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Home , Diluvium, Geography of Chicago, Glacial Lake Iroquois, Gunz (geology), J Harlen Bretz, Lake Border Moraine

STATE OF

WILLIAM G. STRATTON, GoHntor DEPARTMENT OP REGISTRATION AND EDUCA'l'ION VERA M. BINKS, Dj,«UJr

DIVISION OP THE STATE GEOLOG ICAL SURVEY M. M. LEIGHTON, Cbl;J URBANA

B U L L E T I N N 0 . 65, P A 1t T I I

GEOLOGY OF THE REGION

PART II-IBEPLEISTOCENE

BY

J llARLBN BRETZ

Pll.INTED BYUTHOlllTY A OF THE STATE O"l' lLLlNOlS

URBANA, ILLINOIS

1955

STATE OF ILLINOIS

WILLIAM G. STRATTON, Governor DEPARTMENT OF REGISTRATION AND EDUCATION

VERA M. BINKS, Director

DIVISION OF THE STATE GEOLOG IC AL SURVEY M. M. LEIGHTON, Chief URBANA

B u L L E T I N N 0 . 65, p A RT I I

GEOLOGY OF THE CHICAGO REGION

PART II - THE PLEISTOCEN E

BY

J HARLEN BRETZ

PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS

URBANA, ILLINOIS

1955 ORGANIZATION

ST ATE OF ILLINOIS HON. WILLIAM G. STRATTON, Governor

DEPARTMENT OF REGISTRATION AND EDUCATION HON. VERA M. BINKS, Director

BOARD OF NATURAL RESOURC ES AND CONS ERVAT IO N HON. VERA M. BINKS, Chairman W. H. NEWHOUSE, PH.D., Geology ROGER ADAMS, PH.D., D.Sc., Chemistry R. H. ANDERSON, B.S., Engineering 0 A. E. EMERSO�. PH.D., Biology LEWIS H. TIFFANY, PH.D., Po.D., Forestry W. L. EVERITT, E.E., PH.D., Representing the President of the University of Illinois DELYTE W. MORRIS, PH.D. President of Southern Illinois University

GEOLOGICAL SURVEY DIVIS IO N

M. M. LEIGHTON, PH.D., Chief STATE GEOLOGICAL SURVEY DIVISION Natural Resources Building, Urbana M. M. LEIGHTON, PH.D., Chief Esm TOWNLEY, M.S., Geologist and Assistant to the Chief VELDA A. MILLARD, Junior Assistant to the Chief HELES E. McMORRIS, Secretary to the Chief RESEARCH (not including part-time personnel) GEOLOGICAL RESOURCES GEOCHEMISTRY ARTHUR BEVAS, PH.D., D.Sc., Principal Geologist FRANK H. REED, PH.D., Chief Chemist FRASCES H. ALSTERLUND, A.B., Research Assistant GRACE C. JOHNSON, B.S., Research Assistant Coal Chemistry Coal G. R. YOHE, PH.D., Chemist and Head ]ACK A. Sums, M.S., Geologist and Head RUDOLPH L. PEDROTTI, M.S., Research Assistant G. H. CADY, PH.D., Senior Geologist and Head, Emeritus Geologist ROBERT M. KOSANKE, PH.D., Physical Chemistry RAYMOSD SIEVER, PH.D., Geologist }OHS A. HARRISON, M.S., Associate Geologist J. S. MACHIN, PH.D., Chemist and Head PAUL EDWIN PorrER, Pu.D., Associate Geologist KENNETH B. THOMSON, PH.D .• Physicist HAROLD B. STOSEHOUSE, PH.D., Associate Geologist JUANITA WITTERS, M.S., Assistant Physicist MARGARET A. PARKER, M.S., Assistant Geologist TIN Boo YEE, M.S., M.A., Assistant Chemist (on leave) DANIEL L. DEADMORE, B.S., Research Assistant M. E. HOPKINS, M.S., Assistant Geologist KEsNETH E. CLEGG, M.S .• Assistant Geologist Fluorine Chemistry G. C. FINGER, PH.D., Chemist and Head Oil and Gas ROBERT E. OESTERLING, B.A., Assistant Chemist RAYMOSD H. WHITE, B.S., Special Research Ass{stant BELL, PH.D., Geologist and Head A.H. RICHARD H. SHILEY, B.S., Special Research Assistant LESTER L. WHITISG, B.A., Associate Geologist KLINE, PH.D., Associate Geologist Chemical Engineering WAYNE F. MEESTS, Assistant Geologist DOROTHY E. RosE, B.S., Research Assistant H. W. }ACKMAN, M.S.E., Chemical Engineer and Head MARGARET 0. 0R03, B.A., Assistant Geologist R. J. HELFINSTINE, M.S., Mechanical Engineer and }ACOB VAN DES BERG, B.S., Research Assis/ant Supervisor of Physical Plant P. W. HENLINE, M.S., Chemical Engineer B. J. GREENWOOD, B.S., Mechanical Engineer Engineering }AMES C. McCULLOUGH, Research Associate (on leave) PAUL A. VlITHERSPOON, M.S., Petroleum Engineer and ROBERT L. E1s...o;1.ER, B.S., Assistant Chemical Engineer Head WALTER E. COOPER, Technical Assistant FREDERICK SQUIRES, A.B., B.S., Petroleum Engineer, EDWARD A. ScHAEDE, Technical Assistant Emeritus CORSEL MARTA, Technical Assistant

Industrial Minerals X-Ray ]. E. LAMAR, B.S., Geologist and Head W. F. BRADLEY, PH.D., Chemist and Head DosALD L. GRAF, PH.D., Geologist }AMES C. BRADBURY, A.M.• Assistant Geologist Analytical Chemistry ROBERT J. CROSK, M.S.• Assistant Geologist 0. W. REES, PH.D., Chemist and Head RAYMOSD S. SHRODE, M.S., Assistant Geologist L. D. McVICKER, B.S., Chemist EMILE D. PIERRON, M.S., Associate Chemist Chy Resources and Cl ay Mineral Technology DONALD R. DICKERSOS, B.S., Assistant Chemist FRANCIS A. CooLICAN, B.S., Assistant Chemist RALPH E. GRIM, PH.D., Consulting Clay Mineralogist CHARLES T. ALLBRIGHT, B.S., Research Assistant W. ARTHUR WHITE, M".S.• Associate Geologist WILLIAM J. ARMON, B.S., Research Assistant HERBERT D. GLASS, PH.D., Associate Geologist RAYMOND ISAAC, B.S., Research Assistant Ass stant Geologist EDWARD C. JosAS, M.S., � PHYLLIS KERN, B.A., Research Assistant EUGENE LANGE, Technical Assistant Groundwater Geology and Geophysical Exploration GEORGE R. ]AMES, Technical Assistant FRANK C. FoLEY, PH.D., Geologist and Head LOIS W. RUFFNER, Technical Assistant MERLYN B. BuHLE, M.S., Associate Geologist FRANCES L. ScHEIDT, Technical Assistant ROBERT E. BERGSTROM, PH.D., Assistant Geologist ]OHN W. FosTER, M.S., Assistant Geologist MINERAL ECONOMICS A

Physics CONSULTANTS R. J. PIERSOL, PH.D., Physicist, Emeritus Geology, GEORGE W. WHITE, PH.D., University of Illinois RAL H E. GRIM, PH.D., University of Illinois Topographic Mapping in Cooperation with the Unite:! P L. E. WORKMAN, M.S., Former Head, Subsurface States Geological Survey. Di,11ision *Divided time Ceramics, RALPH K. HURSH, B.S .• Uni'i.'ersity of Illinois Jfechanical Engineering, SEICHI Ko:szo. M.S .• Unit=ersity June 1, 1954 of Illinois GENERAL ADMINIS TRATION (not including part-time personnel)

LIBRARY OTHER TECHNICAL SERVICES Research Associate ANNE E. KovA,.,DA, B.S., B.L.S., Librarian W!d. DALE FARRIS, RUBY D. FRISON', Technical Assistant BEULAH M. USFER, Technical Assistant A. W. GoTSTEIN, Research Associate GLESN G. PooR, Research Associate• MINERAL RESOURCE RECORDS GILBERT L. TISBERG, Technical Assistant \\...AY:S-E \\"". �OFFTZ, Supervisory Technical Assistant VIVIAN GORDON, Head Do:so\"OS M. WATKISS, Technical Assistant MARGARET A. BRYANT, B.A., Research Assistant SuE J. Cvs:�•HNGHAM, Terhnical Assistant FINA:\'CIAL RECORDS BETTY CLARK, B.S., Technical Assistant ]EAXINE CLI!\IER, Technical Assistant VELDA A. MILLARD, In Charge Clerk-Typist III ANS P. OSTROM, B.A., Technical Assistant LEO>IA K. ERICKSO>I, LOUISE J. STREEVER, B.A., Technical Assistant VJRGI"IA C. SANDERSON, B.S., Clerk-Typist II MARISE GUARDALABESE, Technical Assistant ]OA>l>I M. DUNBAR, Clerk-Typist I IRMA E. SAMSON, Clerk-Typist I PUBLICATIONS CLERICAL SERVICES MARY CECIL, Clerk-Stenographer II I ]A'1E V. OLSON, B.A., Associate Technical Editor Clerk-Stenographer III BARBARA ZEIDERS, B.S., Assislanl Editor MARY M. SuLLI\' A", Clerk-Stenographer I I MEREDITH M. CALKl'1S, Geologic Draftsman ETHEL M. HE>!WOOD, B.A., LYLA ;\OFFTZ, Clerk-Stenographer II PHYLLIS J. BARHA-'d, Clerk-Stenographer I TECHNICAL RECORDS LILLIA>I WEAKLEY, Clerk-Stenographer I SHIRLEY CoLVl'1, Clerk-Stenographer I BERE:"llCE REED, Supervisory Technical Assistant BARBARA BARHAM, Clerk-Stenographer I MARILYN DELA:"lD, B.S., Technical Assistant MARY J. DE HAAS, Messenger-Clerk I

GE!\"ERAL SCIENTIFIC INFORMATION AUTOMOTIVE SERVICE GLE"" G. PooR, In Charge• lRE�E H. BE:"lSO:"l, Technical Assistant ROBERT 0. ELLIS, Automol-i'i:e .._lfechanic Lois L. REED, Technical Assislanl EVERETIE EDWARDS, Automoli've Mechanic DAVID B. COOLEY, Aulomoiit•e Mechanic's Helper

June 1, 1954 *Divided time CONTENT S

PAGE Chapter I-Introduction...... 11 Location and extent of the Chicago region...... 11 Importance of the area...... 11 Purpose of the investigation...... 13 History of the investigation...... 13 Acknowledgments ...... 14 Previous publications...... 14 Chapter II-Topography...... 15 Introduction ...... 15 Physiographic province.... 15 Relief and altitudes...... 15 Topographic maps...... 16 Geologic factors ...... 17 Topographic processes...... 17 Streams...... 17 The cycle of ...... 17 Topographic age of the Chicago region ..,...... 18 ...... 18 ...... 19 Waves and shore currents...... 19 Winds...... 21 Drainage...... 21 Rivers ...... 21 ...... 22 ...... 22 DesPlaines River...... 23

Minor streams...... 23 Submerged portion of the Chicago plain. 24 levels .... 25 Topographic features .... . 27 Uplands...... 27

Moraine ridges .... . ·'· 27 Valparaiso morainic system ...... 27 Tinley ... 28 Lake Border ...... 28

The lake plain...... 29 Shore features of ...... 29

Valleys... . ''I" .•...... · · · · · · · · · · · · · 30 Constructional valleys ...... 30 Salt Creek ...... 30 Flag Creek Valley .. . 31 Des Plaines Valley north of Lyons...... 31 Valley of West Fork North Branch, Chicago River ...... 32 Valley of North Branch, Chicago River ...... 32 Valley of Skokie River ... 32 Calumet River Valley.. 33

Erosional valleys ...... 33 DesPlaines Valley south and west of Lyons ...... 33

Sag Valley...... 34 Sawmill Creek Valley...... 35 Valleys on the frontal slope of the .... 36 Valleys of Hickory and Marley creeks ... 36 Valley of Mill Creek...... 36 Valleys draining flats west of the ...... 39 Valley of ...... 39 Valley of Plum Creek...... 40 PAGE Chapter III-Glacial geology ...... 42 Introduction ...... 42 Drift ...... 42 ...... 43 ...... 43 ...... 43 Karnes...... 43 terraces...... 44

Valley train ...... : ...... 44 Glaciolacustrine deposits...... 44 Deltas...... 44 Offshore deposits ...... 44 Beach deposits ...... 44 Eolian deposits...... 45 Source of drift materials...... 45 Thickness of the dri ft ...... 45 Differentiation of drift sheets ...... 46 Classification ...... 47 Stratigraphy ...... : ...... 48 Bedrock topography ...... 51 (?) stage...... 57 Sub-Lemont drift in the buried Hadley Valley...... 57 Lemont drift...... 57 Type locality ...... 58 Thickness...... 58 Character in the type locality...... 58

