and H . W . Straley. Further Studies of " C a r o l i n a Bays." (Abstract). Geol. Soc. Amer., Proc. for 1937, 104-105, 1938.

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Prouty does not regard the studies made by himself and his associates as conclusive. With commendable caution he says in his main paper: "It is realized that more detailed and extensive mapping and checking of critical points is necessary before the meteoric theory can be firmly established." His latest contribution, while published only in abstract form, seems even more cautious in its support of the meteoritic interpretation. The many weaknesses of the meteoritic hypothesis previously disclosed, and the peculiar value attached to magnetic evidence by students of supposed meteorite craters, demand that evidence of this nature presented in support of the meteoritic origin of the oval Carolina craters should be fully analyzed and tested. It is to this analysis and testing that we now address ourselves. Q U A N T I T A T I V E INSUFFICIENCY OF T H E M A G N E T I C

EVIDENCE

Prouty and his associates present evidence of magnetic highs in the vicinity of comparatively few bays. Only five cases are specifically cited and figured in Prouty's paper, but general reference is made to other "small" positive anomalies found in some bays of the Myrtle Beach area. As it is stated that magnetic highs were found in connection with "most of the bays studied," it would appear that some failed to show the anticipated positive anomalies. Later unpublished surveys are said by Prouty to show magnetic highs near two additional bays, while MacCarthy published a survey by Prouty of a third additional bay. Prouty refers to unpublished surveys of an area of ten square miles near Syracuse, South Carolina, including the bay last mentioned and five smaller examples. Thus, while surveys are reported from the vicinity of thirteen bays, surveys of six only have been made available to the public. The few surveys reported and figured are very incomplete. Prouty's illustrations (see Fig. 23) are likely to produce upon the reader of his paper an impression unduly favorable to the meteoritic hypothesis because, for the most part, they show highs southeast of the bays and no highs elsewhere. Only the critical student will realize that this impression is wholly erroneous, because of the fact that the large areas where no highs are shown have not

23: Magnetometer observations around Singletary Lake, White Lake, and large bay N W from White Lake. (After Prouty in Journal of Geology, 43: 200-207, 1935.) FIGURE

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yet been surveyed. In no case has there been published a complete magnetometer survey of an entire bay and its vicinity. T o have any value as evidence a survey must completely cover not merely one bay but an entire region which includes a number of bays so distributed as to make the test conclusive for or against the meteoritic hypothesis. Such a survey obviously will be costly in time and money. Yet such a survey alone can provide evidence of critical value. The work thus far published has been largely "of a reconnaissance type," as Prouty points out. The method employed appears to have been in the nature of prospecting those areas where, according to the meteoritic hypothesis, large meteorites might be expected to lie buried. Complete surveys about bays, showing whether there are other magnetic highs not expectable under the meteoritic hypothesis, have yet to be published. T h e survey of an area of ten square miles near Syracuse, South Carolina, including one large and five small bays is not yet available to the public. We have only the statement of Prouty and Straley that the survey shows "a spot high or spot highs to be associated with each of the bays in the proper positions to support the meteoric theory," but also "two minor spot highs which have no present apparent connection with the bays." T h e oval bays are developed on the surface of sedimentary deposits which overlie crystalline rocks containing formations known to affect the magnetometer. Under these conditions it should be evident that limited prospecting of a few bays only, involving surveys largely limited to areas where the meteoritic hypothesis requires magnetic highs, and resulting in the finding of one or more highs somewhere near the southeastern ends of most but apparently not all of the few bays studied, and some highs not associated with any bays, provides evidence quantitatively insufficient to have great weight. This would remain true even if the magnetic highs were found exactly where anticipated and if they were of the type reasonably attributed to buried meteoritic bodies. But when, as shown below, the qualitative character of the evidence is far from satisfactory, its quantitative insufficiency becomes all the more striking.

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Magnetic Tests Q U A L I T A T I V E INSUFFICIENCY OF THE M A G N E T I C

EVIDENCE

Analysis of the magnetic evidence develops serious qualitative defects. It appears, in the first place, that when the magnetometer surveys were first undertaken it was expected that the magnetic highs would be found toward the southeastern ends of the bays, or but a short distance farther southeast, on the line of prolongation of the bays' major axes. T h u s early surveys in the Myrtle Beach district were concentrated in such areas, the observations being, "with few exceptions, largely made in, and not far outside, the bays." In these early magnetometer investigations "the differences in the readings were small and were thought at the time to be inconclusive." Later partial surveys of a small bay near Little River in northwestern Cumberland County, North Carolina, and of Dial Bay, southwest of Florence, South Carolina, showed much larger positive anomalies; but in the first case the high was some distance to the southwest of the axial line of the bay prolonged southeastward and relatively far from the bay, while in the second case it was northeast of such axial line and relatively close to the bay. Despite these marked discrepancies in relative position, the two highs were apparently accepted as indicating the presence of buried meteorites responsible for the two bays. Additional partial surveys showed other highs far off to one side or the other of the prolonged axial lines of other bays. As these surveys progressed it was found that there were more cases in which the high was found to the southwest side, or "a little to the east of south of the southeast end of the elliptical depression." It was further observed that the high formerly assigned to Dial Bay could be brought into the majority group by assigning it to another bay (Woods Mill Bay) next northeast of Dial Bay, and by seeking a high for Dial Bay still farther off to the southwest. As Prouty has informed the writer, " W e did not connect high A (the one formerly assigned to Dial Bay) with bay A (Woods Mill Bay) until our work elsewhere suggested this." Such is the explanation of the title under Figure 2 of Prouty's paper (Fig. 24A of the present volume) which reads: " T h e high magnetic area located southeast of Dial Bay is

li

¿- go è ! CL. C U 0«S u y CA .. » J5 w >« U "¡A (J « ^ pQ .a — T3 é Q*0 •5 S .2 tû 2 © o V : -s?-« •a 1 - z'= c5 C I o g® fc ° U c (A .ti O U f> ! S3 •5 •£ tf) c U te SO h elow the surface of the ground "produce discordant results, the depths derived from the magnetic formula being from two to sixteen times the depths derived by the trigonometric method"; that the meteorites were probably "largely or wholly volatilized by the heat developed when their motion was checked," yet the meteorites pursued courses under ground "concave to the southwest." In order to make Singlctary Lake bay with its three highs fit better into the hypothetical scheme, it is represented as probably consisting of two overlapping bays. (Aerial photographs show that Singletary Lake occupies a perfect single oval basin.) " T h i s supposition is confirmed by the discovery of two distinct highs in the exact position demanded bv Prouly's rule." Comparison of MacCarthy's Figure 4 with Prouty's Figure 3 shows lhat this degree of accordance results from omitting the larger high of the original survey and considering only two smaller highs. Even so, the westernmost high is a little west of south instead of southeast of its bay end, and thirty per cent farther away than Prouty's rule requires.

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magnetic highs with reference to the bays is wholly fortuitous, under which condition we must, according to the law of chance, expect many more highs off to the side of axial lines than on such lines. Inspection of the partial surveys thus far published shows magnetic highs northwest and northeast of the nearest adjacent bays as well as southeast of them, and highs northeast of the major axes of bays as well as southwest of such axes. T h e predominance of any one group is in no case greater than might be fully accounted for on the basis of chance, especially when the paucity and incompleteness of the data are taken into account. C A U S E OF M A G N E T I C

HIGHS

While the distribution of magnetic highs in the Coastal Plain area appears to be fortuitous in so far as the bays are concerned, it is of course causally related to something. T w o possibilities suggest themselves. In the Coastal Plain sediments are numerous beds of iron-cemented sandstone and gravel, "crusts of limonite," "irregular deposits of limonite," and local lenses of limonitic ore. Whether iron exists in the Coastal Plain beds in a form and in quantity sufficient to account for some of the magnetic highs reported by Prouty is a question deserving attention. Beneath the Coastal Plain beds are the ancient crystalline rocks and other formations which contain materials affecting the magnetometer at the surface of the plain far above. T h i s fact has enabled Prouty and his associates to detect the sloping surfaces of two distinct peneplanes buried deeply under the Coastal Plain sediments and to outline the buried Triassic basin near Florence, South Carolina, and trace it northeastwardly into North Carolina. 14 T h e r e are several facts which strongly suggest that the magnetic highs recorded by Prouty in his surveys about the bays are caused not by buried meteorites but by material in the older rocks underlying the Coastal Plain deposits: (a) Since the Coastal Plain formations are in the shape of a " W i l l i a m F. Prouty. " C a r o l i n a Bays" and Elliptical Lake Basins. Jour. Geol., 43: 200-207, 1935. See p. 200. Gerald R. MacCarthy, W i l l i a m F. Prouty, and J. A. A l e x a n d e r . Some Magnetometer Observations in the Coastal Plain A r e a of South Carolina. Jour. Elisha Mitchell Sci. Soc., 49:20-21, 1933.

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great wedge which is thickest near the coast and thins progressively toward the inner border of the plain, magnetometer readings affected by material in the older formations should show small anomalies near the coast where the older rocks are deeply buried and much larger anomalies farther inland where the covering beds are greatly reduced in thickness. It is significant, therefore, that in the Myrtle Beach area on the coast, where the depth to the older rocks is estimated at 1,200 to 1,500 feet and possibly more, Prouty found positive anomalies so small as to be thought inconclusive (gy, 377, and approximately 507 on tracings of his surveys kindly furnished by Professor Prouty); whereas fifty to sixty miles farther inland, in the vicinity of Turbeville, South Carolina, and Elizabethtown, North Carolina, where the depths to the older rocks are estimated at only 500 and 800 or goo feet, much larger anomalies were found (200Y and 6ooy or more; Figures 2 and 3 of Prouty's 1935 paper). There is significance also in the fact that Melton and Schriever obtained only noncommittal results in three bays out of four examined, the three with little or no anomalies being located near the sea.18 The one showing a marked magnetic high was near the thin inner edge of the Coastal Plain. There is, of course, no systematic increase in the strength of positive anomalies going inland from the coast, for the simple reason that the highs in a single locality vary greatly in intensity due to the magnitude and intensity of the cause responsible for them. The important point is that no large positive anomalies have been reported from near the coast where the older rocks are deeply buried, whereas a number have been reported from farther inland where the older rocks are nearer the surface. Prouty recognized this highly important fact and wrote: "Observations on bays near the coast give, in general, weaker anomalies than do those farther inland." He sought to explain the fact by assuming "more rapid disintegration of the ferruginous bodies [buried meteorites] in the coastal area due to the presence there of sediments more highly charged with sodium chloride." (b) If material in the older rocks is really responsible for the F. A. Melton, personal communication.

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high magnetic areas found about certain bays, the depth to this material must be equal to, or greater than, the thickness of the Coastal Plain sediments. In response to an enquiry by the present writer Prouty replied: " T h e calculated depth to the hypothetical meteoric bodies is, seemingly, deeper than the Coastal Plain sediments unless the body has been considerably deflected toward the west or unless the meteor ricochetted on the crystallines." It is not quite clear how past deflection of the meteoritic mass could affect the present influence of that mass upon the magnetometer or modify calculations of depth based on present magnetometer readings. T h e important point, however, is that these readings do indicate that the cause of the magnetic highs lies below the Coastal Plain sediments and in the older rocks. (c) If material in the older rocks is responsible for high magnetic areas found about the bays, elongation of highs in a northeast-southwest area or recurrence of highs in a chain extending northeast-southwest might be anticipated. This should be the case because the Appalachian structure, including infaulted and infolded Triassic basins, has this trend. Unfortunately, all of the partial magnetometer surveys thus far figured are too incomplete to reveal what lies to the northeast and southwest of a small local area. But the magnetic high located southeast of White Lake (Fig. 23) shows lobate extensions toward both the northeast and southwest. T h e high southeast of Singletary Lake (Fig. 23), incomplete toward the northeast, suggests possible elongation in that direction. T h e new high (see Figure 9 of MacCarthy's paper earlier cited) discovered northwest of White Lake by later surveys is strikingly elongated in a direction north of east. Far more significant is the result of a recent (unpublished) survey by Prouty and his associates near the southeastern end of Jones Lake, not far from the other lakes mentioned above. At this point a prominent high was discovered where sought for, and it was believed that a good case conforming to the rule discussed on earlier pages had been found. But as the survey was extended it revealed, according to Prouty, 16 "a very large linear high with northeast-southwest trend passing to the south of Jones Lake and making our readings 16

William F. Prouty, personal communication.

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there of little value." Prouty informed the writer that the limited high first found southeast of Jones Lake and at first believed to conform to the rule for distribution of positive anomalies proved to be only a slightly higher portion of the linear high in question. It seems not unreasonable to suppose that more complete surveys in other regions, where local highs are now attributed to buried meteorites, may show that these also are strongly developed portions of linear highs trending northeast-southwest with the structures of older rocks. Prouty reports by letter that he and his associates have found "a number of well defined linear highs with general NE-SW trends. These seem to indicate conformity to structure lines in the crystallines beneath." MacCarthy in his latest paper describes linear highs trending northeast and recognizes that they may be caused by structural features of the crystalline rocks beneath the Coastal Plain sediments. In conclusion, it appears that the evidence thus far developed by magnetometer surveys offers no support to the meteoritic hypothesis of bay origin: first, because it is too fragmentary and incomplete and too contradictory to indicate any genetic relationship with the bays; and second, because certain of the data thus fai available show linear trends and regional variations of intensity strongly indicating that magnetic material in crystalline rocks beneath the Coastal Plain cover is responsible for the magnetic highs revealed by the surveys. T h e absence of meteoritic material about the craters, together with the absence of any reliable evidence indicating the existence of meteorites buried beneath the surface, must be regarded as a defect of the meteoritic hypothesis well-nigh fatal. SUMMARY OF DISCUSSION OF METEORITIC

HYPOTHESIS

Our long discussion of the meteoritic hypothesis of bay origin, justified, we believe, by the importance and novelty of the hypothesis and by the support it has received in important quarters, leads to the conclusion that this hypothesis cannot survive critical analysis. We have tested the competence of the hypothesis to explain some two dozen or more characteristic features of the oval bays, and in every instance except one, and that one not of dis-

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criminative value, the facts observed are not in accord with deductions based on the meteoritic explanation. We have not stressed the fact that the vast area covered by the supposed shower of meteorites, and the vast number of meteorites required to produce the number of oval bays existing in that area, place the hypothetical shower far outside the range of anything ever known to have occurred. There always remains the possibility that Nature may have accomplished in one instance what she never, within our knowledge, accomplished previously. But while it is hazardous "to limit Nature" as to what she can and cannot do, all experience justifies the expectation that whatever she does will be done in accordance with natural law. We can, therefore, deduce the reasonable consequences of a meteoritic shower of whatever magnitude and compare the deduced consequences with the facts actually observed. We have done this, and the result has been a striking discordance between the expectable consequences of the hypothesis and the facts observed on the ground, so striking indeed as seriously to discredit the meteoritic explanation of origin for the oval craters of the Coastal Plain and their associated sandy rims. We turn therefore to seek another explanation which will more adequately account for the facts observed.

IX The Hypothesis of Complex Origin

O

U R STUDY of the curious craters of the Carolina coast has established a large number of facts, some of them new, some of them previously reported but heretofore disputed. The establishment of these facts on a firm basis enables us to lay down a somewhat elaborate series of requirements which any satisfactory hypothesis of crater origin must meet. Obviously, the more complex the requirements to be satisfied, the greater the probability that a hypothesis which does satisfy them is the correct explanation of a given phenomenon. Let us, therefore, set forth the requirements which must be met by any acceptable theory of origin of the oval craters and their bordering rims. We shall then be in a position to suggest another working hypothesis of crater origin and to test its validity. R E Q U I R E M E N T S O F A SATISFACTORY

HYPOTHESIS

T o explain successfully the origin of the oval craters and their sandy rims the hypothesis must account for the following facts: (A) Many of the craters are of remarkably perfect oval outline. (B) In some localities the ovals are prevailingly elliptical, in others distinctly ovoid or egg-shaped. (c) Many craters are highly irregular in outline. (D) All gradations in form exist, from craters of the most regular outline to those highly irregular. (E) Oval craters have axial trends almost always directed between south and east, most of them ranging between S io° E and S 55° E(F) There are wide departures from the prevailing direction; elliptical craters are the most consistent in trend, with axes directed more or less nearly southeast; ovoid craters are most variable in trend, but as a rule have axial directions more nearly southward, their narrow ends pointing in this direction.

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(G) Craters vary in size: some are a few hundred feet, many one or two miles, and some three or four miles in longest diameter. (H) T h e craters are remarkably shallow in comparison with their great areal extent. (1) T h e craters descend below the level of the surrounding plain and below the bases of their bordering rims, as if they were depressions caused by removal of part of the Coastal Plain material. (j) Both large and small oval craters show considerable variation in degree of ellipticity. (K) Oval craters normally are not true ellipses or true ovoid forms but show systematic bilateral asymmetry, the northeastern sides usually being more sharply curved than the southwestern. (L) Craters sometimes occur in systematic groups, with a distinct group pattern apparently determined by some preexisting topography or structure. (M) Oval craters, while abundant on parts of the Coastal Plain, are apparently absent from the Piedmont and other Appalachian provinces. (N) Many craters are bordered by rims of sand; but (o) Many craters similar in all other respects have no rims associated with them. (p) T h e rims, when present, rarely completely surround a crater; incomplete rims are sometimes erratically distributed but normally are highest and broadest about the southeastern quadrants of the depressions. (Q) Multiple rims, nearly but not quite concentric, and from two or three up to six or eight and possibly more in number, occur about some craters. (R) Such multiple rims tend to be best developed and farthest apart toward the southeastern ends of oval or ovoid craters, converging or merging or disappearing toward the northwestern ends. In some cases the multiple rims are chiefly confined to the eastern sides rather than the southeastern ends of craters. (s) A wide space sometimes intervenes between an outer rim

Hypothesis of Complex Origin

153

or series of rims and an inner rim or series within the same crater; this distribution pattern may be repeated in adjacent craters. (T) T h e rims are of relatively insignificant size, the volume of material contained in them being but a small fraction of the material removed to form the craters. (u) T h e convergence of multiple rims of the same crater and the junction of contiguous rims of adjacent craters do not give rise to combined rims of unusually large size. O n the contrary, such combined rims may be unusually small and may locally disappear. (v) T h e r e is no systematic relation between the size of the bays and the size of their bordering rims. Large bays may have small rims or none, and small bays may have large rims. (w) Many rims are relatively flat-topped or broadly rounded in cross section, frequently with steeper slopes inward toward the crater and outward toward the adjacent plain. (x) T h e composition of the rims is remarkably uniform, the material consisting for the most part of clean, fairly coarse white or buff quartz sand. (Y) Material composing the Coastal Plain in which the craters are excavated is often strikingly dissimilar to the material composing the rims. (z) Bedrock fragments of Coastal Plain sediments are not found in the rims. (AA) Coastal Plain sediments normally remain undisturbed in a horizontal position below the sandy rims and in the crater walls. Occasionally there is slight indication of slumping inward toward the craters but no uptilting of beds causing them to dip outward away from the craters. (BB) Many craters have channels draining into or out of them, (cc) These channels frequently cut across rims bordering the craters. Such is the array of facts which must receive reasonable explanation before any hypothesis of crater origin can receive general acceptance.

154

Hypothesis of Complex Origin T H E H Y P O T H E S I S OF C O M P L E X

ORIGIN

T o account for these significant facts respecting the Carolina craters the writer offers what may for the sake of simplicity be called "the hypothesis of complex origin." More fully stated, it is "the artesian-solution-lacustrine-aeolian hypothesis." It supposes that artesian springs, rising through moving groundwater and operating in part by solution, produced broad shallow basins occupied by lakes, about the margins of which beach ridges were formed by wave action and dune ridges by wind action. It is this hypothesis of complex action that we must now explore. T h e major problem involved in any explanation of the Carolina craters is to account for their form and orientation. The fact that the craters are oval rather than circular, and that these elongated forms have their major axes prevailingly more or less nearly parallel in any given locality, with trends usually varying between S 55 0 E and S io° E, must be convincingly accounted for by any hypothesis that is to gain general acceptance. Obviously a first step in the quest for a satisfactory explanation is to determine what factors in the physical environment of the Carolinas correlate with the direction of crater elongation. It at once appears that the regional slope of the Coastal Plain coincides fairly closely with the axial trends of many of the elongated craters. But all efforts to find a causal connection between crater form and orientation on the one hand, and regional slope of the Coastal Plain on the other, encounter an insuperable difficulty. The craters, being of relatively small size, should be related to local surface slopes on which they have been developed, rather than to the average or regional slope. There can be little question but that the former surface of the Coastal Plain, however uniform its regional inclination, was gently undulating, with local slopes toward all points of the compass. T h e craters show no such diversity of orientation as genetic relationship to so variable a surface would imply. Their elongation is demonstrably independent of the direction of inclination of the immediate surfaces in which the basins were excavated. In the same way, crater elongation is parallel to the major trend of Coastal Plain

Hypothesis of Complex Origin

155

drainage, but frequently not to the courses of individual neighboring streams. More hopeful lines of enquiry are based on the degree of parallelism existing between direction of crater elongation and the initial direction of groundwater flow through unconsolidated surface sands; also between direction of crater elongation and dip of underlying formations, and perhaps also the direction of artesian flow within those formations. Strictly speaking, "groundwater" includes all water in the zone of saturation, and occurs either under water-table conditions or under artesian conditions. T o avoid employing such terms as "phreatic water" and "piestic water," more accurate but not in general use, the terms "groundwater" and "artesian water" are employed throughout these pages. By "groundwater flow" is meant the movement of water under water-table conditions; by "artesian flow" is meant the movement of water under artesian conditions. While the present direction of groundwater flow may be highly variable, especially near the surface where the Coastal Plain is much dissected by streams, there can be little doubt that prior to stream incision the initial flow of the groundwater must have been prevailingly from northwest to southeast in the Carolina Coastal Plain. It seems safe to assume, further, that such initial flow of groundwater through the Coastal Plain beds, while deflected to some extent by variations in permeability, would in general be far more constant in direction than that of surface waters controlled in their movements by superficial undulations of the Coastal Plain. The directions of rock dip and artesian flow are, as we shall later see, not easily determined. But available evidence indicates that throughout areas occupied by the oval craters the direction of the dip of formations as well as the direction of artesian flow in aquifers not far below the surface is in general more or less strongly from northwest to southeast. With respect to both groundwater flow and artesian flow it is doubtful whether directions of flow at the time of crater development were any more variable than are the observed directions of crater elongation. It is therefore pertinent to investigate the possibility of any genetic relation-

156

Hypothesis of Complex Origin

ship between the form and orientation of craters on the one hand, and the directions of rock dip, normal groundwater flow, and artesian flow on the other. It will be convenient to begin with the consideration of groundwater flow. E F F E C T S OF GROUNDWATER

FLOW

In order to understand what effect, if any, groundwater flow may have u p o n the form and orientation of craters in such a deposit as the surface sands of the Carolina Coastal Plain, w e must review certain general principles respecting the flow of water through sand. 1 It was long ago determined, and is easily demonstrated experimentally, that w h e n water moves upward, through loose sand the latter tends to become " q u i c k . " T h e grains of the submerged deposit tend to separate rather than to be compacted. A weight placed u p o n the underwater surface of the sand will sink quickly to the bottom of the affected deposit. A n object at the bottom can easily be drawn upward through the mass to its surface by an attached string. If a part of the submerged sand be heaped up, it instantly flows and flattens out. If a crater be excavated in the sand, the side walls instantly flow in until a nearly level subaqueous surface is reestablished. T h e sand has lost its normal subaqueous angle of repose, and attempts to make it maintain even a moderate slope are ineffectual. (See Fig. 3 7 A , p. 189.) O n the other hand, if the direction of the m o v i n g water be reversed and it moves downward through the sand, even at a very slow velocity, the character of the submerged deposit instantly changes. T h e sand becomes firm and compact. A weight placed upon the underwater surface of the sand will rest solidly u p o n that surface. A n object at the bottom can only with great difficulty be drawn through the compacted mass to the surface. Excavated 1 T h e writer is indebted to his colleague Dr. W a l l e r H. Bucher and to Mr. Bedrich Fruhauf, Research Associate in Civil Engineering at C o l u m b i a University, for directing his attention to the possible bearing on the Carolina craters problem of the principles of groundwater flow here reviewed. Mr. Fruhauf offered valuable suggestions on the basis of engineering experience in this country and in Europe. Special acknowledgment is due to Professor Donald M. Burmister of the D e p a r t m e n t of Civil Engineering at C o l u m b i a w h o , with the aid of special apparatus designed by him, explained and demonstrated the pertinent principles of groundwater flow.

Hypothesis of Complex Origin

157

craters and bordering ridges in the subaqueous deposit tend to maintain the forms given them. T h e sand will not merely stand at its subaqueous angle of repose; it will maintain nearly or quite vertical walls (Fig. 37) bordering excavations carefully made under I

Lines of flow of water through sand in which a lake basin L has been excavated. Diagram based on apparatus designed by Professor Donald M. Burmister of Columbia University. FIGURE 25:

water in the compact deposit. Stop the movement of the water, and instantly the sand slumps to the normal subaqueous angle of repose. For a proper understanding of o u r problem, it is in the highest degree important to remember that w h e n water moves through loose sand at certain critical velocities the grains behave differently according to whether the water is m o v i n g against or with gravity; and that the difference is not merely one of degree: the character of the deposit and its behavior are sharply contrasted according as the water is moving u p w a r d or downward. Another long-established principle of water movement through sand or other pervious material is equally important for our study. Imagine a tank with glass sides, Figure 25, partially filled with loose sand in which the lake basin L has been excavated. Water admitted through the tube T enters the compartment C and passes through openings in the screen S into the sand deposit. T h e water escapes from the sand at the opposite end of the tank through a second screen S' into compartment C ' , f r o m w h i c h the rate of its outflow may be regulated by an outlet tap near the bottom. So long as the water in compartment C is higher than that in compartment C ' , there will be a flow of water from C to C '

158

Hypothesis of Complex Origin

through the sand. If coloring matter be introduced at properly selected points near screen S, lines of flow of the water will be clearly visible through the glass wall of the tank. As shown by the arrows, on approaching the open lake the lines of flow will first descend, then rise again, finally entering the lake in directions at right angles to the wall of the basin near A. The rightangle flow at this boundary is the direct result of two independent conditions which the flow must satisfy: (1) there must be no creation or annihilation of water at the boundary or elsewhere, and (2) the resistance to the flow in the sand is sensibly infinite as compared with that in the open basin. (M. King Hubbert, "The Theory of Ground Water Motion," Jour. Geol., 48: 844-847, 1940, and "The Motion of Ground Water," New York Academy of Sciences, Trans., 3: 39-55, 1941.) Water leaving the lake near D enters the sand at right angles to the basin wall. As soon as the flow of water through the sand is fully established, it becomes apparent that the principles discussed above come into play. On the upcurrent side of the basin, near A, the water is rising. Consequently the sand on that side of the basin tends to become "quick." Slumping or flowing will occur if the tendency in question is sufficiently pronounced. The wall of the basin here easily breaks down, and the shoreline migrates from A to B. The material between the earlier and later positions of the basin wall is in part spread over the basin floor, shallowing the lake, a change not shown in the diagram for the sake of simplicity; and in part carried out of the basin in case there is an outflowing stream. On the downcurrent side of the lake, near D, the outgoing water is descending. Hence the sand here tends to be compacted and held in place; the shoreline is relatively stable. The net result is that the lake basin "tends to enlarge in the upcurrent direction but to remain stable in the downcurrent direction. With the foregoing principles in mind let us consider the action of groundwater flowing from northwest to southeast down the slope of the Carolina Coastal Plain and encountering lake basins excavated by any cause in the superficial loose sands of the plain. Let us assume that the lakes are more or less circular in form,

Hypothesis of Complex Origin

159

not an unreasonable assumption in view of the tendency of irregular lake basins in loose or poorly consolidated sand quickly to acquire rounded outlines, as explained elsewhere in this volume. For reasons outlined above, the northwestern sides of the lake basins will be less stable than the southeastern sides. Groundwater flowing into the northwestern sides will there rise through the sands, tending to make the deposit less coherent and more subject to easy removal. If the outflow of water is sufficiently great, the sand will become more or less "quick," with consequent slumping or even flowing. With less voluminous outflow, the sand may merely be rendered unstable by constant seepage and thus more easily attacked by waves and currents. In either case, the northwestern sides of the basins will progressively advance toward the northwest or up the groundwater current, which in general will be up the regional slope of the Coastal Plain. This action is supplementary to, but may be concurrent with, the radial enlargement of basins due to the slumping or flowing of saturated sand from the periphery toward the center of basins being excavated by artesian springs. T h e southeastern sides of the basins, on the contrary, will show no such marked tendency toward migration. Wave erosion may indeed cut back these shores to some extent. But because the lake waters are here descending into the sands, the latter will tend to be better compacted and less easily disturbed than on the northwestern sides of the basins. T h e net result must be an elongation of the basins into more or less oval forms with their long axes directed more or less nearly northwest-southeast. T h e reader should understand that application of the foregoing principles of groundwater flow to the Carolina craters constitutes a hypothetical explanation of their evolution. It is in no sense a statement of facts. But it is an explanation founded on wellestablished principles of hydrodynamics. Its validity has been demonstrated on a small scale in the laboratory. T h e expectable consequences of the explanation agree with facts observed in the field. A t a single stroke it accounts, on the basis of groundwater behavior alone, both for the more or less oval form of the Carolina craters and for their prevailing orientation. Obviously the explanation is entitled to serious consideration.

i6o

Hypothesis of Complex Origin E F F E C T S OF R O C K D I P AND A R T E S I A N

FLOW

Let us next consider the effect of rock dip and artesian flow as related to the form and orientation of craters. In the discussion im-

26: A. Artesian waters escaping through opening O in im pervious bed form an artesian spring at S which excavates a circular basin. B. Enlargement of the opening OO', increases flow of artesian spring S and basin is enlarged. C. Upcurrent enlargement of opening from O to O " causes migration of artesian spring to position S', thereby transforming circular basin into oval basin. FIGURE

mediately preceding we assumed the existence on the Carolina Coastal Plain of lake basins formed by any cause. In our statement of the hypothesis of complex origin it was postulated that in this region artesian springs were a major cause of lake-basin development. Let us imagine an undissected coastal plain (Fig.

Hypothesis of Complex Origin

161

26A) covered with loose sand, below which an impervious bed caps an artesian aquifer dipping gently but distinctly toward the right. Let us further assume that the aquifer is so porous as to permit relatively rapid flow of water under artesian pressure, and that the direction of flow is in general down the dip. At O a fracture or other opening permits escape of artesian water to the surface where it forms an artesian spring S and develops a more or less circular basin in the loose sand as finer particles are carried away by outflowing surface waters. If the impervious bed is highly soluble or subject to slow mechanical disintegration when in contact with moving water, the opening O will gradually be enlarged (OO', Fig. 26B). T h e reader should understand that both Figure 26 and the text over-simplify conditions actually found in nature, since the upper sands must be full of water, and groundwater movement must be three-dimensional. (See page 175.) With increased enlargement of the conduit a new situation develops. Water in the artesian aquifer will flow toward the opening from all directions, but the rate of flow will vary with the direction. The greatest rate of inflow will be from the upstream, the least from the downstream direction; while inflow from either side will be at intermediate rates. The net result will be a maximum upwelling of artesian waters in the position indicated by the vertical arrows in Figure 26C. As this position migrates progressively upcurrent the artesian spring will migrate to S', and the circular basin will be transformed into an oval basin. Such oval could be essentially elliptical if the opening produced in the impervious bed were very long in proportion to its greatest width, especially if the basin were developed on the surface of a thick overlying deposit of loose sand. Or the oval basin could be of the ovoid type if ready solution or disintegration of the impervious bed and favorable conditions of water movement caused rapid lateral expansion of the opening (O", Fig. 26C) coincident with its upcurrent migration, to give a more or less pear-shaped aperture not obscured by too great a thickness of overlying loose sand. A similar result could be produced if solution of underground channels greatly increased the flow of water from an

162

Hypothesis of Complex Origin

artesian spring situated on the surface of a thick overlying deposit of loose sand. For if the volume of uprising waters be so increased as to cause basin excavation on a progressively larger and larger scale, the result must be to produce an egg-shaped or ovoid basin. Under all the assumed circumstances the small end of the egg will, on a southeast-sloping coastal plain, normally point toward the southeast. It should be understood that the foregoing explanation, to even a greater degree than that based on groundwater behavior, is essentially hypothetical. It is an invention by the writer to account for certain facts not fully explained by groundwater movement alone. In the nature of the case, the actual formation of the Carolina craters has not been and could not be observed. But as a working hypothesis the explanation appears to have certain merits entitling it to serious consideration. T h e deduced consequences of the explanation are nicely matched by facts observed in the field. A t a single stroke it explains both the origin and the form of elliptical and ovoid bays, and the approximate parallelism of their axes in directions trending more or less nearly northwestsoutheast. If the theoretical considerations presented in this and in the preceding section are sound, both ordinary groundwater flow and artesian flow may affect the form and orientation of the bays. T w o

CRITICAL

TESTS

In a coastal plain like that of South Carolina and adjacent states it is not easy to determine the dip of the formations over different areas. T h e beds are so nearly flat that dips are usually imperceptible. A single formation may vary considerably in composition and texture, while different formations may as a whole bear much resemblance to each other. A surface deposit of loose sand blankets much of the area, and outcrops of the underlying formations are over great areas relatively few in number and of limited exposure. Well records rarely give data adequate for close correlation. Reports on the region commonly stress the difficulty of determining areal distribution of beds, formational boundaries, and the position of specific horizons in depth. It has long been known

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163

that the axis of a broad, low anticline trends roughly northwestsoutheast through the Cape Fear area of North Carolina. Cooke reports by letter that this structure brings the Peedee formation almost to the surface at Wilmington, North Carolina, and along the Waccamaw River in northeastern South Carolina, whereas at Charleston the top of the same formation lies 500 feet below sealevel. Where so broad and low a structure in a southeast-dipping coastal plain is concerned, these facts are not necessarily inconsistent with prevailing southeast dips over southeastern North Carolina and northeastern South Carolina, or with such dips in overlying or underlying beds from which shallow artesian waters may have reached the surface in the past, as they still do to some extent at present. T h e prevailing northeast-southwest strike of the Snow Hill member of the Black Creek formation (next below the Peedee), as shown on certain geological maps of this part of North Carolina, is suggestive of prevailing southeast dips (roughly S 40° or 50°E) in the tiers of Coastal Plain counties on either side of the North Carolina-South Carolina boundary. Similarly, in southeastern South Carolina and the adjacent portion of northeastern Georgia the formations carrying artesian waters at shallow depths appear to dip more strongly southward, since their outcrops strike more nearly west across the gently rising surface of the plain. If we make allowance for some variations in the directions of outcrop and transform the inclined outcrops into true directions of strike, we can deduce a range of dips varying roughly from S io° E to S 30° E. There thus appears to be a distinct difference in prevailing dip in the northern part of the bay country and in the southern part. It may reasonably be questioned whether the dip of the Coastal Plain formations, when so nearly flat as to be determined only with difficulty and then often doubtfully, can affect the form or orientation of basins developed in overlying surface sands. T h e uncertainty is not lessened when we add the element of artesian flow through the faintly dipping beds. Such flow, while perhaps relatively rapid in open gravels and cavernous limestone, may be exceedingly slow through certain other formations. T h e direction of flow is, moreover, governed by other factors than dip,

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notably the location of recharge and discharge areas, and variations in the permeability of the formations traversed. It has been shown by Stringfield, Warren, and Cooper2 that a discharge area offshore, northeast and east of Savannah, is probably responsible for the fact that prior to the recent great withdrawal of artesian water from wells at Savannah '.'the artesian water converged toward that area from the southwest, west, and northwest." Under the conditions described it would obviously be hazardous to predict that a given dip of formations, even if definitely known, must give rise to a certain direction of artesian flow or a certain form or orientation of basins produced by artesian springs. We can, however, approach the matter from a different angle, and say with some reason that if the formations of the Coastal Plain do dip more strongly southward in the southern part of the bay country, as they appear to do, and if such dip directly or indirectly affects the orientation and form of the bays, then the average orientation and the average form of bays should be somewhat different in the northern and southern areas. Confining our attention first to the problem of orientation, we can say that if the hypothesis of artesian spring migration updip is valid, and applicable to the region in question, the elongated craters of the first area (southeastern North Carolina and northeastern South Carolina) ought to show average trends more or less nearly southeast, whereas elongated craters of the second area (southeastern South Carolina and northeastern Georgia) should show average trends distinctly more strongly southward. Comparison of the average trends of crater elongation in these two areas thus becomes of special interest. For the northern part of the region of abundant oval craters or bays the axial trends of 224 bays in eleven counties of southeastern North Carolina and northeastern South Carolina were measured on aerial photographs, aerial mosaics, soil survey maps, and one local county map (Marion County). No satisfactory topographic maps were available for this region. (An advance sheet of the Nixonville quadrangle, covering much of the Myrtle 2

V. T . Stringfield, M. A. Warren, and H. H. Cooper, J r . Artesian Water in the Coastal Area of Georgia and Northeastern Florida. Econ. Geol., 36:698-711, 1941.