Other exposures...... 59 Le mont drift in younger ...... 64 Lemont drift in the buried Hadley Valley ...... 66 Correlation ...... 67 Joliet and Lemont dri ft...... 68 Additional localities...... 68 stage ...... 69 Tazewell substage ...-...... 69 Bloomington ( drift ...... 69 Pre-Valparaiso?) topogra phy ...... 70 Tills exposed in the Sanitary and Ship Canal ...... 76 Gravel exposed in Dolese and Shepard quarry ...... 78 Cary substage ...... : ...... 78 Valparaiso drift ...... 78 Thickness...... 78 Till ...... 79 Eskers ...... 79

Karnes...... ··· .....·················· ········ 80 Kame terraces ...... 81 Correlation ...... 81 Tinley drift...... 81 Thickness ...... 81 Till ...... 82 Eskers...... 82 Karnes ...... 82 Frontal outwash...... 82 Glaciolacustrine deposits ...... 83 Correlation ...... 83 Lake Border drift...... 83 Valley train...... 83 Glaciolacustrine deposits ...... 86 Correlation ...... 86 PAGE Offshore deposits on the floor of Lake Chicago ...... 86 Boulders ...... 87 Hobart sections ...... 89 Other sections ...... 90 North Shore Channel sections ...... 92 Mankato substage...... 93

Glacial river bars ...... ·...... 93 Sag outlet channel...... 93 DesPlaines outlet channel ...... 93 Glacial river bars near the Chicago region ...... 94 Recent stage ...... : ...... 95 Character...... 95 Floodplains...... 95 Alluvial fans ...... 95 Slope-wash deposits ...... 95 Sw amp deposits ...... 95 Groundwater deposits ...... 96 Wind deposits...... 96 Shore deposits...... 96 Correlation ...... 96 Geologic aspects of soils...... 96 Thickness ...... 97 Character ...... 97 Correlation ...... 98 Chapter IV-Glacial history ...... 99 Pre- erosion...... 99 Early Pleistocene erosion ...... 100 Pleistocene epoch...... J 00 Character of the Pleistocene epoch...... 100 Centers of accumulation ...... 100 Thickness and movement of the ice sheets ...... 101 Causes of glaciation...... 102 Length of the Pleistocene epoch ...... 102 Life of the Pleistocene epoch...... 102

Nebraskan age ...... ' ...... 103 Aftonian age ...... 103 Kansan age...... 103 Yarmouth age...... 104 Illinoian age ...... 104 Sangamon age ...... 104 Wisconsin age ...... 104 Tazewell subage ...... 105 Bloomington (?) glaciation ...... 105 Lemont glaciation ...... 105 Post-Lemont, pre-Minooka interval ...... 106 Cary sub age ...... 106 Valparaiso glaciation ...... 106 Tinley glaciation ...... 107 Lake Border glaciation...... 107 Lake Chicago time ...... 108 Causes for the Lake Chicago stages ...... 109 The Glenwood stage ...... 113 The Bowman ville low-water stage ...... 117 The Calumet stage ...... 117 Mankato subage...... 119 The second Calumet stage ...... 119 The Toles ton stage ...... 120 Post-Toleston, pre- time...... 123 Radiocarbon dating ...... 128 ILLUSTRATIONS

FIGURE PAGE 1. Map showing location of all quadrangles referred to in this bulletin and the numbers of the geologic maps in the Chicago region ...... 12 2. Physiographic divisions of the Middle West, showing the location of the Chicago region 16 3. Drainage map of the Chicago region, including lakes, canals, and the ·larger ditches and temporary streams ...... 20 4. Contour map of a portion of the lake bottom in the Chicago region 24 5. Distribution of topographic features of the Chicago region 26 6. Channel of Calumet River on the lake plain at South Holland . 33 7. Profiles of Sawmill Creek ...... 35 8. Vanished postglacial lakes near Orland Park and Palos Park. 37 9. Vanished postglacial lakes of Mt. Forest Island 38 10. Driftwood in lower part of alluvial fill in Plum Creek Valley 39 11. Marl, peaty clay, and beneath alluvium in Plum Creek Valley. 40 12. Fragments of deer antlers and a well-worn mammoth tooth from deposits in Plum Creek Valley...... 40 13. Planed and striated bedrock surface. 42 14. Development of successive moraines by minor readvances in general retreat of an . 48 15. Moraines and associated fe atures in northeastern Illinois ...... 49 16. Generalized columnar section of the Pleistocene deposits of the Chicago region .. . 50 17. Diagrammatic cross section of the Pleistocene deposits of the Chicago region .. 51 18. Generalized map of bedrock valley system in the Chicago region ...... 52

19. Preglacial drainage ...... 53 20. Contour map showing bedrock surface in vicinity of Joliet 54 21. Cross section of buried Hadley Valley and its overlying drift 55 22. Lemont till in ravine wall ...... 57 23. Lemont till overlain by Valparaiso till ...... 58 24. Contact between Valparaiso and Lemont tills . 58 25. Coarse gravel beneath till. 58 26. Swallow Bank, Palos Park Forest Preserve 60 27. Gravel-filled channel in Le mont silt .. . 62 28. Delta foreset bedding in Le mont drift .. . 62 29. Foreset bedding in Le mont drift ...... 63 30. Mass of cemented gravel in pit ...... 64 31. Cross-bedded sand in Lemont drift ...... 64

32. Masses of Lemont drift included in Tinley till ...... 65

33. Sketch showing masses of Lemont drift included in Tinley till ...... 66

34. Pre-Valparaiso valleys tributary to Sag Valley ...... 72

35. Pre-Valparaiso bluffs, Tinley moraine, and "Hairpin" Creek...... 74 36. Section in kame...... 75 37. Till masses in poorly sorted gravel ...... 82 38. Imperfect foreset bedding in Tinley fro ntal outwash ...... 83

39. Glacial river bars on the Des Plaines valley train ...... 84 40. Section in glacial river bar, DesPlaines valley train ...... 85 41. Glaciated pebbles dredged from lake bottom .... . 88 42. Core sample from lake bottom...... 89 43. Calcareous concretions from lacustrine sediments .... . 90 44. Baker's station 33 along North Shore Channel. . 91 45. Northern part of the northern hemisphere showing areas glaciated during Pleistocene ti me. 101 46. Boulders from the bed of the glacial river in the DesPlaines transmorainic valley ...... 110 47. Boulder pavement in DesPlaines outlet channel ...... 110

48. Another view of boulder pavement...... 110 49. Glacial lakes Whittlesey, Saginaw, and Chicago ...... 111 50. Moraine correlation across ...... 112 51. Changing levels in the Lake Michigan basin from the Glenwood stage to the present time.. 115 52. Sketch map of the Chicago region during the Glenwood stage of Lake Chicago . 116 53. Sketch map of the Chicago region during the Calumet stage of Lake Chicago .. 118 FIGURE PAGE

54. Sketch map of the Chicago region during the Toleston stage of Lake Chicago ... . 119 55. with three outlets ...... 120 56. Diagrammatic cross section showing oscillations of the shoreline across the Chicago plain .. 122 57. Reconstruction of the vanished sea cliffs and spit connections of the North Shore district .. . 124 58. Ni pissing ...... 125 59. Potholes in floor of Toleston channel ...... 127 60. Water-worn grooves in floor of Toleston channel ...... 127 61. Changes in level in the in centi meters per century ...... 131

TABLE

Classification of the Pleistocene epoch ...... 47 GEOLOGY OF THE CHICAGO REGION

PART II-THE PLEISTOCENE

BY

J HARLEN BRETZ

ABSTRACT

The events most concerned in the making of the surficial physical features of the Chicago region came late in its geological history. Glaciation of subcontinental pro­ portions was part of that extraordinary experience of the northern half of , and is the theme of this report. Earlier (preglacial) events, recorded in the bedrock be­ neath the glacial record, are outlined in portions of Part I of this bulletin. The stages of Pleistocene glaciation in North America were fourfold, and each suc­ cessive invasion of glacial ice partially or even completely destroyed evidence of earlier ones in many places. The glacial history of the Chicago region as now interpreted includes records of the two later glacial episodes, the Illinoian and the Wisconsin. But the record is incomplete for each glaciation and understandable only by comparison with the glacial history of adjacent regions. Starting with the description of the features of the area and the processes by which they were formed, the author proceeds to a systematic treatment of the succession of drift sheets, glacial-lake stages, and Recent changes. Radiocarbon dating is also discussed. Although this bulletin is not a compilation of previous studies, earlier students have laid the foundation and outlined the principles which, tested and approved as research in Pleistocene history of North America has advanced, are the fundamental building stones of today's interpretations. Some rejections and revisions of previous conclusions have been inevitable because of our increasing knowledge under more favorable conditions for checking early ideas and for elaboration of concepts. This bulletin is not a final, complete elucidation of Chicagoland's glacial history. Many problems remain unsolved, much new and significant data will be discovered. CHAPTER I - INTRODUCTION

LOCATION AND EXTENT OF are 87° 30' and 88°, the bounding parallels THE CHICAGO REGION are 41 ° 22' 30" and 42 ° 15'. This is nearly 26 miles east and west by 55 miles HE CHICAGO REGION, in the northeast­ north and south. Two of the 28 quad­ Tern part of Illinois, borders on Lake rangles which fill the block are entirely on Michigan and extends from Indiana almost Lake Michigan, hence do not appear in this to Wisconsin. There are no generally ac­ group. Two are so largely lake surface that cepted boundaries; the industrial cities of the fraction of a square mile of land in each Hammond and Gary, Ind., and Joliet and is made a part of the adjacent quadrangle Waukegan, Ill., are often included in the to the west. Five of the quadrangles have Chicago region. For the purposes of this varying proportions of land and water, and report, the Chicago region, or "Chicago­ the remaining nineteen are entirely land. land," will be considered as that area in­ cluded in the topographically mapped por­ Only the northern fourth of each of the + tions of 24 quadrangles of the southernmost quadrangles has been Geological Survey (fig. 1). Thus defined, mapped topographically and geologically. the region overlaps about 1.3 miles into The overlap on the four southern quad­ Indiana on the southeast and falls about rangles made it possible to include aH of 17 miles short of reaching the Wisconsin Cook County in the mapping. line on the north. All of Cook County is The topographic and geological maps are included, with small portions of DuPage, available separately from the Illinois Geo­ Will, and Lake counties, Ill., and of Lake logical Survey. The geological maps, num­ County, Ind. Since all quadrangle bounda­ bered as shown in figure 1, are also avail­ ries are latitude and longitude lines, fol­ able in a set covering the area described in lowing the standard practice of the United this report. Where reference is made to States Geological Survey, no political a geological map, the map number in the boundaries are used. The total area is set is given, both for convenience in finding 1064 square miles. the map and to differentiate it from the Each of the Chicago region quadrangles topographic map, which is not numbered. measures 7% minutes of arc (1/8 of a Although the topographic maps are used as degree) on a side. Because the Chicago the base for the geologic maps, the overprint­ region is nearly halfway from the equator ing of the geologic pattern partially masks to the pole, a degree of longitude here has the topographic contours, and references are a length only about three-fourths that of made to the topographic maps for features a degree of latitude, and therefore the quad­ best shown on them. rangles are not square. Each measures 8.65 6.45 6.50 miles north and south and to IMPORTANCE OF THE AREA miles east and west. Because of northward convergence of the meridians, the northern The area of Cook County, Ill., is 933 edge of each of the northernmost quad­ square miles and its population in 1940 was rangles is about one-twentieth of a mile +,063,342, making an average of 4,355 shorter than the southern edge of the south­ people to the square mile, which is exceeded ernmost ones. by few areas of similar size on the earth. This group of contiguous quadrangles There are few greater concentrations of constitutes a block 1/2 degree (four quad­ varied industries than in the Chicago re­ rangles) wide and 7/8 degree (seven quad­ gion, and no greater railroad network radi­ rangles) long. The bounding meridians ates from any city in the world. [ 11 ] 12 INTROD UCTION

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FIG. 1.-Map· showing location of all quadrangles referred to in this bulletin and the numbers of the geologic maps in the Chicago region. HIS TORY OF THE INVESTIGATION 13

For the well-being of this great metro­ HISTORY OF politan center, modern engineering has pro­ THE INVESTIGATION vided a safe water supply and an adequate The topographic base maps for the Chi­ sewerage system, both conditioned by fac­ cago region are the product of a cooperative tors which are geological. The engineering arrangement between the United States problem of adequate foundations for the Geological Survey and the Illinois State towering structures which commerce de­ Geological Survey and bear the names of mands irrvolves geological considerations. both organizations. Shortly after the com­ The common building brick, used in great pletion and publication of the entire set, quantity in the construction of Chicago, is the Illinois State Geological Survey com­ a local product of local earth materials. missioned the writer to make a geological Concrete, the rival of brick in many wars survey of the 2+ quadrangles, to prepare a and its superior in some, contains crushed geological map of each for overprinting on from Chicago's numerous quar­ the topography, drainage, and culture, and ries. Sand, for filling and for building pur­ to write a geological report on the region poses, comes into Chicago from the inex­ which would be suited to the needs of lay­ haustible supplies heaped up in the men and students. along the nearby Indiana lake shore. Sand and gravel dredged from the floor of Lake Field work began in the summer of 1930, Michigan has many industrial uses. the writer being assisted by George H. Otto. During the summer of 1931, Mr. Otto took charge of the collection and interpretation PURPOSE OF of all ·subsurface data on unconsolidated THE INVESTIGATION deposits and Edward H. Stevens became The purpose of the present investigation assistant to the writer. This arrangement is to assemble, interpret, and make available was continued during the following summer. basic geological data on the Chicago region. Approximately nine months of field work This information is needed ( 1) for the con­ was sufficient to cover the region in the tinued development and efficient use of min­ detail planned. eral resources of soil, stone, clay, gravel, Part I of the report was written largely sand, and groundw�ter ; (2) for engineering in 193+. As funds for printing the geo­ analysis and design of foundations and other logical maps were not immediately forth­ engineering works relative to earth ma­ coming and it was desirable that they ac­ terials ; ( 3) for land-use planning; and ( +) company the report, publication of Part I for perfecting our knowledge of the natural was deferred. It was decided to publish historr of the area. the report with a much-reduced ( 2 miles to Several universities, colleges, and high the inch), folded geological map inserted schools in the area teach geology, which in the book and to distribute the full-scale makes for constant demand for geological maps later. Accordingly, the report ap­ descriptions and interpretations of the Chi­ peared in 1939 as Part I of Bulletin 65 of cago region. The interest of many intelli­ the Illinois State Geological Survey. gent laymen adds to that demand. The Because man-made changes along the lake geologically recent glacial history is well recorded and may be fairly readily read 'shore had been extensive during the two from the unconsolidated deposits and their decades after the topographic maps ap­ topographic forms, the much older bedrock peared, the shorelines were resurveyed in history from outcrops and quarry walls. 1936-37-38, and the topographic maps re­ Scenic features of the great belt of natural vised with these data and with corrected parks, the forest preserves of Cook County, and additional highway information. The virtually all have geologic elements, the geological maps were printed during 1942 explanation of which is attempted in the and 1943 and their distribution announced following pages. in 1943. 'IN TROD UCTION

The present part, Part II, concerns the field by W. vV. Atwood, Eliot Black.welder, topography of the region and the geology and N. M. Fenneman, who were students of the exposed glacial deposits. Other parts, at the time and who all subsequently be­ dealing with subsurface glacial deposits, came authorities in North American ge­ buried bedrock. topography, stratigraphy of ology. The topographic maps used as a base the exposed bedrock. forn1ations, and vari­ in the Chicago folio were four 30-minute ous mineral resources, are in preparation. quadrangles, covering a little less than two­ thirds of the area treated in the present re­ ACKNOWLEDGMENTS port. The horizontal scale of these maps was 1 to 62,500 (approximately one mile to Field conferences with other workers the inch ), and three of them had only 10- have been of great value in the development foot contour intervals. Though actually of interpretations which appear in Parts I smaller maps than those used in this study, and II of this bulletin. Sharing in these each one covered four times as large an conferences have been M. M. Leighton, area, and far less detail could be shown Chief of the Survey, George E. Ek.blaw, on them. Furthermore, great changes in Head of the Engineering Geology and culture and considerable changes in the Topographic Mapping Division, H. B. lake shore had taken place, and Alden's Willman, Head of the Stratigraphy and excellent report no longer sufficed. Areal Geology Division, Carl A. Bays, In addition to this general treatment on Lewis E. Work.man, and Leland Horberg, the Chicago area, there are many other pub­ formerly geologists of the Survey, D. J. lished papers on various aspects of the Fisher, of the Department of Geology, Uni­ region's geology, some earlier, some later versity of Chicago, the late John R. Ball than the folio of 1902. The earliest geo­ and W. E. Powers, of the Department of logical report seems to be H. M. Bannis­ Geology, Northwestern University, and I. ter's "Geology of Cook. County," appearing D. Scott, of the Department of Geology, as Chapter XIII in Vol. III of the Geo­ University of Michigan. The faithful and logical Survey of lllinois in 1868. Contain­ intelligent assistance of E. H. Stevens and ing only 17 pages of text and no maps or George H. Otto has aided considerably in illustrations, it reports only a reconnaissance covering the field geology. examination of the county. The author was The entire text has been critically read aware, even at this early date, of the glacial, by Dr. Willman, and Chapter IV was read glaciofluvial, and lacustral origin of the un­ by Dr. Scott and G. M. Stanley, of the consolidated materials and the Niagaran Department of Geology, University of () age of the underlying limestone Michigan. Their criticisms and suggestions bedrock.. have resulted in some modifications of form and interpretation. The writer assumes re­ The earliest significant paper in the sponsibility for all statements, however, ex­ region's geological bibliography is Edmund cept where qualified by reference to others. Andrews' "The North American Lakes Considered as Chronometers of Post-Glacial Time," published as Article I of Volume II PREVIOUS PUBLICATIONS of the Transactions of the Chicago Academy This investigation is, of course, not the of Science in 1870. Between this time and first one devoted to the subject of the ge­ the date of Alden's Chicago folio, several ology of the Chicago region. An earlier papers bearing on the region's glacial and treatment of the entire field was published postglacial history appeared, the most im­ in 1902 as the Chicaqo folio (No. 81) of portant ones by G. K. Gilbert, Frank. Lev­ the United States Geological Survey. It was erett, J. W. Spencer, R. D. Salisbury and written by William C. Alden, who for many W. C. Alden, and F. B. Taylor. Specific subsequent years was in charge of Pleisto­ references to these and other studies that cene geology for the United States Geo­ bear on Chicagoland's geology are given in logical Survey. Alden was assisted in the the proper places in the text of this report. CHAPTER II - TOPOGRAPHY

INTRODUCTION and drainage), it is low and almost unrecognizable unless one studies Although most of the drai�age of the a drainage map. It is so low that man has Chicago region now goes to the Mississippi trenched it with the Chicago Sanitary and River the region belongs topographically to Ship Canal, the water supply for Chicago the l;ke section. Much of it beats the im­ being taken from Lake Michigan and the press of a former submergence under the storm and sewage discharge sent to the waters of the Lake Michigan basin. Much Mississippi. consists of undulating glacial moraines de­ posited along the margin of the Lake Michi­ Relief and altitudes.-Within the gan lobe of the last ice sheet, which here limits of the Chicago region as herein de­ moved southwestward out of the basin. fined, the total relief of the land surface is Elongated parallel to the lake margin, these only 227 feet. The lowest part is the lake moraines are traceable in great curved belts shore, the mean level of the lake in 1926 southward from Wisconsin into and across being 578 feet above the sea.2 The bottom the Chicago region, eastward into Indiana, of the DesPlaines Valley on the extreme and thence northeastward into Michigan. western margin of the region is almost as Most of the slopes of the region descen.d to­ low-585 feet above the sea. The highest ward the lake, but most of the detritus of place is a hilltop a mile and a half south the underlying unconsolidated deposits, of the village of Frankfort {Frankfort glacially excavated from the bed of the lake, quadrangle) which is ringed by the 805 con­ has been carried upgrade to its present lo­ tour line. There is an 800-foot hilltop six cation. miles north of New Lenox (Mokena quad­ rangle), and several 790-foot hill tops are Physiographic province.-The great plain shown on the Hinsdale, Mokena, and of the North American continent, cen­ Frankfort quadrangles. The highest point trally located, is wholly shut off from the indicated on any railroad grade in the region Pacific on the west by mountain ranges and is on the Elgin, Joliet, and Eastern line, plateaus, and is largely shut off from the four miles east of Brisbane (Brisbane quad­ Atlantic on the east. But, .as an almost rangle), at 771 feet. The railroad grade uninterrupted lowland, it stretches from descends westward from this point for 11 the Gulf of Mexico to the . miles to Joliet ( B.M. 546), three miles Three major physiographic provinces of this west of the western limits of our region. plain are recognized1 : the Gulf Coastal Nearly half of the 1064 square miles of Plain on the south, the low Laurentian Pla­ Chicagoland, as shown in the 24 quad­ teau on the north, and between them the rangles, is a monotonous plain, largely lake­ Interior Plains, consisting of the Central bottom, recording earlier and higher stages Lowlands on the east and the Great Plains of standing water in the Lake Michigan province on the west. The Chicago region basin. The altitude of this plain above the lies in the Eastern Lake section of the Cen­ lake of today is almost nowhere more than tral Lowlands and is crossed by a major 60 feet. This flat terminates to the north. drainae;e divide, the water parting between west, and south against higher, rolling mo­ the Great Lakes-:-St. Lawrence and the rainic country, some of it hilly. The rough­ systems. Though it is a est country lies in the vicinity of the Des- maior divide {between the North Atlantic "Though some quarries and clay Pits have floors be­ low lake level. they are not natural features of the land lFenneman, N. M., Physical divisions of . the United States map in Physio.,.raphy of Western United States : ;urface and. unless constantly pumped, they promptly fill New 'y ork. McGraw-Hill, 1931. with groundwater. 15 [ ] 16 TOPOGRAPHY

Plaines and Sag valleys on the Sag Bridge small high-gradient postglacial streams have and Palos Park quadrangles, its roughness cut the eastward slope into a maze of due largely to dissection of the morainic up­ ridges and valleys. Wooded, high, and over­ lands by many postglacial stream valleys. looking the adjacent lake, it has become one Steep bluffs up to 100 feet high may be seen of the choicest of Chicago's suburban resi­ in this district, a·s at the toboggan slide in dential districts. the Forest Preserve near Palos Park. Topographic maps.-The 2+ maps cov­ The Mokena quadrangle is similarly a ering the Chicago region show the relief of district mostly in slopes due to stream dis­ the region by brown contour lines. In thus section, but because the major valley walls depicting the elevations and the character were formed before the last glaciation and of slopes, they are topographic maps. They were mantled with glacial drift, the slopes also show water (lakes, swamps, streams, are smoother and gentler than in the Sag and canals) in blue, and culture (the works Bridge quadrangle immediately to the north. of man, such as cities, towm, highways, A narrow zone of rugged topography on railroads, and land boundaries ) in black. the Highland Park quadrangle closely mar­ The horizontal scale selected for the gins the lake. It is the one place in Chi­ mapping was I /2+,000. One inch on the cagoland where morainic country borders map thus represents 2+,000 inches on the Lake Michigan, where no old lake bottom ground it depicts. This comes very close to flat intervenes. Because the moraine here is 2 5/8 inches on the map equalling a mile 75 to 100 feet above the lake, dozens of on the ground. The contour intervar

I /SUPERIOR -""'\, I �-;(! E R N I ! UPLAND I LAKE I I \ \ I \ \ \ ' I (.it-., -....,_ f \ z \ -�, - \ \ 4. \ I ..l \ ()... \ I \ \ \ I \ \\--� ? SECT�� I- ' ' --�--i- �--1, TILL "'1 I�' PLAINS Q::- \ ""� v Q> I � ·�� t'/ ' <(,,� c, I