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165

Beach area, was received later, but added nothing of value to measurements previously made.) For the southern part of the region of abundant oval bays the axial trends of 157 bays in eight counties were measured on aerial photographs, aerial mosaics, soil survey maps, and topographic quadrangles. As averages for different counties have variable significance, depending upon the number of distinctly oval bays suitable for measurement shown on photographs and maps conveniently available, the number of bays measured in each county is indicated. T h e total range of axial directions in each county and for each general region are likewise indicated; also the general average direction as determined (a) by adding the averages for the several counties and dividing by the number of counties; and (b) by averaging all measurements of individual bays for the entire area. T h e results are given in Tables 1 and 2. T h e marked contrast in axial directions of bays in the northern and southern parts of the area in which oval bays are most abunTABLE A V E R A G E A X I A L T R E N D S OF O V A L

.

State

County

1

B A Y S IN N O R T H E R N

No. of Bays Measured

Average Direction

P A R T OF

AREA

Total Range

32 0 40° 40° 450 40° 40° 43 0

North Carolina Bladen 7 counties Brunswick 123 bays Columbus Cumberland Hoke New Hanover Robeson

94 3 3 5 4 10 4

S47°E S 48° E S 50° E S 50° E S 490 E S 48° E

S S S S S S S

E-S E- S E-S E- S E-S E-S E-S

65° E 50° E 55 0 E 6o° E 6o° E 6o° E 51° E

South Carolina Dillon 4 counties Horry 101 bays Marion Marlboro

6 40 23 32

S 340 E S 440 E S 40° E S37°E

N-S - S S 20° E - S S 250 E - S S II° E - S

50° E 67° E 490 E 55 0 E

S

5

I ° E

Total number of bays: 224 Total range: N - S - S 6 7 0 E General average (by counties): S 450 E General average (by individual bays): S 46° E

166

Hypothesis of Complex Origin TABLE 2

AVERAGE AXIAL TRENDS OF O V A L BAYS IN SOUTHERN PART OF AREA State

County

South Carolina Allendale 4 counties Bamberg 98 bays Barnwell Hampton Georgia 4 counties 59 bays

Burke Effingham Jenkins Screven

No. of Bays Measured

Average Direction

10

S 18° E S 240 E S 240 E S23°E

N-S-S 550 N-S - S 4 8 ° N-S - S 3 5 0 S 6° E - S 450

S S S S

N-S - S 5 6 ° E S 2 0 0 E - S 240 E S 8° E - S 20° E S 26° W - S 450 E

17 49 22

12 2

4 4«

140 22° 120 170

E E E E

Total Range

E E E E

Total number of bays: 157 Total range: S 26° W" - S 56° E General average (by counties): S 190 E General average (by individual bays): S 20° E • T w o oval depressions (out of a total of 41) in Screven County appear on aerial photographs and maps with trends of S 26" W and S 2 1 ° W. For discussion of SW-trending bays see pp. 185, 186, 261, 262, 264.

dant is shown in maps of the two groups of counties (Fig. 27). Here the average axial direction for each county is graphically represented, and the consistency with which these average directions trend more nearly southeast in the northern area and more strongly south in the southern area is truly remarkable. In the northern group of counties no satisfactory material suitable for measurement of axial directions was easily available for Scotland County; but there is no reason to suppose that axial directions in this county are appreciably different from those in the three counties bounding it on the northeast, southeast, and southwest. In the southern group of counties Aiken is not plotted. While aerial photographs show some typical forms in this county, topographic maps on which the writer was dependent for most of the axial measurements suggest typical sinkholes, distinctly elongated and with more or less parallel axes, but having somewhat irregular outlines. Since, as shown elsewhere in this volume, there is every gradation from typical oval bays to typical sinks, and since experience shows that true oval bays with regular out-

CUMBERLAND

SCOTLAND R O B E S O N MARLBORO

DI L L O N COLUMBUS

MARION

BRUNSWICK

27: A x i a l trends of basins in northern (A) and southern parts of area of abundant oval bays. FIGURE

(B)

i68

Hypothesis of Complex Origin

lines are very frequently represented on topographic maps as irregular depressions,3 there is much justification for including Aiken County in the above tabulation and map. But because of possible doubt as to the authenticity of the Aiken bays, this county is omitted. T h e average trend of Aiken County basins is S 2 i ° E. Colleton and Jasper Counties appear to have only rare and poorly developed oval bays. Adequate material of satisfactory character for axial measurements was not in our possession for either county. Figure 27, showing average axial directions of oval bays in each county, gives no clue to the variations in directions of individual bays. T o show the extent of these variations the graphs reproduced in Figure 28 were prepared. T h e basis for these graphs was the measured axial directions of the 381 bays represented in Tables 1 and 2. Inspection of these graphs reveals at a glance the percentage of the total number of bays (224) measured in the northern area and the percentage of the total number of bays (157) measured in the southern area, which are oriented in any given direction. It is apparent from Figure 28 that in the northern area more of the bays measured trend S 50° E than in any other direction, although the average direction for all bays measured is S 46° E. In the southern area more of the bays measured trend S 26° E than in any other direction, whereas the average direction for all bays measured in this area is S 20° E. T h e graphs further show axial trends of the southern bays to be more variable than trends of the northern bays. A contrast in form of bays in the two areas, indicated in Figure 27, is discussed later. It should be borne in mind that the statistical data discussed above, employed in compiling the tables of axial trends by counties and used as the basis for Figures 27 and 28, are representative rather than comprehensive. They refer to less than four hundred bays in two regions where these forms are numbered by the thousands if not by tens of thousands. T o procure all available photographic representations of bays in these areas would be a very costly undertaking. T o measure all the bays thus 3

T h i s fact should not cause surprise in view of the very faint relief of the forms in question and the often difficult nature of the wooded or marshy terrain.

A . NORTHERN

B.

PART OF BAYS AREA

SOUTHERN PART OF BAYS AREA

28: Graphs show regional contrast in axial directions and percent of total number of oval bays measured which are oriented in directions indicated. Concentric lines show percentages, radial lines show directions. Because regional contrast in axial directions is more significant than percentages of bays oriented in particular directions, percentage values of concentric lines are different in the two diagrams in order that total length of graphs may be the same and their general directions thus more easily compared. FIGURE

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Hypothesis of Complex Origin

represented would be a very time-consuming undertaking. T h e greater degree of precision thus secured would not alter general conclusions or greatly increase the certainty of those conclusions. Measurements were limited to bays in which the oval outline was sufficiently perfect to make determination of axial directions reasonably safe. A much larger number of poorly formed bays remains unmeasured because axial directions could not be determined with assurance. For some areas aerial mosaics showing many excellent oval bays were available; for others only individual photographs of a limited number of bays were at hand. For some areas topographic maps exist; for others none have been prepared. Some county and soil maps show many bays with remarkable precision; others show none at all even where many are present. T h u s the quantity and quality of photographic and cartographic material readily available for measurement of axial trends varied greatly in different parts of the region. T h e great contrast in number of bays measured in different counties is in part due to differences in the number of perfectly formed bays in those counties; but it is also in no small degree due to differences in the quantity and quality of material conveniently available for study. These points are emphasized because the reader should know the limitations of the statistical data employed and the danger of making any fine or close comparisons where the data used are so incomplete that more abundant material might conceivably alter computed average trends of bay axes by a few degrees. It is not believed, however, that more abundant data would alter general results in any appreciable measure or change in any degree the conclusions to which the evidence points. T h e writer spent several days in the laboratories of the Agricultural Adjustment Administration at Washington inspecting aerial photographic mosaics of most of the Coastal Plain of the Carolinas and large parts of Virginia and Georgia, in order to determine the areas in which oval bays are well developed and to detect any abnormalities in axial directions which might affect the problem of bay origin. He is confident that the data represented in the tables and illustra-

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171

tions given above are properly representative of vast numbers of bays in the areas studied. T h e observed fact that in the northern part of the bay country, where dip of beds is presumably in a direction approximately S 45 0 E, the average trend of the elongated craters is in the same direction, and in the southern part, where dip of beds is presumably more strongly southward, the average trend of the craters is likewise more strongly southward, suggests the possibility that updip migration of artesian springs is at least in part responsible for the elongated form and parallel trend of the craters. We now direct our attention to a second test of the hypothesis of artesian spring migration. It has been shown that updip migration of an artesian spring should lead to the development of elliptical basins in case there is no marked progressive enlargement of the openings by which the artesian waters escape from the aquifer into overlying beds; whereas the basins should be eggshaped or ovoid, with the small ends of the eggs pointing downcurrent (or down-dip), in case the openings through the impermeable bed are progressively and greatly enlarged up the dip. The (relatively) impermeable bed may be clay, shale, or other material little subject to solution; or it may be a marl, limestone, or other soluble formation. It may even happen that the aquifer and the relatively impervious cap are parts of the same horizon, as where a limestone carries great quantities of water under artesian pressure and escape is upward through occasional fractures, solution openings, or other passageways formed in the upper part of the limestone itself. It would seem logical, therefore, to suppose that elliptical craters will prevail where beds are relatively insoluble or where highly soluble beds are rare; and that ovoid craters will prevail where highly soluble beds are most abundant. It will later be shown that there is no area occupied by the craters which is not now or was not formerly underlain by one or more soluble beds. But it is equally true that some parts of the Carolina Coastal Plain have a greater proportion of soluble beds, or more highly soluble beds, than do other parts of the plain. Southeastern North Carolina and northeastern South Carolina, where the Cretaceous beds cover much of the area, are relatively

Index mosaic of aerial photographs covering part of Bladen Co., N.C. Note elliptical form and S E trend typical of bays in N part of bay country. One bay in SE corner, one in N W corner, and two SW of center, are occupied by remnants of lakes (black areas) being encroached upon by peat bogs. Elizabethtown on the Cape Fear River shows on S border of mosaic, to left of center line. N is at top, and fairly large bay (White Lake Bay) in SE corner is 2 >4 miles long, measuring to outer edge of white sand rim. (AAA.) FIGURE 29:

30: Index mosaic of aerial photographs covering part of Barnwell Co., S.C. Note ovoid form and more nearly southward trend typical of bays in S part of bay country. T h e little town Elko is N W of center on railway, and entire area is covered by Williston, S.C., topographic quadrangle. N is at top, and larger ovoid bay just SW of center is 14 mile in length. (AAA.) FIGURE

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poor in highly soluble formations. It is precisely here that elliptical bays predominate and have their most perfect development (Fig. 29). In southeastern South Carolina and northeastern Georgia, where Tertiary beds cover much of the area, soluble formations are more abundant. And it is precisely here that eggshaped or ovoid bays are most numerous (Fig. 30). Thus the hypothesis that the curious craters of the Carolina coast owe their form and orientation in part at least to updip migration of artesian springs appears to be doubly supported by the field evidence. R E S U L T S OF C O M B I N E D GROUNDWATER AND A R T E S I A N

FLOW

We have seen that groundwater flow operating alone and artesian flow operating alone are each capable of accounting satisfactorily for the elongated form and the generally parallel trend, more or less northwest-southeast, of the Carolina craters. Both processes account for the fact that while multiple sand rims are often developed about the southeastern ends of the craters (for reasons explained elsewhere) they are almost unknown about the northwestern ends. This is because both processes involve progressive encroachment of the craters toward the northwest, with consequent destruction of any rims beginning to form there. But neither process accounts for certain puzzling features of the craters, observed on aerial photographs. In the southern part of the bay country, where the prevailing axial trend of the craters is more strongly southward, trends are also more variable than in the northern area, some of the craters trending almost due southeast, a few north-south, and a very few west of south. Occasional craters (Fig. 32) show one or two rims about the northwestern end where normally rims are absent. Throughout the bay country there are found individual craters and even groups of craters (Fig. 36) with multiple sand rims mostly on one side of the basin rather than about the southeastern end. Finally, there are some complex craters in which older and later oval basins having distinctly different axial trends appear to be combined (Figs. i6„ 34, and 35). Possibly some of these anomalies may find explanation in the combined action of groundwater flow and

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artesian flow. Let us first deduce the expectable consequences of such combined flow. In Figure 31 let O represent a fracture or other opening by which artesian water escapes from an aquifer through an impervious bed into overlying loose sand. Let the arrows A, A, indicate the direction that the uprising artesian waters would take if unaffected by groundwater flow, and the arrows G, G, the direc-

31: Effect of artesian flow A A combined with groundwater flow GG. To make clear the principle, lines of flow are over-simplified.

FIGURE

tion of groundwater movement if unaffected by artesian flow. The actual movement of the combined artesian and groundwater flow will be a resultant of the two flows, along some such path as that represented by the arrows A G , A G . The artesian spring S will thus appear at the surface some distance downcurrent (groundwater current) from a point directly over the aperture O which permitted escape of the artesian water, and will tend to excavate a circular basin at the place of surface outflow.

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It is evident that the particular path of flow indicated by the arrows A G , A G , will depend upon the comparative strength of artesian flow and groundwater flow. At the point of emergence from the aperture O the artesian flow may be concentrated in a jet of limited diameter and relatively high velocity. But as the artesian water rises, it may be expected to spread more widely through the sand, to lose velocity, and to mingle more and more with the groundwater. It seems reasonable, therefore, to assume that the artesian flow will be progressively more and more influenced by the groundwater flow. For this reason the arrows A G , AG, in Figure 31 are represented as pursuing a curved rather than a rectilinear course. Further consideration will doubtless convince the reader that in nature the balance of forces represented in the combined artesian and groundwater flow must be a varying balance, because of the fact that neither artesian flow nor groundwater flow remains constant in volume or in velocity. Should solution or erosion enlarge the opening (O, Fig. 31) through the impervious bed, thereby increasing the volume and perhaps also the velocity of artesian flow, the uprising waters will ascend more directly toward the surface. In other words the ascending current, originally moving along the path AG, AG, will progressively be shifted to the path A'G', A'G'. In consequence the artesian spring will migrate progressively from the position S to the position S', with the further consequence that what was a more or less circular basin at S will be transformed into an elliptical or ovoid basin with major axis parallel to the general direction of groundwater movement. Increase of artesian head could precipitate an identical sequence of events. The same result must be produced if the artesian flow remains constant and groundwater flow weakens. Such weakening might be seasonal or secular, due to the advent of an annual period of scanty rainfall or to change in climate from one that is humid to one more arid. Or the change might be permanent, as when stream incision permits escape of groundwater elsewhere. Under any of the conditions outlined above, the artesian spring will migrate from S to S' and an elongated crater will be produced.

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On the other hand, the path of upward flow will shift from A'G', A'G', back toward AG, AG, and the artesian spring from S' toward S, if the artesian head be gradually reduced by lowering of the intake area, by stream incision into the aquifer, by development of excessive leakage into overlying beds, or by seasonal or secular drought over the area of intake. T h e physical conditions cited in the preceding two paragraphs by no means exhaust the list of possible changes competent to produce migrations of artesian springs up or down the slope of a coastal plain parallel to the direction of groundwater movement. But they are sufficient to show that such migration could not have been a rare phenomenon but, on the contrary, must have been the rule wherever artesian waters rose through sand saturated with moving groundwater. Indeed, it seems most probable that such spring migration occurred repeatedly, now in one direction, now in the reverse. In these considerations we seemingly find a third explanation for the existence of elliptical and ovoid craters on the Carolina Coastal Plain elongated in a general northwestsoutheast direction. It is shown elsewhere in this volume that the period of great artesian spring activity and crater excavation belongs to the recent geologic past, when the surface of the Coastal Plain was substantially undissected. Stream incision has afforded lower outlets for many of the shallow artesian water horizons, while abundant development of artesian springs, frequently accompanied, no doubt, by enlargement of the orifices through which the waters escaped from the aquifers, has possibly played a part in reducing the artesian head. Whatever the causes, artesian spring activity today seems rare and weak in comparison with what it is postulated to have been during the period of maximum crater excavation. We apparently witness merely the dying phases of a process once of dominant importance. On the other hand, groundwater flow, while highly irregular as compared with conditions prior to Coastal Plain dissection, may well be stronger relative to artesian flow than when the latter was at its maximum. As a result, the weakened artesian upflow, where it still persists, is apt to be strongly deflected downcurrent

32: Salters Lake Bay, Bladen Co., N.C. Peat bog is encroaching upon lake from its borders, most extensively from NW. Note outlet channel to S; irregular waves of white sand migrating eastward with maximum development about SE quadrant; invasion of small bay to N W by bulging extension of Salters Lake Bay; and double sand rims at N W ends of both these bays. White lines are roads, black and gray dots are trees. N is at top, and total length of double crater is 1 % miles. Compare Figure 29. (Agricultural Adjustment Administration.) FIGURE

by groundwater movement, or along some such path as that represented by the arrows A G , A G , Figure 31. T h u s a spring w h i c h migrated from S to S' (Fig. 31) in the period of m a x i m u m artesian activity, thereby excavating an elongated basin, is apt to be f o u n d back at S now that artesian activity has waned. In the foregoing considerations we seemingly find a reasonable explanation for the fact that b o i l i n g springs or fountaining springs have thus far been reported more frequently from the south-

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eastern ends of basins than from the northwestern ends. And since peat bog development takes place more rapidly in stagnant than in agitated waters, we further find a possible explanation for the fact, observed in certain aerial photographs (Figs. 29, 32, and 33) and noted by Buell (see Chapter I I I above), that where lakes in elongated craters are being progressively filled by peat bogs, open water remains longest in the southeastern ends of the basins, the area in which spring action appears to be most frequent. Buell 4 attributed this phenomenon to prevailing southwest winds, which agitate the water more on leeward than on windward sides of the lakes, and to shallower depths in the northwestern ends of the basins. It will be noted, however, that in Salters Lake (Fig. 32) and certain other lakes peat is advancing lakeward from leeward shores where such agitation as is due to wave action should be at a maximum. T h e open water is toward the southeastern ends of the lakes but is often completely surrounded by peat. This may be adequately explained by the fact that certain vegetation can gain foothold and survive in shallow water even if the water is greatly agitated. Suggs Mill Pond bay (Fig. 33) is exceptional not only for the beautiful series of concentric beach ridges about its southeastern end but also for the peculiar manner in which the open water partially surrounds a central area filled with vegetation. At least one fountaining spring is known to exist under water off the southeastern shore. T h e distribution of open water and vegetation within this basin seems opposed to that part of Buell's interpretation based on wind agitation. It is not necessarily inconsistent with the spring agitation hypothesis, although the latter must be supplemented by some further explanation in order to account fully for the pattern of open water. Further study will doubtless throw more light on this problem. At present, the number of artesian springs observed still fountaining in the craters, the number of lake basins known to be incompletely filled with peat bogs, and the number of basins for which we have depth measurements is in each case extremely small—far too small in comparison with the enormous number of existing craters to con4

Murray F. Buell. Peat Formation in the Carolina Bays. Bull. Torrey Bot. Club,

66:483-487,

1939.

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stitute a trustworthy demonstration of the validity of any hypothesis. A l l w e can say is that the few facts observed in these particular categories appear to be in harmony w i t h the explanation of crater origin presented above. EXPLANATION

OF

PUZZLING

FEATURES

T h e fact that elongated craters of elliptical or ovoid f o r m may reasonably be e x p l a i n e d by the c o m b i n e d action of artesian flow a n d g r o u n d w a t e r flow opens the way to rational e x p l a n a t i o n of certain p u z z l i n g features of the craters described o n an earlier page. If the axial directions of elongated craters are related b o t h to the d i p of beds (direction of artesian flow?) and to the direction of g r o u n d w a t e r flow, it w o u l d seem reasonable to suppose that w h e r e d i p of beds and g r o u n d w a t e r flow are substantially in the same d i r e c t i o n , the axial trend of the craters should b e rather u n i f o r m l y in that direction. Local deflections of either c o n t r o l l i n g factor m i g h t result in craters d e p a r t i n g f r o m the normal trend, b u t such departures should be l i m i t e d in n u m b e r and for the most part of m o d e r a t e a m p l i t u d e . It was earlier shown that in southeastern N o r t h C a r o l i n a and northeastern South C a r o l i n a b o t h d i p of formations and original g r o u n d w a t e r flow were presumably toward the southeast, the slope of the surface and the d i p of the formations both b e i n g in that general direction. It has also b e e n noted that the trend of elongated craters in this r e g i o n is exc e p t i o n a l l y u n i f o r m , this b e i n g the area responsible for the early o p i n i o n that the craters never vary widely f r o m the direction S 46° E. O n the other hand, w h e r e d i p of beds and associated artesian flow

are in o n e direction and g r o u n d w a t e r flow in a different

FIGURE 33 (on facing page): Suggs Mill Pond Bay, Bladen Co., N.C. Note multiple beach ridges of sand about SE end, migrating dunes of outer rim of SE quadrant, open water (black) at SE extending up either side, and vegetation filling N W and central areas. Excavation on S shore admits water to dam whence it escapes through outlet channel not clearly shown. N is toward outer margin of page, and length of bay is 2^4 miles, measured to outer sand rim. T h i s bay appears in N W corner of Fig. 29. (Agricultural Adjustment Administration.)

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direction, if crater elongation depends upon relative strength of the two flows at any given point, and such relative strength is variable depending upon which type of flow is there dominant,

34: Complex bay 7 miles SW of Bishopville, Lee Co., S.C. Divergent axes of older and later parts of crater indicated by white lines. Many bays nearly obliterated by cultivation of fields. N is at top, and main crater is one mile in length. (Fairchild Aerial Surveys, Inc.) FIGURE

trends of crater axes should be variable, normally ranging somewhere between the direction of artesian flow and that of groundwater flow. We have seen that in southeastern South Carolina and in northeastern Georgia the surface slopes southeast while the beds below the surface dip more nearly south, suggesting that near-surface groundwater flow may be roughly S 45 0 E while artesian flow, if more or less nearly down the dip, may vary from S io° E to S 30° E. We hive also seen that in this same region the

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183

axial trends of the elongated craters are more variable than in the north, the variations for the most part having much the same range as the assumed differences in direction of the two types of

F I G U R E 35: Open Bay W of Coward, Florence Co., S.C. An outlet channel drains bay toward NW. Note slightly ovoid form and fact that bay appears to occupy site of an older crater, part of which is visible toward SE. Arrow points N. Length of main crater 214 miles. (Fairchild Aerial Surveys, Inc.)

flow. It thus appears that throughout the bay country the observed facts respecting axial trends of craters conform to expectations deduced from the hypothesis that such trends are jointly related to artesian and groundwater flow. Explanation of other peculiarities of certain craters depends upon the fact that the relative strengths of artesian and groundwater flow vary in time as well as in space. If in the same place, dominant groundwater flow at one time tends to excavate a crater trending in one direction, whereas later increasingly vigorous artesian flow tends to result in a crater having a different trend, this change in conditions should be reflected in craters of

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Hypothesis of Complex Origin

more complex form or variable orientation. Craters of this hybrid type need not be numerous, since a crater once formed under one set of conditions might not readily be changed in form or

FIGURE 36: Ovoid bays S of Elko, Barnwell Co., S.C. Note systematic occurrence of multiple sand rims about E sides of craters, as though they had all been shifted toward W. N is at top, and largest crater is about I/2 mile in length. (Agricultural Adjustment Administration.) orientation even when conditions change. Only in case conditions change during the period of active crater excavation, and change sufficiently drastically to start excavation well to one side of a crater previously started, can we expect forms which will today reflect the conflict in conditions under which they were produced. As previously noted, aerial photographs show a certain number

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of bays or craters which seem to be of a hybrid or composite type. In Figure 34 one observes some elliptical and some ovoid forms, many of them nearly obscured by cultivation. T h e largest oval appears slightly more pointed toward the southeast than toward the northwest. More significant, it seems to be developed largely within an earlier crater which projects southeastward beyond the later form. The axis of the later crater seems to be deflected more strongly southward than was the axis of the one first formed. In Figure 4 it appears that the crater within the inner rim has an axial trend slightly different from that of the crater outlined by the outer rim. That the later crater slightly transects the earlier one is more clearly indicated in Figure 19B, where the broken line xy prolongs the inner border of the earlier form. T e n Mile Bay in Figure 16 has a narrower southeastern end and an axial trend more strongly southward than what appears to be an older crater projecting beyond its southeast border. T h e large bay west of Coward, South Carolina (Fig. 35) seems to show similar relations, but for reasons not obvious one or two minor craters appear in the preserved remnant of the earlier form. Many ovoid craters, especially in the southern part of the bay country where axial trends are more variable, have a succession of sand ridges or rims about their eastern sides rather than about their southeastern ends (Fig. 36). A westward migration of the locus of crater development, consequent upon increasing strength of artesian flow more or less downdip, would account for the observed facts. It is usually observed in these cases that slight migration of the crater updip toward the northwest has accompanied lateral displacement toward the southwest or west. T h e triple rims of Watts Bay (Fig. 5) in the Myrtle Beach district may place this crater in the class of aberrant forms here treated, although the rims are less clear and the relationship to a contrast in directions of groundwater flow and artesian flow is not evident. That a few of the elongated craters should trend north-south and a very few somewhat west of south may be explained as the result of local peculiarities in the dip or internal structure of Coastal Plain beds, the occasional local control of fractures upon direction of spring migration, the influence of valley incision in deflecting groundwater movement in directions other than normal,

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and other special circumstances. Reference is made elsewhere to an apparent oval bay nearly four miles due east of Estill in Hampton County, South Carolina, having a trend approximating S 2o° W. This bay is represented on the Varnville topographic quadrangle as containing two ponds surrounded by marsh of irregular outline. Aerial photographs show that the depression possesses an outline in part oval and in part irregular and that it is associated with other similar imperfect ovals trending in the same general direction. T h e association of forms strongly supports the interpretation that the depressions are true oval bays of somewhat unusual trend and imperfect outline. T h e same appears to be true of Enecks Bay on the Shirley quadrangle in Georgia, more fully described elsewhere in this volume. T h e group of bays represented on the Hilltonia quadrangle, Georgia, six miles east of the town of Hilltonia, are seen on aerial photographs to have distinctly ovoid outlines for the most part, with some of the longer axes trending north-south or slightly west of south. In these cases, and as a general rule, bays having trends west of south are more or less imperfect in form, as if not all factors required for typical crater development had been present. There remains one more aberrant feature of occasional craters the explanation of which is not wholly clear. T h e normal upslope migration of craters, whether under the influence of groundwater flow or artesian flow or of both combined, satisfactorily accounts for the prevailing absence of sand rims about the northwestern ends of the craters. Here sapping and undermining would counteract any tendency to rim development, whether beach ridges or dune ridges. An alternative explanation, and one perhaps equally valid, is that dominant winds from a westerly direction (northwest-west-southwest) would drive waves away from northwestern shores and blow accumulating sand back into the lake, thus preventing the formation of either type of sand ridge. Both explanations may apply in varying degrees to different craters. Where occasional sand rims, sometimes single and sometimes multiple, do exist about the northwestern ends of craters, cessation of undermining due to weakening of groundwater or artesian flow or to shifting of the artesian spring back toward the southeast might conceivably explain the presence of

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rims in a zone where they are usually lacking. But weakening of both groundwater flow and artesian flow must have been general throughout the bay country as streams cut their valleys below the level of crater development, whereas rims about the northwestern ends of craters are exceptional features. Local variations in wind direction are a conceivable but not a satisfying explanation. Professor J . Hoover Mackin suggests that variations in perviousness of the strata involved might cause variable local response to a general lowering of groundwater level. The best case of rims at the northwest known to the writer is shown in Figure 32, where both Salters Lake bay and the smaller bay to the northwest of it have distinct sand rims which are in part double, while the long narrow bay to the southwest of Salters Lake bay, and partially obscured by the latter, seems to have a particularly prominent single rim about its northwestern end. This case is exceptional also in the manner in which the Salters Lake crater has "bulged" forward into the small crater northwest of it, as though the forces extending the larger crater to the northwest had in the smaller crater encountered an area of diminished resistance. One may imagine that here a heavy sand rim about the southeast quadrant of the smaller crater has been driven northwest into the latter, to give the abnormal double rim at the northwest end of the big crater. But the history is not clear, and the rims about the northwestern ends of the two smaller craters cannot be so explained. The remarkable nature of the contact between Salters Lake crater and its small neighbor to the northwest can best be appreciated when one remembers this fact: throughout the bay country whenever one crater intersects or is intersected by another, one of the two (presumably the younger) almost invariably possesses a perfect outline in no wise affected by the other; and the perfect crater may be either the larger or the smaller, and may lie in any direction whatsoever from the one intersected. All types of intersection are shown in Figure 29, in which Salters Lake bay (southwest of the center) is unique. Despite an occasional form the significance of which is not wholly clear, it remains true that all the characteristic features of the Carolina craters and most of the aberrant features find com-

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Hypothesis of Complex Origin

plete and reasonable explanation under the hypothesis of artesian spring excavation of craters modified by groundwater flow. This fact inevitably gives one a considerable measure of confidence in the hypothesis. A L T E R N A T I V E POSSIBILITIES

We have seen that the elongated craters trending northwestsoutheast can be accounted for in three distinct ways: by seepage of groundwater into the northwestern sides of lake basins; by the northwestward migration of artesian springs; and by the deflection of uprising artesian currents toward the southeast, alternately more strongly and less strongly, by variable strengths of groundwater flow. There are two other possible causes of crater elongation which deserve attention. Engineering studies have shown that when water under pressure from below attempts to rise through saturated loose sand toward the surface of the ground, there commonly develops a type of action producing what is sometimes called a "boil." At various points where resistance to upward movement is first partially overcome, columns of water start to move upward. Water and sand begin a vigorous circulation or "boil," the overlying sand dropping into the area of agitation and descending, while the water of the boil ascends higher and higher through the mass by a sort of stoping process. As the boil ascends, the diameter of the disturbance normally increases, for a time at least, until the form of the resulting column of agitated water and sand is that of a slender inverted cone. Ultimately the disturbance reaches the surface and the boil bursts forth as a violently agitated mass of sand and water. This action is easily reproduced in the laboratory with the aid of such apparatus as that represented in Figure 37 (explanation on pp. 156-7), designed by Professor Donald M. Burmister of Columbia University. It is believed that action of this type was general over the undissected Carolina Coastal Plain when countless artesian currents from shallow aquifers were rising through sand saturated with slow-moving groundwater. Professor Walter H. Bucher called the writer's attention to the possibility that, where a boil of the type described above is affected by groundwater moving in a constant direction, the finest sediment

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189

in the agitated area may tend to be shifted more and more in the direction of groundwater flow. If the result should be a blocking of pore spaces in undisturbed sand on the downcurrent side of the A

B

37: Laboratory demonstration of behavior of sand under water. A. Stoping action in process, causing sand boil at surface of sand through which water is ascending. B. Compacting action of descending water permits retention of steep subaqueous slopes in sand. Apparatus designed by Professor Donald M. Burmister of Columbia University. FIGURE

boil, there would be a tendency for this blocking to increase in the upcurrent direction. Simultaneously, groundwater coming into the area of agitation on its upcurrent side would aid in loosening and moving sand on that side. T h e net result would be an upcurrent migration of the boil and of any basin resulting on the surface. T o what extent blocking by fine sediment would aid a process which groundwater movement is in any case competent to effect is difficult to say. Professor Bucher further pointed out that the low dome of water formed where a boil rises to or near the surface and then flows off laterally in all directions must be affected in shape by groundwater flow. T h e r e is a tendency to shorten upcurrent radii and lengthen downcurrent radii of the outflowing water of the

igo

Hypothesis of Complex Origin

dome; in other words, to transform the circular dome or boil into one more or less ovoid in plan with the long axis in the direction of groundwater flow. T o what extent this action may have influenced the form of the Carolina craters is problematical. In any case it is interesting to note that whereas the form and orientation of these craters originally seemed the most inexplicable of all their characteristic features, we now have a variety of possible explanations, certainly not less than five, all associated with the flow of groundwater, dip of sediments, flow of artesian water, or with combinations of these. STATEMENT OF THE HYPOTHESIS OF C O M P L E X

ORIGIN

Our discussion of the hypothesis of complex origin of the Carolina craters has thus far dealt chiefly with the primary element of the hypothesis: excavation of the craters by artesian waters as modified by groundwater flow. We must now integrate the results of this discussion with other aspects of the problem to give a more complete statement of the hypothesis. It is believed that when the Atlantic Coastal Plain emerged from beneath the ocean, rainfall gave rise to surface streams which flowed approximately northwest to southeast down the surface slope, to shallow groundwater movement in the same general direction, and to a deeper underground circulation which moved through the sediments in greater or less degree down the prevailing dip of the beds. As the Coastal Plain formations consist of numberless lenses of sands, gravels, and other pervious deposits, alternating and interfingering with lenses of clay and other impervious beds, it frequently happened that water entering pervious layers higher up the slope did not proceed far before it found a natural means of escape to the surface, whether because an overlying lens of impervious material had thinned out and disappeared, because fractures or solution channels offered passageways through overlying beds, or for other reasons. Before surface streams had entrenched themselves deeply and thereby afforded opportunity for subsurface waters to escape at lower levels, the outflow of artesian springs on the nearly flat surface of the plain must have been a phenomenon of major importance. We should picture, vast stretches of the Coastal Plain

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191

having the surface dotted with literally countless springs, many so small that their waters might filter away through the surrounding soil, others so large that surface streams flowed from them in definite channels carved during their escape, and all boiling or fountaining in greater or less degree due to the artesian pressure of water entering the sediments farther u p the slope. Other large portions of the Coastal Plain surface had few or no such springs because impervious layers near the surface or other unfavorable geological conditions constrained the waters to continue under ground until they reached areas where escape to the surface was easy. T h e immediate surface layer of the Coastal Plain was then, as now, prevailingly of sand, whether because surface weathering and wash had produced a residue of quartz grains from the decomposition of surface formations or because advance and retreat of the sea had left a coating of wave-washed sand. Immediately below the loose surface sand there was usually a sandy loam. Because surface streams were not yet deeply entrenched, the groundwater level must at that time have been very close to the surface of the plain. Consequently the upwelling artesian springs reached the surface in a layer of loose sand or sandy loam effectively saturated with water moving slowly toward the southeast. Under these conditions elliptical and ovoid basins with axes more or less nearly parallel were formed in the manner already indicated. Enlargement of the basins was accentuated as saturated loose sand slumped or flowed freely inward from all directions or as sandy loam disintegrated and moved more slowly, while outflowing surface streams carried fine material in suspension and in solution from the basins. Where the surface was underlain by soluble formations, such as limestone, marl, or arkosic sands, progressive solution modified the artesian spring basins and developed channels or caverns under ground and sinkholes and similar karst phenomena on the surface. Some sinkholes resulted directly from the solvent action of descending local rain water, others may have resulted from the caving in of underground channels and caverns in the soluble

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Hypothesis of Complex Origin

beds, while still others were developed by waters upwelling to the surface. T h e resulting "sinks" served in part as intakes for descending surface waters and in part as exits for uprising artesian waters, depending upon local conditions. T h e same openings might serve first one purpose, then the other, as changes in groundwater level, underground circulation, and other local conditions occurred. In localities where compact material was at or close to the surface, sinkholes exhibited the irregular outlines commonly observed in limestone regions and many of them were of small size and relatively deep. But where the soluble formation was buried under a thick cover of loose sand, the surface depressions tended to be comparatively shallow, of regular outline, and, despite small openings below, of relatively large diameter. T h i s was because loose sand slumping into a cavity moves inward as well as downward from all sides, with the result that the surface depression may have a diameter many times that of the cavity into which the sand below slumps, while the irregular outlines of the smaller opening below are practically lost in the greatly enlarged outline at the surface. T h e subsidence crater thus produced in loose sand will be scarcely perceptible if the quantity of material slumping into the underlying cavity is small, while even a large amount of underground slumping will leave a surface crater relatively shallow. A deep crater in the overlying sand could be produced only in the improbable event that great quantities of the material were carried off through underground passageways and effectually disposed of where they could not impede continued sand removal. Relatively large, shallow, regular craters would be the rule, elongated to oval forms where underground cavities were notably elongated, artesian springs had migrated, or groundwater flow had caused elongation of surface basins. Where compact clayey loam or other resistant material slumped as the result of removal of underlying soluble material, the surface depressions would not necessarily be much larger than the areas of slumping below and might retain highly irregular outlines. So long as the groundwater level lay close to the surface of the

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193

Coastal Plain, many of the artesian spring basins and their closely related sinks were occupied by lakes. According to the hypothesis, countless lakes of elliptical or ovoid form dotted large areas of the plain wherever geological conditions favored the development of countless artesian springs or the formation of subsidence basins. Where the groundwater level was lower or where geological conditions did not bring to a given region abundant supplies of water under artesian pressure or favor the development of subsidence basins, lakes were rare or lacking. Across the lakes winds drove waves and currents which attacked the shores and moved material along their borders. Because of wave refraction and in obedience to the law that irregularities of youthful shores tend to become smooth in later stages of development, irregularities of the lake shores would in time disappear and the lakes would thus acquire regular outlines. T h e transformation would take place quickly where the lake basins had formed in loose sand, especially if the initial outline of the lake were fairly simple, with only minor irregularities. Where a lake basin with greater irregularities was developed in loam or where, as might occasionally happen, a lake basin formed in a thin layer of loose sand had shore irregularities of large magnitude due to irregular solution of underlying formations, attainment of the simpler form would be long delayed. Where a highly irregular basin was formed in clayey loam or more resistant material, the shore irregularities might not be reduced before the lake was extinguished by downcutting of the outlet, by filling of the basin, or by drop of groundwater level. It appears that many of the Coastal Plain lakes were reduced to remarkably perfect oval forms, but that more retained a greater or less degree of irregularity, while others continued highly irregular. This accords well with the fact that the lakes developed under a variety of geological conditions. Wave work on the shores of the lake in time developed sandy beaches, quickly where loose sand was already available, more slowly where sandy loam had to be reworked and sand separated from silt and clay. Sometimes waves and currents transported sand along shore, building bars across the mouths of reentrant bays or

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Hypothesis of Complex Origin

in front of the somewhat sharper curves at the ends of the oval basins. Whenever sand cast upon the lake-shore beaches or revealed on the lake floor at low water was dry, it was subject to transportation by the winds. T h u s it happened that ridges of wind-blown sand accumulated about the margins of many basins and encroached upon the land immediately to the rear. O n small lakes the beaches were characteristically insignificant features; but there was no limit to the height and breadth that the dune ridges might acquire. Progressive deepening of river valleys tended toward one end: the ultimate extinction of the lakes through the lowering of the groundwater level below the bottoms of their basins. T o the same end operated the filling of lake basins with peat and other deposits. In time most of the lakes were transformed into dry depressions or into marshy basins called "bays." Consequent on the lowering of groundwater level, descent of any surface waters concentrated in the oval basins may have accentuated solution under the bays, a possibility suggested by Professor F. A . Melton. Relatively few basins, specially favored by local conditions, still contain open lakes or patches of open water in the midst of progressively expanding marsh or peat deposits. In time these remaining water bodies will be drained or filled; and ultimately further dissection of the Coastal Plain by headward-growing branches of the major streams will destroy every trace of the countless basins and their contained lakes which once diversified broad areas of the Coastal Plain surface. Such is the history of the initiation, development, and extinction of the curious Carolina bays, according to the artesian-solution-lacustrine-aeolian hypothesis of their origin. It remains to test this hypothesis of complex origin: first, by determining whether the hypothesis will adequately account for the long list of observed facts catalogued in the early part of this chapter; and second, by deducing from the hypothesis new consequences and confronting these newly deduced consequences with new or previously recorded facts. If the hypothesis can successfully meet these two critical tests, it will have a valid claim to consideration in any future study of the Carolina bays.

X

Competence of the Hypothesis of Complex Origin

I

T IS believed that the hypothesis of complex origin of the Carolina bays does offer a satisfactory explanation of every significant fact known about the bays, as set forth in the first part of Chapter IX. Let us consider these facts in the order there presented. (A) PERFECTION

OF O V A L

OUTLINE

T h e remarkably perfect oval outline of many bays (Figs. 29, 30) is adequately explained. Lake basins formed in loose sand by upwelling artesian springs or by slumping of sand into underground cavities tend to be more or less oval, for reasons already fully set forth in the statement of the hypothesis. Normal development of lake shores under wave attack tends to perfect the regularity of outline. It has elsewhere 1 been demonstrated that waves operate to extinguish salients and that the mature shore of a continental border will be a relatively straight or simply curved line. T h e same principles applied to the development of a lake shore lead inevitably to the conclusion that the ultimate outline of a lake must be more or less circular or oval. Departures from such outline result in salients, and these are attacked by waves until eliminated. If lake shore irregularities are on a grand scale, and if material composing the shores is very resistant, transformation to the ultimate form may be infinitely slow. But where, as in the case of many Carolina bays, the shores consisted of loose sand or weak sandy loam, the change must have been rapid. Since the development of the basins took place under conditions calculated to give an initial form of unusual symmetry, transformation to the ultimate rounded pattern would not only be 1 Douglas Johnson. Shore Processes and Shoreline Development. 58.1 pp., York, 1919. See pp. 74-76 and 339-344-

New

196

Competence of the Hypothesis

exceptionally rapid, but the form achieved in a given time would be of exceptional perfection. Raisz 2 has shown that in Massachusetts the rounding of lakes is notable in glacial outwash plains composed of sand. Round and oval lakes are common in similar deposits in Minnesota and elsewhere. Conditions on the Coastal Plain with its cover of loose sand were far more favorable to the rounding process. Hence it should not be considered unduly surprising that many lakes of a rare perfection of outline developed under conditions exceptionally favorable both to the initiation of symmetrical basins and to the further regularization of their borders. Any condition or combination of conditions resulting in markedly more vigorous wave activity in one direction than in others will tend to produce an elongated or oval rather than a circular lake. Winds from the northwest or southeast, if sufficiently preponderant in duration or in intensity, could account for the northwest-southeast-trending oval basins of the Coastal Plain. In the case of the Carolina craters the supposed conditions of origin fully account for the production of oval rather than circular basins without the intervention of wind action, and studies of prevailing, dominant, and maximum winds offer no support for the aeolian hypothesis of crater elongation. (B) E L L I P T I C A L A N D OVOID C R A T E R S

That the oval craters are in some localities nearly elliptical in outline (Fig. 29) and in others more egg-shaped or ovoid (Fig. 30) follows directly from that element of the hypothesis which involves artesian spring migration without notable enlargement of the aperture (O, Fig. 26) in some cases, with such enlargement in other cases. Progressive enlargement should give ovoid craters, and we have seen that this form of crater is most frequent in that part of the bay country where the underlying rocks include the largest proportions of soluble materials, presumably most favorable to the enlargement of apertures through which artesian waters escape toward the surface. More detailed correlation of 2 Erwin J. Raisz. Rounded Lakes and Lagoons of the Coastal Plains of Massachusetts. J o u r . Geol., 42:839-848, 1934.

Competence of the Hypothesis

197

individual elliptical and ovoid bays with rarity or abundance of soluble underlying formations is impracticable (a) because of the rarity of exposures in a plain largely blanketed with a surface covering of sand and loam, and consequent limited knowledge respecting the position of formation boundaries; (b) because of the erratic distribution of certain marl layers largely concealed under the sand cover, new areas of which are reported from time to time; and (c) because of the possibility that soluble beds now partly removed or transformed to insoluble types may have been responsible for ovoid craters not now correlatable with soluble deposits. It should be understood, however, that the hypothesis of complex origin does not exclude the possibility of accounting for elliptical and ovoid outlines of craters in other ways. T h u s groundwater flow alone might, under certain circumstances, account for ovoid craters with narrower ends directed southeast. If water movement into the northwestern sides of the basins were from a wide arc (say from north, northwest, and west) instead of from a narrow arc (northwest), thus enlarging the basin in all those directions pari passu with its upcurrent migration, an ovoid outline would result. Again, if erosion and regularization of the shores of a lake with unconsolidated sandy shores take place under the influence of winds which blow with dominant strength through a fairly wide arc, as for example from S 10 o E to S 8o° E, wave erosion would tend to enlarge most rapidly those borders of the lake toward which such winds blow. T h e result would be an egg-shaped lake with the narrower end pointing toward the dominant winds, which would be toward the southeast in the hypothetical case mentioned above. If, on the contrary, the dominant wind blew through a very narrow arc, say S 40 o E to S 500 E, more rapid extension of the lake in that one direction would give an egg-shaped basin with the narrower end pointing with the dominant wind, or northwest in this imaginary case. All that can be said is that no satisfactory evidence has been found in support of the idea that these latter methods of producing ovoid rather than elliptical craters have been operative in the bay country.

198

Competence of the Hypothesis (c)

IRREGULAR

CRATERS

W e have already seen that the hypothesis here under discussion involves the production of irregular lake basins wherever soluble beds are near the surface, or where clayey loam or other more or less compact beds overlie the soluble formations and are not themselves overlain by a thick blanket of loose sand. Even where thick sand covers the surface, large-scale slumping due to irregular removal of large areas of soluble rock will produce large irregular subsidence craters. Underground waters upwelling through and eroding a more or less compact loam and carrying away the finer material may likewise develop irregular basins. (D) T R A N S I T I O N A L

FORMS

T h a t under the hypothesis there must be every gradation from the most regular to the most irregular basins is apparent from the assumed conditions of basin development. Irregular basins develop unless the surface formations consist of a fairly thick deposit of loose sand, weak sandy loam, or other material easily subject to slumping or flowing and easily eroded by lake waves. If there exist wide variations in thickness of sand cover, in composition and consistency of loam, in size and shape of slumped areas, in stage of development of lake shores under wave attack, and in other critical factors, there would of necessity be all gradations in basin form from the most irregular to the most regular. (E) P A R A L L E L I S M O F A X I A L T R E N D S

T h e hypothesis of complex origin offers reasonable explanation of the observed degree of parallelism in the long axes of oval basins. Both groundwater and artesian water moved prevailingly down the slope of the Coastal Plain or more or less down the dip of its component beds, in a general southeasterly direction. According to the hypothesis, elongated craters developed by groundwater flow, by migration of artesian springs, or by both combined must have axes trending in the same general direction. Attempts to correlate trends of crater axes with present wind

Competence of the Hypothesis

199

directions have failed. During the Glacial Period, when high pressures prevailed over the North American ice cap, it might be supposed that winds from the northwest would have been more continuous and stronger than now. Hobbs's 3 studies of glacial anticyclones have demonstrated the great importance of air currents flowing outward from the ice, but he is of the opinion 4 that in areas so remote as the Carolinas and northeastern Georgia winds from the northwest need not then have been of dominant importance, although he does believe that the cyclonic winds of that period were enormously increased in vigor. Dr. Charles F. Brooks, 5 professor of meteorology at Harvard University, has expressed the view that "the northwest winds of winter are quite likely to have been much stronger during the ice age than at present, for the continual high pressure area would have been much more developed, and, correspondingly, the low pressure area." If northwesterly winds were in any notable degree dominant during the Glacial Period, such a condition might have contributed in some measure to elongation of the basins in a northwest-southeast direction. Dr. Erwin J. Raisz 6 concluded from studies of Massachusetts lakes that there was a tendency for lakes in unconsolidated sands to become elongated in the direction of maximum wind velocities. (F)

D E P A R T U R E S FROM P R E V A I L I N G T R E N D S

T h a t the winds could not have been a controlling influence is indicated by the fact that the bays, even in a single restricted locality, show appreciable departures from the average direction of axial trend, while a few show very great departures. Such variations are fully explained by the hypothesis of complex origin, 3 W . H. Hohbs. T h e Role of the Glacial Anticyclone in the A i r Circulation of the Globe. Amer. Phil. Soc., Proc., 54:185-225, 1915. T h e Glacial Anticyclones; the Poles of the Atmospheric Circulation. Mich. Univ. Stud., Sci. Ser., No. 4, 198 pp., New York, 1926. T h e First Greenland Expedition of the University of Michigan. Geog. Rev., 17:1-35, 1927. See pp. 24-32. 4 W. H. Hohbs, personal communication. 5 Charles F. Brooks, personal communication. 0 Envin J. Raisz. Rounded Lakes and Lagoons of the Coastal Plains of Massachusetts. Jour. Geol., 42:839-848, 1934.

200

Competence of the Hypothesis

under which axial trend depends upon a variable balance between directions of groundwater flow and artesian spring migration. We have seen that the observed tendency for elliptical craters to trend nearly southeast in a high proportion of cases, and for ovoid craters to show more variable trends with an average direction more strongly southward, is in accord with geological conditions in the two areas where these contrasted types of crater are respectively most abundant. Aberrant trends in these and other regions are reasonably explained by local variations in groundwater flow or artesian spring migration due to a wide range of geologic and topographic factors, including variations in composition or dip of beds, influence of joints or other structures, and excessive solution of beds or incision of surface valleys locally affecting movements of subsurface waters. (G) V A R I A T I O N S IN SIZE OF C R A T E R S

T h e observed variations in size of basin are fully accounted for under the hypothesis of complex origin, since there are no fixed limits to the extent of slumping of saturated sand, to subsidence due to solution of underground soluble beds, or to the extent of artesian spring migration. T h e processes may operate to a very limited extent where conditions are unfavorable, to a very great extent where the reverse is true. Or similar conditions may cause many small sinks or small springs in one area, a few large ones in others. (H) S H A L L O W N E S S OF C R A T E R S

Shallow craters are to be expected under the artesian-solutionlacustrine-aeolian hypothesis. Slumping due to solution of beds under a thick cover of loose sand or weak sandy loam, even when extensive, normally gives craters which are shallow in comparison with their areal extent, as was made clear in the statement of the hypothesis. Slumping of more compact beds at or near the surface gives craters normally deeper than those formed at the surface of a thick cover of sand; but even these are most commonly shallow as compared with their area, although some small sinkholes may be relatively deep. Basins formed by spring action in

Competence of the Hypothesis

201

loose sand or weak sandy loam are characteristically shallow. We shall later see that the large shallow craters known as bays are often intimately associated with very small and often irregular sinkholes which are occasionally deep in comparison with their breadth. ( 1 ) C R A T E R FLOORS BELOW P L A I N

LEVEL

T h e hypothesis of complex origin, involving as it does removal of part of the Coastal Plain material by leaching or by stream transport, requires that the resulting craterlike depressions should descend below the general level of the plain, and hence below the bases of any rims of sand later deposited about them. This is in contrast with the segmented-lagoon and crescent-shaped key hypothesis of Cooke (applied to the Myrtle Beach bays alone), in which the oval basins exist only by virtue of the fact that oval rims of sand are built upon the lagoon or lake floor. (J) VARIATIONS IN ELLIPTICITY OF CRATERS

Any amount of variation in ellipticity of oval basins is permissible under the hypothesis here considered, because the length and breadth of the ovals are affected by such variable factors as extent and rapidity of spring retreat, extent of underground solution and slumping, strength and direction of winds, resistance of shores to wave erosion, and so on. (K)

B I L A T E R A L A S Y M M E T R Y OF C R A T E R S

T h e observed bilateral asymmetry (Figs. 1, 4, 5, 10, 11, 14, 35, 42) of the oval depressions is an expectable feature of lake basins formed in unconsolidated materials by one set of forces and later subjected to forces operating from a different direction. According to the hypothesis, oval basins trending more or less nearly northwest-southeast were produced by the combined action of groundwater flow and artesian flow. If lakes in the oval basins were later subjected to the influence of winds blowing prevailingly from the west or southwest, the windward or northeast shore would be more effectively eroded by waves than the leeward or southwest shore, and most extensively eroded where these winds blew across

202

Competence of the Hypothesis

the maximum expanse of open water, or in the central part of the northeast shore. Toward the two ends of that shore, wave erosion would progressively weaken because the expanse of open water progressively diminishes toward the two ends of the oval. T h e result would be to sharpen the curvature of the northeastern shores of the lakes, producing the systematic asymmetry of the basins actually observed. We shall later see that dominant winds in the bay country do come from the west and southwest. ( L ) D I S T R I B U T I O N A L P A T T E R N S OF C R A T E R S

It is obvious that either topography or structure may affect the distribution of basins formed according to the hypothesis of complex origin. Underground waters welling up to the surface in a region consisting of parallel beach ridges and swales will, other things being equal, form springs in the low swales rather than in the higher beach ridges. On the other hand, if the swales contain sufficient silt and clay to render them impermeable, this structural condition may force the uprising waters to reach the surface on the ridges of coarse, permeable sand. In either case the resulting basins will tend to form in rows or chains parallel to the preexisting ridges and swales (Figs. 3, 7, 12, 13, 14); compact groups of basins (Fig. 7, Lewis Ocean Bay group and Cotton Patch Bay group) rather than chains will tend to develop in isolated, nonlinear, low areas, provided silt and clay in such areas do not block the egress of upwelling waters. Joints or faults in the Coastal Plain beds may determine the routes followed by upwelling waters and thus indirectly determine the pattern of surface depressions. (M)

L I M I T S OF DISTRIBUTION OF C R A T E R S

T h e occurrence of typical oval basins on certain parts only of the Coastal Plain and their absence from the Piedmont and other Appalachian provinces are normal consequences of the hypothesis here discussed, because the combination of conditions required to produce such basins is highly specialized, occurring in certain parts of the Coastal Plain but not in others and being wholly absent, so far as is known, from all the Appalachian provinces.

Competence of the Hypothesis

203

(N) P R E S E N C E O F S A N D R I M S

Whether or not rims of sand occur about basins formed according to the hypothesis of complex origin depends upon the favorable conjunction of several fortuitous circumstances. If the basins are developed in loose sand or in material from which sand can readily be separated, if lakes occupy the basins, if wave action concentrates sand in beaches and beach ridges, and if these beaches and beach ridges are so located that winds blow landward across them at times when the sand is dry and hence easily moved, then sand rims of considerable magnitude, consisting in part of beach ridges and in part of dune ridges, will accumulate wherever this favorable combination of circumstances exists. It is thus implicit in the artesian-solution-lacustrine-aeolian hypothesis that many basins will be bordered by rims of wave-deposited or wind-drifted sand. (O) A B S E N C E O F S A N D

RIMS

On the other hand, if basins develop in compact, resistant material which does not readily supply abundant sand, if the bottoms of the craters are above groundwater level or if swamp vegetation occupies the depression before lake waves have opportunity to accumulate beaches or beach ridges, if beaches and beach ridges fail to form where prevailing winds can blow the material landward, or if beaches are submerged or even moist when winds might otherwise transport sand to positions of safe accumulation, then only limited deposits of wind-blown sand, or none at all, may form about the basins. Thus many basins with insignificant rims and many without any rims are to be expected under the hypothesis here considered. (p) Locus

OF M A J O R SAND A C C U M U L A T I O N

T h e conditions favorable to rim accumulation would rarely exist about the entire border of a crater, and for this reason it is expectable, under the hypothesis here discussed, that rims should completely surround a basin only in exceptional cases. A degree of irregularity in the distribution of partial rims is to be expected

204

Competence of the Hypothesis

in many cases, because the various factors affecting rim accumulation will be differently combined in different places. Thus a distinct rim on the southwestern side of a crater (Figs. 1, 5), about the southeastern end (Fig. 5), or even about the northwestern end (Fig. 32) should be anticipated in individual cases, even though these are not the normal loci of major sand accumulation. T h e fact that rim development is normally most pronounced about the southeastern quadrants of the basins (Figs. 1, 4, 5, 10, 1 1 , 14, 15, 32, 33, 42, 43) may reasonably be explained under the hypothesis of complex origin. According to this hypothesis, elongation of the oval basins results chiefly from the retrogressive migration of upwelling artesian springs or the retrogression of northwestern margins of the basins due to groundwater flow. T h e southeastern ends of the craters are therefore the oldest, and beach accumulation by wave action has there been longest in progress. T h e northwestern ends of such basins have been kept young by the assumed retrogression, and beaches, if formed, were soon destroyed by the same process. T h e net result would be an excessive accumulation of beach sand about the southeastern portions of the lakes. This excess of beach sand along the southeast shores of the lakes would, under the influence of winds blowing from the west, southwest, or south, accumulate about the southeast quadrants of the basins. For sand along that part of the shore southwest of the long axis of the oval basin would by these winds be carried back into the lake to fill the depression or to fall prey to further wave action. Orily that part of the sand along the shore northeast of the axial line would by these winds be carried landward to accumulate beyond reach of the waves. Northwesterly winds would tend to build sand rims about both southeast and southwest quadrants. Winds from the east, northeast, and north would tend to build rims about the southwest quadrants. Hence if in the region of the bays the dominant winds actually came from a westerly direction (northwest, west, and southwest), there should result some accumulation of wind-blown sand about the southwest quadrants, especially about their southeastern portions; but major accumulation would be about the southeast quadrants. Appreciable

Competence of the Hypothesis

205

accumulation might take place about the northeast quadrants, where wind directions were favorable but supplies of beach sand less abundant. Minimum accumulation should be about the northwest quadrants, where by hypothesis dominant wind directions and supplies of beach sand were least favorable. O n an earlier page it has been shown that excessive erosion of the northeastern shores of the lakes by waves driven by dominant west or southwest winds could reasonably account for the sharper curvature of these shores. It must therefore be asked whether such erosion would not undermine and destroy any beginnings of sand rims along this border of the lake. T h e answer is that the period of erosion of lake shores to produce the observed degree of asymmetry would in large part normally precede the period of major sand accumulation. Regularization of lake shores, like regularization of shores of the sea, may simultaneously involve both wave erosion and wave deposition. T h e deposits of this early period may, depending upon their location, be subject to destruction by later erosion. But after the outline of the shore has been adjusted to the forces operating upon it, and the shore profile of equilibrium is everywhere established, future changes are slow and usually progressive in a given direction for relatively long periods of time. Where prograding prevails, beach ridges (often later transformed into dune ridges by wind action) are developed. Where retrograding is the rule, the wave-cut cliff normally has a beach at its base; and frequently to the rear of this beach or at the top of the cliff there is a ridge of dune sand derived from the beach and constantly renewed as the cliff is cut back. Such rims of dune sand frequently are found along rapidly retreating seashores. They must all the more be expected along the slowly retreating shores of small lakes cut in sandy loam or other material which rapidly supplies to waves and winds unlimited quantities of loose sand—provided, of course, that the winds blow in a direction favorable to sand accumulation on the border of the basin. Even if spring retrogression and dominant northwest winds of the Glacial Period contributed nothing to the concentration of sand along shores of the southeastern portions of Carolina lake basins, there to be carried by dominant winds to the southeastern

2O6

Competence of the Hypothesis

38: Hypothetical distribution of wind-drifted sand rims (dotted, dashed, broken, and thin solid curved lines mark outer boundaries of rims) about oval bay with dominant winds (shown by long arrows) from N W , W, and SW. Total sand deposit resulting from all these winds is marked TSD.

FIGURE

quadrants of the basins, the observed facts concerning sand accumulation can nevertheless reasonably be accounted for under the artesian-solution-lacustrine-aeolian hypothesis of bay origin. In Figure 38 let it be supposed that the oval is a lake elongated in a northwest-southeast direction, this being the direction of the long axes of most oval bays. Let it be further supposed that around the shores of this oval lake sand is evenly distributed in beaches

Competence of the Hypothesis

207

and is equally available to winds blowing from all directions. T h e n winds blowing from the northwest will blow sand from the northwestern shores into the lake; but sand from the southeastern shores will be carried landward to form a sand deposit the outer border of which is represented by the dashed line lettered N W . Westerly winds will similarly form the deposit bounded by the broken line lettered W , and southwesterly winds the deposit bounded by the dotted line lettered SW. T h e outer solid line lettered T S D (total sand deposit) expresses the fact that the combined deposits formed under the assumed conditions will be greatest (either broadest or highest or both) about the southeast quadrant of the oval lake, and will thin out progressively toward the northwest on the one hand, and toward the south, southwest, and west on the other. It thus appears that the hypothesis of complex origin will, independently of all other considerations previously discussed, fully account for the observed major concentration of sand about the southeast quadrants of the craters, providing we assume that winds from the sector northwest through west around to southwest (a) are stronger than those from other directions or (b) blow for a longer time or (c) blow while sand is drier and more easily moved than when other winds are blowing. T h e validity of this and other possible assumptions will be appropriately tested in a later chapter. Here we have only to note that a potentially reasonable deduction from the artesian-solution-lacustrine-aeolian hypothesis will fully account for the observed fact that major sand accumulation takes place about the southeastern quadrants of the Carolina bays. (Q) M U L T I P L E

RIMS

T h e hypothesis of complex origin fully explains the observed fact that multiple rims, nearly but not quite concentric and from two or three up to eight or more in number, occur about some of the basins (Figs. 4, 5, 15, 16, 17, 33, 39, 40). As we have already seen, the sand rims, according to the hypothesis in question, are in part beach ridges and in part dune ridges formed about the shores of lakes. It is obvious that if the levels of some of the lakes

2O8

Competence of the Hypothesis

were to fluctuate notably, such lakes would have a succession of concentric shorelines. Bordering those shorelines which endured for relatively long periods of time sandy beaches would develop, and the sands of such beaches would by the winds be built into dune ridges of greater or lesser prominence. T h e number of such ridges or rims encircling any given lake basin is limited only by the number of different levels at which the lake surface may stand. T h e nearly but not quite concentric pattern of the successive rims is imposed by the shape of basins having sides or floors sloping gently toward the centers of the depressions, but not everywhere at the same angle of slope, and by the retrogression of northwestern shores previously discussed. T h e hypothesis under discussion necessarily involves a lowering of lake levels as the incision of streams into the Coastal Plain lowered the groundwater level of interstream areas. Presumably this lowering was, under normal conditions, very gradual; and when such was the case the lake waves and winds might in many instances build only imperceptible beach ridges not detectable today. But where sand supply was unusually abundant, concentric rims of appreciable size might result even when lowering was steadily progressive and slow. Concentric ridges may result from wave action at a stationary lake level. Successive beach and dune ridges form indefinitely along the stable shores of oceans or large lakes wherever abundant supplies of sand or gravel are eroded from neighboring headlands, brought in by rivers, or otherwise made available to the waves at a constant horizon. So long as supplies of sand were available along the shores of lakes occupying the oval basins, whether from wave erosion of basin margins or from the slumping or flowing of quicksand, beach ridges would continue to form in the same horizontal plane until lake level changed. While lowering of lake levels may normally have been progressive and slow, conditions in the Coastal Plain must have favored relatively sudden drops of the water surface in certain lakes. Streams working headward into interstream areas must in some cases have tapped, and drained relatively suddenly, some of the many lenses of coarse sand and gravel so abundant in the Coastal

Competence of the Hypothesis

209

Plain sediments. T h e solution of limestone layers and the consequent opening up of lower outlets must have occasioned some of those sudden drops of lake level with which students of karst regions are familiar. Retreat of falls or rapids in outlet channels, even if but a foot or two in height, would cause relatively sudden drops of lake level when these worked backward into the lake basin. Expansion of the lake basin, by spring migration or otherwise, into an area of lower land, thereby developing a new and lower outlet, would precipitate the same result. In this connection it is interesting to note that some basins have outlets toward the northwest (Figs. 3, 4, 20, 35, 40), from what are presumably the newest parts of the basins. T h a t some of the oval basins of the Carolina coast should exhibit several strongly developed sand rims is thus a simple and readily explicable consequence of the hypothesis which interprets these rims as beach or dune ridges formed about the shores of basins formerly holding lakes. (R) DISTRIBUTION

OF

MULTIPLE

RIMS

T h a t the multiple rims discussed in the preceding section tend to be best developed and farthest apart toward the southeastern ends of the basins and closer together or lacking toward the northwestern ends may readily be explained on the basis of conditions which appear to be expectable under the hypothesis here discussed. Attention has earlier been directed to certain factors which may have been responsible for a greater accumulation of sand in the southeastern ends of the lake basins than in the northwestern ends. Such an excess accumulation, whatever its cause, would favor the development of more beach ridges than would be formed where sand supply was more limited. On an earlier page we have shown that rims of dune sand are apt to be insignificant or completely lacking about the northwestern ends of many basins, apparently because the winds responsible for building these forms blow from directions which do not favor dune sand accumulation in that region. Northwestward migration of artesian springs, supposedly responsible for excavation of the basins, or groundwater sapping of the northwesterly sides of the basins, would also tend to prevent the formation of

Competence of the Hypothesis

211

multiple rims about the northwestern ends of the bays. For earlier beach ridges or ridges of dune sand, if developed there, would be destroyed as the depression expanded in that direction. It is not surprising, therefore, that most oval craters provided with multiple rims at the southeast have none at the northwest. Multiple rims at the northwest are apt to occur only when spring migration and groundwater sapping are not active and lake level has been repeatedly lowered. In the statement of the hypothesis the fact that some craters have multiple rims on their eastern sides rather than about their southeastern ends has tentatively been attributed to a westward displacement of these basins consequent upon a progressive change in relative strength of groundwater flow and artesian flow. Whether or not this be the sole explanation of the phenomenon, it appears to be a reasonable consequence of the hypothesis as outlined. (s) SPACING OF

RIMS

Both the fact that in certain bays (Figs. 39 and 40) a wide space intervenes between an outer rim or series of rims and an inner rim or series, and the further fact that this distribution pattern may be repeated in adjacent bays, find reasonable explanation under the hypothesis of complex origin as outlined in the preceding chapter. We have already seen that sudden drops in lake level may reasonably be anticipated in a basin that has a water surface dependent upon the position of groundwater in lenses of coarse sand or gravel subject to sudden tapping by encroaching surface streams, or that is developed in a layer of limestone or other material subject to solution and rapid changes in subterranean drainage, or that is drained by outlet streams having falls or rapids, or that has opportunity to expand into areas of lower level. Any such drop of lake level would give a broad belt within the basin where rim development would not be perceptible, separating an outer belt, where one or more rims had formed during a stable or slowly falling lake level, from an inner belt of like character and origin. That adjacent basins should exhibit identical patterns of rim distribution would merely imply that they were

F I G U R E 40: Elliptical and ovoid bays 5 miles SE of Marion, Marion Co., S.C., showing outer and inner rims similarly spaced in neighboring bays. N is at top, and largest bay is 134 miles long. T w o large bays have outlet channels toward W. (Fairchild Aerial Surveys, Inc.)

Competence of the Hypothesis

213

affected by the same shifts in lake level because subject to the same geological or topographic control. (T) S M A L L SIZE OF R I M S

T h a t the rims should be of relatively insignificant size, with the volume of their contained material amounting to but a fraction of the material removed to form the basins, follows directly from the artesian-solution-lacustrine-aeolian hypothesis. According to this hypothesis of complex origin the basins are formed quite independently of the processes producing the rims. T h e rims are formed subsequently, if at all, where waves build beach ridges or winds build dune ridges with part of the sand cast up on the shores of lakes occupying the depressions. T h u s the hypothesis here under discussion does not merely explain the relatively insignificant size of the oval rims; it requires that the rims should be of small size and volume as compared with the size of the basins and the total volume of material removed to form them. (U) C O M B I N E D R I M S

SMALL

T h a t the convergence of multiple rims of the same basin and the junction of contiguous rims of adjacent basins do not give rise to combined rims of unusually large size is quite in harmony with a hypothesis which involves major rim production about one quadrant only of the basins, and very often not even there. In an earlier section (R) the fact that multiple rims in one part of a basin might converge toward an area where one rim only, or even none, existed was fully explained. T h e reasoning, which there explained the presence of a single rim or no rim, is equally applicable to cases where a single rim of small size exists. According to the hypothesis of complex origin the sandy rims are formed occasionally by waves about the southeastern halves of the basins, more commonly by winds which transport sand most effectively when blowing from the sector northwest-west-southwest. Sand is also deposited about the basin margins by winds blowing from other directions, but in such relatively small quantities as to produce in most instances a mere film or a relatively thin coating of wind-blown material, rather than a rim several

214

C o m p e t e n c e of the

Hypothesis

feet high. As a result, when two or more basins are so closely adjacent that their rims overlap, it must almost always happen that the prominent rim about the eastern or southern sides of one basin combines with the insignificant film or thin coating of wind-blown sand about the western or northern sides of a neighboring basin or basins to produce a compound rim not appreciably greater than the larger rim entering into the combination. Even where both of two contiguous basins have prominent rims near their junction, the combined rim at the point of contact may be unusually small or may locally disappear for any one of several reasons. T h e zone of contact may be an area where accumulation of sand by wind deposition would have been greatly reduced in any case. Wave erosion on present or formerly existing lakes in the basins may have undermined the basin walls and consumed much or all of any rim which did exist. It has elsewhere been shown that the rims are not high and narrow like those thrown up around explosion craters, but broad and relatively flat, a fact further discussed in section (w) below. Under these conditions a narrow strip of upland between two closely adjacent basins could not under any circumstances support a broad rim, and might be so wind-swept as to prevent the accumulation of any appreciable deposit of drifted sand. T h e conditions actually observed seem wholly compatible with what should be expected under the hypothesis here discussed. (v)

R I M SIZE I N D E P E N D E N T O F C R A T E R SIZE

T h a t there is no systematic relation between the size of the oval bays or craters and the size of their bordering rims follows inevitably from a hypothesis which attributes rim formation to wave action and to wind transportation of sand from lake-shore beaches. T h e size of the beaches, the quantity of sand they contain, and the strength and duration of winds are affected by variations in the dimensions of the basins only to a limited degree or not at all. Of far greater influence are the nature of the material in which the basin is formed, the kind and quantity of vegetation bordering the depressions, the rapidity with which the water body is transformed into a peat bog, and other factors not necessarily

Competence of the Hypothesis

215

related to basin size. Variations in these dominant factors must, under the hypothesis, result in the development of small rims or no rims about some very large bays and relatively large rims about some very small bays. (w)

F O R M OF R I M S

T h e observed form of the sand rims, broad and low, relatively flat-topped or faintly rounded in cross section, frequently with steeper slopes inward toward the crater and outward toward the plain, is adequately explained under the hypothesis here considered. Beach ridges not infrequently have the form described. The sand rims about the Carolina bays believed to represent beach ridges are thus in no respect abnormal. Many of the sand rims, and those best showing the type of transverse profile described above, are, under the hypothesis in question, interpreted as ridges of wind-blown sand. In the pine forests of the Carolina Coastal Plain, wind-drifted sand does not normally pile up into high dunes or ridges. There are local exceptions to this statement, but ordinarily grasses do not grow on the loose sand in sufficient luxuriance to hold the grains in place and thus to cause successive additions to build higher and higher a narrow ridge close to the sand's place of origin. Instead, the sandy surface remains comparatively well exposed, and winds sweeping across the top of the growing rim pick up material and carry it farther and farther from the lake shore. There appears to be little tendency, even on areas of nearly bare loose dry sand, for prominent "waves" of sand, barchanes, or other types of high barren dunes to develop, perhaps because trees and bushes are sufficiently abundant to transform the most regular winds into a confusion of diverse and changeable air currents, perhaps because in any case the ordinary winds of this region are too variable. Whatever the reasons, examination of areas in which wind-blown sand is today clearly migrating prevailingly in one direction shows that the winds tend to build broad and relatively low deposits of sand rather than high dunes and ridges whether of the migratory or fixed type. In the case of sand deposits about basins, similar action by the winds should give broad, relatively low rims, with surfaces nearly

216

Competence of the Hypothesis

flat or faintly rounded as to general form, although faint hummocks and basins of a subdued dune topography might well be formed. T h e advancing outer or leeward margin of the sand accumulation would often be relatively steep, just as ordinary "waves" or dunes of advancing sand have steep frontal slopes. T h e inner margin of the deposit, bordering the shore of a present or formerly existing lake, might well be steepened by the erosion of waves generated on the lake surface or by the enlargement of the basin due to spring sapping and slumping. (x)

COMPOSITION

OF

RIMS

It follows from the hypothesis of complex origin that the rims, being the product of wave action or of wind transport of material picked up from lake beaches, should consist predominantly of clean, fairly coarse quartz sand. During formation of the basins, artesian spring action presumably played an important role in removing clay and silt from surrounding beds, leaving behind a concentrate of sand. Wave work would further separate sand from silt and other fine material, with the result that resistant quartz grains, very abundant in the Coastal Plain deposits, would be a major element in beach ridges built of the residual material. Further sorting occurs during wind transport, fine particles being carried to remote distances, while the coarser sand is left near its place of origin. By such a double or treble concentration the hypothesis accounts adequately for the coarseness and cleanness of sand found in the rims. Where the sand transported to form rims of dune sand was free from iron, or the iron was deoxidized or the iron content reduced by leaching, the sand would appear white. Where faintly ironstained, buff sands would result. T h e latter are not infrequently observed, especially in pits descending well below the surface of rims exploited for commercial sands. (Y) R I M DEPOSITS U N L I K E C O A S T A L

PLAIN

DEPOSITS

T h a t the Coastal Plain material in which oval basins are formed should normally be strikingly dissimilar to the material composing the rims follows as a matter of course from the hypothesis

Competence of the Hypothesis

217

here considered. As stated in the preceding section, most of the rims consist of quartz sand separated from the Coastal Plain sediments by a treble process of sorting and concentration, while other rim deposits have been doubly concentrated. T h e residual concentrates must differ notably from the beds from which they were derived, except in those cases where the parent formation was itself a relatively coarse, clean sand. Such cases occur, and here the danger of confusing rim sand with original Coastal Plain sand is theoretically present. Practically, there is nearly always enough contrast between the two types of sand to make distinction relatively easy. In the far more numerous cases where the oval basins are developed in red loam or other Coastal Plain deposits, the contrast between Coastal Plain material and rim material is very striking. (z)

BEDROCK FRAGMENTS A B S E N T FROM R I M S

Frequently beds of limestone, shell marl, coquina, chert, ironcemented sandstone, and other resistant material are close to the surface in parts of the Coastal Plain where oval basins are abundant. T h e observed fact that bedrock fragments of these materials are not found in the rims, something very difficult to explain under the meteoritic hypothesis, finds full explanation under a hypothesis which accounts for most of the rims by aeolian transport. Only particles small enough to be borne by the winds could, under this hypothesis, be found in rims of dune sand, unless carried there by man or some other extraneous agency. Fragments of bedrock are not likely to be found in the limited number of rims consisting of beach ridges, partly because small waves on small lakes could scarcely cast anything but sand upon the beaches, but chiefly because the hypothesis under consideration accounts for the basins in a manner which would not normally leave fragments of bedrock in a position to be reached by the waves. (AA) N O UPTILTING OF C O A S T A L P L A I N

BEDS

T h e hypothesis of complex origin satisfactorily accounts for the observed fact that Coastal Plain sediments normally remain undisturbed in a horizontal position below the sandy rims and in the

2i8

Competence of the Hypothesis

basin walls, as well as for the further fact that occasionally there is indication of slight slumping of beds inward toward the basins, but no evidence of uptilting of beds causing them to dip outward away from the depressions. Excavation of the basins by upwelling artesian waters, their modification or formation by the solution of underlying beds of limestone or other soluble formations, and their enlargement by groundwater sapping or wave erosion of lake shores will not normally disturb the structure of adjacent beds. Occasionally, however, undermining of a basin wall, with consequent inward slumping of beds forming that wall, is to be expected. On the other hand, the processes here involved would not cause such uptilting of beds with consequent outward dips as is characteristic of explosion craters. (BB)

O U T L E T AND I N L E T

CHANNELS

The fact that many depressions (Figs. 4, 5, 15, 17, 20, 32, 35, 40, 42) have channels draining into or out of them is to be anticipated under a hypothesis which involves the enlargement of basins by upwelling waters that overflow into adjacent surface streams. In some cases, overflowing waters would enter adjacent lower basins before encountering normal drainage channels. Thus channels draining into basins, as well as channels draining out of them, are to be expected under the hypothesis here considered. (cc)

CHANNELS TRAVERSE

RIMS

Because the channels just referred to are formed early in the history of basin development, whereas the sand rims bordering the basins come into existence later and grow by the slow accretion of wave-deposited or wind-drifted sand, it is implicit in the artesian-solution-lacustrine-aeolian hypothesis that the channels in question should frequently cut across the rims. T h e channels, being antecedent to the rims, may cross them at the locus of major sand accumulation as well as elsewhere. Only in case waves or winds deposited sand faster than the stream in a channel could remove it would the channel be blocked. There is evidence that blocking of outlet channels has frequently occurred, although this may have been after the groundwater level of the region was

Competence of the Hypothesis

219

lowered and after lakes nearly or quite ceased to overflow into channels cut when the outflow was considerable. A very small or intermittent outflow should be sufficient to keep open a channel into which only limited quantities of sand are slowly moved by weak wave action or slowly drifted by the winds. T h i s no doubt accounts for the very large number of outlet channels still partially or completely open long after incision of surface streams has lowered the groundwater level, and after most of the lakes have been transformed into peat bogs from which water may flow only in small quantities or only after periods of unusually heavy rainfall. SUMMARY

In an earlier chapter we listed some twenty-nine categories of specific facts concerning the Carolina bays which must receive reasonable explanation under any hypothesis entitled to our confidence. W e then outlined the essential features of a new hypothesis of crater origin, called for convenience the artesian-solution-lacustrine-aeolian hypothesis, or more simply the hypothesis of complex origin. Finally we have in the light of this hypothesis reexamined in turn each of the twenty-nine categories of facts previously catalogued and have found that, without a single exception, the facts find full and reasonable explanation on the basis of processes or conditions inherent in the hypothesis. As was earlier pointed out, the more complex the requirements to be satisfied by a hypothesis, the more severe is the test to which it is subjected, and hence the greater the probability that a hypothesis successfully meeting such a test is valid. It would be difficult to devise a severer test of a proposed explanation of the Carolina bays than that furnished by the long list of specific facts which we have found to be satisfactorily explained by the artesiansolution-lacustrine-aeolian hypothesis. T h i s fact alone is sufficient to commend the proposed explanation to our serious consideration as a working hypothesis of bay origin. T h e artesian-solution-lacustrine-aeolian hypothesis of bay origin may in time suffer amputation of some of its parts or may eventually give place to some other and very different explanation.