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I Frn. 2.-Physiographic divisions of the Middle West, showing the location of the Chicago region. STREAMS 17 selected was five feet. Since contour lines nations of limestone, , and shale by definition are level lines, every place members in the well logs record changes in through which a given contour passes is at local depths of submergence, in distances to the same altitude. Slopes thus are shown bordering land, in steepness or gentleness of by a series of parallel or subparallel con­ slopes on that land, and perhaps also in tours, the slope being at right angles to the climate and vegetative cover. lines. Altitudes are printed on every fifth line, which is also a thicker line. Where TOPOGRAPHIC PROCESSES successive contours on the map are shown The unconformities which separate some close together, slopes are steep ; where far of these ancient marine sedimentary forma­ apart, the land depicted may appear to the tions, and especially that very marked un­ eye to be almost level. conformity between the overlying uncon­ Altitudes to the foot are printed at many solidated materials and the subjacent upper­ road intersections and other places on the most marine formation, record periods much maps. Those preceded by the letters B.M. like the present-of exposure to the atmos­ indicate the existence there of a permanent pheric attack of wind, weathering, rain, run­ bench mark with the precise altitude in­ ning water, groundwater, and in some cases scribed on it. The altitude of any place glacial ice. During such times the principal not on a contour line or elevation point events were destructional. material can be estimated with an error not greater was broken up and carried away instead of than five feet. Altitudes are reckoned from being added, as in the making of the sedi­ mean sea level. The level of Lake Michi­ mentary formations. These unconfom1ities gan varies, but averages about 580 feet are old land surfaces now buried beneath above sea level. By subtracting 580 from later deposits. the altitude, therefore, one may know how STREAMS high any point is above the lake. During the periods of exposure, drainage GEOLOGIC FACTORS ways were carved out by the concentration The Chicago region is the cumulative re­ of the run-off from rainfall into streams. sult of many and varied geologic factors, Between such stream valleys were residual some of which are operating today and some elevations, perhaps still carrying summit of which were wholly different from those remnants of the original surface. A definite of the present. The factors now in oper­ sequence of changes in this attack is known ation have had control for so short a time as the cycle of erosion. relatively that the region's physiognomy is The cycle of erosion.-ln the initial still dominated by the impress of processes stages of the cycle, the major drainage long since nonfunctional here. Although not courses are determined by whatever slopes conspicuous in the details of our hills, val­ the newly exposed land may have. These leys, basins, and plains, bedrock is neverthe­ become the major stream valleys as they less the foundation beneath all other ma­ are deepened by the vigorous flow on youth­ terials and has yielded much debris for the ful, high gradients. Because of the deepen­ surface deposits, whose general distribution ing, relief of the region increases toward a and altitude also depend on the buried topog­ maximum. Small tributary streams can raphy of the bedrock. The geological never cut deeper than the main stream at events recorded by the half-mile and more point of junction and, when traced up­ of lithified marine sediment beneath were stream, must by reason of their own gradient like nothing occurring in the region today, be progressively higher than the main. Into except in the depths of Lake Michigan. the tributaries enter still smaller streams, When the bedrock material was being ag­ the branching pattern of the whole much gregated, shallow seas covered the region like that of a tree. Finally, the ravine and and consistently caught and kept the waste gully twigs of the drainage system, well up contributed from distant lands. The alter- on the slopes of the divide, are supplied only 18 TOPOGRAPHY by slope runoff not concentrated into youthful, therefore, chiefly by the existence streamways. Only this slope wash can re­ of numerous swamps, lakes, and undrained duce the residual hilltops, and this process basins, by the lack of marked valley-widen­ is very slow indeed compared with the rate ing and the lack of well-developed dendritic of major valley deepening. drainage pattern. The streams, however, by deepening their The present cycle of erosion began here valleys, reduce their gradients and thereby with retreat of the last ice sheet from the reduce their erosive ability. Undisturbed at region. This is not to say that Chicago­ this work, they must finally cease downcut­ land's topography is compounded wholly of ting. Valley-bottom widening will have al­ late glacial and genetically associated forms, ready begun in these later, slower stages of plus what changes stream erosion has been deepening, and it will eventually become the able to superimpose on them. Some valleys, dominant, and finally the only, method of in the Mokena and Sag Bridge quadrangles valley enlargement. By this time, tributaries in particular, predate that last glaciation and subtributaries will have multiplied and yet are eroded in glacial drift. They were lengthened back into the divide areas so that made after an earlier glaciation and were the transportation system for removal of still usable for drainage after the last of the slope-wash debris is functioning at its best. ice sheets overrode this region. They are Youth in the erosion cycle is past ; the region records of an earlier cycle of erosion that is now mature, with the maximum number assuredly progressed further than the present of drainage ways, the maximum amount of one. And there are a few bedrock projec­ slopes, and almost all surfaces the product tions through the glacial deposits which of erosion by running water. Surviving were hilltops of a preglacial topography. remnants of the original surface are to be The visualization of that marked uncon­ found only on hilltops, if at all. The major formity, that preglacial land surface of the streams have now reached base level, the bedrock, must depend very largely, how­ lowest gradients on which the region's run­ ever, on well-log data. When other regions off will flow and still carry its load of of northern Illinois and southern Wiscon­ detritus. This base-level condition ad­ sin are considered, it appears possible that vances progressively up toward all head­ the late youth or early maturity of this waters as old age approaches. Lowering of preglacial bedrock topography is itself the upland slopes continues and finally is the second cycle recorded by the bedrock sur­ only erosional change possible. Relief and face. There appears to have been an earlier steepness of slopes are now decreasing as cycle that progressed essentially to pene­ the hills are lowered. The peneplain stage planation, and the peneplain seems then to is being approached-the penultimate prod­ have been rejuvenated by uplift of what uct of the attack by running water during is now the upper Mississippi drainage area, a cycle of erosion. and perhaps the present Great Lakes area Topographic age of the Chicago re­ as well. An amplified statement of the evi­ gion.-The topography of the Chicago re­ dence for this concept appears in Chapter gion is exceedingly youthful. Lake Michi­ IV. gan has proved a local base level for GLACIERS eastward-flowing streams, and under pres­ ent conditions they can never do much val­ The glaciation of the northern half of ley-deepening on the plain because of inade­ North America occurred during the latest quate gradients. Westward-flowing stream or Pleistocene epoch. Four times the ice water has more than a thousand miles to go sheets formed in the higher latitudes of the before reaching sea level in the Gulf, and, continent and spread southward to invade with altitudes here of only 600 to 700 feet the northern part of the United States. above that level, valley-deepening by main Four times climatic amelioration brought streams flowing to the Mississippi is also about their destruction. Later invasions did severely limited. We judge the region to be not coincide in outline with preceding ones. ' WA YES AND SHORE CURRENTS 19

\Vhere later ice sheets fell short of the erosion by large waves entering from deep, limits reached by earlier ones, the older gla­ open water into the shallower tract and cial drift deposits lie unburied. Where one there dragging bottom. Calumet, Wolf, drift sheet was overridden in a subsequent and George have been shut off from present ice invasion, it may survive beneath the Lake Michigan by the growth of beach younger deposit. In the Chicago region, ridges during the latest stages of the glacial erosion of older drift by the later ice was lake's history. Details on this subject will more common, and earlier glacial deposits be found in later chapters. survive beneath the latest drift only locally. During retreat of the ice front across the Generally exposures and excavations show western morainic upland, before Lake Chi­ the latest deposits to rest on bedrock. cago's history had begun, one stage was marked by ponding of meltwater between LAKES the ice front on the east and abandoned Besides the overlap of Lake Michigan, morainic ridges and hills on the west. A which is one of the great lakes of the earth row of four lakes existed at this time, their and more than 20 times as large as the Chi­ rather flat bottoms now shared by the Palos cago region itself, there are seven named Park, Tinley Park:, Harvey, Steger, and lakes within the region. The largest of Dyer quadrangles. Three were somewhat these, Calumet Lake, is a shallow pan origi­ smaller than the present Calumet Lake ; one nally about 3 1/3 square miles in area, but had about twice the area of Calumet Lak:e. it is constantly being reduced by marginal All were very shallow and probably were filling. Calumet Lake quadrangle, taking its completely obliterated by deposition of sedi­ name from this centrally placed lake, also ment before the ice front withdrew farther contains Wolf Lake and Lake George. east. The ice front constituted part of the Wolf Lake is partly in Illinois and partly in retaining wall on the east, as it did on the Indiana ; Lake George is wholly in Indiana. east and north for Lake Chicago a little \VolfLake covers about 1 1 /2 square miles ; later. There are no shoreline records of Lak:e George today is only about a tenth of these lakes ; a laminated clay overlying gla­ a square mile in area. Comparison of the cial drift constitutes the best evidence for Calumet Lak:e sheet of 1938 with the Calu­ their former existence. met sheet, whose latest survey date is 1899, The 24 topographic maps show dozens of shows several changes in outline of these ponds and small lakes whose basins are water bodies and particularly a great shrink­ wholly artificial. Most of them are on the age of Lak:e George during the 40-year in­ lake plain. Some are park: lagoons, and terval. Most, if not all, of these changes many are abandoned pits and quarries that are from marginal filling, channel dredging, were excavated below the water table. None and drainage alterations as industry has de­ in this category is to be considered evidence veloped here. Calumet and George are that the region is topographically young. shown today to have the same surface level WAVES AND SHORE CURRENTS as Lake Michigan. Wolf Lake's surface in 1927 was 2 feet higher than Michigan's During the existence of Lake Chicago, mean level. three definite levels occurred, each main­ The three lakes are merely shrunken rem­ tained long enough for waves and shore nants of that larger expansion of Lake currents to cut cliffs and, to an even greater Michigan during the final glacial retreat extent, to build bars, beaches, and spits. from the Great Lakes region. Because that These old shorelines record lake levels ap­ vanished lake had a higher surface and dis­ proximately 20, 40, and 60 feet above Lak:e charged to the Mississippi, it has received Michigan today. An interesting history is the name of Lake Chicago. It, of course, recorded in them, which is more fully was the cause of the levelness of the Chi­ treated in a later chapter. The wave and cagoland plain, to some extent by fillingbut current work during these three stages was to a much greater extent through bottom much like that going on along Lak:e Michi- 20 TOPOGRAPHY

Frn. 3.-Drainage map of the Chicago region, including lakes, canals, and the larger ditches and temporary streams. RIVERS 21

gan today : shore eros10n m places de­ RIVERS creased the land area, while deposition Before the natural drainage was inter­ along the shore in other places added to fered with, there were three rivers in the it. As noted above, there was bottom ero­ region. The Chicago and Calumet rivers sion also. flowed sluggishly in shallow channels across WINDS the eastern flat to Lake Michigan. l t would be a misnomer to call these channels \V ave work is the consequence of wind valleys. The DesPlaines River, with a acting through an intermediary agent, but better gradient, flowed southward from the wind also makes topographic changes di­ northern morainic tract onto the same flat rectly. This is best shown in ancient dunes but then turned westward to enter a deep which closely parallel old shores where sand valley and cross a high part of the western blown back from those shores lodged and morainic country. Joining the Kankakee accumulated. To a very limited extent, River west of Joliet, the two formed the winds have done the same thing along pres­ , one of the Mississippi's large ent shores, but man has largely obliterated affiuents. The divide between the Chicago them in adapting the coastal stretch to his and DesPlaines rivers was only a few miles own purposes. East of Gary, Ind., how­ wide and so low that a continuous swampy ever, growth along the present shore tract connected the two streams. During: has produced many square miles of wild and the epoch of exploration, Marquette, Tonti, attractive country. Indiana has a state park Joliet, LaSalle, and others were able in wet of about three square miles in these dunes, seasons to travel by canoe, without portag­ fifteen miles from Gary. Many other tracts ing, between the Great Lakes and the in this dune belt are summer home incorpo­ Mississippi River by way of this swamp. rations, resorts, and picnic places well The three rivers still exist but their rout­ known to Chicagoans. ings have been greatly modified. Three drainage canals have been cut across the DRAINAGE divide. The earliest one, the Illinois and Michigan Canal, has long been abandoned. A drainage map of Chicagoland, show­ The largest one, the Chicago Sanitary and ing every temporary streamway however Ship Canal, takes the discharge of the Chi­ slightly incised, nevertheless has large cago River westward along the site of the blank areas. Much of the moraine country swamp above noted and pours it, with con­ still has its constructional slopes and no siderable added water from Lake Michigan, integrated drainage ways. Most of the old into the DesPlaines River at Lockport. A lake bottom is untouched by running water smaller one, the Calumet Sag Channel, simply because water does not run on its takes the Calumet discharge in a similar flat surface. To get adequate gradient for fashion from the St. Lawrence drainage storm and sanitary sewers, the Sanitary Dis­ across another place on the low divide and trict of Chicago has had to provide 1 + adds it to the main canal at Sag Bridge pumping stations, where the total discharge village. Thus the natural drainage has all of trunk sewers is lifted an average of 15.3 been shifted to the Mississippi. The former feet, 3 and started again at the higher level mouths of Chicago and Calumet rivers now on a gravity flow toward the drainage are outlets from Lake Michigan, and a canals. Many hundreds of undrained tracts third has been constructed in \Vilmette to in the uplands are still occupied by swamps supply the North Shore Channel, a canal and some by lakes. Larger swamps cov­ feeder to add volume to the North Branch ered tracts of low, flat plain when the city of the Chicago River. Besides these addi­ was young, disappearing as man has ditched, tions to the region's normal runoff, almost sewered, and filled for the needs of a me­ all the "·ater consumed by the five and a half tropolis. million people in metropolitan Chicago is "The smallest lift is 5.3 feet, the largest is 36 feet . pumped from the lake into the water m'ains 22 TOPOGRAPHY and eventually finds its way westward along parallel to the lake shore. The Little Calu­ the drainage canals. To make room for the met, southern and longer of the two, or­ main canal, several miles of the DesPlaines iginally flowed westward almost to Blue course were shifted bodily to more favorable Island, there turned right, and flowed back: lateral positions. These new routes are essentially in the direction from which it marked "Diversion Channel" on the Sag had come. Before 1870, it flowed all the Bridge, Palos Park, and Berwyn sheets. way back into Indiana, entering the lake near Miller, east of Gary. There was CHICAGO RIVER then no trunk channel northward to South The Chicago River consists chiefly of two Chicago, no differentiation into two streams. branches, the North Branch and the South Instead, what is styled the Grand Calumet Branch, and the trunk stream below their was only the lower portion of the Little junction is only a mile long to its mouth Calumet, its water flowing eastward, back­ on the shore of Lake Michigan. The North tracking nearly 25 miles from Blue Island Branch has two tributaries, the West Fork to reach the lake. So sluggish was this and Skokie River. All flow southward for stream that beach and dune deposits actu­ miles subparallel to the lake shore, finding ally were blocking its entrance into the their way along sags that separate various lake in 1870. Earlier maps show an open moraines and old beach accumulations which mouth at Miller. Nearly coincident with are themselves elongated subparallel to the this blocking was the opening of an arti­ shore. In other words, the valleys occupied ficial channel from the lake shore at South by these streams are largely inherited from Chicago to Calumet Lake. This channel earlier conditions and are not the erosional became the trunk of the two Calumets, with consequences of these streams. More than the flow of Grand Calumet reversed. Ob­ half the total length of the North Branch viously, such reversals as this and as that streams is on the lake plain where the gra­ of the South Branch of the Chicago River dient is about two feet to the mile. In the are possible only in very low-gradient moraine country to the north, gradients are streams. about half again as great. The Calumet Sag Channel was opened in The South Branch of the Chicago River 1922. It taps the Little Calumet in the originally headed in the swampy divide and abrupt bend at Blue Island, leads all Calu­ flowed northeastward. This stream has been met water westward, and thus reverses the dredged and its flow reversed, so that Lake flow between Blue Island and South Chi­ Michigan water now discharges southwest­ cago. The :Mississippi-St. Lawrence divide ward along the trunk: to the junction of the in the latitude of Blue Island was shifted two branches and thence along the South about 50 miles farther east by this change, Branch into the Chicago Sanitary and Ship as far as LaPorte County, Ind. Canal, eventually entering the DesPlaines Another diversion of Calumet River has River at Lockport. Thus North Branch been made a little \vest of the Indiana water now flows "up" the South Branch to Dunes State Park. Burns Ditch, across the reach the Mississippi drainage system. barrier of dunes, carries all Calumet dis­ charge from the east directly to the RIVER and reverses the river for a few miles west There are two Calumet rivers also, the of the head of the ditch. The river has Little and the Grand Calumet. They bring been "beheaded" by this canal. It is an Indiana runoff westward into Illinois and artificial stream piracy. join about a mile south of Calumet Lake on Below Lockport, where the combined the quadrangle of the same name. The discharge of the Calumet Sag and the Sani­ trunk stream continues northward 7 1/2 tary and Ship canals enters the DesPlaines miles to Lake Michigan at South Chicago. River, it has been augmented by the total Like the North Branch streams, and for discharge of the Chicago system and all of the same reason, the two Calumets are sub- the Calumet system west of Burns Ditch; MINOR STREAMS 23 plus the discharge from Lake Michigan side of the river. They are Long Run, through the three artificial outlets, as well Fraction Run, Spring Creek, and Hickory as the pumpage from all crib intakes into Creek with its tributary Marley Creek. the Chicago city water mains. The total Farthest to the southwest is the head of westward discharge allowed since 1938 by Jackson Branch, the only stream of the the War Department, from Lake Michigan region to enter the . and its former tributaries, the Chicago and Unnamed streams are more numerous but Calumet rivers, is 1500 cubic feet per are largely temporary, their water courses second. indicated on the maps by interrupted blue DESPLAINES RIVER lines. Some are vigorously eroding streams, though most of them have had too small a Heading 40 miles north of the Illinois­ volume and too low an original gradient Wisconsin state line, the DesPlaines River to cause much stream erosion. On the flows southwardsubparallel to the lake shore Highland Park sheet 18 small streams are as far as Lyons, on the Berwyn quadrangle. indicated as mouthing along the lake shore,4 There it turns southwestward and so con­ and many of them have several tributaries. tinues across the Sag Bridge quadrangle to Only one is more than a mile long. All leave the Chicago region at Lemont. Near head on the eastern part of the crest of the Lockport, 9 1/2 miles from Lemont, it Highland Park: moraine at altitudes of receives the discharge of the Sanitary and 650 to 685 feet. Gradients of 100 feet to Ship Canal, which here falls about 39 feet the mile are common. This is an enormous through penstocks. This is the only hyd ro­ figure when compared with the gradient of electric plant utilizing Chicagoland drain­ Skokie River-3 feet per mile-imme­ age. About 17 1 /2 miles farther down­ diately west of and paralleling the moraine stream is the junction of the DesPlaines ridge. With such favorable gradients, and Kankakee rivers, their confluence form­ thesesmall-volume, temporary, wet-weather ing Illinois River, the longest and lar gest streams have been able to cut steep-sided stream in the state. ravines 50 to 60 feet deep. The low gradient of the Skokie was an inherited MINOR STREAMS slope, and the stream, despite its perennial A few perennial streams drain from the character, has been unable to erode more uplands of the Chicago region into the Des­ than a channel for itself. Plaines and Calumet rivers. Thorn Creek Another region of youthful, vigorously enters south of Calumet City from the south expressed ravines is found on the Sag Bridge side of the Little Calumet. Thorn Creek and Palos Park: quadrangles, where high has three named tributaries, Deer Creek gradients were provided by the steep bluffs and , which join it at of DesPlaines and Sag valleys that were Glenwood, and North Creek, which enters cut across the western morainic upland. it half a mile south of Thornton. Tinley These river bluffs are 7 5 to 100 feet high, Creek enters the Calumet Sag Channel near comparable to the coastal bluffs above Alsip, and Mill Creek joins it near Palos described. Ravine development, however, Park. On the west side of the DesPlaines is considerably less than on the Highland River, Indian Creek enters at Half Day, Park: quadrangle. There are two reasons Buffalo Creek at \Vheeling, Higgins Creek for this. At the North Shore ravines, waves and Willow Creek near Orchard Place, and shore currents have constantly carried Salt Creek at Riverside, Flag Creek at away the detritus brought down by the Tiedtville, and Sawmill Creek between streams ; hence gradients at the mouths Lemont and Sag Bridge. Four other named have never been decreased bv stream depo­ streams, all in the southwestern part of sition. In contrast, neither Sag Valley nor the region, flow into the DesPlaines from DesPlaines Valley has been used, during the Chicago region, but they enter it west •By using contour groups that !'how ravine f,orm� of Chicagoland ; all drain from the east instead of the interrupted blue lines, 29 can be counted. 24 TOPOGRAPHY