220

Competence of the Hypothesis

But if so, it should not be through lack of a conscious effort to subject it to critical tests. That the hypothesis has so well supported the severe test applied to it in the present chapter entitles it to some measure of confidence. But we are not yet justified in accepting the hypothesis as a wholly satisfactory explanation of the origin of the curious craters of the Carolina coast. W e must devise other tests which may prove more searching and possibly reveal weaknesses in the hypothesis hitherto unsuspected. It is to this task that we turn our attention in the next chapter.

XI T h e Artesian Phase of the Hypothesis

I

N O U R attempt to examine yet more searchingly the artesian-solution-lacustrine-aeolian hypothesis of bay origin and to test critically its competence to explain adequately the oval craters of the Carolinas and parts of Georgia, we can most conveniently pursue our enquiries along several successive lines. First let us scrutinize the artesian phase of the hypothesis and determine whether we have satisfactory evidence that shallow artesian waters were of common occurrence in this particular area at the period when the bays were formed. Then let us ask whether there is evidence that geological conditions were favorable to the escape of such waters to the surface at countless points over the vast expanse of territory where bays are now found. Let us ask, too, whether we have any indication that upwelling springs of subterranean water were in fact a phenomenon of widespread occurrence and quantitative importance in this particular plac^ and at that particular time. Finally, do we have reasonable grounds for supposing that such artesian springs could excavate oval basins of the type constituting the Carolina bays? Closely associated with the problem of underground water behavior and the formation of oval craters is the question of karst topography which enters into the hypothesis. We must therefore ask and answer these questions: Do limestones or other materials now or formerly soluble occur below the surface in regions occupied by the bays? Are undoubted sinkholes or other karst phenomena associated with the bays? Can one trace a transition from typical sinkholes to typical oval bays having bordering rims of sand? Is there other evidence that sinkholes and oval bays are genetically related? As to the lacustrine phase of the hypothesis, it is pertinent to ask: Are there now existing, in the Carolinas or elsewhere, lakes occupying shallow basins or craters identical in character with

222

Artesian Phase

the basins occupied by typical oval marshy bays? And is there any evidence to indicate that the oval basins now filled with peat bogs did in fact formerly contain open water? T h e aeolian phase of the hypothesis suggests three critical questions: Are there elsewhere in the world basins bordered by complete or partial rims of sand reasonably attributed to aeolian deposition? Is there evidence of extensive aeolian transport of sand from basins in the Carolina bay country? And do the dominant winds of this region, blowing when sand can effectively be transported, come from a westerly (northwest-west-southwest) sector? When the foregoing questions have received such answers as can be given, it will be pertinent to raise a comprehensive question of more general nature: Does the artesian-solution-lacustrineaeolian hypothesis satisfactorily account for all facts thus far known about the Carolina bays; or do there remain certain facts so doubtfully or so incompletely accounted for that one must for the present hesitate to accept this hypothesis as a full and wholly satisfactory explanation for all phenomena exhibited by these curious craters? Let us now proceed to answer as best we can the enquiries listed above. F O R M E R ABUNDANCE OF S H A L L O W ARTESIAN

WATERS

T h e first question demanding our attention is whether we have satisfactory evidence that there formerly existed, in those parts of the Carolina and adjacent Coastal Plain occupied by oval bays, such artesian conditions as are required by the hypothesis here under discussion. It is obvious that in answering this question we are necessarily limited to observations of present conditions, supplemented by logical reasoning as to what the corresponding conditions must have been in the past. T h e remarkable extent to which artesian conditions now exist in the Atlantic Coastal Plain is too well known to require elaborate discussion, although those unfamiliar with the area are too apt to think only of strata well below the surface from which flowing water is secured by relatively deep wells. Such deep artesian waters do exist in the Coastal Plain, and faults, joints, or

Artesian Phase

223

other favorable structures may have permitted these deeper waters to rise naturally to the surface at many localities. Leakage from deep artesian aquifers is known to occur, and Morgan1 believes that, in New Mexico, leakage similar to that responsible for large artesian springs near Roswell takes place in other parts of the basin where the artesian aquifer is 1,000 feet or more below the surface. In this instance the escaping waters rise through relatively permeable sand, sandy shale, cavernous gypsum and limestone, and relatively impermeable shale and red beds, to supply a major part of the water encountered in the surface valley fill. "Natural leakage of artesian water from the San Andreas limestone is believed to be the principal source of the shallow ground water." But some may hesitate to assume that fractures or other openings would, especially in a sedimentary series containing layers of relatively unconsolidated shales or clays, conduct such waters from great depths to the surface at many points thickly distributed over vast expanses of territory. Obviously artesian waters at shallower depths would, other things being equal, have more opportunities of forcing their way to the surface and so might give rise to artesian springs upwelling under pressure at numerous points. It thus becomes of interest to know to what extent artesian waters have been proven to exist at moderate depths in parts of the Coastal Plain where oval bays or craters are abundant. South Carolina is the "bay state" par excellence: it includes all the most important bay areas except a few counties across the northeastern border in North Carolina and still fewer across the southwestern corner in Georgia. If, therefore, we can establish the existence of abundant artesian waters at moderate depths throughout the Coastal Plain of South Carolina, we shall have gone far toward demonstrating the validity of this phase of the artesian-solution-lacustrine-aeolian hypothesis of bay origin. For the South Carolina area we fortunately have C. Wythe 1 Arthur M. Morgan. Geology and Shallow-Water Resources of the Roswell Artesian Basin, New Mexico. Office State Engineer New Mexico, Bull. No. 5, 95 pp., 1938. Also published in State Engineer New Mexico, 12th and 13th Biennial Repts. for >934-1938, 155-249, 1938. Supplemented by personal communication.

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Artesian Phase

Cooke's recent report on the "Geology of the Coastal Plain of South Carolina" 2 (hereafter for convenience referred to as Cooke's 1936 Bulletin), which summarizes and adds to our knowledge of the region in which we are chiefly interested. From Cooke's 1936 Bulletin we can secure sufficient data to determine at least the minimum extent to which artesian waters are now encountered at moderate depths in the most important region of oval bays. At precisely what depth the presence of artesian water becomes significant for our discussion it is not easy to say. It is conceivable that water under pressure in a stratum of coarse sand, gravel, cavernous limestone, or other aquifer lying 500 or 1,000 feet below the surface might reach that surface at many points if the overlying beds consist of lenses of pervious and impervious material favorably disposed to permit leakage, or if the overlying beds are partly or wholly of material sufficiently consolidated to be extensively fractured by jointing or faulting. Escape of waters from deeper aquifers is less probable, from aquifers nearer the surface more probable. Many artesian wells in the Coastal Plain of South Carolina tap aquifers lying from 500 to 1,000 feet below the surface, and a few have depths of from 1,000 to 2,000 feet. But far more numerous are the wells less than 500 feet in depth. In the pages that follow we shall consider only those wells 300 feet or less in depth which appear to tap water under hydrostatic pressure. This will perhaps give us as fair an idea as we can get of the extent to which artesian waters in the bay country at present lie close enough to the surface to have reasonable possibility of reaching that surface by penetration along natural passageways. T h e limiting figure chosen is inevitably based on personal judgment, and its value is not subject to demonstration. We can only say that the closer to the surface artesian waters lie, the greater 011 the average is their chance of escape, it being understood of course that the determining factor is not depth per se but the degree of imperviousness of the formations overlying the aquifer. In examining data on artesian conditions it must be borne in mind that the figures given in well records are not directly com2 C . Wythe Cooke. Geology of the Coastal Plain of South Carolina. U. S. Geol. Surv., Bull. No. 867, 196 pp., 1936.

Artesian Phase

225

parable, since some wells are located on the upland surface of the plain, others in the bottoms of valleys cut below the plain surface. Except in the dissected hill country toward the inner portion of the Coastal Plain, a region lying for the most part outside the bay country, the relief between valley floors and upland surface in the South Carolina plain varies from 25 to 50 feet where the streams are small and but moderately entrenched and from 50 to 100 feet where streams are larger and have cut deeper, while only near large rivers does the relief locally rise to 150 or 200 feet. In a locality of the latter type a well on the valley bottom 300 feet deep might tap an artesian water horizon which from the adjacent upland could only be reached by a well 500 feet deep. Were topographic maps available for the whole region, one could exclude from consideration all artesian wells located in valleys more than a given number of feet below the upland surface. Unfortunately such maps are available for but half of the area to be studied in South Carolina. Were one to exclude all wells located near large rivers, the result would still be unsatisfactory since in some areas even large rivers are not cut far below the adjacent upland, while in others wells at some distance from a large river, but in the valleys of small streams not shown on available maps, might be much below the upland. Fortunately our present object is merely to gain a rough idea of the extent to which artesian waters are now found within a moderate distance of the surface in areas where oval craters or bays are abundant. This will be sufficiently well accomplished if we disregard the local variations in surface elevations of wells. Especially is this true in view of the fact that, in the records to be considered, the number of artesian wells located on or near the bottoms of valleys cut as much as 150 feet below the adjacent upland is relatively small. Most of the wells cited were drilled from the surface of the upland or from the sides or floors of relatively shallow valleys. Furthermore, many wells in the deeper valleys are less than 200 feet deep, some of them less than 100 feet, in which cases the distance of the aquifer below the adjacent upland would usually still be not greatly in excess of 300 feet and often less. Finally, there is nothing particularly significant

22Ô

Artesian Phase

about the figure 300 arbitrarily chosen as the limit of depth for wells to be considered here. As will later appear, we might have selected 400 or 450 feet as the limiting depth without profoundly affecting our final conclusions. In considering present artesian conditions as revealed by well records, it will be pertinent to our purpose to include wells in which water rises toward the surface without actually overflowing. It is theoretically conceivable that in some wells of this type the water is not under artesian pressure but merely represents ordinary groundwater moving into the opening until it is filled to the level of the water table. Inasmuch, however, as it is common practice in the Coastal Plain to case wells down to the particular aquifer from which it is desired to secure water, it seems safe to assume that most wells in which water rises high above the bottom have in fact tapped water under greater or less artesian pressure. If with the foregoing points in mind one turns the pages of Cooke's 1936 Bulletin (especially pages 162-188), examining his descriptions of hydrologic conditions and his tables of well records for each county, he will quickly discover that water under artesian pressure is present at moderate depths throughout the regions where the oval bays abound. Out of twenty-two counties in which bays occur, nineteen, according to Cooke, have wells 300 feet or less in depth from which water either flows or rises well toward the surface of the ground. Of the three exceptions one county (Richland) is in the hill country where typical bays are not usually developed and where information as to artesian conditions is scanty. While this county forms an exception so far as Cooke's records are concerned, the writer secured the record of a well 100 feet deep at Congaree in which water rises twothirds of the way to the surface. T h e second county (Georgetown) is thus far known to have a few bays only in its extreme southwestern corner. Artesian flows are common in this county from wells 400 to 700 feet in depth, but no data on shallower wells are given by Cooke. In the third county (Bamberg) it is stated that flowing wells can be obtained anywhere in the southeastern two-thirds, while "information about the northwestern part is

Artesian Phase

227

scanty." T h e only flowing wells mentioned have depths of 450 feet or greater. Wells 50 to 85 feet and 150 feet deep are mentioned, but the height to which water rises in them is not stated. Cooke's records for the nineteen counties contain data on one hundred and eight wells which are 300 feet or less in depth. An occasional county may have but one or two such shallow wells included in the data given (the data are admittedly very incomplete), while a few others may have as many as ten or fifteen; but in general the one hundred eight wells are widely distributed over the Coastal Plain. Nearly half of them are flowing wells or wells in which the water level rises above the surface of the ground. In the remainder the water rises notably in the wells, in most cases relatively close to the surface. Of the one hundred eight wells, seventy-three are 200 feet or less in depth, and thirty-two are 100 feet or less, a few being as shallow as 35 or 40 feet. The thirty-two shallow examples include their fair proportion of flowing wells. These figures alone would be sufficient to establish the widespread occurrence of artesian waters at moderate depths in the South Carolina Coastal Plain, but there is abundant evidence that such waters are of far more common occurrence than the well records just cited would indicate. In the first place, the records tabulated by Cooke do not pretend to be complete. They are based chiefly upon data collected in 1917, and apparently the records given are intended to be merely representative examples. In the case of one county only is it specified that the table given "includes all the wells of which records are on file." Elsewhere it is stated that "records of some of the wells are given below," "the depths of some representative wells are shown below," or tables headed simply "Wells in County" are inserted in the text without further comment. Enquiry among local inhabitants shows that artesian wells occur in far greater numbers than the examples listed by Cooke and that this is especially true of shallow artesian wells, the deeper wells being more apt to be recorded than the more numerous shallow wells. Enquiries made by the writer, in fourteen localities only, elicited data on fifty-four wells not included among those cited from

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Artesian Phase

Cooke's tables. Half of the fifty-four were flowing wells, and fortyone out of the fifty-four were less than 100 feet deep. Often the artesian waters first tapped in drilling are of inferior quality or are under insufficient pressure to overflow, whereas by going deeper the driller is certain of securing excellent water which will flow at the surface. Under these conditions the only well records available often reveal the existence of deep artesian waters but fail to show the presence of one or several shallower artesian horizons. But we do find in Cooke's text such comments as these: "Another water-bearing stratum . . . lies 400 feet or less below the surface, but is little used because water from it does not generally overflow"; "Several less productive waterbearing strata are passed through before the principal stratum is reached"; " T h e water in the Santee limestone and the Cooper marl is presumably hard, but there are few data at hand regarding the quantity or quality of this water, as the drillers of most of the wells of which there is record found it desirable to tap formations below the Santee"; " T h e driller of the town well at St. Matthews (310 feet deep) reports water at a depth between 60 and 80 feet that rose within 6 feet of the surface, and a fine supply of water between 258 and 290 feet. It was necessary to use a strainer because of the loose sand"; "At Mayesville four flowing wells range in depth from 200 to 250 feet . . . There are other water-bearing beds at 30, 65, and 160 feet." The widespread extent of shallow artesian horizons is often indicated by the text, in some cases when no table of well records is given. "Water of excellent quality can be obtained anywhere in Dillon County within a few hundred feet of the surface. Many of the wells flow"; "Water of good quality can probably be obtained from the Tuscaloosa formation anywhere in Lee County within 400 feet of the surface"; "Water can be obtained at moderate depth anywhere in Orangeburg County. Deep wells generally pass through several water-bearing beds, some of which will yield flows almost anywhere in the southeast half of the county and in the lower parts of the northwest half"; "Records indicate that flows can be obtained almost anywhere in the east

Artesian Phase

229

half of Sumter County at depths less than 200 feet below the surface." We have shown that artesian waters at moderate depths occur abundantly throughout the bay country of South Carolina. Since the structural and stratigraphic features found in this state are known to extend under the bay regions of North Carolina on the northeast and Georgia on the southwest, artesian conditions demonstrated to exist throughout the region of typical oval bays in South Carolina may reasonably be assumed to hold good for adjacent portions of the two bordering states. We are not dependent upon this assumption, however. For the Coastal Plain of North Carolina we have the report of Clark, Miller, Stephenson, Johnson, and Parker, containing a valuable discussion of water resources of the plain by L. W. Stephenson and B. L. Johnson. 3 T h e principal areas of known bays in North Carolina are included in Scotland, Robeson, Hoke, Cumberland, Bladen, and New Hanover Counties. Stephenson and Johnson report for Scotland County that "abundant supplies of very soft water may be obtained from the Patuxent formation over the entire county at depths of from 50 to 300 feet. No assurance can be given that, when the water-bearing beds are tapped, the water will overflow, although it may do so at the lower levels along the streams. T h e most that can be expected is that the water will rise near enough to the surface to come within reach of ordinary pumps." In discussing Robeson County these authors state that "at Red Springs [which is in a region of bays] and in the immediate vicinity there are a number of flowing wells with depths ranging from 40 to 100 feet." T h e present Hoke County formed parts of Cumberland and Robeson Counties at the time of the report. Concerning Cumberland County the authors state: " T h e principal artesian water horizons in Cumberland County are furnished by the Patuxent formation. Good supplies are to be expected from the more porous sand beds of this formation at moderate depths (100 to 300 feet) over most of the county." In 3 L. \V. Stephenson anil B. L. Johnson. T h e Water Resources of the Coastal Plain of North Carolina, in T h e Coastal Plain of North Carolina, N. C. Geol. and Econ. Surv., Rept. No. 3, Pt. 2, 333-483, ig 1 »-

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Bladen County, where oval bays are particularly abundant, "in general, the prospects for obtaining potable artesian water supplies are good in all parts of the county. . . . In most places . . . a water-bearing bed or beds will be encountered between the depths of 50 and 300 feet." From New Hanover County, which includes an area of oval bays near Wilmington, fourteen wells from 42 to 100 feet deep are listed, none of which overflow but in all of which the water rises more than halfway toward the surface. In nine of these the water stands 15 feet or less below the top of the well. There are also listed eleven wells from 100 to 200 feet deep, three of which overflow while water in most of the others rises within 3 to 40 feet of the surface. Typical oval bays4 appear on aerial photographs of portions of Columbus County and much of Brunswick County. Stephenson and Johnson, under the heading Columbus County, state that "no county in the Coastal Plain of the State [North Carolina] has a greater number of flowing wells. . . . At elevations not exceeding 65 or 70 feet above sea level natural flows may in most places be obtained. At greater elevations . . . the water will not rise above the surface." From Brunswick County four wells varying in depth from 37 feet to 250 feet are cited, two of these overflowing, and the water in a third (103 feet deep) rising to within 13 feet of the surface. From the eight counties (Hoke County then forming parts of Cumberland and Robeson Counties) included in the bay region of southeastern North Carolina, Stephenson and Johnson cite a total of ninety-nine wells less than 300 feet deep. Of these thirty-nine are 100 feet or less in depth; nearly half of them flow, while in most of the others the water rises to within 15 feet or less of the surface. Forty-five wells are from 100 to 200 feet deep, more than half being flowing wells, while in most of the others the water rises to within 15 feet or less of the surface. Only fifteen of the wells are from 200 to 300 feet deep; seven of these flow, while in most of the other eight the water rises to within 30 feet * L a k e Waccamaw, a large lake of irregular oval shape, has l>eei) called a hay l>y some writers, but it is questionable whether it should be compared with the oval craters here discussed.

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or less of the surface. It is clear from these figures that artesian waters at shallow depths are abundantly found in the bay country of southeastern North Carolina. In Georgia the principal areas of bays thus far known are included in Burke, Jenkins, and Screven Counties. That artesian waters occur at moderate depths throughout these areas is made clear by the reports of McCallie 5 and of Stephenson and Veatch.8 McCallie reports from Burke and Screven Counties twenty wells 300 feet or less in depth, eighteen of which overflow at the surface. These wells tapped water-bearing strata at depths of 50, 100, 150, 180-190, and 285-295 feet. Stephenson and Veatch state that "at Girard [Burke County] several non-flowing artesian wells range in depth from 200 to 300 feet," and cite three other wells 250 to 300 feet deep in different parts of the county, two being flowing wells. With reference to Jenkins County, these authors state that "artesian water can probably be obtained anywhere in the county at depths of 300 to 600 feet or more," and cite two wells at Perkins "about 300 feet deep" in which water rises to within 17 feet of the surface and "several fine artesian wells . . . 200 to 500 feet deep" in the vicinity of Herndon. From Screven County they cite three wells somewhat less than 300 feet deep, two overflowing and the water in the third rising to within 12 feet of the surface. We have demonstrated the occurrence of artesian waters at shallow depths throughout the whole of the country where oval bays have thus far been found in considerable numbers. The statement of LongwelK Knopf, and Flint, 7 that "along the Atlantic coast . . . most of the artesian wells are only 100 to 300 feet in depth," implies an abundant development of shallow artesian waters. The implication is valid and holds true for all of the bay country. The lower of the two figures mentioned might 5 S . W. McCallie. A Preliminary Report on the Underground Waters of Georgia. Ga. Geol. Surv., Bull. No. 15, 370 pp., 1908. 6 L. W. Stephenson and J . O. Veatch. Underground Waters of the Coastal Plain of Georgia. U. S. Geol. Surv.. Water-Supply Paper No. 341, 539 pp., 1915. Otto Veatch and L. W. Stephenson. Preliminary Report 011 the Geology of the Coastal Plain of Georgia. Ga. Geol. Surv., Bull. No. 26, 466 pp., 1 9 1 1 . 7 C . R . Long well, A. Knopf, and R . F. Flint. Textbook of Geology. 514 pp., New York, 1932. See p. 89.

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indeed be reduced since very many of the wells are considerably less than 100 feet and not a few are less than 50 feet deep. U P W A R D E S C A P E OF A R T E S I A N

WATERS

We must next enquire whether the structural and stratigraphie conditions in the bay country are such as to favor the natural escape upward of artesian waters located anywhere from 30 to 300 feet below the surface. T h e answer is emphatically affirmative. T h e Coastal Plain does not normally consist of individually distinct pervious strata extending continuously from their outcrop areas seaward for indefinite distances, with similarly distinct and continuous impervious beds above and below. Instead, the Coastal Plain is made up of a vast number of overlapping and interfingering lenses of more pervious and less pervious material —sand, clay, gravel, marl, shale, limestone, chert, shell rock, kaolin, hard marlstone, sandstone, buhrstone, fuller's earth, and other deposits. Unconformities are abundant, and whole formations, themselves made up of interlocking lenses of materials of varying porosity, may sometimes appear as larger lenses or erosion remnants in the general series. T h i s and the similarity of materials and structures in certain of the formations make stratigraphic studies and areal mapping of formations peculiarly difficult, the difficulty being mentioned by Cooke on many of his pages. Some of the formations may be relatively free of calcareous beds and carry excellent water. Others may contain much lime and yield hard water. T h i s shows that water moves parallel to the bedding of these formations more readily than across it. Yet the interfingering of lenses and the porosity of much of the material favor a certain amount of leakage. Cooke points out that, even where the basal Tuscaloosa formation is buried, "its store of water is added to by seepage through the porous formations (Black Mingo, McBean, Barnwell, and Brandywine) that overlie it." If seepage downward is possible at some places under the pull of gravity, leakage upward may elsewhere occur under hydrostatic pressure. Very large areas of the bay country are covered by the four formations named above, through which

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upward escape of artesian waters from underlying aquifers would be facilitated. Other large areas are covered by such pervious formations as the partially dissolved Cooper marl and Santee limestone, which commonly give rise to numerous sinkholes. T h e Duplin shell marl also covers large areas of bay country, and one may infer that this relatively thin calcareous formation would facilitate leakage from below, although Cooke does not discuss its permeability. Other formations that are as a whole more impervious would permit some leakage wherever lenses of pervious material happened to be favorably disposed. We must conclude that conditions very generally favor the natural escape to the surface at many points of artesian waters existing at moderate depths. Thus far we have been considering the artesian conditions observed at the present time. A little consideration will assure us that shallow artesian waters must have been vastly more abundant in the past, and that their escape to the surface must have been a far more common phenomenon than it is today. Incision of stream valleys has lowered the water table throughout most if not all of the Coastal Plain, drained many shallow aquifers completely, and afforded a lower outlet to others. Where today water rises but part way to the surface in wells, it may have reached the surface along natural passageways prior to stream dissection of the plain. Many a shallow stratum of pervious material that today contains no water, and many more containing only downward percolating rainfall or slowly moving groundwater, must then have held water under artesian pressure ready to escape upward wherever opportunity offered. We must picture the newly uplifted Coastal Plain, with its smooth original surface inclined seaward and its subsurface structure of interlacing lenses of pervious and impervious material, as receiving the rainfall poured upon it, drinking it in freely where pervious beds reached the surface, only to yield it up again farther down the slope wherever the descending waters found access to the surface at a level lower than that of intake. The upwelling waters must have emerged through saturated surface deposits, for before streams had incised their valleys the

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groundwater surface and the surface of the ground must have been sensibly coincident, except where original inequalities of the plain gave low islands of drier land in the maze of marshes. We must have had, in short, a vast expanse of undissected plain in which copious springs surged up in the bottoms of lakes or swamps, or over the drier islands, wherever pervious beds or natural passageways of any kind permitted escape of subsurface water under artesian pressure. Only where lenses of clay or other impervious material formed the surface, or were so close to it that subterranean waters could not readily flow around and over the lenses before reaching the surface, would the upwelling of waters be wholly absent. It thus appears that observed artesian conditions in the Coastal Plain of today, and logical deduction as to what artesian conditions must have been in the undissected Coastal Plain of the geological yesterday, fully meet all requirements of the artesian phase of the hypothesis of bay origin here under discussion. It remains to ask whether there is any evidence indicating that upwelling waters did actually reach the surface in the manner indicated; and whether there is any reason to believe that they could, under favorable circumstances, give rise to oval basins or craters like those of the typical oval bays. W I D E S P R E A D O C C U R R E N C E OF ARTESIAN

SPRINGS

Perhaps the best evidence that upwelling artesian waters did reach the surface of the plain would be their persistence in favorable localities today. We must expect such waters to be at present a rare phenomenon as compared with conditions prior to disssection; for it will be exceptional areas only in which the deepening of adjacent valleys has not afforded adequate facilities for effective drainage of pervious beds at levels below the general surface. Wherever water can issue more or less continuously, even if slowly, from valley sides or upon valley floors, it has little chance to accumulate in aquifers in sufficient volume for considerable hydrostatic pressure to develop at the points of issue. We then have to do with springs and seeps of the usual type fed by ordinary groundwater. Where, however, we find the

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water surging up in unusual volume and with unusual force, we may suspect, even if we cannot prove, that we have to deal with waters which have accumulated in a pervious stratum under sufficient hydrostatic pressure to be forced upward through any opening, artificial or natural; waters which accordingly are essentially artesian in their mode of occurrence. Although conditions favorable to the occurrence of such upwelling waters are far less common now than prior to dissection of the Coastal Plain, they appear to exist in sufficient abundance to lend substantial support to the hypothesis here under discussion. These upwelling waters are often known to the natives as "boiling springs," not because the waters are hot but because of the vigor with which they surge upward. In some localities they are called "fountains" or "fountain springs," and the water is said to "fountain up." Berkey and Kerr, 8 studying underground water conditions of the little-dissected plain of northern Berkeley County, South Carolina, noted a number of copious springs, locally called "fountains," rising from the underlying Santee limestone. This water was believed by them to have entered the aquifer at a slightly higher elevation some miles to the northwest. Its content of calcium was notably greater than that of surface waters on the immediately adjacent plain, indicating partial solution of the limestone formation during its passage under ground. According to Cooke, Fair Spring, also in northern Berkeley County but a little southeast of the area just mentioned, "boils up through a hole about 1 foot square in rock that appears to be limestone [Santee limestone?] but is not readily accessible." At Eutaw Springs, eastern Orangeburg County, according to Cooke, "the main spring boils up as a bold stream into an oval basin, at the farther end of which it sinks and flows underground for 100 yards, to reappear as a good-sized creek tributary to the Santee (River)." In describing the "fissured and cavernous nature" of the "Great Carolinian Bed of Marl" of this general region (probably Santee limestone and Cooper marl for the most part, according to Cooke), Ruffin 9 writes of "sinks" which s

Charles P. Berkey and Paul F. Kerr, personal communication. "Edmund Ruffin, Report of the Commencement and Progress of the Agricultural Survey of South Carolina for 1843. 120 pp., Columbia, 1843. See p. 19.

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take in water and of others which "vent bold springs and enormous discharges of 'rotten limestone water.' " He states that "the strong boiling up of such springs" is of frequent occurrence, and adds: "These marlstone fountains, when of great volume, are objects of remarkable beauty." Big Spring on the west bank of Lynches River near Bethune in Kershaw County "is said to flow 350 gallons a minute" according to Cooke, who adds that the "water doubtless comes from the Tuscaloosa," a formation free from limestone which is the most important source of artesian water in South Carolina. This spring is in the area of the dissected Congaree Sand Hills, fifteen miles northwest of the nearest known oval bays in Lee County, so we must consider the possibility that the outflow is that of normal groundwater draining from adjacent hills. The spring is, furthermore, in the intake area of the Tuscaloosa, where its beds are exposed at or close to the surface and receive the water carried southeastward under overlying formations to be tapped by artesian wells in counties nearer the sea. Neither of these facts, however, precludes the possibility that the spring represents escape of waters locally accumulated under artesian pressure in one of the many pervious layers of the Tuscaloosa. Perhaps the great volume of outflow may be held to favor the latter interpretation, as does also the fact reported by Cooke that the water "issues from the Tuscaloosa formation under considerable hydrostatic pressure."10 The temperature of the water is reported to be 57°F. Hammond 11 reports that in the Sand-Hill region along the whole western edge of the South Carolina plain "the spring branches, and even streams of considerable size, sink into the sands . . . and are lost or reappear at distant points in the form of springs, called 'boiling springs,' which issue from the earth with considerable force, throwing out no inconsiderable amount of fine sand to be conveyed onward by the streams. It is to the undermining action thus carried on by these underground drains that Professor 10

Italicized by present writer. Harry Hammond. Physico-geographical and Agricultural Features of the State of South Carolina. U.S. 10th Census, 1880, 6:461-504, 1884. See p. 489. See also Report of South Carolina State Board of Agriculture, 726 pp., Charleston, 1883. See p. 118. 11

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Tuomey attributed the occurrence of numerous circular depressions of the surface, met with on the elevated flats of this region and holding ponds of water during a considerable part of the year." In North Carolina the upwelling waters are also known, and in some cases the boiling springs or fountains issue on the floors of lakes occupying typical oval craters bordered by rims of sand. Prouty 12 noted that some of the lakes in the bay region of southeastern North Carolina "have their chief water supply from lakebottom springs." A well-known example is White Lake in Bladen County, where on quiet days, when the lake surface is not ruffled, one may see sand on the lake bottom thrown upward several feet by the vigorous upwelling of water from fountain springs about 200 feet out from the southern shore. As reported by Prouty and by Dr. Girard Wheeler, one of my junior associates who visited the principal lakes in this region, White Lake, Jones Lake, Suggs Mill Pond, and others have no incoming streams or none of any volume, but have relatively strong outflows through permanent natural channels which locally have been artificially deepened. T h e writer visited several of these lakes in company with Professor Prouty and concurs in the popular belief, shared by Prouty and Wheeler, that the strong outflows are due in part to water upwelling from the lake bottoms. A t the time of his visit, Wheeler found the strongest outflow of any lake coming from Suggs Mill Pond and reported a "very strong inflow of water on bottom from springs which are said 'to fountain' over an area of several square feet." Since these lakes, and adjacent lands from which meteoric water may drain into them under ground, cover several square miles of territory in a region of fairly abundant rainfall, it would seem to the writer unsafe to assume that the chief supply of the lakes is artesian in character. Springs of large volume occur in the small part of Georgia (Burke, Jenkins, and Screven Counties) where typical oval bays are thus far known to occur, but available descriptions rarely state whether or not the water surges up with notable vigor. W e 12 W i l l i a m F. P r o u t y . " C a r o l i n a 43:200-207, 1935.

Bays" and

Elliptical

Lake

Basins. J o u r .

Geol.,

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read of springs which yield "several million gallons daily," "500 gallons per minute," "sufficient water to operate a small gristmill," and so on; but only occasionally is it specifically stated that the water rises under pressure. Stephenson and Veatch's reference 13 to "bold limestone springs" in Jenkins County may imply such a condition, for as an example they cite Magnolia Spring in the north central part of the county which "yields several million gallons daily of hard sulphurous water." Elsewhere 14 these authors include this spring with other large springs the water of which rises "through limestone caverns" and "evidently comes from great depths." " T h e largest of these springs is Blue Spring [in Dougherty County]. . . . The water at this place rises under considerable pressure through a roughly circular opening in limestone, and has an enormous flow." According to McCallie, 15 another Blue Spring, in Jefferson County but close to the Burke County line, "boils up through white sand in the bottom of a circular basin several feet in diameter." Concerning these springs Veatch and Stephenson make this interesting statement: "As they appear to be connected with subterranean streams, many of them may be described as natural artesian wells." The reason given for making this suggestive comparison is hardly valid as stated, for, while artesian wells do tap water which flows through pervious beds, and sometimes even through cavernous beds, they do not normally connect with what may properly be called "subterranean streams." Nevertheless it is significant that these authors recognize the artesian character of the springs in question. Textbook discussions of artesian conditions commonly recognize that artesian waters may escape upward along a fault which cuts an aquifer but usually fail to note that no fracture is necessary for the production of such artesian springs. It seems highly probable that for every "fissure spring" 13

L. W. Stephenson and J . O. Veatch. Underground Waters of the Coastal Plain of Georgia. U.S. Geol. Surv., Water-Supply Paper No. 341, 539 pp., 1915. See p. »92. 14 Otto Veatch and L. W. Stephenson. Preliminary Report on the Geology of the Coastal Plain of Georgia. Ga. Geol. Surv., Bull. No. 26, 466 pp., 1911. See pp. 49-50. 15 S. W. McCallie. A Preliminary Report on the Underground Waters of Georgia. Ga. Geol. Surv., Bull. No. 15. 370 pp., 1908. See p. 124.

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due to the upward escape of artesian water along a fault fracture there are many "artesian springs" due to upward escape along other types of natural passageways. T h e many cases throughout the entire bay region in which oval basins not fed by surface streams and not now occupied by lakes have prominent outlet channels carrying perennial streams of appreciable volume, sometimes inhabited by fish eight to ten inches long, may perhaps be accepted as evidence of upwelling artesian waters concealed in the impenetrable swamps of the bays. T h a t such outlet streams were far more numerous in the past is indicated by the large number of outlet channels which appear to carry water only occasionally and by the still greater number which appear entirely abandoned and partially or completely blocked with sand. T h e upwelling waters have in this discussion been classed as artesian waters because it is believed that, for the most part at least, they occur under conditions which are essentially artesian in character. It should be noted, however, that the important consideration for the hypothesis of bay origin here under investigation is not the particular conditions which cause subsurface waters to be under pressure sufficient to make them flow out upon the surface, but rather the existence of that pressure per se. If one believes that conditions other than artesian are responsible for the boiling or fountaining springs observed today; if one believes that the term "artesian" should be restricted to flowing wells like those in Artois and should not be applied to wells in which water rises to or near the surface without overflowing or to springs which surge up from below under strong hydrostatic pressure and overflow copiously; and if one believes that, on the original undissected Coastal Plain, waters may have entered pervious strata, moved southeastward under ground, and finally reappeared as upwelling springs of notable force and volume without having become true artesian waters, then he may hold these opinions and still accept the fundamental principle involved in what has here been called the "artesian" phase of the artesian-solution-lacustrine-aeolian hypothesis of bay origin. It is not the name which matters nor even the precise underground

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conditions connoted by the name. It is the widespread occurrence of upwelling waters, genetically associated with the excavation of elliptical craters, that constitutes an essential element of the hypothesis. C O M P E T E N C E O F ARTESIAN SPRINGS TO PRODUCE CRATERS

The last enquiry under this phase of our discussion is this: Have we any support for the conception that upwelling spring waters, possibly modified by groundwater flow, are competent to produce large but shallow basins of symmetrical outline? Perhaps the best support would be the presence of upwelling waters in a series of circular or oval basins in all stages of development. For obvious reasons it is difficult if not impossible to secure this type of evidence. According to hypothesis, the normal period of bay formation belongs to the past, before the incision of streams below the plain surface had lowered the groundwater level and caused most of the fountaining springs to cease flowing. In the exceptional cases where such springs persist today, they should be found in two types of localities: those where surface geological conditions were favorable for the formation of broad shallow basins and those where such favorable conditions did not exist. In the first type of localities the shallow basin or bay will long ago have been formed, in which case the upwelling waters must, according to the hypothesis here under consideration, normally come to the surface far out in the interior of the basin. Occasionally one or more fountaining springs might be found near the basin margin. But as the hypothesis involves slumping or flowing of water-soaked sand or loam toward the center of the basin, and as this process would normally extend progressively outward from the point where the excavating process began, it follows that upwelling springs at or near the margins of basins must be exceptional. The central parts of most of the basins still supplied with water are practically inaccessible, either because the basin holds a treacherous peat bog covered with an almost impenetrable growth of swamp vegetation or because it holds a lake which is deep enough in its central portion to conceal the floor from inspection.

Artesian Phase

241

T h u s all we could ordinarily expect to see where upwelling waters still reach the surface in localities favorable to basin formation would be streams flowing through outlet channels draining lakes or impenetrable swamps occupying the shallow depressions. Such outlet streams are very numerous in the bay country, and, as earlier noted, abandoned channels, sometimes partially or completely blocked with sand, indicate that they were far more numerous in the past. Only rarely could we expect to discover the upwelling springs themselves in the more accessible part of some marshy bay or in the shallower part of some lake. Of the latter we have several examples, notably the boiling springs observed upwelling from the floors of White Lake and Suggs Mill Pond in North Carolina. In time, search may discover boiling springs still welling up copiously from the bottom of some of the marshy bays, although the task of finding such springs in basins filled with swamp deposits is more difficult, not only because of the impenetrable nature of typical bays but also because the bays represent a senile stage of basin development, in which upwelling waters are less apt to be found than in the lacustrine stage. There remain the examples of fountaining or boiling springs reaching the surface where geological conditions proved unfavorable to the formation of large, shallow, symmetrical basins. T h e presence at the surface of a resistant formation, such as limestone, marl, sandstone, or a clayey loam, would prevent the slumping and flowing of loose material which according to hypothesis causes the development of such basins. T h e result would be much the same if the resistant formation were merely near the surface but covered with a layer of sand too thin to permit the slumping and flowing process to operate freely. Under these conditions we should observe the upwelling waters escaping from crevices or cavities in limestone, marl, or other material, or issuing from the sands of relatively small surface depressions. If the upwelling waters excavated any basins, these would be of limited size. In resistant material, the basins might be symmetrical in some cases, though often they would, presumably, be more or less irregular in outline. If excavated in a thin covering of surface sand concealing resistant material immediately below, the basins while small might be cir-

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cular or oval because of limited slumping of the thin sandy layer, or might be irregular because of the interfering influence of underlying resistant materials. It seems inevitable that upwelling springs reaching the surface under the conditions just described would be the ones most readily observed today. For a variety of reasons, therefore, it is to be expected, under the hypothesis of origin here discussed, that in most bays or lakes no upwelling waters would now be observed, and that most of the upwelling waters we do observe would be found in small and often irregular depressions. T h e facts reported by Berkey and Kerr 16 for the area in eastern Orangeburg County and northwestern Berkeley County, South Carolina, cited on an earlier page, come as close as any to establishing a genetic connection between upwelling waters and the origin of marshy bays. T h e i r studies led them to conclude that water entering the Santee limestone in the sinkhole region about Eutawville to the northwest, where the land is from 100 to 120 feet high above sealevel, flowed under ground toward the southeast, there to emerge at elevations of from 50 to 90 feet as fountaining springs of water relatively rich in calcium. T h e region of emergence is a region not only of fountaining springs but also of numerous swamps locally called "bays"; and these investigators reached the conclusion that the swamps as well as the springs were fed by the same underground waters. It is true that the swamps, as shown on the contour map of the region, Chicora quadrangle, South Carolina, are not symmetrical ovals and would scarcely be recognized as features identical with the oval bays described and pictured by Melton and Schriever. Nevertheless, some of them (e.g., T o d d Bay) do show evidence both of oval form and bordering sand rims, while aerial photographs demonstrate beyond doubt that this marshy area is a region of many incipient or poorly formed oval bays, some of them with multiple sand rims. Powell Bay is a very large ovoid basin with three sets of major rims, all but the first set being displaced to the west and north of an earlier set, in the manner discussed elsewhere in this volume. Pigeon Bay is another large ovoid with multiple rims. If Berkey and Kerr are 16

Charles P. Berkey and Paul F. Kerr, personal communication.

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243

correct in their belief that these swamps or bays are supplied by water rising under pressure from the underlying Santee limestone, their studies may perhaps be accepted as adding some measure of support to the artesian phase of the hypothesis here under discussion and to the genetic association of typical sinkholes with typical bays. T h e competence of upwelling springs of notable force and volume to produce large, shallow basins of symmetrical outline in water-soaked sand or sandy loam is not readily subject to demonstration. We have examples of boiling springs issuing on the floor of such basins in loose sand covering the Coastal Plain in southeastern North Carolina. We have countless outlet channels of considerable size testifying to former outflows of water from basins now occupied by marsh deposits, and many channels through which much water still escapes from the basins. These facts are admissible as evidence in favor of the hypothesis that upwelling waters did produce the basins; but they do not demonstrate such an origin for the basins. We can only say that the facts observed are those we should expect to find in case the hypothesis be valid. As to the competence of a relatively localized excavating force to produce a very large shallow basin of symmetrical form in unconsolidated sand or other incoherent material, judgment must apparently rest on logical reasoning guided by experience with the behavior of such deposits on a small scale. Such reasoning has led two investigators, working nearly a hundred years apart in time but on the same features and in the same locality, to identical conclusions. After the artesian phase of the present hypothesis had been formulated and tested, a search of Coastal Plain literature was instituted to discover whether any previous investigator had recorded observations which would tend either to validate or to destroy the conception of bay development involved in the hypothesis: namely, the slumping or flowing of water-soaked sand toward centers of excavation, the slumping process expanding progressively outward from such centers until large shallow craters of symmetrical outline had been produced. No record was found of an investigator's having observed the slumping process in operation on a large scale. But it was discovered that in 1848 Michael

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Tuomey, 1 7

studying the oval bays of the Barnwell, Orangeburg, and other districts in South Carolina, had pictured progressive enlargement of the craters from small beginnings in precisely the manner independently conceived by the present writer nearly a century later. T h e process is not novel, and since it can often be observed on a small scale it is perhaps surprising that it has not more frequently been invoked in connection with study of the bays. T u o m e y attributed removal of the sand, as the writer has likewise done in connection with the formation of certain bays by solution, to downward escape through underground conduits or "drains," as he called them; but the process of crater development must be much the same whether the initial excavation results from solution of soluble beds and downward movement of overlying sand, from upwelling of artesian waters and removal of finer material in suspension and in solution by the overflow, or from both processes combined. T h e pertinent part of Tuomey's discussion is quoted herewith: " T h e circular form of these depressions is easily accounted for. Any sheet of water, in so incoherent a soil as that covering the surface of this region, however irregular its outline, would soon become circular, because the projecting irregularities would be washed away. Neither is it difficult to understand why the depth should be so slight, and the form not conical, like lime-sinks. T h e sandy surface, when completely saturated with water, becomes almost semi-fluid, and as sand is removed by the drain, of course this semi-fluid mass flows in towards the centre, and, by extending the circumference, prevents any material change in depth. And after the pond has become dry, this tendency towards the lower points still continues until the surface becomes nearly level." T h a t T u o m e y thought the bays were circular instead of oval is not surprising, for on the ground, and without the aid of good maps or aerial photographs, it is difficult to discriminate oval from circular forms. T h e process described, operating alone and from a fixed point, would indeed give circular basins. But as we have elsewhere shown, there are other factors affecting bay formation which 17 Michael Tuomey. Report on the Geology of South Carolina. Geol. Surv. South Car., 293 PP-> Columbia, S.C., 1848. See pp. 143-144.

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245

may reasonably account for oval forms having a certain rough agreement in axial direction. SUMMARY

O u r enquiry into the artesian phase of the artesian-solutionlacustrine-aeolian hypothesis of bay origin has demonstrated that this phase of the hypothesis supports well the tests to which we have subjected it. T h e r e is abundant evidence that artesian waters at shallow depths are of common occurrence in the Coastal Plain today, and sound reason for believing that they must have been a far more common phenomenon prior to stream dissection of the plain. Upwelling springs of subterranean water under strong hydrostatic pressure now issue at many points on the surface of the plain where bays are found, and such springs must have been far more numerous during the period when the bays are believed to have been formed. T h e known presence of springs in bays still in the lacustrine stage of development, the evidence of strong outflows of water, either now or formerly, from many bays at present filled with vegetation, and the conclusion independently reached by T u o m e y in 1848 and by the writer in his recent studies that basins excavated in the deposits which form the surface of much of the Coastal Plain must tend to be broad and shallow and to have symmetrical outlines, all support the conception that upwelling waters are competent to produce the type of basins constituting the bays. It must not be supposed that the artesian springs are directly responsible for basin excavation. T h e y are too localized, the currents associated with them are too quickly dissipated in the lake waters, and they are normally too far removed from outlet channels to aid in removal of sand from the developing basin. T h e y are chiefly instrumental in assuring constant agitation of sand in the central portions of the basin, toward which points material from the periphery is constantly slumping and flowing. Such agitation throws finer material into suspension, reduces coarser material to finer sizes, and promotes the slow but in the long run effective solution of so-called insoluble matter. Add to this the finer material brought into the basin by groundwater seepage along shores, by

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slumping and flowing of saturated material, and by wave erosion of basin borders, as well as the finer products of wave attrition, and the products of solvent action on floors and sides of basins, and we have a bulk of material in suspension and solution, increased by constant wave agitation throughout the basin, which with long lapse of time must be very great. It is the removal of this material by overflow through outlet channels, plus whatever quantities of sand may be transported to the outlets by waves and currents, which creates the void into which saturated material from the basin borders may continue to flow until the dimensions of the basin are truly remarkable. Not every oval basin classed as a bay owes its existence, directly or indirectly, in large measure to artesian spring action. T h e term "bay" connotes a type of surface form, not a mode of origin. Our task is to discover the origin of the particular type of form in question. If it appears that in the creation of oval bays different processes operated to a different degree in different cases, we can only record that fact. In the next chapter we shall show that certain oval bays may have been produced without the intervention of artesian spring action. Yet it remains true that artesian springs appear to have played a major role in developing the vast number of oval bays covering the Carolina Coastal Plain.

XII The Solution Phase of the Hypothesis

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H E S E C O N D phase of the artesian-solution-lacustrineaeolian hypothesis of origin of the Carolina bays must now be critically examined. In this connection, we must first answer the question: D o limestones or other materials now or formerly soluble occur below the surface in regions occupied by the curious oval depressions? Much of the area in which oval bays are abundant (Fig. 2) has a thick surface covering of Pleistocene sands and gravels together with some clay. Coarse sands and gravels are abundant and seemingly offer ample opportunity for uprising waters to reach the surface over most of the bay country. Beneath the Pleistocene lie the Tertiary and Cretaceous formations in which the artesian water horizons are chiefly found. It is the extent to which soluble materials are found in these beds that is of interest in the present discussion. WIDESPREAD O C C U R R E N C E OF SOLUBLE BEDS

In South Carolina, the bay country par excellence, the Tertiary formations outcropping in the known regions of abundant bays are the Waccamaw, Duplin, Hawthorn, Flint River, Cooper, Santee, Barnwell, McBean, and Black Mingo; the Cretaceous formations are the Peedee, Black Creek, and Tuscaloosa. Of these the Waccamaw is prevailingly an abundantly fossiliferous marl, sandy marl, or limestone. 1 T h e Duplin is chiefly shell marl. T h e Hawthorn contains a "hard brittle shale that resembles silicified fuller's earth, but fine sandy phosphatic marl or soft limestone is probably the most widely distributed." T h e Flint River, developed in a 1 Data respecting the several formations are based chiefly on C. W y t h e Cooke's "Geology of the Coastal Plain of South C a r o l i n a . " Bulletin 867 of the United States Geological Survey, supplemented in certain cases by personal observations. Quotations are from Cooke.

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limited area only near the Georgia border, is represented by small outcrops showing lumps of chert or silicified limestone and sand. T h e deposit is believed to be the equivalent of the Suwannee limestone or Byram marl, developed farther south and west. It is underlain by soluble beds mentioned below. T h e Cooper marl and the Santee limestone together make u p what was earlier called the "white limestone" of South Carolina, otherwise known as "the Great Carolinian bed of marl." Sinkhole topography is so characteristic of areas underlain by these beds that, when they do not outcrop, their extension is often inferred on the basis of solution phenomena. T h e Barnwell consists chiefly of fine to coarse sand but at the base "is a bed or zone of marl or limestone," apparently equivalent to the Santee limestone. "Exposures of this bed are rare, but the presence of soluble material underground is indicated throughout much of the Barnwell area by many shallow undrained depressions." T h e McBean formation consists principally of sand, thin beds of greenish glauconitic marl, clay, fuller's earth, and lenses of silicified limestone. T h e Black Mingo is largely made up of sands, shales, and a silicified limestone, or buhrstone. It thus appears that every one of the Tertiary formations covering significant portions of the South Carolina bay region contains one or more beds which either is now subject to solution or was so subject in its original condition. Of the Cretaceous formations represented, the Peedee "consists chiefly of gray sandy marl interbedded with thin ledges of hard marlstone." T h e Black Creek "consists principally of very dark gray laminated clay and micaceous sand," but contains in its upper part the "Snow Hill marl member" carrying a large and characteristic marine molluscan fauna. T h e shell deposits are silicified in places. Descriptions of outcrops suggest that sand and clay predominate. T h e Tuscaloosa consists chiefly of sand, much of it arkosic, with interfingering lenses of clay, and some gravel. Water passes so readily through the sand and gravel that this formation is one of the most productive water-bearing formations in South Carolina. T h e arkosic sands are subject to alteration and solution. O n the basis of a reconnaissance field study, Dr. Girard Wheeler 2 2

Girard Wheeler, personal communication.

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concluded that solution and removal of iron and alumina from the arkosic sands of the Tuscaloosa had been profoundly effective. Sinkholes are a noticeable element of the topography on interstream uplands underlain by the Tuscaloosa, and certain of these sinks have been interpreted by L. L. Smith 3 as due to the removal of iron and alumina in solution. T h u s all three Cretaceous formations outcropping in the South Carolina bay country contain beds now soluble or formerly soluble. T h e geological conditions in adjacent portions of North Carolina and Georgia where bays are well developed closely resemble those in South Carolina. In most cases, formations described above extend across the border into the neighboring states without notable change in character. It seems reasonably certain that neither in Georgia nor in North Carolina are areas of abundant bays underlain by beds devoid of soluble matter. In Georgia, sinkhole phenomena are especially notable in Burke and Screven Counties, the two counties containing the most numerous oval bays as far as present knowledge goes. Veatch, Stephenson, and others have attributed the sinks in Screven and Burke Counties to underground solution of the Chattahoochee limestone and soluble beds in the McBean formation. Outcrops in the Savannah River bluffs along the northeastern borders of these two counties reveal many layers of material now or formerly soluble, including ordinary limestones, soft chalky limestone, flint breccia from foraminiferal limestone, marl beds, silicified coquina, and buhrstone (silicified fossiliferous limestone). Southwest of the river, wells sunk below the upland and walls of stream valleys reveal marl beds, limestones, fossiliferous flint breccia from former limestone layers, and buhrstone. Obviously, soluble beds are abundantly developed under areas of oval bays in Georgia. Information for the southeastern part of North Carolina is less satisfactory. Topographic maps for this area are not available, so the extent of sinkhole phenomena attributable to underground removal of soluble material is not readily determined. Nevertheless we know that the most extensive developments of oval bays 3 Laurence L. Smith. Solution Depressions in Sandy Sediments of the Coastal Plain in South Carolina. Jour. Geol., 39:641-653, 1931.

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thus far observed occur in areas underlain by (1) the Black Creek formation of South Carolina (which in turn is underlain by the more or less soluble Tuscaloosa), which has the Snow Hill marl member in its upper portion (exposed only along the southeastern part of the Black Creek outcrop), and upon which there rest widely distributed and often large patches of Duplin marl, the true areal extent of which is unknown since recent surveys have revealed patches hitherto unsuspected because of the effective covering of surface sands; (2) possibly the Castle Hayne marl (near Wilmington), correlated by Cooke with the Santee limestone; (3) the Waccamaw marl, underlain by the Peedee formation containing sands and marl beds; and (4) Pleistocene deposits, underlain by the Peedee sands and marls, Castle Hayne marl, and Waccamaw marl (possibly also Trent marl). Studies on the ground by Dr. Girard Wheeler 4 elicited information concerning the discovery, in well borings and in excavations for locks and dams, of shell beds and marl in several localities (between Fayetteville and Elizabethtown) in a region mapped as the outcrop area of the lower and middle horizon of the Black Creek formation, the deposit among those mentioned which is characteristically most free from soluble materials. It thus appears that the geological formations outcropping in the bay country of South Carolina and adjacent portions of Georgia and North Carolina either contain beds now or formerly soluble or are immediately underlain by formations containing such beds. This latter point is of importance in a region where the less soluble formations are only moderately consolidated and of small to moderate thickness (usually 100 feet or less, and never more than a few hundred feet). Solution of limestone covered by 800 feet or more of firmly consolidated massive sandstones and conglomerates, shaly sands, and shales has been known to produce spectacular sinkhole topography in the massive and insoluble overlying beds/' In the Coastal Plain deposits of the bay country we 4 5

Girard Wheeler, personal communication. Paris B. Stockdale. Monllake—An Amazing Sinkhole. Jour. Geol., 44:515-522,

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must expect soluble beds at lesser depths to affect poorly consolidated overlying formations at many places. Some investigators have rejected the idea that solution has played a significant role in the development of the curious oval depressions or bays because they could find no clear correlation between the distribution of the bays and the distribution of limestone at or near the surface. But when account is taken of soluble beds other than limestone, of insoluble beds known to have been derived from limestone or other soluble formations, and of present or formerly soluble beds found in depth as well as at or near the surface, it becomes evident that formations subject to solution have been present wherever the bays are found. T h i s fact does not of itself prove a genetic relation between soluble deposits and bay phenomena. T h e observed association might be fortuitous. But it does answer in the affirmative the first of the questions earlier posed: Do limestones or other materials now or formerly soluble occur below the surface in regions occupied by the bays? WIDESPREAD OCCURRENCE OF SINKHOLES

W e must next answer the question as to whether undoubted sinkholes and other karst phenomena are commonly found wherever the oval bays are developed. As previously indicated, there are no topographic maps for that portion of the bay country extending into North Carolina. Hence we are deprived of one valuable means of determining the extent of sinkhole topography in this particular area. W e do know, however, that formations which give rise to sinkhole topography in Georgia and South Carolina extend northward into North Carolina. Soil survey reports refer to many slight depressions with numerous swamps and ponds, but correlation with sinkholes usually is not explicit. As noted below, descriptions of topography in soil survey reports are as a rule purely empirical, and sinkholes are seldom specified as such even when typically and abundantly developed. In the case of South Carolina, the soil survey reports often mention "pond-like depressions," "depressions without any outlets," "small areas completely surrounded by higher land which have water standing on or within a foot or so of the surface the year

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round," "occasional low depressions on interstream areas containing more or less water throughout the year," "low, basin-like depressions, or ponds, which hold water after rains," "well defined depressions from 3 to 10 feet lower than the surrounding country," and so on. In relatively few cases a sinkhole origin for the depressions is either suggested or specifically accepted: "In some sections of the Coastal Plain similar depressions have been traced to the leaching out of portions or all of the stratum of limestone or of marl, and in this county the depressions may have been caused in a similar way" (Marlboro County; in most of this county removal of iron and alumina from thick beds of highly pervious arkosic sands may be a more probable explanation). "Marl and phosphate beds underlie some of the county, as is evidenced by the outcrops and sinkholes" (Williamsburg County). "In several places there are deep saucerlike depressions without any drainage outlet and appearing somewhat like sinkholes in a limestone country" (Bamberg County). "Limestone lies near enough to the surface to produce a number of lime sinks and lime sink ponds" (Orangeburg County). The fact that areas of abundant and typical sinkholes (such as are found in parts of Berkeley and Hampton Counties) are described in purely empirical terms, without specific reference to the origin of the closed depressions, demonstrates that absence of the word "sink" or "sinkhole" in a soil report does not mean that sinkholes are not present. It is in geological reports and on topographic maps that we find most abundant evidence as to the wide development of sinkhole topography and other karst phenomena in the bay region of South Carolina. Almost a century ago Sir Charles Lyell 0 called attention to the frequent occurrence of "lime-sinks or funnel-shaped cavities . . . arising from natural tunnels and cavities" in the underlying Tertiary white marl and limestone. Lyell also refers to "the linear arrangement so common in lime-sinks in South Carolina and Georgia," and adds: " T h e walls of such 'sinks' are vertical, and 6 Sir Charles Lyell. Travels in North America. Vol. 1. 316 pp., London, 1845 (see for example pp. 175176). Observations on the White Limestone and Other Eocene or Older Tertiary Formations of Virginia, South Carolina, and Georgia. Quart. Jour. Geol. Soc. London, 1:429-442, 1845. See p. 434.

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the strata exposed to view consist usually of clay and sand, which rest upon the limestone." Michael Tuomey 7 three years later repeatedly referred to the removal by solution from calcareous rocks of a portion or all of the lime. With respect to one group of beds he writes: "In many instances there is little more left than the silica and alumina of the marl, with a trace of lime; and the latter ingredient rarely exceeds six per cent." T h e development of sinkholes as a result of such solution was more than once mentioned by Tuomey. He also described the shallow sinks toward the inner margin of the Coastal Plain now believed to result from the removal of iron and alumina of arkosic sands; but he attributed them to downward removal of surface sands through vents giving rise at lower levels to "boiling springs." Glenn 8 cited the occurrence of small lakes formed "in basins or sink holes whose underground outlet has become stopped up." Calhoun 9 described "the karst type of topography" so extensively developed over regions underlain by limestone and marl, noting that "the more soluble parts have been leached out, leaving the marl many feet beneath the present surface of the ground." L. L. Smith 10 recently referred to the numerous sinks due to solution of marls and attributed other sinks, found in regions not known to be underlain by calcareous beds, to removal of iron and alumina from the feldspathic constituents of arkosic sands. These are random citations from a literature filled with references to the widespread development of sinkhole topography in the bay country of South Carolina, often in areas from which the soluble beds have been nearly or completely removed. It is on topographic maps that one can best determine the extent to which sinkhole topography is developed in association with the more or less oval craterlike depressions called "bays." Such maps are available for part of the central and most of the south7 Michael T u o m e y . Report on the Geology of South Carolina. Geol. Surv. South Car., 293 pp., Columbia, S.C., 1848. See pp. 143, 144, 165. " L . C. Glenn. South Carolina. Jour. School Geog.. 2:9-15, 85-92, 1898. See p. 14. 9 F. H. H. Calhoun. Limestone and Marl Deposits of South Carolina. South Car. Agric. Exp. Sta., Clemson Agricultural College, Bull. No. 183, 27 pp., 1915. See p. 20. 10 Laurence L. Smith. Solution Depressions in Sandy Sediments of the Coastal Plain in South Carolina. Jour. Geol., 39:641-653, 1931.

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western section of the South Carolina bay region. Some nineteen quadrangles are involved, and they cover outcrop areas of nine out of ten of the Tertiary formations (all but the Waccamaw) represented on Cooke's geological map of the Coastal Plain of South Carolina. There are three additional quadrangles (covering outcrop areas of the Tertiary Barnwell sand and the Cretaceous Tuscaloosa formation) which show baylike depressions but not typical bays. Of the nineteen quadrangles covering the typical bay country, there is not one which fails to show sinkhole topography. T h e closest approach to failure is the Cummings quadrangle, which shows one fairly good oval bay, one bay more irregular, and one apparent sinkhole. Where a topographic map shows but one or a few closed depressions there is, of course, always the possibility that roads, dams, or other obstructions not shown on the map have cut off the heads of former normal valleys or ravines, or that quarries or other artificial excavations are represented. In the present case the quadrangles to the southwest, west, northwest, north, northeast, and east (quadrangles southeast and south of the Cummings quadrangle lie outside the bay country) all show what appears to be undoubted sinkhole topography; but in no case are the sinks close to the two bays on the Cummings quadrangle. Elsewhere the sinks are commonly not far from oval bays, and often the two features are intimately associated. Even where bays are few or poorly developed, sinkholes are often present. That solution phenomena are substantially coextensive with the region of bay development in that part of South Carolina for which topographic maps are available appears to be fully established. In the three quadrangles where bay like sinks rather than typical bays are found, there is no question as to the important role played by solution. One may question whether the shallow basins of this area should be called bays, and whether in any given instance solution of calcareous material or arkosic material is responsible for the topographic effects observed. But that solution has been active in these areas, mapped as outcrop areas of the Barnwell sand (Tertiary) and the Tuscaloosa (Cretaceous), cannot be doubted. In the bay region of Georgia the development of sinkhole topog-

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raphy is fully as striking as in most parts of South Carolina. Sir Charles Lyell, in reports cited above, commented on this phenomenon, describing one sink 80 feet deep which had nothing but sand and steatitic clay exposed in its walls. Although lime or marl was rarely observed, he inferred its presence in depth where fairly typical bays have since been found, especially in Screven and Burke Counties. Later geological reports have frequently commented on the numerous sinks of this region, while soil survey reports for counties in or near the bay region cite "many sinkholes" and "lime sinks" (Jenkins County), "numerous sinkholes" (Screven County), "partially filled in depressions of limestone sinks" (Bulloch County), and "numerous sinkholes" (Screven County). Of the nine topographic quadrangles available for that portion of Georgia known to contain true bays, every one shows an abundant develop ment of sinkhole topography. The writer's field observations, covering chiefly the bay country of South Carolina and adjacent parts of Georgia, show that sinkhole topography is even more extensively developed than indicated by the topographic maps. About the northwestern end of Tony Hill Bay and southeast of Piney Bay, Lodge quadrangle, South Carolina, 11 several typical sinkholes 50 feet in diameter and one 150 feet across were observed where the map shows none. East of Wadboo Swamp Bay, Bowman quadrangle, South Carolina, and only a hundred yards from its marshy margin, is a typical sink 50 feet in diameter, whereas the nearest sinks represented on the map are more than three miles distant. No sinks are shown in the vicinity of Dial Bay and its associated bays, Mayesville quadrangle, South Carolina, but traversing the roads encircling these basins one observes many small ponds occupying closed shallow depressions suggestive of sinks. Both south and east of Elko, Williston quadrangle, South Carolina, are regions of typical sinkhole topography exhibiting many large and small sinks and sinkhole ponds not shown on the map. South and southeast of Denmark, Bamberg quadrangle, South Carolina, where the map shows a number of sinks of various sizes and shapes, field observations show many 11 Localities and quadrangles are cited for the benefit of those who may wish to examine the maps or verify observations in the field.

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others, some of large size. In many cases the sinkholes are not large enough to be represented on maps of the scale 1:62,500; in some cases they are not deep enough to be caught by contours having a lo-foot interval. But whatever the cause, there can be no doubt that sinkholes are far more numerous in South Carolina than existing maps indicate. This statement applies equally to those portions of Georgia that exhibit oval bays and for which contour maps are available. In northeastern South Carolina, where topographic maps are lacking and soil survey reports make no specific mention of sinkholes, field observations at a number of points demonstrate the existence of well-developed sinkhole topography. Lack of topographic quadrangles in southeastern North Carolina and lack of extended field work in that area make impossible any definite conclusion respecting the northeastern extremity of the bay country. We can only say that throughout most of the bay country there is a truly remarkable development of sinkhole topography, occasionally with other karst phenomena, and that the association of oval bays with sinkholes is prevailingly close, sometimes so intimate that bays and sinks are completely intermingled. T R A N S I T I O N F R O M S I N K H O L E S TO O V A L C R A T E R S

Our next enquiry is whether one can trace a transition from typical sinkholes to typical oval bays having bordering rims of sand. T h e answer is that every possible stage of such transition is evident in the field. T h e following observations, based in part on the writer's field notes and in part on studies of maps and aerial photographs, refer to typical examples which could be multiplied indefinitely. 12 Four and a half miles east of the center of Wilmington, North Carolina, elliptical bays are associated with irregular depressions holding water or marsh deposits in such manner as to suggest an intimate relationship between the two (Fig. 4 1 ; see also Fig. so). Some of the bays have borders in part irregular, while some of the smaller depressions approach the bays in form. T h i s area was not visited by the writer, and the intimate association observed in the 12 The general reader may pass over the pages printed in smaller type. Locations are cited and, where available, topographic quadrangles are named, for the benefit of those who may wish to examine the maps or verify observations in the field.

4 1 : Elliptical bays intimately associated with irregular depressions resembling sinks 41/2 miles E of center of Wilmington, N.C. N is at top, and elliptical bay in N E corner is about \/2 mile in greatest diameter. (Fairchild Aerial Surveys, Inc.)

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aerial photograph does not demonstrate a genetic relationship between the two types of forms. T h e depressions suggest sink topography, and elsewhere undoubted sinkholes are quite as intimately associated with undoubted oval bays. One of the writer's junior associates, Dr. Arthur Howard, examined in the field a number of the depressions in the Wilmington area, finding some occupied by cypress, black gum, and other trees, while neighboring basins were grassy swales. He reported by letter that the pattern of some of the depressions suggested surface settling over underground channels, but he could not be certain that they were true sinks. Beginning about ten miles northwest of Darlington, South Carolina, and continuing at intervals for several miles toward Society Hill, the field observer sees a number of large but shallow sinks, 10 to 20 feet deep, often containing ponds. Some of these are bordered by small rims of white sand and closely resemble typical bays. Those without rims might pass for ordinary sinks. In the walls of a few some evidence of slumping is observable in red or mottled red and pink loam exposed below orange sand overlain by white sand, as if solution of beds below had caused the depressions. A mile north of Pineville School, Bowman quadrangle, South Carolina, is a marshy depression of striking oval form, except that the southeastern end, where two outlet streams drain east and southeast, appears imperfectly outlined. Although this is a more nearly perfect representation of an oval bay than many shown on topographic maps, its rounded northwestern end has every appearance of a sink dropped abruptly some 5 or 6 feet below the general level of the plain. As in most typical bays, there is no rim about the northwestern border. T h e southeastern end was not reached because of roads impassable at the time of the writer's visit. Polk Swamp and adjacent marshy depressions. Bowman quadrangle, South Carolina, are rudely oval northwest-southeast-trending depressions which have the appearance of true bays but generally lack distinct rims on the south and east. Undoubted sinkholes were observed in this region, and a native reports that a well on the edge of Polk Swamp passed through 5 feet of muck, then sand, and below that a shell bed, striking "rock" at a depth of 30 feet. In this connection it is interesting to recall that Prouty 1 3 found that a shell bed, exposed on either side of one of the bays near Myrtle Beach, South Carolina, was missing under the bay itself, and attributed such disappearance to solution by increased circulation of groundwater resulting, in his opinion, from puncturing of the bed by meteorites. A few miles west of the south end of Polk Swamp is what appears to be an ordinary bay, except that its western side is a steep wall, 10 to 15 feet high, exposing red loam and closely resembling the walls of sinkholes in this region, many small examples of which were observed. It is fair to ask whether steep walls about marshy oval depressions, similar to the walls found in sinkholes of the same region, are necessarily to be accepted as an indication of relationship to such sinkholes. T h e answer must be "no"; similar scarps are often produced in similar beds by very diverse causes. It is quite conceivable that lakes formerly occupying oval depressions 13

William F. Prouty, personal communication.