ravine growth, by main streams adequate to SUBMERGED PORTION OF THE CHICAGO remove such detritus. Consequently, every PLAIN ravine is likely to show an alluvial fan de­ posit on the flat floor of the larger valley, The Chicago plain is clearly emerged lake the effect of which has been to check the bottom and records a former submergence deepening, if not actually to cause some of about 60 feet maximum. If this plain filling in the lowermost portion of the was fashioned largely by subaqueous proc­ ravme. esses in the geologically recent past, one The second reason is that in the North may inquire if a similar plain now under­ Shore district, waves have been driving the lies the marginal portion of Lake Michi­ cliff back by undercutting while the ra­ gan. The question is answered affirmatively vines have been growing. This has short­ ened ravines at their lower ends and con­ by an inspection of the numerous soundings sequently has actually steepened the origi­ on the two 1926 Chicago Lake Front charts nal gradients on which they started to grow. of the United States Lake Survey. Con-

FIG. 4.-Contour map of a portion of the lake bottom in the Chicago region. After Hough. Depth of water in feet. LAKE LEf/ELS 25 tours drawn by Hough" for these sound­ Measurements during the past century ings show a slope as gentle as that now ex­ show that there is an annual fluctuation of posed which continues out under the lake about 1 foot in lake level, the high coming for about 10 miles to a depth of 60 feet. in late summer, the low in midwinter. Sea­ Beyond the limits of Hough's map, the Lake sonal variations in snowfall, melting, Survey's Coast Chart 7 5, 1939, shows that rainfall, and evaporation are held account­ the bottom slopes gently out into the lake able for this one-foot annual range. for another 10 miles, its gradient being A larger cycle of about 11 years, with a scarcely half again as great as on Hough's larger range in levels, is recognized" and has map or on the landward plain. Therefore, been correlated with the sunspot cycle of the Chicago plain may be visualized as con­ that duration.7 Sunspot minima and maxi­ tinuing under Lake Michigan for 20 miles ma are already known to affect terrestrial offshore at much the same slope as its land weather, producing corresponding extremes portion. The procedures by which this in rainfall and evaporation. When the partly emerged, partly submerged plain has algebraic sum of the annual cycle is plus, been formed will be discussed later in this the annual mean lake level is rising; when report. it is minus, the mean level is lowering. The range in level throughout the 11-year LAKE LEVELS cycle is not a constant value. Reading The earlier stages of standing water m from highest summer to lowest winter the Lake Michigan basin, during some of level in each cycle, the range has varied which almost the whole of the Chicago from 2 3/-1- to nearly 5 feet. The most plain was submerged, will be dealt with marked change on record came immediately more fully later. Since there is no lowering after the making of the topographic maps in water surface through Mackinac Strait, used in this report. By 1929, the level of the present Lake Michigan stage is de­ Michigan (and Huron) had risen almost termined by the level of the outlet of Lake 5 feet from the all-time low of 577.35 in Huron. Were the St. Clair River outlet 1926. to become deepened, the lake surface would The solar cycles themselves are variable, lower ; were it to be dammed, the surface and there may be larger rhythms in their would rise. succession than 've have yet detected which Yet with no change in location, altitude, may become apparent in the next few cen­ or capacity of this outlet, the level of Lake turies. They have been occurring in the Michigan varies. The United States Geo­ postglacial, prehistoric past. logical Survey's first topographic survey of Stability of lake levels \v ithin the limits Chicago, dated in the 1890's, bears the figure of the annual range is highly desirable. 581 printed on the lake surface. The second The high water of 1929 lifted storm waves survey, whose maps are used for this re­ and floating ice high against harbor and port, carries the statement, "Mean elevation shore structures and against vulnerable sea­ of lake surface in 1926 5 78 feet above sea cliffs, which caused damage amounting to level." In January 1926, the lake surface millions of dollars. \Vood8 argued convinc­ actually stood as low as 577.35, the lowest ingly that forecasting the larger fluctuations since observations began in 1835. In 1838 is within the ability of modern science, and it had stood at 58-1-.69, the highest on record 6Musham, H. A., Rhythmic fluctuation5 of the levels of the Great Lakes : Western Soc. Eng. _Tour., vol. 48, in a century of observation. The total pp. 185-196, 1943. Musham reported that an inter­ measured range of lake level thus is 7.34 mediate low level has occurred 7-8 years after a maxi­ mum high and has been 5ucceeded by an intermediate feet. Based on these dates and figures alone, high within about 3 years. The minimum low has oc­ curred 11-12 years after the maximum high. Then be­ there seems to have been a startling decline tween the minimum low and the next maximum high, there has been another intermediate high, 15 years after in volume of the lake. The problem is not the beginning of the cycle, and another intermediate low, 18-19 years after the beginning of the cycle. This com­ that simple, however. pound rhythm is found in the accurate records since 1855. It has been repeated three times between 1855 and 1930. "Hough, J. L .. The bottom deposits of southern Lake 'Wood, Sidney M., The cvcles of the Great Lakes : Michi,2"an : Tour. Sedimentary Petrology, vol. 5, no. 2, Bull. As'°c. State Eng. Socs., Oct. 1936. pp. 57-80, 1935. 1Ibid. 26 TOPOGRAPHY

KEV

� Glacial n·1er botfo..,

SCALE 3_ - 4 ...... �

FIG. 5.-Distribution of topographic features of the Chicago region. UPLANDS 27

that controlling works at the outlet, guided One -born river utilized such a by the forecasts, can give that stability. ground-moraine belt. Postglacial drainage has followed some of them, giving rise to TOPOGRAPHIC FEATURES the various tributaries of the North Branch of Chicago River, to the DesPlaines River The major topographic features of the upstream from Lyons, to Salt Creek, and Chicago region can be grouped under four to Flag Creek. categories : ( 1 ) the morainic uplands to Valparaiso morainic system.-The Val­ the north, west, and south, (2) the lake paraiso moraine is the widest of the six, plain partially enclosed by these uplands, and therefore the least ridgelike. I ts full ( 3) the shore features of Lake Chicago and width does not come within the region ; its successor, Lake Michigan, and ( 4) the its frontal edge lies on the Joliet and Whea­ stream-occupied valleys, some inherited from ton quadrangles to the west. Its irregular the glacial topography, some eroded by inner margin is traceable from an inter­ streams working largely in glacial drift, section of the region's western boundary 2 though locally in bedrock. or 3 miles west of Elmhurst southeast by south to an intersection of the southern UPLANDS boundary 2 or 3 miles south of Matteson. Moraine ridges.-Generally the ridges The Valparaiso moraine constitutes most are not readily recognized in views across of the western uplands and contains the the region. Rarely do the moraines have highest parts of the entire region. There is definite linear crests or marked lateral more relief and more rough country in this slopes. Instead, each is more like an elong­ moraine than in any of the others, though ated series of partially coalesced and over­ the relief and roughness are not wholly due lapping hills. The elongation becomes clear to the moraine itself. The moraine's re­ on a map, where many miles of country lief, caused by unequal deposition of the can be seen at once. The elongated moraines Valparaiso glacial drift, rarely exceeds 50 might be thought of as belts of upland feet. An older topography buried beneath rather than ridges. The abundance of un­ the Valparaiso drift sheet, and reflected in drained depressions on them testify to the its surface irregularities, has locally twice immaturity of their drainage. as great relief. There are six separate mappable units in Three named lakes, two named sloughs, this category, all traceable across the re­ and a large number of unnamed marshes gion's boundaries into adjacent country. and swamps lie in the abundant undrained Orientation of these linear moraine tracts depressions that so commonly typify mo­ is dominantly northwest by north, south­ rainic topography. Some of the deeper de­ east by south. In the southern quadrangles, pressions appear to be parts of pre-moraine the orientation is northwest-southeast and stream valleys that became blocked but not well into the southeastern corner of the obliterated by the Valparaiw drift deposits. region ; the one moraine present trends Two stream-made valleys cross the moraine approximately east-west. These orientations -that of the DesPlaines River and of are definite records of the shape of the Hickory Creek. Both are parts of the pre­ glacial front and are successively younger moraine buried relief, resuming their orig­ from west to east. Two of them were built inal function after the Valparaiso ice dis­ before the recorded beginning of Lake Chi­ appeared. cago, and four are contemporaneous with The suburban towns of Lombard, Hins­ the early history of that glacial lake. dale, Clarendon Hills, \Vestmont, Downers Separating these marginal moraines are Grove, and Orland Park are wholly within similarly elongated lower tracts of ground­ the moraine boundaries. Villa Park is moraine, across which the ice front re­ partly on the marginal moraine and partly treated more rapidly than it did across the on ground moraine immediately to the east. moraine ridges, hence deposited less drift. Salt Creek as far downstream as Western 28 TOPOGRAPHY