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may have had their shores sharpened into cliffs by wave action wherever those shores were unusually high. It must be observed, however, that where the initial topography was undulating enough to give shores high in some places and low in others, the outline of a lake forming on that surface is likely to be very irregular. Lake basins developed from below, without regard to surface topography, are more likely to be somewhat circular or oval in outline, with some parts of the shore low and gently sloping, others high and steep. Such development from below might assume the form of mechanical excavation by artesian springs or solution to produce sinks. In the descriptions here given, the obvious resemblance of some bay walls to sink walls in the immediate vicinity is recorded as a fact not open to dispute, regardless of what the explanation may be. Transition forms covering the whole range from typical bay to typical sink exist, and this fact must be given whatever weight it is entitled to receive. Swallow Savanna, Peeples quadrangle, South Carolina, is of special interest in this connection. While the origin of the name "Swallow" in the present case is unknown to the writer, the terms "swallow" and "swallow holes" are often applied to sinkholes in limestone regions where water is "swallowed." Swallow Savanna is bordered on the west or northwest by a steep wall 15 to 20 feet high, wholly comparable with the walls of many sinkholes. Red loam is exposed in the wall and occasionally in fields on the adjacent plain. T h e depression, like many sinks, contains a central lake bordered by a swamp. On the edges of the depression two typical sinkholes are shown on the topographic map, both somewhat oval, with long axes trending northwest-southeast. In this region are countless other sinkholes, large and small, many but not all of which show northwest-southeast elongation. About the southeast quadrant of Swallow Savanna and extending up its eastern side is the most spectacular ridge of white and buff sand found associated with any bay observed by the writer. Rising rather sharply 8 to 10 feet in height and having a breadth of 400 feet, it appears more striking than much broader but less steeply sloping ridges found in the Myrtle Beach and other areas. T h e form of the main depression is oval, with long axis trending north-northwest-southsoutheast. It thus appears that Swallow Savanna is a typical bay which at the same time possesses characteristics of a sinkhole and is closely associated with what appear to be typical sinkholes showing the normal trend of bays. Levy Bay, Peeples quadrangle. South Carolina, is a large example of the transition type of depression exhibiting features characteristic of both bays and sinks. Its long axis trends but slightly east of south for a distance of more than two miles. In places its walls are steep and from 6 to 10 feet high, suggesting slumping of surface loam underlain by soluble beds. At the southeast there is a distinctly developed triple rim of white sand, the central member of the series being strongly marked, the other two less conspicuous, with wooded grassy or swampy swales between the ridges. From Shell Bluff, Greens Cut quadrangle, Georgia, southeastward a few miles along the old Savannah and Augusta Road and within two miles of the road 011 either side, one may count some thirty-two depressions, large and small, which appear to be typical sinkholes, many of them containing

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water, most of the others marshy, but some of them dry. They occur on the upland surface of a plain underlain by limestone, marl, and layers of silicified coquina and flint breccia representing former limestone beds. Few would hesitate to classify these forms as sinkholes of the ordinary type. Yet twentytwo of the thirty-two show long axes trending from nearly north-south to nearly east-west, or within the limits of axial trends of most oval bays, a majority of them approximating the trend northwest-southeast. Some of the depressions are rounded, others highly irregular in outline, but both map and aerial photographs show that many have the oval form typical of the bestdeveloped bays. From some of them white wind-blown sand is being drifted over the upland as is usual in the case of oval bays, and in a few cases enough of this sand has accumulated to form a low ridge or rim. T h e student of bays can hardly hesitate to classify the larger and more perfectly oval forms having northwest-southeast trends as true bays. T h i s group of depressions, therefore, seems to show every gradation from typical sinkhole to fairly typical bay. Some ten of these depressions are in alignment with a rectilinear segment of Beaverdam Creek and one of its tributaries, suggesting fracture control of uprising or downseeping waters and of surface erosion. Southwest of Buxton and Myers Store, Ellenton quadrangle, Georgia, is a large oval depression measuring over a mile in length, with long axis trending slightly east of south. Its marshy, wooded floor is locally called Oliver Pond. Small quantities of wind-blown sand are found about its borders in places, but no true rim was observed, only the northeast quadrant having been visited. Southeast of the store is a second and larger oval depression measuring nearly two miles in greater diameter, its flat floor containing grass, and brush interspersed with bodies of water, the whole being known locally as Mobley Pond. Its longer axis trends slightly more east of south than does that of Oliver Pond. N o true rim of sand was observed along the southwestern side or at the southeastern end, the southeast quadrant not having been visited. Aerial photographs leave no doubt that both these depressions are ovoid bays lacking well-developed sand rims. It has already been shown that such rims are not always found in association with depressions which in every other respect conform to the standard type of oval bay. Yet both Oliver Pond and Mobley Pond have steep walls in some places, which rise 20 to 40 feet above their marshy floors, and gently sloping walls in others, after the manner of certain large sinks. Both are intimately associated with typical sinkholes of irregular form, constitute part of a terrain suggesting "knob and sink" topography, and occur in a region underlain by limestone, marl, and a flint breccia derived from a foraminiferal limestone. They are apparently transition forms between typical sinks and typical oval bays. An even more perfect transition form is found in the depression about a mile long northeast of McBride Church, represented as irregularly oval on the topographic map, Hilltonia quadrangle, Georgia. T h e trend of the oval is nearly north-south, and about its southeast quadrant there is a typical rim of apparently wind-blown sand, white on the surface but buff-colored in depth. This rim has a height of 5 or 6 feet and is roughly a hundred yards in breadth. A drainage ditch cut through the white and buff sand rim trenches

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the red loam of the Coastal Plain deposit to a depth of 3 to 5 feet, showing that the sand rim is not a heaped-up accumulation of Coastal Plain debris and that the depression is actually "sunk" into the Coastal Plain formation. T h e walls of the depression rise steeply for 30 feet in places, gently elsewhere, to an upland of characteristic "knob and sink" topography. Typical small sinks are numerous in the immediate vicinity. A similar transition form is the depression more than a mile farther east, except that in this case there is no good development of an associated sand rim. Aerial photographs show that both are ovoid bays with the narrow end of the oval in each case pointing slightly east of south, and with eastern sides more strongly curved than western. Three miles north-northeast of Millhaven, Hilltonia quadrangle, Georgia, is a group of nine small lakes or ponds not visited by the writer. T h e y occur in a region of associated sinkholes and oval bays and, on the basis of map inspection, would probably be tentatively assigned a sinkhole origin by anyone familiar with the general geology of the area. Most of these water bodies are more or less oval in outline, one of them trends northeast-southwest, one north-south, two slightly east of south, and five distinctly northwest-southeast. These relations suggest that the basins are transitional in character between typical sinks and typical bays. Six miles east of Hilltonia, Georgia, the topographic quadrangle of the same name shows a cluster of ten or more marshy depressions, some rudely circular or oval as represented on the map, but most of them highly irregular in outline. T h e aspect as seen on the map is that of typical sink topography. Aerial photographs show that these depressions must be classed with true bays. Most of them are really ovoid in form, some of them with sand rims about their southeast quadrants, the smaller ends of the egg-shaped outlines being directed strongly southward (from about S 20° E to about S io° W). On the Shirley quadrangle, South Carolina and Georgia, typical sinkholes, most of them rounded or irregular in form, are represented as abundant on the upland southwest of the Savannah River. Where the sinks are more or less oval in form, the axes show highly variable trends, but perhaps with a few more trending northwest-southeast than in any other one direction. Associated with these undoubted sinks are two marshy depressions of exceptionally large size (nearly a mile in major diameter), of remarkably perfect oval form but with that type of asymmetry characteristic of oval bays—sharper curvature on the more easterly side. One of them certainly and the other apparently has a drainage outlet, another feature relating them to many typical bays. Of the two, White Pond has its major axis trending northwestsoutheast and would almost certainly be classed with normal bays if it occurred in a region where such forms were abundant. T h e other, Enecks Bay, would also be classed with normal bays but for the fact that its major axis trends northeast-southwest. Both have steep walls in places, such as are found in many sinks and bays. T h e student must frankly be puzzled as to whether he should group these large oval forms with sinks or bays. He is likely to suspect that he is dealing with an intermediate or transition type of depression. Aerial photographs will confirm him in this impression. These show every transition from irregular to oval sinks, thence to undoubted ovoid bays

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with poorly developed sand rims about their southeast quadrants. T h e rudely circular sink represented by two depression contours just east of Blue Springs School on the topographic quadrangle is seen on the aerial photograph of this area to be distinctly ovoid in outline, with the small end of the oval directed slightly east of south. Enecks Bay as shown on the photograph is rudely ovoid but with its eastern side obscured by cultivation of sandy fields. There is faint suggestion of a sand rim toward the southern part of the southeast quadrant, but not distinct enough to be conclusive. T h e outlet channel toward the southeast is very clear. T h e curved western side of this depression is so distinctive and the narrow southern end so typical of ovoid bays that it seems impossible to do otherwise than class it with other oval bays of more normal trend; yet its affinity with true sinks seems equally obvious. T h e Oliver quadrangle, Georgia, shows approximately five dozen depressions, many of which contain marshes or ponds. T h e majority of these depressions are small, and most investigators would probably be inclined to put them all in the class of sinkholes. Yet the number of these depressions elongated in some northwest-southeast direction slightly exceeds the number that are rounded or elongated in other directions (north-south, east-west, or northeast-southwest). Furthermore, the remarkably oval form and large size of Jarrell Pond, its northwest-southeast trend, and its more sharply curved northeastern side relate it closely to the typical oval bays of other localities. Aerial photographs show that the basin of Jarrell Pond is really ovoid, with the small end of the oval directed nearly south, the axial trend thus being quite different from that shown on the map but still in the range of typical bay axes. Less typical northwest-southeast-trending ovals are found just north of Eureka Springs in association with a northwest-southeast-trending closed depression which is a typical sinkhole containing a small pond not shown on the map. An area of special significance is represented on the southern part of the Bamberg quadrangle. South Carolina. T o the east, south, and west of this area are typical oval bays, those to the south being exceptionally perfect examples. Yet a glance at the southern third of the Bamberg quadrangle would lead one to class it with ordinary karst regions. Sinkholes and irregular knobby hills alternate in endless confusion. A second look impresses one with the fact that there is a notable tendency for sinkholes to be elongated in a northwestsoutheast direction. Four and a half miles southwest of Bamberg along the Olar road, near benchmark elevation 194, a group of three sinks, each deep enough to require two lo-foot depression contours, shows well this tendency. Examination on the ground confirms the substantial accuracy of the map, and shows the presence of red loam in the steep walls and a pond in the largest depression at the time of the writer's visit. A few hundred yards to the southeast is a larger and shallower oval depression trending northwestsoutheast, apparently a true sinkhole but with some accumulation of white sand about its southeastern quadrant. T o the northwest and west are other sinks elongated in a northwest-southeast direction; and farther west, near Salem Church, are four oval sinks of which the three larger have parallel axes trending northwest-southeast. While there are in this region some excep-

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tions to the normal trend, the writer left the area with a strong conviction that the prevailing trend of elongated sinks was too pronounced to be fortuitous, and that there must be some relationship between the trend of groundwater movement, trend of elongated sinks, and trend of oval bays. Farther southwest of Bamberg on the road to Olar and in the northern part of the Olar quadrangle, South Carolina, there is a nearly round depression, half a mile in diameter and represented by two to-foot depression contours, located a mile east of Govan. T h e north and west walls are unusually steep in places, with frequent exposures of red loam. T h e southeastern wall carries a coating of what is apparently wind-drifted white sand. O n the floor of this rounded basin and a little east of its center, there extends from north to south a ridge of sand a few feet high and 130 feet wide in places. At its ends the ridge curves westward toward tangency with the curving walls of the depression, in the manner typical of beach ridges. T h e southern end of the ridge is partially outlined by the lower of the two depression contours. Observation on the ground leaves little doubt that this is a true beach ridge, formed toward the eastern side of a lake occupying the floor of the circular depression in such manner as to give an oval lake to the west trending nearly north-south. T h e resulting form is thus intermediate between an ordinary rounded sinkhole with steep walls and an oval bay with an inner beach ridge and the beginnings of an outer rim of wind-blown sand. Only a few miles to the southeast are found two exceptionally perfect oval bays, one of which has what appears to be a beach ridge s feet high and 10 to 15 feet wide (between Alligator Bay and the bay next southwest). T h e other, Doussoss Bay, has an apparently wind-blown white sand rim 6 to 10 feet high and approximately 300 feet wide about its southeastern quadrant, inside of which a narrower beach ridge (?) is observed. Thus in the circular depression east of Govan we have an example which at first sight would be accepted as a typical sinkhole but which when examined in the field shows features closely relating it to neighboring typical oval bays. T h e southwest quarter of the Varnville quadrangle, South Carolina, shows a dozen or more closed depressions of the sinkhole type associated with two marshy ovals draining through outlet channels into near-by creeks. One might think it possible in this case to distinguish true sinkholes from true bays. But study of aerial photographs casts doubt on the possibility of such distinction. Horse Pond, northwest of Hopewell Church, occupies what appears from the map to be an irregularly oval sink, while the marshy oval just south and draining westward to Brier Creek looks more like a typical bay. Yet the resemblance of the two on the map is striking. Aerial photographs show that the southern depression is indeed a remarkably perfect bay of strongly ovoid outline. But they also show that the Horse Pond depression is likewise ovoid, though less perfect in outline, and that the smaller end of the oval is oriented in the same direction as its neighbor. Horse Pond basin seems to show some accumulation of sand about its southeast quadrant, but the photographic evidence is not conclusive. Nevertheless, one cannot escape the conviction that the two basins represent different stages in the evolution of a common type.

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Four and a half miles southwest of Horse Pond is an elongated basin trending slightly west of south and containing, according to the map, a larger and a smaller pond. T h e appearance is that of a typical sinkhole of distinctly irregular outline. Aerial photographs show that the northern three-fifths of this basin has the smoothly curved outline of a typical oval bay. T h e character of the southern two-fifths is obscured by cultivated fields, but one suspects greater irregularity here. Were the axial trend of this depression S so 0 E instead of S i o ° W , one would not hesitate to call it an imperfect oval bay. Every gradation from typical sinkhole to perfect large oval bay with sinklike walls on one side may be seen on the Talatha and Williston quadrangles, both in South Carolina. T h e southeastern corner of the Talatha quadrangle exhibits twenty-one closed depressions, many more or less irregular in outline, all but four of which are elongated in a northwest-southeast direction. Approximate parallelism in the trend of the major axes is striking in the case of the larger depressions, some of them from one-third to one-half mile in length. O n the adjacent portion of the Williston quadrangle this parallelism is noted in the case of many closed depressions, but a considerable number are rounded or show trends in other directions. Farther east (just west of the road running from Elko south to Barnwell) are several unusually large depressions, two of them nearly three-quarters of a mile in length and represented by two lo-foot depression contours. Both of these larger basins are rather irregular in detail of oudine, after the manner of many sinks, but both are rudely oval in general aspect, both have major axes trending northwest-southeast, and both show a sharper average curvature of their northeastern sides, after the manner of typical oval bays. Other smaller depressions are likewise more or less oval in outline, some trending northwest-southeast but others north-south or even slightly west of south according to the map. Aerial photographs (Figs. 30 and 36) show that many of these depressions are typical ovoid bays with sand rims about their eastern or southeastern sides. T h e northernmost of the two larger basins described above has a clearly defined ridge of sand built on the faintly sloping southeastern and eastern wall of the depression. T h e ridge is thus within the basin and is 3 or 4 feet high and approximately 100 feet wide. There can be little doubt that it is a typical beach ridge built about the southeastern quadrant of a lake formerly occupying the depression, the present pond (not shown on the map) found in the lower part of the basin being the shrunken representative of this lake. Except for steep walls, in places 20 to 30 feet high, showing exposures of buff and red loam and moderate irregularity of outline, we have here a typical bay with an associated sand rim. Yet it is intimately associated with and shows transition features toward typical sinkholes of all sizes which are far more numerous in this region than the topographic map indicates. Still farther east and more significant for our study are three large oval depressions in the east-central part of the Williston quadrangle. T h e first of these (immediately southeast of Reynold) is about a mile long with major diameter trending northwest-southeast. O n its northwestern side is a fairly steep wall, and, where it is traversed by the highway, horizontal beds of red loam are exposed. Toward the southeast the contours suggest an outlet drain-

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FIGURE 42: Blackville Bay, Barnwell Co., S.C. Note ovoid outline, stronger curvature of N E as compared with SW side, rim of white sand (partly covered with vegetation) about SE quadrant, outlet channel toward SW, and part of town of Blackville on W border. Railroad crosses bay and its sand rim. Just SE is another ovoid bay nearly as large as Blackville Bay, but partially obscured by sand dunes in NW and cultivated fields in SE end, whence an outlet channel drains toward SW. Other dark patches are oval bays and irregular sinks (?). N is at top, and largest bay is nearly 11/2 miles in length. (Agricultural Adjustment Administration.) age channel, b u t this area was not visited. Aerial p h o t o g r a p h s show that this depression has the o v o i d f o r m a n d the more strongly curved northeast border typical of many bays a n d confirm the impression of an outlet channel to the southeast. T h e second depression, immediately northeast of the first, is k n o w n as Peters Pond. It measures a mile a n d a half along its m a j o r diameter, which trends very slightly east of south. U n l i k e typical bays, its western side, which

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is more irregular than the eastern, has the sharper average curvature. T h e contours suggest a former outlet channel toward the east, but this point wis not examined on the ground, its possible significance not being appreciated when the writer traversed the borders of the depression. In places on the west the depression is bordered by steep walls 20 feet or more in height, leading up to the gently rolling plain below which the basin is sunk. On the eastern side so much wind-blown sand has been deposited that one gets the impression of a large sand rim, but examination seems to establish that the ridge is a residual of the Coastal Plain sediments over which sand from the basin has been drifted. Aerial photographs show that this is a composite of two bays with smoothly curved outlines beautifully developed and outlet channels opening both eastward and southward. T h e combination of typical sink features with typical bay features is striking. T h e third depression, Blackville Bay (Fig. 42), seems definitely similar to the other two, yet marks a further stage in the transition to typical bay. It has, indeed, been cited in the literature as a good example of an oval bay with well-developed sand rim. T h e aerial photograph fully justifies the citation. T h e outline, although represented as rudely elliptical on the topographic quadrangle, is quite as perfectly ovoid as any bay could possibly be and still show the sharper curvature of the northeastern side. T h e major axis trends S 25° E and measures nearly a mile and a half in length. As is so often the case, the western and northwestern portions of the depression are bordered by steep walls. In places the walls are 30 to 40 feet high and expose red loam, gravel and red loam mixed, a mottled pink and red clayey loam, with possible marly layers. At one point an apparent dip of the beds downward toward the depression was observed, as if due to down-bending or slumping in that direction, but the possibility that the apparent bedding is a weathering phenomenon was not excluded. About the southeastern quadrant of the basin is as perfect a sand rim as one ever encounters in the most typical oval bays. It is in every respect a duplicate of the Myrtle Beach examples, except that it is higher than most of them and a more prominent feature in the landscape. Composed of snow-white sand, drifted into mild dune topography in places, the ridge rises to altitudes of 10 feet or more and has a breadth of 400 feet where measured. T h e photograph indicates a breadth of over 1,000 feet in places. One cannot fail to class the Blackville ovoid basin and its prominent sand rim with other typical oval bays. On the other hand, how can one fail to class it with the typical sinkholes with which it is so closely identified and into which, through adjacent basins, it imperceptibly grades? In Blackville basin we seem to have a depression which is at the same time sinkhole and oval bay. G E N E T I C R E L A T I O N OF SINKHOLES T O C R A T E R S

In earlier portions of this chapter it was demonstrated that limestones or other materials now or formerly soluble occur below the surface of regions occupied by the curious oval bays of the Carolina and Georgia coasts, and that undoubted sinkholes and other karst

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phenomena are closely associated with the bays. T h e detailed facts set forth on the pages immediately preceding abundantly demonstrate that one can trace every gradation from typical sinkhole to typical oval bay bordered by prominent rim of sand. The question naturally arises: Are sinkholes and oval bays variations of the same basic type of landform? Or are they distinctly different types when fully developed, but so related to each other genetically that characteristics of one frequently appear in association with the other? Perhaps this is a matter of definition. Certainly the natives of the Carolinas and Georgia sometimes apply the name "bay" to marshy depressions of large size showing features characteristic of sinkholes and forming part of a group of basins many of which are undoubted sinkholes. We might call those large oval depressions bordered by steep walls "sinkholes," and those occupying shallow depressions virtually on the surface of the plain "bays." Even so, we would have to define "wall" and "steep" since there is every gradation between faintly sloping border a few feet high and vertical scarp many feet high. Also, we would have to decide how much of the depression must be bordered by a "steep wall" to make it a sink, since there is every gradation from basins entirely surrounded by such a wall to others lying on the surface of the plain except for a few feet where some undulation of the plain terminates abruptly in a small scarp at the basin's margin. We are faced with the inescapable fact that gradations between typical sinkhole and typical oval bay are so frequent and so imperceptible that it is not possible on any rational ground to say when one of the intermediate forms should be called a sinkhole and when a bay. Another possibility is to draw a distinction between elliptical and ovoid forms calling the former "bays" and the latter "sinks." In support of such a distinction is the fact that the ovoid forms are more abundant in the southern part of the areas where soluble beds are more frequently found not far below the surface and where undoubted sinkholes are more numerous. The additional facts that both elliptical and ovoid forms trend prevailingly in northwest-southeast directions, show sharper curvature of their northeastern sides, frequently contain single or multiple beach

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ridges best developed about the southeastern ends of the basins, and have major accumulations of dune sand about their southeastern quadrants, require explanation. Such explanation could perhaps be based on the ground that both types of basins were in their development influenced by similar or identical subsurface geological conditions, while both eventually contained lakes and suffered the same consequences of wave and wind action. It is more difficult to maintain the proposed distinction and satisfactorily explain the observed gradations between elliptical and ovoid forms, the repeated intermingling of the two in the same locality, the occurrence of ovoid forms as shallow surface basins without sink characteristics and equally the occurrence of elliptical forms resembling sinks depressed below the surface, as well as the apparent combination of an older elliptical and later ovoid outline for the same basin. For each of these situations a possible explanation can be invented. But the necessity of such special explanations weakens confidence in any proposal to recognize as two distinct types of basins, genetically unrelated, (a) the shallow elliptical basins early discussed by Glenn, Melton, Cooke, and others, and (b) the (sometimes) deeper ovoid basins described and figured in parts of this volume. Even if we recognize such a distinction as valid, we must further recognize that every possible gradation between the two types is found in the field, that all of them have been called "bays" both in popular usage and in scientific literature, and that both must therefore be included under the broad term "oval bays." T h e facts suggest that the two types of basins are genetically related, but that solution has played a variable role in their development, from a minimum in some cases to a maximum in others. T h e question then arises as to whether there is other evidence that some genetic relationship exists between typical sinkholes and typical oval bays. T h e fact that beds now or formerly soluble underlie areas where bays are abundant suggests that solution has played a role in the formation of both sinks and bays. Frequent elongation of sinkholes and prevailing elongation of oval bays in a direction parallel to the movement of subsurface waters suggest that both may be genetically related to the flow

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of such waters. We have earlier seen that ovoid bays are theoretically explicable on the assumption that artesian springs migrated in a direction opposite that of artesian flow, pari passu with progressive solution of beds through which the water was moving; or on the assumption that groundwater flow sapped the northwestern borders of the basins. We have also seen that for every welldeveloped elliptical or ovoid bay there are many others of irregular outline, so that oval sinkholes elongated in the direction northwest-southeast appear to be quite as abundant in proportion to irregular sinkholes as are oval bays similarly elongated in proportion to irregular bays. There are many reports of shell rock and other soluble material encountered in wells driven near the margins of bays and occasionally on their floors, while silicified limestone and silicified shell rock have likewise been reported from such wells and the latter type of material has been recovered from the marshy bottom of occasional bays. There is also the report by Prouty, earlier cited, of shell rock exposed in a canal beyond the margins of a bay but apparently wholly dissolved where the bay was formed. "Knob and sink" or karst topography is closely associated with some bays but lacking where others are developed. It is difficult to escape the conclusion that solution has played a variable but important part in the development of oval bays as well as in the development of sinks. Certain other observations suggest a genetic relationship between sinks and bays. In the course of field work and map studies, the writer was impressed by the fact that in many instances a group of well-developed oval bays is located some miles southeast of, and some 20 to 50 feet lower than, a prominent group of welldeveloped sinkholes. Such geographic relationship suggests that water entering the sinkhole areas flowed seaward through the Coastal Plain formations to rise to the surface where the bays are found: in other words, that the sinkholes are the intake areas, the bays the outlet areas for circulating groundwater. It was later discovered that Berkey and Kerr had previously come to such a conclusion respecting the Eutawville area studied by them in South Carolina. In his study of the topographic maps, Eutawville and Chicora quadrangles, South Carolina, the writer noted that

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many typical sinkholes pit the surface of the Coastal Plain where this lies from 120 to 140 feet above sealevel northwest of Milligans in Orangeburg County. Southeast of Milligans from five to ten miles, and at elevations ranging from less than 100 up to 120 feet, are many marshy and wooded areas which appear on aerial photographs of the region as true elliptical or ovoid bays. T h e best of these, Toney Bay, is of marked ovoid outline with indications of sandy borders at the southeast. Again, northward and eastward from Eutawville the map shows one of the finest sinkhole areas in the state of South Carolina, at elevations of from 100 to 120 feet. Aerial photographs show no oval bays in this sector, though poor examples occur just to the west. From six to ten miles southeast of Eutawville, and at elevations of 90 feet and less, begins a broad expanse of marshy plain in which true ovoid bays with multiple sand rims and many incipient or poorly formed oval bays are shown on aerial photographs. It was in this marshy plain that Berkey and Kerr found active springs the waters of which were unusually high in calcium. They concluded that these waters had entered intake sinks about Eutawville and flowed southeastward to emerge in the region of marshy bays as fountaining springs. Since sinkholes are also found in the midst of bay areas in some localities and typical oval bays in the midst of sinkhole groups elsewhere, and since the two forms are so abundant that one cannot start from an area of bays and travel very far in any direction without encountering groups of sinkholes, it is difficult to be sure that the observed geographic arrangement is anything more than a chance relationship. About all we are justified in saying is this: While the observed distribution of areas where typical sinkholes predominate and areas where typical oval bays predominate is not sufficiently striking to have probative value, it is suggestive of the possibility that sinkholes tend to predominate in intake areas, bays in outlet areas. It would be a serious mistake, however, to conclude that descending waters always give rise to sinks alone, and ascending waters to bays alone. T h e true relationship appears to be less simple. The frequent intimate intermingling of typical sinks and typical bays in the same locality, and the observed gradations

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from sinks to bays, suggest that while descending waters may favor the development of sinks, and uprising waters the development of bays, both types of circulation may often play a significant role in the development of both types of surface form. T h e whole picture of solution in relation to bay development seems to acquire coherence and probability if we imagine that rain, descending upon a coastal plain composed of interfingering lenses of less permeable and more permeable material, enters most freely the more permeable layers. T h e water then flows seaward beneath overlapping layers of less permeable material, until thinning out of the latter permits it to rise. As the water is now under hydrostatic pressure, it may reach the surface through permeable beds or through fissures or other openings leading upward. If the permeable beds are also soluble, ordinary sinkholes and other karst features will develop throughout the intake area. Should the surface of the plain at the intake area slope seaward so uniformly that surface runoff enters the developing sinkholes chiefly from one side, the sinks may tend to become elongated in the direction of the surface slope. Since most plains are irregularly undulating in detail and local runoff in such cases must take highly variable courses, it is doubtful how far sinks developing in the manner indicated would show parallelism in axial direction. T h e detailed form of sinks in the intake areas will depend in part upon the physical and chemical composition of the soluble bed and on whether it is covered by other permeable but insoluble material. If the soluble material outcrops on the surface, the sinks may have sharply defined margins and steep walls where the material yields readily to direct solution by running water descending joints or other openings, but not to atmospheric weathering or to slow seepage through the mass. Where weathering and disintegration due to seepage are effective, the sinks may enlarge rapidly and develop gently sloping walls which grade imperceptibly into the surrounding plain. If the soluble formation is covered by a permeable but insoluble layer of some thickness, the sink may have sharp margins and steep walls if the mass of the surface layer is strongly coherent and breaks away in fragments chiefly by undermining as soluble material below is removed. If the surface layer

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is relatively incoherent or wholly unconsolidated, and slumps or washes freely to a low angle as fast as soluble material is removed from beneath it, the resulting sinks will be greatly enlarged and exhibit gently sloping walls with indefinite boundaries. Such a depression may have the essential characteristics of an oval bay, and will then be classed as such. In all cases, water may stand in the sinks when the groundwater level is high or when underground outlets become blocked. There is, however, no necessary or normal relation between sinks and groundwater level in the intake areas, nor do lakes occupying sinks in those areas ordinarily have surface outlets. Conditions must be notably different in the outlet areas where artesian waters are rising to the surface through permeable beds. If the permeable beds at such outlet areas are also soluble, uprising currents may dissolve adjacent material to give open conduits debouching at the surface. So long as artesian water pours from the conduit, it is recognized merely as an artesian spring. But should changes in groundwater circulation cause cessation of flow from the conduit, it will be known simply as a sink. From being an "outlet sink" it may now become an "intake sink" carrying surface water under ground. T h e detailed form of artesian outlet areas will vary with the character of the surface beds in much the same way as sinks vary in the intake areas. Where the surface formation is more or less massive and does not readily disintegrate under the influence of weathering or seepage of water through the mass, the outlets will tend to have sharply defined margins and steep walls. Where the surface formation yields readily to atmospheric weathering or to seepage, or is relatively incoherent or wholly unconsolidated, the outlet areas will tend to have indefinite outer margins and very gently sloping sides. Where the surface formation is loose sand, or material, such as sandy loam, which readily disintegrates into loose sand, conditions in the outlet areas are favorable to the development of exceptionally large and shallow depressions. As we have seen in an earlier chapter, artesian springs bubbling u p through surface sands saturated with the groundwater of an undissected coastal plain tend to develop shallow spring basins of very large

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diameter. This is because the saturated sand flows in from all sides, while waters escaping through surface outlet channels carry off the finer and more soluble components of the mass. These large but comparatively shallow basins, occupied by lakes in their initial stages, elongated prevailingly in a direction parallel to that of groundwater flow or artesian flow or in intermediate directions, and developed in sand or easily disintegrated sandy loam and therefore most likely to have sandy beach ridges and rims of wind-blown sand about their margins, are the typical oval bays in their ideal form. In such forms solution may have played but a minor role in developing the basins. On the other hand, it is obviously possible that solution may in other cases affect the development of the basins in varying degrees, and do so not only when the surface formation is soluble. Once the basins are developed, and groundwater level is subsequently lowered due to incision of streams well below plain level, any waters concentrated in the basins and percolating downward may continue the process of solution. If a soluble subsurface bed is widely affected by uprising waters, or by surface waters descending from the basins after groundwater level has been lowered, with consequent development of caverns or broad sinks, overlying beds must slump into depressions produced in the soluble formation. If there is a thick cover of overlying sands, the surface topography may not clearly reflect the type of sinkhole topography below. A very small opening in depth may give rise to a very large sag in the surface of a thick overlying deposit of loose sand, thus producing a bay in the development of which the role of solution is effectively obscured. But if the cover of sand is thin or if the superficial formation is a sandy loam or other fairly coherent material, the surface topography may reveal what has happened in depth with varying degrees of perfection. Thus we may find, in different regions having somewhat different geological conditions, all possible transitions from basins in deep sand which do not resemble sinkholes at all to basins in sandy loam or other material which are not distinguishable from ordinary sinks. This is what we seem to have in the case of the so-called craters of the Carolina coast and adjacent portions of Georgia. Only when solution is recognized as

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having played a highly variable role in bay formation, often of dominant importance but sometimes apparently negligible, do we find an adequate explanation for all of the observed facts. Even where solution played a prominent role in bay formation we cannot expect to find proof of that fact in the character of waters issuing from the bays today. If artesian spring waters are captured before being diluted with lake or other waters of meteoric origin, they might show high calcium content if solution of limestone be still in progress. Berkey and Kerr found that upwelling spring waters from the Santee limestone area of South Carolina contained 72 to 87 parts of CaO per million, whereas waters from several lakes and marshy bays, collected by Howard and Wheeler after periods of heavier rainfall than usual, showed only 4 to 10 parts per million. In general both the artesian spring action and the solvent action invoked by the hypothesis belong to a period that is past. Where solution operated upon material less solvent than limestone, as for example arkosic sands, the proportion of mineral matter in solution need never have been high. Slow solvent action operating over a long period of time could accomplish all the effects observed. Waters now issuing from the basins, while of such volume as to suggest contributions of artesian origin in some cases, include an unknown proportion of meteoric water, which in wet seasons may be very large.

XIII T h e Lacustrine Phase of the Hypothesis E M U S T next examine the third phase of the artesiansolution-lacustrine-aeolian hypothesis of bay origin. T h e first question to claim our attention is the following: Are there now existing, in the Carolinas or elsewhere, lakes occupying shallow basins or craters identical in character with the basins occupied by typical marshy bays? T h e question must be answered in the affirmative. There are, in the first place, lakes occupying such oval depressions as Swallow Savanna, Peeples quadrangle, South Carolina, with its remarkably perfect rim of white sand. Green Savannah Lake, Allendale quadrangle, South Carolina, may be another example, but whether this northwest-southeast-trending oval has a sandy rim is not known to the writer. T h e same is true of Horse Pond, partially filling one of a group of three northwest-southeast-trending oval basins on the Varnville quadrangle, South Carolina. Many depressions shown on topographic maps as irregular in outline and devoid of water are found on aerial photographs and in field examinations to have elliptical or ovoid shapes and to contain ponds or lakes at least in seasons of moderate rainfall. Some might hesitate to class these and similar lake basins as true bays because they show certain features characteristic of large sinks. No such doubt can attach to the remarkable series of lakes in Bladen County, North Carolina, studied by Prouty and his associates and discussed in earlier pages of the present volume. Topographic quadrangles for this region are not yet available, but the lakes are well shown on the Bladen County soil map and still better on aerial photographs (Figs. 29, 32, and 33). White Lake (southeast corner of Fig. 29) occupies a typical shallow oval basin measuring more than two miles in greatest diameter and trending northwestsoutheast. A "fountaining spring" on its floor contributes significantly to the lake waters which escape through a surface outlet

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Lacustrine Phase

channel at the northwest. A b o u t the southeastern quadrant of White Lake there is a well-developed rim of white sand forming a broad, low ridge. T h e basin is a typical bay except that it is occupied by a lake instead of by a peat-bog marsh. But it is a lake in process of being transformed into a peat bog, encroachment of

FIGURE 43: SE end of Jones Lake, Bladen Co., N.C., showing rim of white sand bordering SE quadrant of its basin. This picture illustrates lacustrine stage of normal bay development. (Photograph by Girard Wheeler.) the latter upon the open water being visible in the aerial mosaic. Singletary Lake, southeast of White Lake, likewise occupies a shallow oval basin nearly two miles long and oriented in a northwest-southeast direction. It drains through a surface outlet to the southeast. A b o u t the southeastern quadrant there is an excellent rim of white sand 5 feet high and 250 feet broad. Here again we have a typical bay basin occupied by a lake. Jones Lake (Fig. 29, S 300 W of center of mosaic, and Fig. 43), northwest of White Lake, is only a little smaller than Singletary

Lacustrine Phase

277

Lake. It occupies an elliptical basin trending northwest-southeast and is drained toward the southeast through an artificial channel excavated in the bottom of a natural surface outlet partially blocked by sand. This sand is part of a conspicuous rim (Fig. 43) some 5 feet or more high in places and very broad and irregular due to dune migration, bordering the southeast quadrant of the basin. Like its neighbors, Jones Lake occupies a typical oval bay depression in which encroaching peat bog has reduced by more than half the original expanse of open water. Salters Lake (Figs. 29 and 32) illustrates a somewhat earlier stage in bay evolution, the elliptical basin in this case being only about half filled with peat bog. The waves of dune sand advancing eastward under impact of dominant westerly winds are strikingly shown about the southeast quadrant of the basin and part way into the northeast quadrant. The outlet channel to the south is clearly visible in the aerial photograph (Fig. 32). According to the soil map, Bakers Lake, about the same size as Jones Lake and located some twenty miles to the northwest, is in all essential respects a replica of the latter. The map shows a surface outlet toward the south, and about the southeast quadrant of the basin a band of the same type of sand as is found about the southeast quadrants of the lake basins previously described. Although Bakers Lake was not visited by the writer, there seems no reason to doubt that it occupies a typical "oval bay" basin. Suggs Mill Pond (Figs. 29 and 33), some five miles east of Bakers Lake, is a larger body of water than any of those described. It occupies an oval basin trending northwest-southeast and measuring nearly two and a half miles in major diameter. The soil map shows a band of sand about the southeastern part of the basin similar to that found about the southeast quadrants of the other lakes described, except that the band is represented as being double in places and does not continue as far up the northeastern side of the basin as in the other cases. The aerial photograph (Fig. 33) shows that the sand forms at least eight beach ridges in places and a broad belt of dune sand about the southeast quadrant of the basin. Through the surface outlet near the southern end of the lake, Dr. Girard Wheeler found a greater outflow of water than

278

Lacustrine Phase

from any of the other lakes and reported a strong inflow of water from "fountaining springs" on the floor of the basin. Once again we have a typical "oval bay" basin occupied by a lake into the waters of which peat bog has advanced far from the northwestern shore. T h e examples cited are sufficient to illustrate the fact that many shallow oval basins, apparently identical in character with typical oval bays occupied by marshes, contain lakes. It is difficult to escape the conclusion that these examples represent an early stage of bay development and that bays now occupied by peat bogs with marshy surfaces formerly contained lakes. LAKES FORMERLY M O R E

ABUNDANT

T h e conclusion just stated leads directly to our second question: Is there any evidence to support the view that typical oval bays now filled with peat bogs did in fact formerly contain open water? There are several lines of evidence which point strongly in this direction. O n earlier pages reference has been made to the fact that the inner margins of bordering sand rims, next to the marsh, are often steeper than surfaces of the rims farther back. It repeatedly happens that a bordering rim, descending toward the marsh with very moderate slope, will suddenly steepen just before contact with the marsh. Where examined, there was no evidence of spring sapping or other present action which would account for the increase in slope. Field studies convinced the writer that he was looking at ancient wave-cut cliffs. T h e term "cliff" is here used in its geomorphic sense, not its popular sense, for loose sand cannot long maintain a steep slope and angles of slope in the so-called cliffs were very low. T h e cliffs have apparently escaped the observation of earlier students of bay origin and attracted the writer's attention only when he began making systematic traverses across typical rims in an effort to discover their origin. While it is true that many bay margins do not, so far as known, exhibit the feature in question, this fact is not prejudicial to the hypothesis of lake occupation. O n many lakes the waves may not have cliffed the bordering rims, and on others cliffs formed long ago may have

Lacustrine Phase

279

slumped or weathered down to merge imperceptibly with the general lakeward slope of the rim. Another strong indication that open water preceded the present marshes is found in the nature of the multiple rims bordering many of the bays. These have been fully described on earlier pages, where it was shown that multiple rims within the basins can be satisfactorily explained only on the hypothesis that they are beach ridges produced by wave action. In form they are identical with ridges of sand cast up by waves along the shores of existing lakes. They are normally concave toward the open bay and, at their ends, curve toward tangency with the shore to which they are attached or of which they are extensions. They sometimes end in free spits and sometimes form bars across what were evidently reentrant embayments of the shore (Fig. 1). They often give evidence of having formed as successive shore ridges about a shrinking water body and sometimes indicate a sudden drop of the water surface to a lower level. In all their relations they bear convincing testimony to the former existence of lakes in those marshy bays which contain such ridges. T h e absence of beach ridges from other marshy bays does not imply that such bays did not formerly contain lakes. Beach ridges large enough to be preserved must have formed in the past, as now they form, only where special combinations of circumstances provided favorable conditions for their development. Furthermore, beach ridges when formed are ephemeral features and normally are cut away once a shore has been fully graded. In many of the basins earlier containing lakes, they may never have formed or may have formed and later been destroyed. T h e nature of the material occupying some of the marshy bays indicates the former presence of lakes. In a few cases sediment, unlike that of the Coastal Plain formations and apparently of lacustrine origin, has been encountered at the bottom of peat bogs occupying oval bays. Studies by Buell of peat formation in several bays, cited in Chapter III, confirmed the former presence of open water. Lakes showing all stages of peat advancement into open water have been cited above, and confirm the view that peat forma-

28O

Lacustrine Phase

tion and marsh growth have been progressive developments, proceeding outward from the shores of former lakes. In the nature of the case it is not possible to prove that all marshy bays were formerly occupied by lakes. As in our study of solution effects, all we can do is to show that lacustrine conditions played an important role in the development of many typical oval bays and presumably played an important part in the history of many others. Whether a lacustrine stage occurred in the history of every true bay depends on how we define "true bay." It is conceivable that oval basins oriented northwest-southeast and containing marsh deposits could be formed without a lacustrine stage. Such basins would not be likely to possess typical sand rims and perhaps should not be classed as true bays. If we limit the expression "true bay" to those marshy depressions which have formerly been occupied by lakes, then by definition every true bay has had a lacustrine stage. But if we apply the expression to all oval depressions oriented in a northwest-southeast direction, occupied by marsh, and bordered by rims of sand, then all we can say is that in the development of such features lacustrine conditions have played a widespread and important but not necessarily essential role.

XIV The Aeolian Phase of the Hypothesis

T

H E F O U R T H and last phase of the artesian-solutionlacustrine-aeolian hypothesis of bay origin must now be subjected to critical examination. T h e first question demanding consideration in this part of our study has been phrased as follows: Are there elsewhere in the world basins bordered by complete or partial rims of sand reasonably attributed to aeolian deposition? BASINS BORDERED BY SAND RIMS

Such rim-bordered basins are by no means uncommon. Blowouts bordered by dunes in areas subjected to wind erosion are miniature examples frequently encountered. In Texas and other parts of the southwestern United States countless small circular, oval, and irregular depressions are bordered by rims, which are usually inconspicuous but sometimes prominent enough to show on very detailed contour maps. (See, for example, Aldine and Humble quadrangles, Texas.) T h e rims have been explained, but whether correctly or not the writer does not know, as the result of wind deposition of material blown from the basins. In the region south of Corpus Christi, Texas (Armstrong quadrangle), many shallow basins holding permanent or temporary lakes have very prominent ridges prevailingly along their northwestern borders. T h e dominant sand-drifting winds are here from the southeast, and field examination by Wallace E. Pratt and the writer in 1926 led to the interpretation that these winds have built the ridges with fine sediment blown from the lake floors or their borders. T h i s interpretation has been confirmed by the fuller studies of W . Armstrong Price. 1 In 1902 the writer published a brief account 2 of saline 1 W. Armstrong Price, Role of Diastrophism in Topography of Corpus Christi Area, South Texas. Amer. Assoc. Pet. Geol., Bull. No. 17, 907-962, 1933. See pp. 932-

935 and 945 946-

2 Douglas Johnson. Notes of a Geological Reconnoissance in Eastern Valencia County, New Mexico. Amer. Geol., «9:80-87, 1902.

282

Aeolian Phase

lakes in eastern Valencia County, New Mexico, which are bordered by ridges of wind-deposited silt and sand so high that travelers have followed a road passing many of the lakes without discovering their existence. I^ke Michigan is a striking example of a large lake basin bordered on the south and east by extensive deposits of windblown sand. Examples could be multiplied, but this is scarcely necessary. T h e deposition of wind-blown sand about lake basins to produce rims of greater or less magnitude is a phenomenon of such common occurrence that the point need not be labored. SAND TRANSPORT

IN T H E B A Y

COUNTRY

T h e second question demanding our attention is this: Is there evidence of aeolian transport of sand from basins in the Carolina bay country so extensive as to account for the building of dune ridges about their margins? Here again the answer is in the affirmative. T h e student of the Carolina bays who examines large numbers of them on the ground cannot fail to be impressed by the evidence of wind transport of sand outward from the basins even where the country is most heavily forested. Some account of this phenomenon has been given on an earlier page, but it may be emphasized here that the red and buff loams so frequently exposed at the surface of the Coastal Plain are often found to be thinly coated with white wind-blown sand as one approaches the borders of the bays. T h e source of the sand cannot be doubted, for even where there is no true rim of sand the abundance of the deposit increases toward the bays and decreases as one goes away from their borders. As previously noted, this coating of wind-blown sand, when it rests upon a low swell or ridge of Coastal Plain sediment close to a bay, gives a false appearance of a prominent dune ridge. The true condition is often revealed where clods of red or buff loam are turned up by the plow in cultivated fields. T h e invasion of plowed fields by wind-drifted sand moving outward from the bays has been observed on all sides of these basins, but rarely to any marked degree about their northwestern borders. This indicates either that the northwestern ends of the bays were poor sources of sand supply, which we have reason to believe was true, or that winds from the east and southeast were not

Aeolian Phase

283

dominant in the bay country, which we also have reason to believe. Where no good rims of sand exist about any part of a bay, wind-drifting of white sand over plowed fields is frequently most conspicuous about the southeastern quadrant, suggesting that adjacent parts of the bay were good sources of sand supply and that winds from some westerly direction were dominant. In some cases the extent of sand invasion is very limited, plowed fields becoming red in color, loamy in composition, and full of clods within fifteen or twenty feet of the bay margin. Elsewhere the sand quite obscures the loam close to the bay, thinning out gradually to disappear entirely some hundreds of feet away. In more than one case freshly plowed fields show a still fresher film of wind-drifted sand thinly coating their surfaces, convincing testimony to continuing if only occasional aeolian transport and deposition. As one example of wind-drift phenomena we may cite observations made on the narrow strip of land separating Junkyard Bay from Islanded Bay on the Manning quadrangle, South Carolina. T h i s neck of land is a faint swell of the Coastal Plain formation rising a few feet above the marshy bays on either side. Lying at the southwest border of the Junkyard oval basin and at the northeast border of the Islanded oval, the strip of land is not at the normal locus of major sand accumulation for either but is placed where some sand deposit might be expected in both, judging from the known characteristics of oval bays as set forth on earlier pages. A traverse of the region shows that toward the east of the strip, at the southeasternmost point of Junkyard Bay, there is no distinct rim. T h e nearly flat Coastal Plain slopes very gently down toward the bay, this slope being covered with wind-blown sand. In places the cover is thick enough to make the road very sandy, but most of the road was muddy at the time of the writer's visit. T h e northeastern border of Islanded Bay lacks a distinct rim, but here also wind-blown sand is in evidence, being visibly drifted over plowed fields full of clods. One may start from the margin of Islanded Bay on a thin wind-drifted sand cover and walk northeast across plowed fields with wind-drifted sand gradually getting scarcer, then over cloddy fields free of aeolian deposit as he crosses a low swell of the Coastal Plain, and thence northeastward down

284

Aeolian Phase

the faint slope toward Junkyard Bay with wind-drifted sand reappearing and increasing in amount until it is a prominent feature near the latter depression. Farther west the traverse is similar, except that there wind-drifted sand is not much in evidence near Junkyard Bay, the last end of the traverse being through marshy pine forest. The wind-drifting of sand is not limited to the vicinity of oval basins with which this discussion is chiefly concerned. Where marshy basins are highly irregular, irregular bands of wind-drifted sand have been observed. The upland bordering river valleys occasionally is coated with sand apparently brought by wind from sandy stretches along the stream. Where other sources of loose sand are readily available for wind transport, great quantities may be moved and may even invade neighboring bays. An illustration of such invasion is shown in Figure 17, where a mass of sand now partially covered with vegetation has moved into the northwestern side of Big Bay, four miles north of Pinewood, South Carolina. It will be noted that this sand movement indicates winds from a westerly sector, such as would cause major sand accumulation about the southeastern quadrants of bays wherever these contain the source of the sand. Migration of sand away from the southeast quadrants under the influence of westerly winds is beautifully shown in Figures 29 and 32. DIRECTION

OF D O M I N A N T

WINDS

The third question to claim our attention is far more difficult to answer. In setting forth the artesian-solution-lacustrine-aeolian hypothesis of crater origin in an earlier chapter we stated that the aeolian phase of that hypothesis would account for the observed major concentration of sand about the southeast quadrants of the oval craters "providing we assume that winds from the sector northwest through west around to southwest (a) are stronger than those from other directions, or (b) blow for a longer time, or (c) blow while sand is drier and more easily moved than when other winds are blowing." T o answer the question as to whether there is valid evidence in support of any or all of these three possible assumptions, we must now enquire into the velocities and

Aeolian Phase

285

duration of winds and the relation of these winds to precipitation, as recorded at stations in or near the region where the oval craters with bordering rims are best developed. Difficulties Confronting Enquiry. Such an enquiry encounters serious obstacles. Adequate records of wind velocities and durations are available for relatively few stations, none of which is in the heart of the bay country. Wilmington, North Carolina, is near the northeast corner of the area in which these craters and their rims are most abundant. Columbia, South Carolina, lies just on the northwestern edge of the area. These are the only two stations that can be said to be in the bay country proper for which adequate records are available. Raleigh is nearly fifty miles north of the northwest corner of the region of abundant bays; Augusta fifteen miles northwest of the southwestern border; Savannah and Charleston forty to fifty miles southeast of the southeast border, measurements in all cases being from main area of numerous bays, not from nearest scattered bays. Even on the flat Coastal Plain two localities forty or fifty miles apart or even fifteen miles apart may experience significantly different air movements and precipitation. Yet records of stations fifteen to fifty miles outside the bay country have value in so far as they offer concordant testimony as to reasonably similar conditions over an extended area. The six localities cited are the only ones for which significant records are obtainable and which at the same time are close enough to the bay country to have value in our study. An even greater difficulty arises from the fact that easily available records of the Weather Bureau are summarized in averages for periods of a month or a year. These averages may mean much or little, according to circumstances. If records over a period of ten years show that at a given station southwest winds blow for an average of 200 hours at an average hourly velocity of 8 miles during the month of January, whereas during the same period northwest winds blow on the average only 100 hours at an average hourly velocity of only 6 miles, one might assume that the southwest winds would be dominant in determining the direction of major sand transport. But if the southwest winds have a relatively constant velocity which never rises much above the average

286

Aeolian Phase

figure of 8 miles an hour, they will be quite incompetent to move sand of even moderate coarseness; whereas if the average of 6 miles an hour for the northwest winds is compounded of a goodly number of hours at 15 or 20 miles an hour with many more hours at 2 to 4 miles, much sand having a coarseness of .5 mm. or under may be moved when the stronger winds are blowing. Even if the figures could be accepted at their face value and compared when both duration and velocity in one case are greater than in another, how is one to compare them when one of the variables is larger, the other smaller? Which will be the more effective in moving sand, winds blowing 100 hours with an average velocity of 8 miles an hour, or winds blowing 150 hours with an average velocity of 6 miles an hour? T h e "prevailing wind directions" for the year and for each month of the year, based on records covering periods varying from a few years to sixty years or more, are published for many stations in the bay country. But these may or may not include a significant proportion of winds strong enough to move sand. They may, furthermore, represent a slight but wholly insignificant mathematical excess in duration of winds blowing in the direction indicated, and such excess may be due to purely local deflection of air currents or the excess may be apparent, not real, due to occasional instead of continuous observations. At Florence in the bay country of South Carolina there are two weather observation stations only one mile apart. T h e published official Tecords for Florence give the annual prevailing wind direction as "southwest" at one station, "northeast" at the other. Maximum recorded velocities for each month and for the year are published for some stations and from these records it may be seen how far direction of strongest wind may differ from direction of prevailing wind. At Charleston the prevailing winds are from the southwest eight months out of the twelve, but for no month is the maximum recorded velocity from that direction. Indeed, at this station prevailing winds and winds of maximum velocity have different directions every month in the year. It is quite conceivable either that a single wind of hurricane violence might move more sand than the prevailing winds of eight months

Aeolian Phase

287

or that the long-continued effect of the milder winds might effect a total transport of sand exceeding that of one or more exceptionally high winds of short duration. Charleston Records Not Typical of Bay Country. Despite these difficulties, if we examine published meteorological data with due appreciation of the limitations to which their interpretation is subject, we may gain information of real value in forming a judgment as to the probable major direction of sand transport by wind action, even if we fall short of a mathematical demonstration of what that direction must be. In attempting such a study for the bay country, we are immediately confronted by the fact that of the six stations previously cited as providing meteorological data sufficiently full for this part of our enquiry and lying close enough to the bay country to be possibly significant of conditions obtaining there, one provides records strikingly out of harmony with those of the other five. T h e records for velocities and duration of winds at Charleston, South Carolina, are so peculiar as to suggest the disturbing influence of local conditions. While prevailing winds are reported by this station as being from the southwest eight months out of the twelve, the winds of highest average hourly velocity are, unlike those at the other stations, from some easterly quarter (northeast or east) every month in the year. It will be noted that Charleston is the most truly maritime of the six stations in question. Of the other two stations located near the sea, Wilmington is some twenty miles up the Cape Fear River and nearly 10 miles from the ocean in an air line; Savannah is from twelve to fifteen miles up the Savannah River and ten miles (air line) from the broad embayment of Tybee Roads. Charleston, on the other hand, is located directly on the shores of such an embayment, on a peninsula projecting well out into it. Even a few miles of plains country, when covered by forests or large buildings or both, is sufficient to reduce wind velocities notably, through friction and disorganization of air currents. It seems reasonable to suppose, therefore, that a station exposed to winds blowing across open water will record abnormally high velocities for those winds. T h e landward component of alternating land and sea breezes, adding their strength to winds from

288

Aeolian Phase

easterly quarters, might conceivably produce a slightly greater effect at the coast than ten miles inland. An enquiry addressed to Mr. J . E. Lockwood, Meteorologist of the United States Weather Bureau stationed at Charleston, elicited the following opinion: "Charleston being right on the coast, there would be every reason to expect our strongest winds from an easterly direction because they would be from the open sea and not reduced by friction of low hills, forests, large buildings, etc." Mr. Lockwood also emphasized the fact that the location of Charleston with respect to paths of hurricanes moving northward and northeastward along the south Atlantic coast would tend to give unusually strong winds from the northeast and east, the effects of which would be fully felt where these winds blow across open water. He further observed that "we feel the effect of the land and sea breezes to a greater extent than the other cities do." It is obvious that under these circumstances meteorological data recorded at Charleston, a "maritime station" located on the coast forty to fifty miles from the nearest border of the bay country, cannot be expected to reflect meteorological conditions in that country. On the other hand, data recorded at the five "inland stations," even though within ten miles of the sea and in some cases forty or fifty miles from the bay country, can reasonably be expected to give a fairly accurate idea of conditions in that country, when due account is taken of the fact that the five stations are located on all sides of the region where bays are most abundantly developed and of the further fact that records from these five stations, while not identical, are harmonious to a truly remarkable degree. Directions of Maximum Average Hourly Wind Velocities. From detailed tabulated data kindly provided for the purpose by Dr. W. R . Gregg, Chief of the United States Weather Bureau, it is possible to determine the directions from which the maximum average hourly wind velocity has been recorded for different months of the year at each of the five stations in question. At Wilmington, North Carolina, the maximum average hourly wind velocity as determined for each month is from the southwest nine months out of the twelve. At Columbia, South Carolina, these

Aeolian Phase

289

strongest average winds blow from the southwest eleven months out of the twelve. These are the two stations closest to the region of the most abundant oval bays and, since the winds in question are of long duration, since their average velocity is relatively high (6.5 to 11.7 miles per hour as compared with 2.3 to 8.7 for other directions), and since they blow both during the hottest months and also during the driest months of the year, there is reason to believe that they are more effective in moving sand than are winds from any other quarter. Even if we pass to the more remote stations, we find evidence that winds from the western sector (northwest, west, and southwest) have the greatest average strength. A t Raleigh, North Carolina, winds from the northwest have the highest average hourly velocities seven months out of the year, those from the southwest three months, making ten months annually that winds from some westerly quarter are on the average strongest. At Augusta, Georgia, the winds having the highest average hourly velocities come from the west ten months, from the southwest one month, making a total of eleven months annually that stronger winds come from a westerly direction. At Savannah, Georgia, these stronger winds come from the northwest four months, from the west four months, and from the southwest one month, a total of nine months annually from westerly quarters. T h u s for all five stations the winds having the greatest average strength month by month blow from some westerly sector for a very large proportion of the year. Directions of Prevailing Winds. Prevailing wind direction is probably far less significant than the direction of winds of greatest average strength, since weak winds blowing a long time may accomplish little or no sand transport. Nevertheless consideration of the directions of prevailing winds in the bay country is worth while, since we cannot exclude the possibility that winds blowing barely strong enough to move sand, but blowing for long periods of time, may determine the major direction of sand transport. Data on prevailing winds are available (in Climatic Summaries published by the United States Weather Bureau) for twenty-three stations located within the area of most abundant oval bays. From such data it appears that out of the twenty-three

290

Aeolian Phase

stations for which prevailing wind records are available over a period of years varying from eight to sixty, one reports the prevailing direction as north, one as northwest, three as west, three as northeast, six as south, and nine as southwest. Thus a majority of stations (thirteen) report prevailing winds from directions (northwest, west, and southwest) which would blow sand from lake beaches toward that part of the bay shores where sand is found in maximum quantity; and six additional stations report prevailing winds from a direction (south) which would account for the observed distribution of sand in view of the fact that there was, as we have seen, a deficiency of beach sand at the northwestern ends of the lakes and an excess at the southeastern ends. Against these nineteen stations reporting winds which might account for the observed sand distribution, must be placed four which would tend to accumulate sand about the southwestern shores, where rims normally are poorly developed or absent. One of these stations is Florence No. 2, only one mile distant from Florence No. 1, which reports prevailing winds from the opposite direction. The unsatisfactory nature of prevailing wind records has already been stressed. Bays with sand rims have been examined near all four of the stations reporting prevailing winds from the north and northeast, and in all cases the distribution of sand is identical with that observed where prevailing winds are from the southwest and west. It is therefore believed that dominant winds rather than prevailing winds are chiefly responsible for sand movement. Directions of Maximum Wind Velocities. Maximum wind velocities recorded over long periods of years may or may not be significant. If the maximum recorded velocity for a given month at a given place represents a single abnormal storm enduring for a brief interval only, it may have produced little effect, especially if the high winds blew when sand was wet. On the other hand, if such a record is representative of recurrent high velocities from the same direction, it may be very significant. Data published in United States Weather Bureau Climatic Summaries are here condensed for what they may be worth. At Columbia the winds of

Aeolian Phase

291

maximum recorded velocity as determined for each month came from the southwest in nine months out of twelve; at Wilmington and also at Raleigh these excessively high winds came from the northwest, west, or southwest nine months out of twelve; at Augusta, from the northwest, west, or southwest nine months out of twelve; and at Savannah, from the northwest, west, or southwest eight months out of twelve. T h u s the figures for maximum recorded wind velocities, as well as those for maximum average hourly velocities, and most of those for prevailing winds are what might be expected if winds from westerly quarters (northwest, west, and southwest) play a significant role in determining the distribution of sand rims about the oval craters. Directions of Dominant Winds. Since duration of winds as well as wind velocity helps to determine the direction of major sand transport, it will be interesting to determine how long as well as how strongly winds blow from different sectors. T h e sectors selected for comparison may be chosen on either of two bases. Assuming that sand was available for transport in equal quantities from all parts of the lake shores, winds from the sector northwest-west-southwest should have greater transporting power than those from the sector northeast-east-southeast, if the observed distribution of maximum sand accumulation is to be attributed to dominant winds. O n the other hand, if there was a greater concentration of beach sand along those shores bordering the southeastern halves or two-thirds of the lakes, winds from the sector west-southwest-south having greater transporting power than those from the sector north-northeast-east would account for the observed facts. It will be best to make the comparison on both of these possible bases. For this purpose the writer has determined, from detailed data kindly furnished by Dr. Gregg of the United States Weather Bureau, the total number of hours in the year that winds blow from each of the two sectors compared (next to last column of Tables 3 and 4), together with the range of mean velocities recorded for these winds (last column of tables). T h e first column of Tables 3 and 4 gives the three directions constituting each of the two sectors compared; the second column gives the lowest average hourly velocity (in miles per hour) determined

Aeolian Phase

2 9 2

TABLE

3

V E L O C I T I E S A N D D U R A T I O N OF W I N D S FROM T H E

SECTORS

N W - W - S W AND N E - E - S E

Direction

Lowest and Highest Average Hourly Velocities (in Miles per Hour) Recordedfor Any Month

Annual Mean of Average Hourly Velocities

Total Total Hours Hours in Tear for for Tear Sector

Range of Mean Velocities for Sector

WILMINGTON, N.C.

NW W SW NE E SE

2.3 - 5-4 4.2 - 8 . 2 6.0 - 10.3

3-7 6-3 8.0

4.96.2 5-3

6.1 7.2 6-3

7-A

8.7 7.6

NE E SE

1.990

4,011

3-7-

8.0

2,380

6.1 -

7.2

4,181

7.3 -

8.6

2,719

5.9-

7.6

1,073 914

393

R A L E I G H , N.C.

NW W SW

365

1,656

11.7

8.6

90

10.2

7-3 7.8

8.8 6.8

7.6 6.0

7-3

5-9

547

6.0 8.2 4-7 1 1 .7 5-7 '

4.8 6.4 8.4

791 1,007 >,537

3,335

4.8-

8.4

3,025

50-

6

3,333

5-5-

6 6

3,007

3-8-

5-5

5-2

5-55-9

6.6 5-44.8

970

1,015 2,196 1,512

660

COLUMBIA, S.C.

NW W SW

4.2

NE E SE

5-5 4-5 4-5

7-4 6.2

6-5

5-7

5°

1,871 609 545

NW W SW

4.4 4.6 4-5

6.9 8.5 7-5

5-5

1,756

5-8

NE E SE

4-7 3-8 3-3

6.2 4.8 4.8

5-5 4-2 3-8

5-1

-5

AUGUSTA, G A .

6.6

865 712 1,071 1,019 917

Aeolian Phase TABLE

Direction IVANNAH, GA. NW

Lowest and Highest Average Hourly Velocities (in Miles per Hour) Recorded for Any Month

293

3 (Continued)

Annual Mean of Average Hourly Velocities

Total Total Hours Hours in Tear for for Tear Sector

W sw

11.2

900

8.0 - 15. I 9.0 - 12.8

11.6 11.4

I.509

1,292

3»7°i

NE E SE

6.6 -

11.0 8-3 - 11.3

9-4 7-9 9-9

1,213 93' 729

2,873

7-2 - 15-3

9.2 - 10.7

Range of Mean Velocities for Sector

11.2 - 11.6

7-9"

9-9

for any month in the year, and also the highest, so that the range of these velocities may be known for each direction of the sector; the third column gives the mean of the monthly records of average hourly velocities, as determined for each direction for the entire year; and the fourth column gives the total number of hours during the year that winds blew from the direction indicated. Data in these first four columns are taken directly from manuscript tables furnished by the Chief of the United States Weather Bureau. From an inspection of these tables it is clear that at every station winds from the westerly (or southwesterly) sector blow both longer and stronger than those from the easterly (or northeasterly) sector, whether we make the comparisons on the first or the second of the two bases discussed above. T h e combined records of wind duration and velocity thus lend support to the conception that dominant winds from some westerly direction are responsible for major sand accumulation east of the long axes of the oval craters. T h e contrast between the duration and velocity of winds blowing from opposite sides of the oval craters does not always appear as great as the contrast between the quantities of sand found on their opposite borders. It is possible that the monthly and yearly

Aeolian Phase

294

TABLE

4

V E L O C I T I E S A N D D U R A T I O N OF W I N D S FROM T H E

SECTORS

W - S W - S AND N - N E - E

Direction

Lowest and Highest Average Hourly Velocities (in Miles per Hour) Recordedfor Any Month

Annual Mean of Average Hourly Velocities

Total Total Hours Hours in for Yearfor Year Sector

Range of Mean Velocities for Sector

WILMINGTON, N . C .

W SW S

4-2

N NE E

6-3 8.0 6.9

1,656

5-5

8.2 10.3 8-3

'>99° 835

4.481

6.3 -

8.0

5-4 4-9 6.2

7.6 7.2 8-7

6.6 6.1 7.2

1.459 1.073 914

3,446

6.1 -

7.2

W SW S

5-5 5-9 5-2

9.0 10.2 7-5

7-3 7.8 6.2

1,015 2,196 802

4,013

6.2 -

7.8

N NE E

5-7 6.5

8.2

5-4

8.8 6.8

6.7 7.6 6.0

1.045 1,512 660

3,217

6.0 -

7.6

W SW S

4-7 5-7 5-1

8.2 11.7 7-9

6.4 8.4 6-3

1,007 1,537 I,446

3.99°

6.3-

8.4

N NE E

4-7 5-54-5

5-9 7-4 6.2

5-2 6-5 5-1

9" 1,871 609

3,391

5-1 -

6.5

8-5 7-5 5-6

6.6

s

4.6 4-5 3-6

5-8 4.6

865 712 1,402

2,979

4.6-

6.6

N NE E

3-7 4-7 3-8

51 6.2 4.8

4-3 5-5 4.2

705 1,071 ^OIG

2,795

4-2-

5-5

6.0

R A L E I G H , N.C.

COLUMBIA, S.C.

AUGUSTA, G A .

W SW

Aeolian Phase

295

TABLE 4 (Continued)

Direction

Lowest and Highest Average Hourly Velocities (in Miles per Hour) Recorded for Any Month

Annual Mean of Average Hourly Velocities

Total Total Hours Hours in Tear for for Year Sector

Range of Mean Velocities for Sector

SAVANNAH, GA.

w sw s

8.0 - 15.1 9.0 - 12.8 8.9- 13.1

11.6

N NE £

6-4- 9-4 6.6 - 11.0 8.3-11-3

11.2

i»5°9 1,292 i,34i

4,142

8.0 9-4 7-9

842 1,213 93'

2,986

11.4

II. 2 -

11J

7-9" 9-'

averages of velocities conceal contrasts far more striking and that averages for the westerly (or southwesterly) sector include a very large proportion of winds strong enough to move sand, whereas averages from the easterly (or northeasterly) sector include a much smaller proportion of such winds. Influence of Moisture. W e must consider the possibility that another factor, conceivably of even greater importance, enters into the problem. T h i s is the factor of moisture. T h u s far we have considered the relative strength and duration of winds from different directions without paying attention to whether these winds blow when sand is dry or when it is wet. Moist sand is not readily picked up by winds and may suffer little or no transportation by even the most violent winds if these are accompanied or immediately preceded by rain. It thus becomes important to know the probable condition of the sand as to moisture content when winds blow from different directions. It is conceivable that long-time wet and dry periods might affect the distribution of sand in several ways. D u r i n g months of maximum rainfall enough moisture may be retained in the soil to prevent even a surface film of sand from becoming thoroughly dry on more than a few of the sunny days of such months, whereas during months of little rainfall the sand may be dry to consider-

2g6

Aeolian Phase

able depths and subject to transportation in large quantities most of the time. In the second place, the burning of grass and brush is more apt to take place in dry seasons, and, when such burning occurs about the margins of the bays, sand otherwise held in place may become subject to transport. Finally, a rise of groundwater level during and immediately following wet seasons may raise the level of water in lakes and marshy bays sufficiently to submerge beach sands which would be exposed to drying and transport during seasons of scanty rainfall when lake and marsh levels were lower. It thus becomes of interest to know the months of greatest and least rainfall and to discover whether the winds of greatest average strength (which we have found to come prevailingly from a westerly or southwesterly sector throughout the bay country) blow when the sand is dry and subject to easy transport. Precipitation records covering periods varying from eight to sixty years have been studied for twenty-eight stations scattered throughout the bay country. From these it clearly appears that the season of maximum precipitation in this region usually comprises the months June to August inclusive, although in some localities the rainy season is shorter, in others longer. The period of minimum precipitation usually follows immediately that of maximum precipitation, normally comprising the months of October, November, and December, but sometimes omitting one of these months and often extending through January. There is usually a shorter dry period in April, occasionally beginning in March or lasting through May. T h e differences between wet and dry months are fairly pronounced, the precipitation usually ranging from 414 to 7 inches in the wetter months as compared with l3 A t o 3V4 inches in the drier months. Direction and Strength of Winds during Dry Season. In Table 5 the precipitation records for the four driest months at each of twenty-eight stations in the bay country are compared with the direction of winds having the maximum average hourly velocity for these same months at the two nearest stations for which satisfactory data are available. We have already seen that these latter stations are either near the border of or from fifteen to

Aeolian Phase TABLE

297

5

PRECIPITATION R E C O R D S FOR THE F O U R D R I E S T M O N T H S A T S T A T I O N S IN T H E B A Y C O U N T R Y , C O M P A R E D W I T H W I N D R E C O R D S A T THE STATIONS FOR W H I C H S A T I S F A C T O R Y D A T A A R E

Four Driest Months

Average Precipitation

NEAREST

AVAILABLE

Direction of Maximum Average Hourly Wind at:

1 . WILMINGTON, N . C . WILMINGTON, N . C .

Mar. Apr. Nov. Dec.

3.29 2.76 2.07 3.04

SW SW SW SW

2. ELIZABETHTOWN, N.C.

Feb. Apr. Oct. Nov.

3.26 2.97 3.04 2.08

WILMINGTON, N . C .

RALEIGH, N . C .

45 mi. SE SW SW £ SW

80 mi. N NW SW NW NW

R A L E I G H , N.C.

WILMINGTON, N.C.

50 mi. N SW NW NW NW

75 mi. SE SW E SW SW

WILMINGTON, N . C .

RALEIGH, N . C .

65 mi. SE SW E SW SW

80 mi. N N E NW NW NW NW

R A L E I G H , N.C.

WILMINGTON, N . C .

75 mi. N N E NW NW NW NW

80 ini. SE SW SW E SW

3 . F A Y E T T E V I L L E , N.C.

Apr. Oct. Nov. Dec. 4.

3.28 2.86 2.24 3-28

LUMBERTON, N.C.

Jan. Oct. Nov. Dec.

3-35 3-'4 2.18 330

5 . RED SPRINGS, N.C.

Jan. May Oct. Nov.

3-38 328 2.19 2-39

298

Aeolian Phase TABLE

Four Driest Months

Average Precipitation

5 (Continued) Direction of Maximum Average Hourly Wind at:

6 . B E N N E T T S V J L L E , S.C.

Jan. Apr. Oct. Nov.

2.16 2.54 1.79 2.25

COLUMBIA, S.C.

WILMINGTON, N.C.

COLUMBIA, S.C.

WILMINGTON, N.C.

75 mi. SW SW SW SW SW

1 1 0 mi. E S E SW E SW SW

WILMINGTON, N.C.

COLUMBIA, S.C.

70 mi. E SW SW SW SW

100 mi. WSW SW SW SW SW

COLUMBIA, S.C.

WILMINGTON, N.C.

70 mi. WSW SW SW SW SW

110 mi. E SW E SW SW

WILMINGTON, N.C.

COLUMBIA, S.C.

80 mi. E SW SW SW SW

90 mi. WSW SW SW SW SW

90 mi. SW SW SW SW SW

100 mi. E S E SW SW E SW

7 . SOCIETY H I L L , S.C.

Jan. Oct. Nov. Dec.

3.19 3.11 2.25 3.29

8 . DILLON, S.C.

Jan. Apr. Nov. Dec.

3.03 3.12 1.89 3.12

9 . DARLINGTON, S.C.

Jan. Oct. Nov. Dec.

2.95 3.04 2.09 2.94

IO. MARION, S.C.

Mar. Apr. Nov. Dec.

3.45 3.18 2.15 3.71

Aeolian Phase TABLE

Four Driest Months II.

Average Precipitation

299

5 (Continued) Direction of Maximum Average Hourly Wind at:

F L O R E N C E , S.C.

Jan. Apr. Oct. Nov.

3.04 3.00 3.00 2.05

COLUMBIA, S.C.

WILMINGTON, N.C.

70 mi. WSW SW SW SW SW

IOO mi. E SW SW E SW

COLUMBIA, S.C.

WILMINGTON, N.C.

70 mi. W SW SW SW SW

105 mi. E SW E SW SW

WILMINGTON, N.C.

COLUMBIA, S.C.

70 mi. E N E SW E SW SW

1 1 0 mi. W SW SW SW SW

WILMINGTON, N.C.

COLUMBIA, S.C.

85 mi. E N E SW SW SW SW

95 mi. WNW SW SW SW SW

COLUMBIA, S.C.

WILMINGTON, N.C.

70 mi. WNW SW SW SW SW

1 1 5 mi. E N E SW E SW SW

1 2 . E F F I N G H A M , S.C.

Apr. Oct. Nov. Dec.

3.32 3.06 2.10 3.25

1 3 . C O N W A Y , S.C.

Apr. Oct. Nov. Dec.

3.07 3.17 2.26 3.34

1 4 . SMITHS MILLS, S.C.

Jan. Apr. Nov. Dec.

2.96 3.13 2.23 3.55

1 5 . KINGSTREE, S.C.

Apr. Oct. Nov. Dec.

2.85 2.72 2.09 3.09

Aeolian Phase

3°° Four Driest Months

TABLE

Average Precipitation

5 (Continued) Direction of Maximum Average Hourly Wind at:

1 6 . SUMTER, s . c .

Jan. Mar. Apr. Nov.

2.58 3-4« 2.07 1.85

COLUMBIA, S.C.

AUGUSTA, G A .

40 mi. WNW SW

100 mi. SW W W W W

sw

SW

sw

1 7 . COLUMBIA, s . c . COLUMBIA, S.C.

Apr. Oct. Nov. Dec.

3.07 2.48 2.09 3.04

sw sw

SW SW

l 8 . RIMINI, s . c .

Apr. Oct. Nov. Dec.

3.12 2.23 1.88 3.28

COLUMBIA, S.C.

AUGUSTA, G A .

40 mi. NW

90 mi. WSW W W W

sw

SW SW SW

w

1 9 . ST. M A T T H E W S , S.C.

Apr. Oct. Nov. Dec.

3.12 2.55 2.00 3.15

COLUMBIA, S.C.

AUGUSTA, G A .

25 mi. NW

75 mi. WSW W W W W

sw

SW SW

sw

2 0 . FERGUSON, S.C.

Apr. Oct. Nov. Dec.

3.06 2.92 2.14 3.09

COLUMBIA, S.C.

AUGUSTA, G A .

60 mi. NW SW SW

IOO mi. W W W W W

sw sw

Aeolian Phase

301

TABLE 5 (Continued) Four Driest Months

Average Precipitation

Direction of Maximum Average Hourly Wind at:

2 1 . ORANGEBURG, S.C.

Apr. Oct. Nov. Dec.

2.87 2.11 1.53 3.11

COLUMBIA, S.C.

AUGUSTA, GA.

35 mi. NNW SW SW SW SW

65 mi. W W W W W

COLUMBIA, S.C.

AUGUSTA, GA.

45 mi. NNW SW SW SW SW

70 mi. W W W W W

COLUMBIA, S.C.

AUGUSTA, GA.

50 mi. N SW SW SW SW

65 mi. W W W W W

AUGUSTA, GA.

COLUMBIA, S. C.

40 mi. W W W W W

45 mi. NNE SW SW SW SW

AUGUSTA, GA.

SAVANNAH, GA.

50 mi. NW W W W W

65 mi. SSE W NW W W

2 2 . BOWMAN, S.C.