Springs and Flag Creek for its entire length �he suburban towns of Arlington are on the Valparaiso ground moraine. Heights, Elmhurst, Western Springs, Palos Park, and Matteson are built on the Tinley Tinley moraine.-East of the Valpa­ moraine. The western part of LaGrange raiso moraine is the Tinley moraine, with and the southern part of Chicago Heights the greatest length in the region of any of also stand on the Tinley. Half Day, Des­ the six moraines. It extends from the north­ Plaines, Bensenville, Hillside, most of La­ ern boundary, a mile east of Mundelein Grange, Oak Forest, Homewood, Floss­ southeast by south to Chicago Heights'. moor, and most of Chicago Heights are on where its course becomes nearly east-west lower ground moraine belonging to the as it is crossed by the southern boundary. Tinley stage. I ts total length on the nine quadrangles in the region is 60 miles. The Tinley moraine Lake Border moraines.-East of the Des­ is much narrower than the Valparaiso, its Plaines Valley in the northern half of greatest width in the region being 5 miles the region, four moraines project south­ its average width about 2 miles. In th� ward from the northern boundary. Known vicinity of Tinley Park, it has an unusually collectively as the Lake Border morainic marked western front that rises 25 feet system, they constitute the northern mo­ above the flat left by one of the four rainic upland. All of them die out on reach­ glacial lakes already noted. It has its great­ ing the lake plain, the westernmost and longest reaching scarcely 25 miles into the est relief, about 60 f�et, in the Mount Forest Island region (Palos Park quad­ region. This dying away is only an inter­ rangle). This may be a composite of the ruption, for the system is found again in Tinley's own relief superimposed on an Indiana and is traceable thence northeast­ older relief beneath, as is the case with the ward and northward into Michigan� thus Valparaiso moraine. describing a great curve closely co form­ ing to the margin of the lake. Undrained depressions, many containing In order from west to east, these moraines swamps and lakelets, are well distributed are the Park Ridge, the Deerfield, the but most numerous on the Palos Park ant! Blodgett, and the Highland Park.9 On the Tinley Park quadrangles where the moraine Waukegan quadrangle, immediately north is roughest. The moraine is transected by of the Chicago region, the sags separating two major valleys, the westward-draining them are less prominent, and recognition DesPlaines and Sag valleys. It is also of all four units is difficult. crossed, in the opposite direction, by eight The total width of the system is about creeks along its 60-mile length. The two 6 miles, the three ground-moraine sags major valleys are older than the moraine · making up nearly half of that width. The the creek valleys are all younger. North of morainic character of the system is very the latitude of LaGrange, Salt Creek clo>ely mildly expressed, and the contacts of margins the western or frontal edge of the ground moraine east of a marginal morainic Tinley moraine, and the DesPlaines River ridge are difficult to determine. The steeper parallels it on the east. Both stream courses frontal slopes of the broad, low moraines, along ground-moraine sags, are consequen� however, are readily recognizable on the on the constructional topography left by the topographic maps from the habitual closer retreating ice sheet. grouping of contours. On the Palos Park quadrangle, the Tin­ In the south where the floors of the ley marginal moraine overlaps the back ground-moraine sags become lower, they slope of the Valparaiso, there being no Val­ were occupied by long narrow bays of Lake paraiso ground moraine of gentler slopes Chicago's highest stage, and today they all and lower relief between. The Valparaiso earn• southward the consequent drainage of ground moraine is widest on the Tinley the North Branch of the Chicago River. Park quadrangle, next to the south, attain­ The easternmost, or Highland Park, ing here a width of 5 miles in the region moraine was built higher than any of the· of the largest of the four extinct glacial �:-!ames first published in Bull. 65, Part J, pp. 55-56, lakes. 1939 SHORE FEA TURES OF LAKE CHICA GO 29

other three. I ts frontal slope rises from 25 low place reaching from Lake Michigan to 40 feet in the steepest constructional to the western moraine uplands. In this slopes to be found among these Lake Border was the swampy divide between the Chicago moraines. Its summit in several places River and the DesPlaines River. stands 50 to 60 feet above the Skokie Valley Many square miles of this plain appear to the west and more than 100 feet above perfectly level to the eye. Such irregulari­ Lake Michigan to the east. ties as exist are islands of the glacial lake, Previously noted is the continuous sea­ or shore features of the three successive cliff facing the lake from Kenilworth north­ stages, or postglacial stream valleys and ward to and beyond the boundary of the channels. One other feature of the plains, region. Except for the southernmost 2 easily overlooked in the field or on the topo­ miles, this cliff everywhere is cut in the graphic map, is a series of faintly shown eastern slope of the Highland Park moraine. steps descending from the convex to the Retreat of the cliff has been in progress concave side. The "risers" in these steps ever since the early stages of Lake Chicago. are low wave-cut cliffs, some of which are The back slope . of the Highland Park masked by beach sand and gravel ridges. moraine thus differs markedly from that of The risers then are shorelines of the stages any other moraine of the region. of the glacial lake. Of two "treads" sep­ Numerous suburban towns of the North arated by a riser, the lower one was eroded Shore residential district have grown up on under water by the drag of the waves which, these moraines, and some of them have on reaching the shoreline, cut the riser. spread their corporate. limits down onto More will be said on this subject later. ground moraine or lake bottom. Four towns The largest of the islands of Lake Chi­ provide names for the four ridges. Norwood cago now standing out in the plain is Blue Park and Elmwood Park stand largely on Island, on the quadrangle of that name. It the Park Ridge moraine ; Northbrook. on is elongated north-south, is 5 1 /2 miles long, the Deerfield; and Winnetka, Hubbard and a little more than 1 mile wide. It is Woods, Glencoe, Highland Park, Ravinia, essentially a portion of the Park Ridge mo­ Highwood, Fort Sheridan, and Lake Forest raine, isolated on the plain about 13 miles on the Highland Park moraine. The Blod­ south of the southern tip of this moraine. gett moraine, smallest of the four, carries It rose as much as 30 feet above the high­ overlapping portions of Lake Forest and est level of the lake. I ts eastern side is a Highland Park in addition to the town for sea cliff, easily recognized in the residential which it was named. sections of Beverly Hills and Morgan Park. Its western side is a row of sand dunes, THE LAKE PLAIN marked now by several cemeteries and coun­ Nearly half of the land area of the region try clubs. The business and residential por­ is the plain which Lake Chicago left when tions of the city of Blue Island stand on the its level was lowered to that of Lake Michi­ southern tip of this "island." gan. It is rudely crescent shaped, with con­ HORE FEATURES OF AKE HICAGO vexity toward the west. Northward it is S L C terminated by the Lake Border moraines ; Accompanying maps (figs. 5, 52, 53, 54, eastward, it continues into Indiana between and 57) show many elongated beach ridges the Tinley moraine and Lake Michigan, the subparallel with the outer and inner mar­ Lake Border moraines being absent here. gins of the crescentic plain. Classified by The southward projections of these moraines their altitudes, there are three groups of into the plain suggest long narrow penin­ them, the two uppermost belonging to the sulas, as indeed thev once \Vere. Elsewhere, Lake Chicago stages (the Glenwood, high­ the outline of the plain is simple. The con­ est and oldest, and the Calumet, interme­ vex western margin is highest, its concave diate) and the lowest including Toleston eastern edge is lowest and descends beneath (lowest) with beach deposits made by the Lake Michigan. Across the crescent is a later Lake Algonquin and Nipissing Great 30 TOPOGRAPHY