Jan. Oct. Nov. Dec.

3.26 2.42 1.99 3.22

2 3 . EDISTO, S.C.

Apr. May Oct. Nov.

3.12 3.10 2.31 2.02

2 4 . BLACKVILLE, S.C.

Jan. Apr. Oct. Nov.

3.31 3.31 2.71 2.03

2 5 . ALLENDALE, S.C.

Apr. Oct. Nov. Dec.

2.60 2.35 1.69 2.74

go2

Aeolian Phase TABLE

Four Driest Months

Average Precipitation

5 (Continued) Direction ofMaximum Average Hourly Wind at:

2 6 . G A R N E T T , S.C.

Jan. Apr. Oct. Nov.

3.17 3.59 2.34 2.49

SAVANNAH, GA.

AUGUSTA, G A .

AUGUSTA, GA.

SAVANNAH, GA.

A U G U S T A , OA.

SAVANNAH, GA.

40 mi. SE NW W NW W

70 mi. NW W W W W

2 7 . WAYNESBORO, GA.

Apr. Oct. Nov. Dec.

2.67 2.47 2.29 3.04

25 mi. N W W W W

90 mi. SE W NW W W

2 8 . MILLEN, GA.

Apr. May Oct. Nov.

2.90 3.15 2.50 2.15

45 mi. N W W W W

70 mi. SE W W NW W

fifty miles outside of the bay country; but comparison with their records has value when stations lying in different directions from a given locality report average stronger winds from the same or a neighboring sector of the compass. Where adequate precipitation and wind records are both available for the same station, as in the case of Wilmington, North Carolina, and Columbia, South Carolina, such records stand alone. Examination of Table 5 indicates that winds from the westerly sector (northwest-west-southwest) are overwhelmingly dominant at every station in the bay country during that part of the year when the least precipitation falls. The tabulated records from the two nearest stations having satisfactory data on the directions of

Aeolian Phase

303

maximum average hourly wind velocities for each dry month total 216. Of these, 11 are records of winds from the east; the remaining 205 are records of winds blowing from the northwest, west, or southwest, records from the latter two directions being in the overwhelming majority. Thus the stronger winds blow from westerly quarters when there is a presumption that sand is, on the average, drier than at other times of the year, when grass and brush fires are presumably most apt to set additional sand free for transportation, and when groundwater level is apt to be lower than usual thus exposing maximum quantities of beach sand to movement by winds. Effect of Grass and Brush Fires. Investigation reveals that the presumption just mentioned is well founded except in one respect (to be discussed later). Precipitation records for the 26 stations in the bay country show that October is a dry month at 23 of them, that November is a dry month at all 28 stations and the driest month of the year at 25 of them, and that December is a dry month at 19 stations, although never so dry as November and, with one exception, never so dry as October. Thus OctoberNovember are preeminently the dry months in the bay country, with the dry period continuing into December. April is a dry month at 23 stations out of 28, with the dry period sometimes beginning in March. According to Ward,3 all the Atlantic coast states lying between Virginia and Florida have this "well-defined . . . minimiim [rainfall] in middle or late autumn (October or November) . . . and a secondary minimum in spring (April)." Enquiry addressed to the Soil Conservation Service elicited the information4 that "The season when [grass and brush] fires are apt to be most prevalent will be after the killing frosts have checked the growth of vegetation, which in this region [Coastal Plain region of North and South Carolina] will be between October 15 to the latter part of November; and again in the spring before growth starts, depending to some extent on the season but usually from February 15 to the middle or latter part of March." 3

Robert DeCourcy Ward. Climates of the United States. 518 pp., Boston, 1925. See p. 189. 4 Walter V. Kelt, personal communication.

304

Aeolian Phase

T h e present writer has observed many brush fires in the bay country during both March and early April. It thus appears that the first-mentioned period of grass and brush fires corresponds closely with the driest part of the year and with a period of dominant westerly (northwest-west-southwest) winds; while the second period of grass and brush fires comes just before or during the second dry season of the year when again there are dominant westerly (northwest-west-southwest) winds. It should be noted that sand can readily be moved by winds not only immediately following grass or brush fires but for a few weeks thereafter. Effect of Variations in Groundwater Level. When we come to study the relation of groundwater levels to wet and dry seasons, we are confronted by the fact that adequate data on groundwater fluctuations in the bay country are not yet available. From reports 5 dealing with the behavior of groundwater in general and with fluctuations of water levels in a limited number of wells in the states of North Carolina and South Carolina, we can, however, draw certain conclusions which are probably not far from correct. It has been found that in plains of low relief, where the surface formations consist of sand or similar highly permeable material, the groundwater level may respond quickly to sudden heavy precipitation, sometimes rising a foot or more for every inch of rainfall within the space of twenty-four hours. Where the groundwater level is far below the surface or the material less permeable, there may be a considerable lag in the rise of groundwater level following precipitation. Relatively heavy precipitation, if distributed over a long period in the summer season of heat and plant growth, may affect the groundwater level but 5 S. W . Lohman. Geology and G r o u n d - W a l e r Resources of the Elizal>elh City Area, North Carolina. U.S. Geol. Surv., Water-Supply Paper No. 773-A, 57 pp., 1936. O . E. Meinzer and L. K. Wenzel. W a t e r Levels and Artesian Pressure in Observation Wells in the United States in 1935. U.S. Geol. Surv., Water-Supply Paper No. 777, 130-139 (North Carolina) and 170-173 (South Carolina), 1936. Also U.S. Geol. Surv., Water-Supply Paper No. 817, 213-228 (North Carolina) and 302-312 (South Carolina), 1937. See also: David G . T h o m p s o n . Some Problems Relating to Fluctuations of Ground-Water Level. Amer. Geophys. Union, Trans. 17th A n n . Meet., Pt. 2, 337-341, 1936; and Department of Interior press release of February 25, 1932, on "Replenishment of Ground-Water Recorded by Observation Well Near Washington, D.C1," 2 pp.

Aeolian Phase

305

slightly, most of the water being taken up by the vegetation and lost by transpiration and excessive evaporation. For this reason replenishment of groundwater and rise of groundwater level are more likely to result from winter rains than from summer rains. In the bay country these winter rains are especially abundant in February at most places but continue into March at some. Groundwater level should then be high during the minor dry period of April. Such observations as we have indicate that in the Carolinas groundwater is normally low during NovemberDecember-January but rises during February and March to a high level in April, remaining relatively high through May and June and even into July. As a consequence, lake levels and water levels in marshes should also then be high. Under these conditions sandy beaches about present lakes, and formerly bordering lakes in basins now occupied by marshes, might be partially covered by water and so furnish less expanse of dry sand to passing winds at that period of the year. T h e situation should be reversed during the major autumn dry season (October-November). Groundwater level would presumably fall during the late summer, in spite of the summer rains, as a result of increased evaporation as temperatures rose and as a result of vigorous plant growth. T h e maximum dry season would insure low groundwater level from late October through January. Such observations as are available suggest that the regime outlined probably holds for the bay country. Water levels in wells in North Carolina and South Carolina (unfortunately not restricted to the bay country) indicate high groundwater levels from sometime in March to sometime in July, and low groundwater levels from sometime in October through January. It thus seems reasonably certain that in the bay country lake and marsh levels are likely to be abnormally low during the very driest portion of the year, thus exposing to strong westerly winds maximum expanses of dry sand. Direction and Strength of Winds during Wet Season. It may be argued that the most favorable time for sand transport is not in the dry season, as suggested above, but in the major summer rainy

Aeolian Phase

3o6

season. In support of such argument it can be pointed out that the abundant summer rains come chiefly in the form of thundershowers, a single one of which has been known to give a quantity of precipitation in excess of the monthly average, and that between such heavy showers there may be days or even weeks of hot, dry weather during which evaporation may be marked and sand thoroughly dried to considerable depths. It thus becomes of interest to know the direction and duration of the strongest average winds during the summer rainy season, June, J u l y , and August. At twenty-three out of the twenty-eight stations these are the wettest months of the year and at all stations they are months when occasional thundershowers alternate with hot, dry periods. In Table 6 the average precipitation for the months of June, July, and August at each of twenty-eight stations in the bay country is compared with the direction of those winds having the maximum average hourly velocity for these same months at the nearest stations for which satisfactory data are available. T h e statements made in introducing Table 5 above are equally applicable to Table 6. TABLE

6

PRECIPITATION R E C O R D S FOR T H E SUMMER R A I N Y SEASON AT STATIONS IN THE B A Y C O U N T R Y , COMPARED WITH W I N D R E C O R D S AT THE STATIONS FOR W H I C H SATISFACTORY D A T A A R E

NEAREST

AVAILABLE

Summer Rainy

Average

Season

Precipitation

Direction of Maximum Wind

Average

Hourly

at:

I . WILMINGTON, N.C. WILMINGTON, N.C.

June July Aug.

5-17

SW

6.94

SW

6-53

SW

2 . ELIZABETHTOWN, N.C. WILMINGTON, N.C. 45

June July Aug.

mi.

SE

RALEIGH, N.C. 80

mi.

5°3

SW

SW

6.16

SW

SW

4.76

SW

N E

N

Aeolian Phase

SO?

T A B L E 6 (Continued)

Summer Rainy Season

Average Precipitation

Direction of Maximum Average Hourly Wind at:

3 . F A Y E T T EV I L L E , N . C .

June July Aug.

5.12 6.22 5.75

R A L E I G H , N.C.

WILMINGTON, N . C .

50 mi. N

sw sw NE

75 mi. S E SW SW SW

WILMINGTON, N . C .

R A L E I G H , N.C.

65 mi. S E SW

sw sw

80 mi. N N E SW SW NE

R A L E I G H , N.C.

WILMINGTON, N.C.

75 mi. N N E SW

80 mi. S E

NE

SW

COLUMBIA, S.C.

WILMINGTON, N . C .

90 mi. SW

100 mi. E S E

4 . L U M B E R T O N , N.C.

June

5.44

July Aug.

570 5.62

5 . R E D SPRINGS, N.C.

June July Aug.

6.08 4-53 5.82

sw

SW

sw

6 . BENNETTS V I L L E , S.C.

June July Aug.

5-52 5-45 5.10

sw

sw sw

SW SW

SW

COLUMBIA, S.C.

WILMINGTON, N . C .

75 mi. SW SW SW SW

n o mi. E S E

WILMINGTON, N . C .

COLUMBIA, S.C.

7 . SOCIETY H I L L , S.C.

June July Aug.

5-34 6-39 5-63

sw sw SW

8 . DILLON, S.C.

70 mi. E June July Aug.

6.08 5-99 5.16

SW

sw sw

100 mi. WSW

sw SW SW

Aeolian Phase

3O8

TABLE

6

(Continued)

Summer Rainy

Average

Season

Precipitation

Direction

of Maximum Wind

Average

Hourly

at:

D A R L I N G T O N , S.C.

g.

COLUMBIA, S.C..

W I L M I N G T O N , N.C.

SW SW SW

HO mi. E SW SW SW

W I L M I N G T O N , N.C.

COLUMBIA, s . c .

SW SW SW

SW SW SW

COLUMBIA, S.C.

WILMINGTON, N.C.

SW SW SW

IOO mi. SW SW SW

COLUMBIA, S.C.

W I L M I N G T O N , N.C.

SW SW SW

SW SW SW

W I L M I N G T O N , N.C.

COLUMBIA, S.C.

SW SW SW

SW SW SW

W I L M I N G T O N , N.C.

COLUMBIA, S.C.

70 mi. WSW

June July Aug.

5.52 551

4.92

I O . MARION, S.C.

80 mi. £

June July

Aug.

II.

4.01 6.33 4.59

90 mi. WSW

FLORENCE, S.C.

70 mi. WSW

June July Aug.

5.46 584

5.19

E

12. EFFINGHAM, S.C.

70 mi. W

June July Aug.

5.79 6.11

5.71

105 mi. E

13. C O N W A Y , S.C.

70 mi. ENE

June July Aug. 14.

5.27 6.61

6.61

110 mi. W

SMITHS MILLS, S.C.

85 mi. ENE June July Aug.

5.66 5-97

7.22

SW SW SW

95 mi. WNW SW SW SW

Aeolian Phase TABLE 6

Summer Rainy Season 15.

Average Precipitation

3°9

(Continued) Direction of Maximum Average Hourly Wind at:

K I N G S T R E E , S.C.

June July Aug.

5-29 6.52

6.12

COLUMBIA, S.C.

WILMINGTON, N . C .

70 mi. WNW SW SW SW

115 mi. E N E SW SW SW

COLUMBIA, S.C.

AUGUSTA, G A .

40 mi. WNW SW SW SW

IOO mi. SW W

L6. SUMTER, S.C.

June July Aug. 17.

6.04 6.03 4-39

w

SW

COLUMBIA, S.C. COLUMBIA, S.C.

June July Aug. 18.

4.30 5-58 5-54

SW SW SW

RIMINI, S.C.

June July Aug.

4.76 7.10 4.84

COLUMBIA, S.C.

AUGUSTA, G A .

40 mi. NW SW SW SW

90 mi. WSW

COLUMBIA, S.C.

AUGUSTA, G A .

25 mi. NW SW SW SW

75 mi. WSW

COLUMBIA, S.C.

AUGUSTA, G A .

60 mi. NW SW SW SW

100 mi. W

w w

SW

1 9 . ST. MATTHEWS, S.C.

June July Aug.

5.76 5-77 5.80

w w

SW

2 0 . FERGUSON, S.C.

June July Aug.

5.60 6.88 6.87

w w

SW

Aeolian Phase

3io

T A B L E 6 (Continued)

Summer Rainy Season

Average Precipitation

Direction of Maximum Average Hourly Wind at:

2 1 . O R A N G E B U R G , S.C.

June July Au g-

4.88 6.64 4-57

COLUMBIA, S.C.

AUGUSTA, GA.

3 5 mi. N N W SW SW SW

65 mi. W

COLUMBIA, S.C.

AUGUSTA, GA.

45 mi. N N W SW SW SW

70 mi. W

COLUMBIA, S.C.

AUGUSTA, GA.

50 mi. N SW SW SW

65 mi. W

AUGUSTA, GA.

COLUMBIA, S.C.

40 mi. W

SW

45 mi. N N E SW SW SW

AUGUSTA, G A .

S A V A N N A H , GA.

50 mi. N W W W SW

65 mi. S S E S S SW

SAVANNAH, G A .

AUGUSTA, GA.

40 mi. SE

70 mi. N W W W SW

w w

SW

2 2 . B O W M A N , S.C.

June

Ju'y

Aug.

4.92

6.53

6.15

w w

SW

2 3 . EDISTO, S.C.

J

une

July Aug.

5-43 5.81 5-93

W

w SW

2 4 . B L A C K V I L L E , S.C.

June July Aug.

5.47 5.60 5.34

w w

2 5 . A L L E N D A L E , S.C.

June July Aug.

5.11 5-97 5.67

2 6 . G A R N E T T , S.C.

June July Aug.

6.52 7.24 5.24

s s

SW

Aeolian Phase

311

TABLE 6 (Continued) Summer Rainy Season

Average Precipitation

Direction of Maximum Average Hourly Wind at:

2 7 . WAYNESBORO, GA.

June July Aug. 28.

4.86 570 5-55

AUGUSTA, GA.

SAVANNAH, G A .

25 mi. N

go mi. SE

w

s s

W SW

SW

AUGUSTA, GA.

SAVANNAH, O A .

MILLEN, GA.

70 mi. SE w S 514 S w 6.31 SW SW 4-97 From these data it appears that during the summer season of heavy thundershowers alternating with hot, dry periods the winds of greatest average intensity blow predominantly from the westerly quadrant (west and southwest) throughout the bay country. Out of the total of 162 wind direction records tabulated, 4 are from the northeast, 8 from the south, and the remaining »50 from westerly quarters (west and southwest, with southwest predominating). When we recall the clear evidence that sources of beach sand are most abundant about the southeastern halves of the bays, it becomes evident that all the wind records, except those from the northeast, or 158 out of a total of 162, are favorable to the observed major accumulation of sand about southeastern quadrants of the bays. 45 mi. N

June July Aug.

Effect of Cyclonic Storms. Our study of seasonal weather records indicates that however we combine the data there is abundant evidence that the winds supposedly most competent to move sand under theoretically favorable conditions come prevailingly from a westerly sector. It is conceivable, however, that even if these long-time averages of weather conditions have significance for our study, they do not tell the most vital part of the story. It is possible that dominant control of sand transport

3i2

Aeolian Phase

may be exercised by daily changes in cyclonic and other atmospheric conditions. In other words, the fact that sand is moved rapidly in a given direction may depend more on the lack of rain for a day or two and on the burning heat of one or several days than on the average conditions of any month or season of the year. Our enquiry therefore shifts to short-time weather changes. In the bay country, winter rainfall is controlled largely by general cyclonic storms, while summer rainfall depends more upon the heavy thunderstorms characteristic of that season. It is therefore of interest to know the directions of stronger winds associated with these two types of storm and their time relations with respect to the precipitation each type produces. In the general cyclonic storm of this area the winds are commonly strongest in its southwestern quadrant where the isobars are most crowded. In this quadrant the winds blow prevailingly from the west and northwest and are usually not accompanied by precipitation, rains falling most rarely with northwest winds and comparatively rarely with west winds and north winds. When the centers of these cyclonic storms pass north of the Carolinas, as they generally do in summer and often in winter, rain is most likely to fall with southerly and southwesterly winds, followed by clearing weather and strong westerly winds which gradually shift into the northwest. When the storm center passes south of the Carolinas, as it sometimes does in winter, rain is most likely to fall with southeasterly, easterly, and northeasterly winds, followed by clearing weather and drying winds from the north and northwest. It would thus appear that sand moistened by rain falling with weaker winds from the south, southeast, east, or northeast should tend to dry out with and be set in motion by stronger winds from the west and northwest. Inasmuch as summer cyclonic storms have precipitation largely in the form of thundershowers, a goodly proportion of the southwest winds of any given year are also free from rain. These summer winds, however, are on the average weaker than those of winter. It thus appears that cyclonic storm conditions on the whole favor movement of sand from westerly quarters more than from easterly quarters. The question may arise as to whether sand made thoroughly

Aeolian Phase

313

wet by rainfall occurring in the southeasterly or northeasterly quadrant of a cyclonic storm could be rendered sufficiently dry in time to be effectively moved by winds of the southwesterly or northwesterly quadrant. Loose sand dries rapidly, and one of the striking characteristics of the bay country is the speed with which its sandy surface loses its moisture following even heavy rains. A few hours of sunshine or of wind will dry surface sands enough to render them easily movable, and winds from westerly quarters may blow for one or two days or even more. Effect of Thunderstorms. When a typical thunderstorm approaches, the wind, which has been light and from a southerly direction earlier in the day, shifts to the east and blows gently toward the approaching storm. " T h i s is suddenly replaced by the violent, sometimes damage-causing, squall wind which blows from the west or northwest directly from the thundershower." 6 Inasmuch as the violent squall wind may, before rain begins to fall, blow for a period varying from a few minutes up to a quarter of an hour or more, dry sand may be transported in notable quantities before being wetted by the drenching shower which follows. T h e writer has seen such a squall in the bay country raise a dust storm of impressive proportions and drive sand like sleet along the ground. It appears, therefore, that winds associated with thunderstorms are more likely to move sand from a westerly direction eastward than in the opposite direction. Effect of Tornadoes and Hurricanes (Tropical Cyclones). T h e spiral winds of tornadoes, blowing 100 to 400 miles an hour or even more, are sufficiently violent to move much sand in a very short space of time. But it does not appear that these tornadoes, with their narrow paths (usually less than 1,000 feet) and rapidly shifting air currents, are sufficiently frequent in the Carolinas and Georgia or involve winds of constant direction over areas sufficiently broad to explain the systematic distribution of sand about the margins of the craters. Hurricanes or tropical cyclones, with wind velocities reaching 100 miles an hour or more and having diameters commonly 6

\V. I. Milham. Meteorology. 549 pp., New York, 1931. See p. 322.

314

Aeolian Phase

ranging from 300 to 600 miles, greatly strengthen easterly and northeasterly winds in the bay country. But these winds are normally accompanied by heavy precipitation which would prevent sand transport. T h e r e appears to be no reason to suppose that these violent storms play a significant role in determining the distribution of sand about the Carolina craters. Summary. If we dismiss, as of no general significance, the effect of violent tornadoes and tropical cyclones upon sand distribution in the bay country and consider only those meteorological phenomena believed chiefly responsible for sand transport in this region, our conclusions are consistent and important. Whether we consider long-range weather records or the daily and hourly changes associated with general cyclonic storms and local thundershowers, conditions are most favorable for the transport of sand in directions which would account for the observed distribution of sand rims about the oval bays. T h e cumulative effect of such diverse lines of reasoning is very impressive. It could only be stronger were we to find direct evidence confirming conclusions reached on the basis of our study of long-range meteorological records and the known behavior of cyclonic and other storms. EVIDENCE OF SAND T R A N S P O R T BY W E S T E R L Y

WINDS

W e have already seen that some such confirmatory evidence is available. T h e best evidence, in the absence of any other satisfactory explanation for the phenomenon, is the actual presence of large accumulations of what appears to be typical dune sand in the form of rims about the southeast quadrants of many bays. But since this is the phenomenon we desire to explain, we seek independent evidence. It is found in the fact, previously discussed, that about some bays possessing no true rims thin deposits of fine white sand of uniform grain size are found most abundantly on the eastern sides of the depressions, thinning out as one proceeds away from the bay margins and having no obvious explanation for their presence in the observed positions except wind transport from sandy shores of the bays or old beach ridges just within their borders. T h e further facts, also discussed earlier, that freshly plowed fields are in time coated with a thin film of the same type

Aeolian Phase

315

of sand, that its presence can only be satisfactorily accounted for by wind transport from the bay margins, and that such transport is obviously most extensive from west to east indicate that sand is today being moved in a direction which, were conditions similar in the past, would account for the presence of sand rims about the southeastern quadrants of the bays. The invasion of Big Bay (Fig. 17) by sand dunes which obviously have advanced from west to east, and the eastward advance of dunes from the zone of major sand accumulation about the southeast quadrants of many bays (Figs. 29 and 32), prove past movement in the direction indicated. Another type of direct evidence of possible value would be testimony of people living near the bays that sand is observed to move most frequently or most effectively when winds are blowing from westerly quarters. The writer has not systematically exploited this last method of determining the conditions of sand transport about the oval craters because of the time required to discover and interview intelligent and observant local inhabitants as to their experience of the matter. As opportunity offered, natives living near bays bordered by deposits of sand were interrogated as to what winds blew sand about most extensively. More often than not, no information was forthcoming, but in a few instances the questioned individual replied without hesitation that westerly winds started the sand moving. In no case was sand movement attributed to winds from a northerly, easterly, or southerly direction, although examination of fields adjacent to the bays proves conclusively that some sand is moved by winds from all points of the compass. The number of informative responses was too small to have independent value, but the unanimity with which the scanty testimony credited observable sand movement to winds coming from some westerly direction may perhaps be accepted as confirming the conclusions based on other considerations. Despite the elusiveness of some aspects of the meteorological side of the bay problem, our study has developed a remarkably consistent body of evidence indicating that the observed development of major sand accumulation about the southeastern quadrants of the oval craters is fully accounted for by the superior effectiveness of strong winds blowing from westerly directions at

3i6

Aeolian Phase

times when sand is most apt to be dry. T h e artesian-solutionIacustrine-aeolian hypothesis of bay origin thus appears to meet successfully one of the most critical tests which could be applied to it. Whatever the origin of the oval craters, the outer rims of sand partially surrounding them seem clearly to have a meteorological as opposed to a meteoritic or other origin. D E F I N I T I O N OF T H E T E R M " O V A L

BAY"

It was earlier pointed out that there are depressions, otherwise identical in character with typical oval bays, which have no rims. T h u s we find that the aeolian phase of the hypothesis is not necessarily involved in the development of all oval depressions called "bays," just as earlier we found that the solution and lacustrine phases, each in its turn, were not essential elements of the picture in every case. It is even conceivable that there may be marshy oval depressions bordered by sand rims especially prominent about their southeast quadrants and therefore deserving to be called typical bays, which owe their basin form and their elongation to simple solution or some other cause independent of headward migration of artesian springs. T h u s as we approach the end of our study we face, in any attempt to define the term "bay," a problem as difficult as it was at the beginning of our investigation. W e then discovered that the term "bay" was in popular practice applied to marshy depressions of every conceivable shape and size. Now we find that even if we restrict consideration to oval bays, the problem of definition is still as troublesome as ever. If we define the features empirically as "more or less oval, shallow depressions having major axes directed approximately northwestsoutheast and occupied by marshes partially surrounded by rims of sand," we exclude basins of identical origin having axes trending in other directions, having lakes instead of marshes occupying the basins, or having rims of sand wholly lacking, and we include basins of identical characteristics in which some one of the processes usually responsible for bay development failed to operate effectively. On the other hand, if we define the features genetically as

Aeolian Phase

317

"basins excavated by headward-migrating artesian springs, modified by solution, temporarily occupied by lakes, and bordered by rims of wind-drifted sand," we exclude (a) some basins of identical or nearly identical characteristics in the development of which one of the processes failed to operate, and (b) very many basins having most of the characteristics of typical oval bays and obviously related to them, but in the development of which one or more of the processes failed to operate. T h e writer is inclined to combine empirical and genetic methods to give some such definition as the following: The particular "bays" which have attracted public attention and which are the subject of present discussion are more or less oval, comparatively shallow basins, usually though not always oriented in directions more or less nearly approximating northwest-southeast, generally containing marshes or lakes or both but sometimes dry, normally produced by artesian spring excavation and by solution operating in conjunction but sometimes by one or the other operating independently, commonly though not necessarily occupied formerly if not now by lakes the waves of which smoothed the contours of the basins and often built beach ridges and bars about portions of their borders, and frequently though not always partially surrounded by rims of sand transported from the basins by wind action. If the foregoing definition seems unduly complicated, the writer would remind the reader that the bays appear to have had a complex and, within certain limits, variable origin and to present a certain degree of variability in their characteristics. If Nature sometimes moves in complex as well as in mysterious ways her wonders to perform, man can only record the complexity and do his best to solve the mystery. T h e foregoing definition states as concisely and as accurately as the writer can the essential nature of the oval bays.

XV Possible Weaknesses of the Hypothesis

O

U R S T U D Y of the remarkable craters of the Carolina coast and adjacent parts of Georgia has demonstrated the incompetence of the meteoritic and other suggested hypotheses to account for many of the observed facts. It has been shown, on the other hand, that these same facts are reasonably accounted for by a hypothesis of complex origin in which the formation of basins in sandy soil by artesian springs rising through moving groundwater, the solution of surface or subsurface beds, the occupation of the basins by lakes, and the transport of sand from lake shores by prevailing westerly winds have all played an important but variable role. Finally, this hypothesis of complex origin has not only supported well the critical tests we have applied to it; it has emerged from those tests greatly strengthened. There remains to be answered a broad question of more general nature: Does the hypothesis of complex origin as set forth in earlier chapters satisfactorily account for all that is thus far known about the Carolina bays; or do there remain certain facts so doubtfully or so incompletely accounted for that one must for the present hesitate to accept this hypothesis as a full and wholly satisfactory explanation for all phenomena exhibited by these curious craters? There are two aspects of the bay problem, not yet considered or not adequately considered, which some may feel justify caution in accepting the hypothesis. WHY

A R E N O T SIMILAR FORMS FOUND E L S E W H E R E ?

If the forms under investigation have been produced by normal terrestrial processes, it is reasonable to enquire how it happens that other regions do not exhibit features comparable with the oval craters of the Carolina coast and their bordering rims. It must first be pointed out that we do not yet know the curious

Possible Weaknesses

319

oval craters of the Carolina coast to be peculiar to that region. They were practically unknown there a few years ago, despite Glenn's early but brief account of them, because the only way in which their true characters can be observed well is from the air. It was only when aerial surveys had been made and the resulting photographs studied by Melton and Schriever that the scientific and general public learned of their existence. When similar surveys are made of other areas and the resulting photographs studied by competent students, or when competent students have flown over such areas, it may develop that the oval basins with their sand rims are less unusual than now appears. In the second place there do exist, in areas already surveyed and studied, features somewhat similar to, although not identical with, the oval bays of the Carolina coast. Melton and Prouty independently report that one or two obscure but unmistakable oval bays are shown on aerial photographs made by the Army Air Corps of an area near Norfolk, Virginia. In various parts of the Coastal Plain of Georgia aerial photographs and soil maps reveal somewhat oval forms not unlike the Carolina bays, although they do not have the same degree of similarity in axial alignment or as frequent or extensive a development of rims as in the Carolina examples. When examining the photographs and maps, the writer tentatively and doubtfully classed them as "oval bays." In Figure 2 only the better examples are located, and some of these are sufficiently doubtful to have interrogation points associated with them. East of Sarasota and north of Fruitville, Florida, is a remarkable series of round and oval basins (Fig. 44) oriented in a northwestsoutheast direction, some of which appear from aerial photographs to have multiple faint shorelines of former lake levels about their borders. More remarkable is their distinct alignment along parallel narrow dark bands suggesting the presence of joint or fault fissures. Prominent sand rims do not appear to be present. Aerial photographs of these forms were brought to the writer's attention by Professor J . Hoover Mackin, but opportunity to visit the region did not occur. T h e writer gave aerial photographs and location map to Dr. C. Wythe Cooke who had such opportunity. He re-

è

T3 "O

8

S S

i « n i»

(J h

CTJ 2 a•. OJ o k
5. 259. 326 Shore zone, passage of rims through, 51, 101

339

Shore-zone activity, 55, 58 Siberia, craters, 126; meteorite fall, 125 Sigma Xi, National Society of the, 29 Silica, bombs, 125, 129; glass, 125, 126, 128, 129 Silting process, 100 Silver, S. C., bays, 17 Singletary Lake, 105, 132, 139 f., 148, 276; bay, 80, 138, 142», 145» Sinkholes, 4g, 166, igi f „ 243; causes, 249, 250; defined, 267; deposits underlying, 248, 249; form in intake areas, 271; form in outlet areas, 272; genetic relation to craters 266-74; one of finest areas, 270; transition to oval craters, 256-66; widespread occurrence, 251-56 Slumping process, 157, 192, 200, 216, 240, 241, 243 Smith, Laurence L „ 49, 249, 253 Smithboro, S. C „ bay, 85, 86 Smiths Mills, S. C., 299, 308 Snow Hill marl member, 163, 248, 250 Society Hill, S. C „ 258, 298, 307 Sodium chloride, 127, 128 Soil Conservation Service, 303 Soils, of bay floors, 15; of bay region, 8; of Coastal Plain and Piedmont compared, 7; see also under types of soil, e.g., Loam, Sand Solution depressions, hypothesis of, 49 f. Solution phase of complex origin hypothesis, genetic relation of sinkholes to craters, 266-74; role of solution in bay development, 271 ff.; transition from sinkholes to oval craters, 256-66; widespread occurrence of soluble beds, 247-51; of sinkholes, 251-56 South Barebone Bay, 15, 21, 76, 80, 83, 103, 110-13 passim South Carolina, 77, 123, 124, 146, 199; d i p of formations, crater trends, 16371; geological formations, 247-49; principal area of known bays, 9, 124, 226: sinkhole topography, 251 ff., 270; soluble beds, 171: waters, 223(7., 304 Spit, curved, 46, 59 Springerville, S. C „ bays, 80, gon, 106, 117« Springs, boiling, 119, 178, 191, 235-43 passim, 253; on floors of bays, 119; fountaining, 119, 178, 179, 191, 235-43 passim; freshwater, 36; see also Artesian, Groundwater

340

Index

Stephenson, L . W., and Johnson, B. L „ » 9 , 230; and Veatch, J. O., 231, 238, 249; and others, report, 229 Stockdale, Paris B „ 250 Stoping process, 188, 189 Straley, H. W., Prouty, W . F„ and, 27. ' j o , 133 Streams, channels affording ingress or egress to, 118; of Coastal Plain, 190, 191, 194; erosion by, 108, 127; subterranean, 238; see also Channels, Groundwater Slringfield, V. T . , Warren, M. A., and Cooper, H. H., Jr., 164 Submarine scour, hypothesis of, 34-36 Suggs Mill Pond, 88, 237, 241, 277; bay, 118, 179, 181 Sumter, S. C „ gon, 300, 309 Sumter County, S. C., 5, 11, 85, 87, 229 Suwannee limestone, 248 Swales, 17, 23, 51. 53, 54, 57, 59, 88, 202, 258; see also Marshes Swallow, term, 259 Swallow Savanna Bay, 80, 90*1, 106, 107, »59. «75 Swamps, see Marshes, Swales Syracuse, S. C., survey, 27, 131, 133 T a l a t h a quadrangle, 264 T e n Mile Bay, 81, 85, 86, 185 Tennessee, meteorites in, 123, 124 Terraces and bays, relative ages, 60 f. Tertiary formations, 174. 247-54 possim Texas, Coastal Plain basins, 5, 32, 281, 321-24 T h a t c h e r , John M. P.. vi. 21 T h o m p s o n , David G., 304« Thunderstorms, 306, 312, 313 T o b i n , Edgar, vi, 323 T o d d Bay, 242 T o n e y Bay, 270 T o n y Hill Bay, 104, 255 Tornadoes, 313 Torpats, Elizabeth P., v Trees occupying bays, 8 Triassic basins, 146, 148 T u o m e y , Michael, 237, 244, 245, 253, 326 Turbeville, S. C., bays and highs, 135, '36. 137. ' 3 8 . '47 Tuscaloosa formation, 228. 232, 236, 247, 248, 250, 254 Tussock Bay, 140

U. S. Geological Survey, vi, 6 U. S. Weather Bureau, 285, 288; Climatic Summaries, 289, 290-303 Valencia County, N. Mex., lakes, 282 Van Burkalow, Anastasia, v Varnville quadrangle, 186, 263, 275 Veatch, J. O., Stephenson, L . W., and. 231, 238, 249 Vegetation in bays, 8; see also Marshes, Peat Venable, F. P., 124 Vidauri, Texas, lakes, 321-24 Virginia. 10, 123, 170, 319 Vitaliano, Dorothy B., v Vulcanism, hypothesis of, 36 Wabar crater, 98 Waccamaw Lake, 23on Waccamaw formation, 247, 250, 254 Wad boo Swamp Bay, 104, 1 i8n, 255 Walker, Charles A., vi; quoted, 67 Ward, Robert De Courcy, 303 War Department, vi, 67 Warren, M. A., and others, 164 Water, principles re flow of, through sand, 156, 159, 188; terminology, 155; see also Artesian, Channels, Groundwater, Lakes Watson, Fletcher, Jr., vi, 24, 65, 69, 81, 123, 125, 143 Watts Bay, 16, 21, 80, 83, 102, 103, 106, 108, 185 Wave action, shoreline development by. 23. 55- " 3 . '59- '93- '95. '99- 2 ° 5 . 259 Waynesboro, Ga., 302, 311 Weathering, 91, 92, 94, 108, 127. 128. 271 Well water levels, relation to wet and dry seasons, 304 Wenzel, L. K., Meinzer, O . E., and. 3040 West Middle School, S. C., bay near. 1 l8tl Wheeler, Clementene W., v Wheeler, Girard, v, 85, 110. • ign, 237, 248, 250, 274, 276, 277 White, Robert, vi, 21 W h i t e Lake, 80, 105, 118, 132, 137, 139, 140, 142», 143. 144, 148, 172, 237, 241. 275. 276 White Pond, 261 Williamsburg County. S. C., 5, 78, 80, 106, 1 i8n, 252

Index Williston quadrangle, 80, gon, 106, 117», '73. »55- «64 Wilmington, N. C., 84, 85, 119, 163, 330, 250, 256, 257, 285, 287; weather records, 285 309 passim Winds, chains of lakes formed by, 36, 40, 43; cyclonic, 311-14; direction of dominant, 284, 291-95, 302; direction of prevailing, 286, 287, 289 f.; direction and strength during dry season, 296303, during wet season, 305-11; dominant, chiefly responsible for sand transport, 290; effect upon distribution of open water and vegetation in basins, 179; excavation of basins by, 32; failure of attempt to correlate axial trends with wind directions, 198 f.; Glacial Period, 32, 199, 205; inadequate

341

records and other difficulties confronting study of, 285; influence upon locus of sand rims, 204, 205-7, upon form of rims, 215, upon peat distribution, 29; records favorable to sand accumulation about southeastern quadrants of bays, 311; rotary currents generated by> 37» 44: sand filling of bays by, 110; sand transport by westerly, 32, 284, 314-16; sand transport outside of bay country, 281 f„ in bay country, 282-84; studies of, offer no support for aeolian hypothesis of crater elongation, 196; velocities, 285, 286, 287, 288 f., 290-95 Woods Mill Bay, 80, gon, 134, 135, 137, '44 Wylie, C. C., 20, 66, 122