Lakes stages, which rose to the Toleston Another subcategory of the Lake Chicago level. The vertical interval between any shore features is the group of cut shorelines, adjacent two of these is approximately 20 the ancient sea cliffs where waves and cur­ feet ; the horizontal spacing is highly vari­ rents eroded instead of depositing. They able. Throughout the Chicago region and alternate with depositional shores along each as far north as , these old shore­ of the three shorelines and range in height lines are as horizontal as when they were from those that are just recognizable to 20 first built. There has been no warping of or 30 feet. The most marked of these cut­ this part of the Great Lakes country in all bank shores are : ( 1) in Winnetka (Evan­ postglacial time. ston quadrangle) , ( 2) in Riis Park and the Though some of these tracts of beach sand Galewood district (River Forest quad­ and gravel are more than a mile wide, linear rangle), ( 3) in Beverly Hills and Morgan elongation along the old shore is still evi­ Park (Blue Island quadrangle), ( 4) in dent. The term beach is here used to in­ Kensington and Roseland (Calumet Lake clude all deposits along the shore in wave­ quadrangle) , ( 5) between Homewood and and current-agitated water. Specifically Hazelcrest (Harvey quadrangle), and ( 6) these linear deposits are made up of beach between North Creek and Deer Creek, ridges built on the land at the water's edge, southeast of Glenwood (Calumet City bars built somewhat offshore at the line of quadrangle). Where feebly developed and breakers, and spits built out at low angles constituting only what are here termed from the land where the shoreline receded "risers" in the plain, they can be identified somewhat in a bay. The more conspicuous within the city in many places only by the · and easily identifiable spits occur : ( 1) near occurrence of a grade, perhaps half a block or in part of Wilmette (Park Ridge and long, interrupting the long level stretches Evanston quadrangles), ( 2) in Evanston characteristic of Chicago streets. and the northern part of Chicago (Evan­ ston and quadrangles), ( 3) VALLEYS in Oak Park and River Forest (River Forest and Berwyn quadrangles), ( 4) north As already outlined, the region possesses of LaGrange Park (Hinsdale and Berwyn two types of free-draining valleys. One type quadrangles), ( 5) in Berwyn and Riverside was made during the moraine-building and (Berwyn quadrangle), ( 6) n-0rth of Ever­ the beach-building, the streams in possession green Park (Blue Island quadrangle), and today having done little to modify their in­ (7) between Thornton and Lansing and herited courses. The other type of valley east -0f East Chicago Heights (Calumet is the product of stream erosion, the courses City quadrangle). Only where dunes have reflecting earlier slopes that determined the grown up on the beach deposits do they routes they follow now. possess any marked relief. In built-up por­ tions of Chicago, many of the more weakly CONSTRUCTIONAL VALLEYS expressed features have almost disappeared. Valleys of this type are most numerous, The noteworthy dune tracts contempo­ raneous with the Lake Chicago beaches are : and most easily recognized as such, in the northern half of the region. The larger ( 1) on the "\Vilmette spit (Evanston quad­ ones drain to the south and belong to the rangle), ( 2) on the west shore of Blue Chicago River and DesPlaines River sys­ Island (Blue Island quadrangle), ( 3) be­ tems. tween Homewood and Thornton (Harvey quadrangle) , ( 4) between Dolton and Salt Creek Valley.-Flowing on Valpa­ Hammond (Calumet City quadrangle), raiso ground moraine and closely hugging and ( 5) east of Dyer (Dyer quadrangle). the front of the Tinley moraine, Salt Creek The highest dunes are on the west side of flows southward for 16 miles (20 miles if Blue Island, near the north end of that measured on the meanders of the channel), belt, where their summits stand 30 feet on the Arlington Heights, Elmhurst, and above the adjacent lake plain. Hinsdale quadrangles, to the northern CONSTRUCTIONAL VALLEYS 31 boundary of the town of Hinsdale. Here it tract of "basin fill," a former closed depres­ turns eastward for 2 miles to cross the sion now obliterated by deposits of surface Tinley moraine and enter the lake plain, wash and organic material. The fill, 1 1/2 northward for 1 1/2 miles to go around miles long, occupies the broadest place in the northern tip of the LaGrange spit, and the valley, six times as wide as at the cross­ southeastward to join the DesPlaines. The ing of Joliet and Wolf roads 1 3/+ miles Hinsdale and Sag Bridge topographic maps farther south. This downstream narrowing show that where the creek turns east, it also has the highest ( 50 to 60 feet) and leaves the morainic sag, and that farther steepest bluffs of any place along Flag south Flag Creek occupies this same sag. A Creek, facts consonant only with the inter­ cursory inspection suggests that Salt Creek pretation above offered. once did not cross the Tinley moraine but On entering the Sag Bridge quadrangle, continued all the way southward along what the valley ends, but the stream continues is now Flag Creek Valley. Field data, how­ past Tiedtville along the west side of the ever, prove that the marshy floor at the head DesPlaines transmorainic valley. From the of Flag Creek separating Hinsdale and basin at the head, the creek descends 55 \Vestern Springs has never been used by Salt feet to the DesPlaines, a gradient of 8 feet Creek and is a fair sample of what all these to the mile. Had Salt Creek ever used Flag constructional valleys would be like if no Creek Valley, it would assuredly have streams had ever utilized them. eroded sufficiently on this gradient to trench In the north-central part of the Hinsdale across the site of the basin fill. quadrangle is an "island" tract of some­ DesPlaines Valley north of Lyons.-The what more than a square mile, separated DesPlaines River heads almost on the Ra­ from surrounding Valparaiso morainic sur­ cine-Kenosha county line in Wisconsin, 40 faces by Salt Creek Valley on the north and miles north of the northern boundary of east and by a marshy valley without through the Chicago region. In this region it crosses drainage on the northwest and south. It is the Wheeling, Arlington Heights, Park almost as low as Salt Creek Valley, with Ridge, River Forest, Berwyn, Palos Park, which it connects at each end of its irreg­ and Sag Bridge quadrangles. Except for one ularly semicircular course. An attractive place on the Silver Lake quadrangle, Wis., explanation for it is that an early Salt Creek its entire course south to Lyons is deter­ flowed through it when the present course mined by ground-moraine sags. For most of was blocked by the ice front retreating its length, it flows on Tinley ground mo­ down the back slope of the Valparaiso mo­ raine and fairly close to the front of the raine. But there are morainic spurs project­ Park Ridge moraine. Its gradient upstream ing into the marshy flat in a fashion that from bedrock outcrops in its channel at stream erosion never could produce or toler­ Lyons is 1 1 /3 feet per mile. ate. This marshy valley never was eroded The valley floor from RiverGrove north­ by Salt Creek drainage, either during glacial ward almost to the Wisconsin line, if not retreat or subsequently, and must be inter­ farther, possesses a fill of gravel and sand preted either as a morainic sag or as the overlying the ground moraine and contain­ trace of a pre-Valparaiso valley not entirely ing the present river channel. This is a obliterated by the moraine deposits. valley train, deposited by a river of melt­ Salt Creek, above its crossing of the Tin­ water fed from the waning ice front during ley moraine, has a gradient of only 2 1 /2 the earliest of the Lake Border stages. The feet to the mile and is the most markedly glacial DesPlaines was far larger than the meandering stream of the region, though the stream of today, for the valley fill is a outline of its valley floor shows little effec­ stream-bed deposit 1 1 /2 miles wide for tive widening by meander undercutting of long stretches. Gravel bars standing 5 to the sides. 10 feet above the surface of this valley Flag Creek Valley.-This creek ( Hins­ bottom fill are part of the glacial-stream dale quadrangle) heads in an elongated deposit and indicate that in the heavy melt- 32 TOPOGRAPHY ing of summertime, this channel was full Valley of North Branch, Chicago River. for the entire width and as deep as the bars -North of Northfield (\Vheeling and are high. The maximum known depth of Highland Park quadrangles), this valley the fill is 15 feet, with the bottom not is confined between the Deerfield and Blod­ reached. 'I'he gradient of the plane surface gett moraines, most of its length having a of the fill is from 1 1 /2 to 2 feet per mile. ground-moraine floor. The Blodgett mo­ Into it, the postglacial river has eroded an raine ends in the northern part of the inner valley, rarely more than 10 feet deep Northfield corporate limits, projecting or more than a quarter of a mile wide. southward here as a small peninsula into 'I'he southern portion of the valley train the fingered northern margin of the lake terminates where the glacial river entered plain. The valley from there to its junction Lake Chicago. The present river continues with the South Branch, in the heart of beyond this for 8 miles across emerged lake­ Chicago, is entirely stream-made. 'I'he bottom beyond River Grove as far as Lyons. course bends back from the lake a little Much of the riparian land along the Des­ to go past the \Vilmette spit and then turns Plaines in Cook County above Lyons has east toward the lake, only to be forced to been acquired by the Forest Preserve, and go 7 miles farther south to get around the several dams have been built to retain suffi­ two spits in Evanston and in the northern cient water during low summer stages for part of Chicago. Erosion by this stream recreational purposes. in the lake plain is most marked in the At Lyons the DesPlaines has encoun­ northeastern part of the River Forest quad­ tered two high places in the buried bedrock rangle where the Calumet or intermediate but has not eroded more than 5 feet into shoreline is crossed and the stream descends the limestone. A dam at Riverside makes across a "riser" between two "treads" of the it impossible now to figure the original plain. Although the valley is only 15 to 20 gradient of the stream surf!lce at this place. feet deep here, meandering has made a flood­ Below the dam, the stream descends 10 feet plain. Some of the crenulate outlines of the in 1 1 /2 miles to the next bedrock portion floodplain are being enlarged today by me­ of the channel. This is the steepest gradient ander undercutting of the bluffs ; others ob­ in any portion of any major stream of the viously are abandoned meander scars. region. Across the lake plain, the river flows on a Valley of West Fork North Branch, Chi­ gradient of about 2 feet per mile. On the cago River.-The ground-moraine sag be­ ground-moraine sag farther north, its gra­ tween the Park Ridge and Deerfield mo­ dient is about 3 feet to the mile. raines (\Vheeling, Highland Park, and Valley of Skokie Rii•er.-The sag be­ Park Ridge quadrangles), determines the tween the Blodgett and Highland Park mo­ course of this stream, and in its southern raines (Highland Park quadrangle) was the portion it determines also one of the long, lowest of this series of intermorainic valleys. narrow bays of Lake Chicago. The West It therefore contained the longest bay of Fork therefore flows southward on ground Lake Chicago, and its present-day stream moraine for 8 miles to Northbrook and on traverses only 4 miles of ground moraine lake bottom for the next 6 miles to its junc­ within the region before reaching and flow­ tion with the North Branch at the southern ing on lake bottom. On the ground-moraine tip of the Deerfield moraine. For its size it floor, Skokie River has a gradient of 4 1/2 has a relatively low gradier.t, 4 feet per mile. feet per mile, but on the bottom of the bay Considerable stretches have been ditched to its gradient is scarcely more than 2 feet per improve the drainage of the valley bottom. mile. 1\1 uch of the stream course in Lake Only in the last 3 miles has the West Fork County has been ditched, and in Cook done anything to make a stream valley in County the Highland Park and Park Ridge the bottom of the morainic sag. At the junc­ sheets show a marsh 3 miles long into which tion with the North Fork, this minor val­ the stream enters at the north end and from ley is 10 feet deep. which it drains at the south end. Since the EROSIONAL VALLEYS 33 map was made, the marsh has been exten­ ern part of Gary. The stream flows SO sively altered by construction of lagoons additional miles to go around the belt of and artificial hills to make a recreational old dunes. which constitute the 2 1/4 mile­ area. I ts existence when the geological map wide barrier. The "valley" of the river for was made is convincing evidence of the most of its length is nothing more than a stream's inability to trench into the lake linear belt of old lake bottom between rows plain. of abandoned beach and dune ridges. The The Lake Border moraines are so narrow river has made nothing more than a channel and have so low a relief that no named for itself and has largely failed to drain tributaries to the streams discussed above the swampy lowland along much of its have developed. Only the DesPlaines River course. Lack of topogr,aphic maps covering possesses such tributaries, and they all drain the Indiana territory traversed by the river from the Valparaiso and Tinley slopes. Ex­ prohibits a statement of its gradient. cepting Salt Creek, all the named streams of this group (flowing in constructional val­ EROSlONAL VALLEYS leys ) have been ditched or possess swamps (or both ) in parts of their courses. One DesPlaines Valiey south and west of such stream, entering the DesPlaines at the Lyons.-At Lyons the DesPlaines River town of DesPlaines, is called Weller's enters one of the two outlet channels of Drainage Ditch on the Arlington Heights Lake Chicago and flows southwestward out sheet. It flows southeastward down the back of the region. Except for the first 3 miles of slope of the Tinley moraine and across Tin­ the course, the valley averages 7 5 feet in ley ground moraine with a gradient of 10 depth and is the transmorainic portion of feet per mile and was clearly a natural the DesPlaines River. The rather com­ drainage line bef.ore ditching. Had it plicated history of this valley, discussed possessed adequate volume with this gra­ more fully in a later chapter, began with dient, stream erosion would have made a trenching across a preglacial divide before definite valley. the building of the Valparaiso and Tinley Calumet River Valley.-Considered as a moraines-therefore during a somewhat river valley, the original course of the Calu­ earlier glaciation. Modified by Valparaiso met River (Calumet City, Blue Island, and and Tinley deposits, it nevertheless again Calumet Lake quadrangles) is strikingly became a river course, this time the outlet aberrant in its 180-degree turn near Blue of Lake Chicago. A little later it carried Island from west to east, and its nearly 25- discharge from glacially ponded water in mile backtrack to the lake. It is only 2 1 /4 the Superior, Huron, and Erie basins, as miles southeast from this original mouth to well as the Michigan basin. During the the west-flowing portion in the southeast- past century, man has considerably altered the valley floor by digging two canals, the Illinois and Michigan Canal of 1848 and the Sanitary and Ship Canal of 1900, and by diverting portions of the postglacial Des­ Plaines channel to make room for the later canal. Some suggestions of old channel mutes are recorded in political boundaries shown on the Sag Bridge sheet. Irregulari­ ties in the line between DuPage and Cook counties and in that between Lyons and Palos townships of Cook County obviously were determined by the DesPlaines channel FIG. 6.-The channel of Calumet River on the of the time. Some parts of these irregular lake plain at South Holland. For most of its length, this river has no valley of its own boundaries now are considerably off the making. nver course. 34 TOPOGRAPHY

The gradient of the DesPlaines trans- , bedrock surface in places is strikingly morainic valley, reflected in the gradient of grooved and pitted with river-made pot­ the Sanitary and Ship Canal, is extraordi­ holes. Both . these features are records ot narily low. The canal water flows on a the large glacial river which drained por­ bottom slope of one in 40,000, or only 1 tions of the glacial Great Lakes during part foot in almost 7 1/2 miles. Torrential of their history. Other stream-washed rains over Chicago sometimes pour storm­ gravel occurs in ridges and mounds on the sewer water into .the South Branch much northern valley wall. It was deposited dur­ more rapidly than the current can carry it ing retreat of the Valparaiso ice and is, away dO\vn the canal. The river several therefore, a little older than the glacial river times has reversed its flow under these gravel on the valley floor, though it is defi­ conditions and polluted the lake with sew­ nitely younger than the valley. age. To help prevent such danger to the Sag alley.-One of the most prominent city's health, floodgates at Lockport (9 miles topographicf/ features of the Chicago region is downstream from Lemont) are opened at the large Y-shaped valley which crosses the such times and the canal surface lowered as western morainic uplands (Sag Bridge much as 11 feet. This provides a surface and Palos Park quadrangles). Viewed gradient in the canal water greater than on the map (fig. 5), the Y lies on its the bottom gradient. The flow can thus be side, the stem to the west, the tips of increased fourfold, and the city's storm the two arms connecting with the lake plain water is drained more promptly into the on the east. The stem and northern arm canal and away from the lake. Not even constitute the DesPlaines transmorainic val­ this was sufficient to the purpose, how­ ley. The southern arm is Sag Valley, and ever, so the Sanitary District constructed that part of the upland between the con­ locks at the mouth of the Chicago River verging arms is called Mount Forest Island. which, when closed, allow no water to pass The Sag Valley arm of the Y, although between river and lake. streamless, is very similar in proportions and One of the most extensive "made-land" in altitude of floor to the arm occupied by tracts of the Chicago region extends along the DesPlaines River. As befits a trunk­ the Sanitary and Ship canal from the city's valley below the junction of two confluents, western boundary to Lemont. The long, the stem of the Y, west of Sag Bridge vil­ narrow made-land units on the maps are lage, is a somewhat wider valley. The gra­ spoil heaps from canal excavation. From dient of the Sag is too low to be read from Willow Springs to the western edge of the successive contour crossings on the val_ley­ region, the Sanitary and Ship Canal has a floor. The Sanitary District's Calumet Sag bedrock floor throughout. In some places Channel has a bottom gradient of 1 foot it has been cut for its full depth into rock­ in 7 miles. The canal drains on this low hence these long, _narrow hills of limestone gradient only because the channel is straight, boulders along the DesPlaines transmorainic · smooth, and uniform in cross section ; the valley floor, utterly unlike river-made valley water in it is 20 feet deep. Thus there is topography. Near Lemont, bedrock crops very little friction with walls or bottom out extensively on the valley floor, and and little internal friction from turbulence. large quarrying operations there have added Natural streams rarely develop so uniform other made-land hills of waste rock. a channel or so low a gradient. The Missis­ The lower slopes of the valley walls at sippi's lowest gradient is twice that of this Lemont are of bedrock, rising to a maxi­ drainage canal. mum of 40 feet above the floor. This part Sag Valley is clearly an abandoned of the valley is trenched in the summit of a stream-eroded feature and its magnitude be­ preglacial divide. speaks a large stream. To say that it is one Considerable coarse river gravel occurs in of two converging outlet valleys for Lake bars and rude terraces along the transmo­ Chicago is to tell only a part of its his­ rainic stretch of the DesPlaines, and the tory. The lower part of its walls expose.' EROSIONAL VALLEYS 35

older drift in many places, locally as much little canyon about 15 feet deep and 1100 as 50 feet thick beneath the Valparaiso feet long, the only completely rock-walled drift. Yet the Tinley moraine descends al­ valley in Chicagoland. The Calumet Sag most to the bottom of Sag Valley and makes Channel has a rock bottom for the full definite' projections into it from each side. length of the Sag Valley, in some places A ridge of gravel, deposited by meltwater cut to a depth of 20 feet.

in close association with the Valparaiso ice­ .- Sawmill Creek Valley This valley (Sag front, extends down the southern wall to Bridge and Hinsdale quadrangles) drains an altitude only 20 feet above the marsh on into the deep DesPlaines transmorainic the bottom. Sag Valley, therefore, is pre­ course entirely from Valparaiso moraine Valparaiso in origin, as is the DesPlaines surfaces and is largely a product of stream Valley below Lyons and the valleys of erosion. From undrained swamps at its Long Run, Spring Creek, Marley Creek, head, Sawmill Creek descends 135 feet to and Hickory Creek. the DesPlaines valley floor 4 miles distant. The Sag is a through valley, scarcely 5 Thirty-five feet of the descent is close to miles long and more than half a mile \v ide the bluffs of the large valley, where the at the bottom. It has no headwater, upland gradient is about 60 feet to the mile. Above tributary system as do the creeks of this the 635-foot contour crossing, the gradient same subcategory. Sag Valley records a pre­ is less than half as steep. Figure 7 shows Valparaiso, large-volume discharge from this graphically and contains information the Lake Michigan basin to the Missis­ necessary to explain this unusual break in sippi. gradient. Briefly stated, the lower part of There is more bedrock showing in the Sawmill Creek has undergone a domestic floor of the Sag arm than in that of the piracy by which its original course has DesPlaines arm. Near Sag Bridge village been shortened half a mile. The abandoned the bedrock is exposed in several abandoned part of the valley lies immediately west of quarries and two active ones, and on the the present mouth. By such shortening, the southern wall of the valley, bedrock crops gradient at the new mouth was abruptly out as much as 50 feet above the marshy increased to something like that shown by floor. Into the bedrock of the southern wall, the row of double dots in figure 7-almost an unnamed tributary stream has cut a as steep as the slope of the DesPlaines

HORIZONTAL SCALE 0 f {- -\ I Mile

I.--- Profile of Sawmill Creek from volley mouth to s15-foot contour 2- ---- Profile of Des Plaines valley bluff 3. -·-·- Profile of abandoned valley floor 4. ·········- Probable profile of destroyed portion of abandoned valley floor 5. •• •• • •.. Probable gradient of the creek at site of the piracy immediately after its occurrence

Fie. 7.-Profiles of Sawmill Creek. 36 TOPOGRAPHY bluff (the steeper part of the dashed line) drift on the adjoining uplands. Most of the over which the stream initially discharged. butk of this part of the Valparaiso moraine Upstream migration of the head of the is made up of an older and conspicuously steepened grade has carried the break in different drift, in which the valleys were profile about twice as far back from the originally eroded. Since the valleys were mouth as it was originally. The gentler modified by the Valparaiso ice, their streams gradient, which continues to the head of have done little to make them adequate the creek, appea·rs to have been determined drainage routes again. by the moraine slopes. On this gtadient, The valley of Fraction Run between less than 12 feet to the mile, the creek has Long Run and Spring Creek (shown by deepened its valley only a little but has contours but not named on the northwest widened the valley floor several times as part of the Mokena quadrangle map) may much as in the steeper downstream portion. belong to the same subcategory. It seems The vigorous downcutting at the site of equally probable that Sawmill Creek Valley the piracy has exposed bedrock for 1200 (Sag Bridge quadrangle), upstream from feet along the stream channel. Most of the the deeply cut ravine portion, dates back outcrop is simply channel floor, but in one to the same episode of pre-Valparaiso stream place the creek has cut 5 feet into the thin­ erosion. It is certain that Hickory and Mar­ bedded limestone. ley creek valleys, now to be described, have Valleys on the frontal slope of the Val­ had the same history. paraiso moraine.-South of the DesPlaines Valleys of Hickory and Marley creeks.­ transmorainic course, two valleys drain Both streams, joining a mile northeast of westward out of the region and are limited New Lenox (Mokena quadrangle), take to the frontal slope of the wide Valparaiso some drainage from the back slope of the moraine belt. From north to south, they Valparaiso moraine and from the Valparaiso are occupied by Long Run (Sag Bridge ground moraine farther east. Reaching the quadrangle) and Spring Creek (Mokena DesPlaines River at Joliet, they thus cross quadrangle). Both valleys in places are the full width of that moraine belt. more than 7 5 feet deep. The streams in The gradient of Hickory Creek across the both have a relatively low gradient, 8 feet Mokena, Tinley Park, and Frankfort quad­ per mile for Long Run and 9 for Spring rangles is . 7 feet per mile, that of Marley Creek. Both valleys have marked widen­ Creek above the junction 6 feet per mile. ings and narrowings of the bottom flat, with Both valleys exhibit the same kind of nar­ marshy places and ditched watercourses in rowings and widenings that are found in some of the widenings. The character of the Long Run and Spring Creek valleys, rnuch narrowings, however, is the clue to the his­ the same marshiness of wide places, and the tory of these valleys. same kind of obstructing morainic piles. At each narrow place knolls and low hills Hickory Creek has the largest tracts of of morainic aspect stand on the valley gravelly knolls of this genesis in the Chi­ bottom and lower slopes. l\fost of the hills cago region. Though there are no known are deposits directly from glacial ice ; some exposures of the underlying older drift, the are composed of water-vvashed gravel de­ gravel piles deposited on the valley bottoms posited in depressions partly enclosed by by meltwater escaping from the Valparaiso glacial ice. Some of the wide places are ice are sufficient evidence that Hickory and marshy because the streams have not yet cut Marley creek valleys are older than the adeauate drainage courses through morainic building of the Valparaiso moraine. knolls immediately downstream. Valley of Mill Creek.-One of the large The conclusion is unavoidable that the swamos of "the region, McGinnis Slough two valleys antedate their partial blockades, near Orland Park (Palos Park quadrangle), that thev therefore are older than the Val­ discharges northward by way of four other paraiso r:laciation. This conclusion is amply swamps to Mill Creek across the corporate supported by the thinness of the Valparaiso limits of Palos Park. For 2 1 /2 miles of EROSIONAL VALLEYS 37

Fie. 8.-Vanished postglacial lakes near Orland Park and Palos Park (Palos Park and Sag Bridge quadrangles). this string of swamps, the descent is only attractive wooded valley whose bluffs near 15 feet, a gradient of 6 feet per mile. There the mouth reach a maximum of 50 feet has been no stream erosion along this stretch, above the valley bottom. the valley being only a line of connected The Palos Park quadrangle map shows morainic depressions. But from the south­ two narrow, deeply cut places in this two­ west corner of the Palos Park incorporation, mile stretch, separated by more than half the stream descends 55 feet in 2 miles to its a mile of broad valley floor centrally located debouchure in the head of Sag Valley. The in section 27. The northern narrows is 25 gradient here is 27 feet to the mile along an feet deep; the southern one has a 40-foot 38 TOPOGRAPHY

Fie. 9.-Vanishecl postglacial lakes o( Mt. Forest lslancl (Palos Park quadrangle). EROSIONAL f/ALLEYS 39

bluff along its southwestern side. Though Tinley ice front, the dam which prevented there is much morainic relief in the topog­ the water from escaping eastward. The mo­ raphy of the Palos Park district, these nar­ raine, when abandoned by the ice, had not row valley portions are unquestionably of been built high enough at all places to postglacial stream origin. Before they were maintain the westward drainage. Four cut, the lowland tracts now draining north­ eastward-flowing creeks took origin across ward through them must have been lakes. the moraine; Tinley Creek (Tinley Park 1 nspection of the topographic map shows and Palos Park quadrangles), draining the that the lake occupying the broad valley Lake Orland flat; an unnamed creek flow­ Aoor between the two narrow places must ing through Oak Forest (Tinley Park and have had a surface altitude of 660 feet Harvey quadrangles), draining part of the above sea level. Its maximum depth to the Lake Tinley Aat; Butterfield Creek (Tin­ top of the fill was probably about IO feet. ley Park and Harvey quadrangles), drain­ A much larger lake existed south of the ing the Lake Matteson flat; and Thorn sou them narrows. It was 3 1 /2 miles J.ong, Creek (Steger quadrangle), draining the backing up into the lower western part of Lake Steger Aat. Drainage from three­ the village of Orland Park. I ts surface fourths of the Lake Tinley flat still goes altitude was 685 feet, its maximum depth westward to Hickory Creek. to the top of the fill about 20 feet, and its All four of these post-Tinley creeks an: area about I 1/2 square miles. McGinnis on low sags across the moraine. Al l origi­ Slough and the string of four marshes arc nally drained from approximately 700 feet surviving remnants in still undrained por­ above sea level down to the highest shore tions of its bottom. The lake's outline was of Lake Chicago, 640 feet above the sea.

very irregular (fig. 8), and it contained Since distances .traversed ranged from 2.1 15 islands. to 5 miles, original gradients ranged from Had the steep-sided, deep Sag Valley not 'I2 to 28 feet per mile. There is a definite been nearby, Mill Creek would never have relation between these gradients and the had the gradient necessary to cut these two amount of dissection by each stream in its he a e But another narrow places in the morainic dams, and adw t rs. variable, volume, standing water, either J'ake or swamp or is involved, and comparisons cannot be made both, would fill these lowlands today. too closely. Hickory Creek, still obtaining It may be noted here that Mount Forest the lion's share of runoff from the Lake Island, across Sag Valley from the Orland Tinley flat, has been unable to erode a and Palos districts and similar in topogra­ valley here because of the low gradient of phy, has been the site of three such post­ the stream. Most drainage of the Aat today glacial lakes drained by the high-gradient is by ditching. streams descending to th e adjacent deep Sag f/alley of Thorn Creek.-Thorn Creek and DesPlaines valleys. The outlines of two heads in Valparaiso moraine country south of them are restored in figure 9 by the of the region, skirts the western margin of method used for the lakes just described­ tracing the highest contour of the former basin that would become closed on itself if a dam were built in the narrow postglacial valley. For the third lake, the Forest Pre­ serve has actually built such a dam, made such an undrained depression, and thus re­ stored the lake. This is Tuma (or Maple)

Lake on the Sag Bridge quadrangle. Valleys drtliuing !Jlacinl fake flats west of the Tinley moraine.-vVhen glacial water covered the four lake Aats in this district, F10. 10.-Driftwood in lower part of alluvinl fill the drainage was westward, away from the in Plum Creek Vnllcy. 40 TOPOGRAPHY

Valley ends downstream short of the mouth of the stream itself. Between Thornton and Glenwood the valley on the plain is very constricted in sev­ eral places, owing largely to half a dozen outcrops of bedrock in the ,·alley Aoor. Yalley of Plum Creek.-Only 2 miles of this valley (south of Dyer) is topographi­ cally mapped on the Dyer quadrangle; most of it, like that of Thorn Creek, lies south of the area mapped. l ts interesting history is set forth in Part I and will be only briefly outlined here. Plum Creek enters the Lake Chicago plain at Dyer, which is built partly on the Glenwood . The strongly de­ veloped Cal um et beach, 15 feet high and half a mile wide, is .J. /2 J miles farther north. The creek was able to erode a valley in the moraine south of Dyer, but its water collected between the two beach ridges to make an extensive swamp, and drainage from the swamp had to follow a circuitous route by way of North Creek to go around Fie 1 IA.-Marl, peaty clay, and sand beneath the Calumet beach at Thornton to reach alluvium in Plum Creek Valley. I I B.-Dia· the Little Calumet. Lack of adequate gra­ gram showing positions of materials in photograph. dient on the lake bottom made it impossible for North Creek to deepen enough to drain a glacial Lake Steger (Steger quadrangle), the swamp. Plum Creek, on appro ching crosses the Tinley moraine in a low place and entering the swamp, deposited silt and in Chicago Heights, and enters Little Calu­ sand in a low alluvial fan. This decreased met River after traversing about 6 miles of the gradient upstream, in the moraine por­ the Lake Chicago plain (Harvey and Calu· tion, and caused considerable alluviation on met City quadrangles). It meanders con­ that valley floor. siderably on the plain, its channel length Then, about 1850, a drainage ditch was in this 6 miles being a little more than IO dug across the Calumet beach ridge, much miles. Its gradient for this stretch is nearly 5 1/2 feet per mile. In its upper course across morainic country, its gradient is 13 feet per mile. Expectable, therefore, are contrasts in valley depths in the two por· tions. In .the moraine, some of the valley bluffs arc 35 and .J.O feet high ; on the lake plain the average is 15 feet. East of Thornton, the creek descends across a riser between two treads of the plain and has cut a valley 25 feet deep. But before the stream reaches the Little Calu­ met, two miles farther by the valley course, Fie. 12.-Fragments of deer antlers and a well· it is on lake bottm so low that no valley worn mammoth tooth from deposits in has been eroded. Therefore, Thorn Creek Plum Creek Valley. EROSIONAL //ALLEYS 41 of it east of the eastern boundary of the deep has been eroded by Plum Creek water Chicago region. Hart Ditch shortened the along the original shallow ditch, and en­ route betwe�n the swamp and the Little trenchment of the alluvial fan at Dyer and Calumet River from 13 1/2 miles to about of the valley-bottom fill south of that town 1 1 /2 miles and increased the gradient of has occurred in less than a hundred years. swamp discharge, including Plum Creek Mammoth teeth, deer antlers, clam and water, from 2 1/2 feet to the mile to nearly snail shells, peat, marl, and driftwood logs 20. In consequence, the swamp has com­ have all come to light in the valley fill be­ pletely disappeared, a valley 15 to 20 feet cause of this entrenchment. CHAPTER III - GLACIAL GEOLOGY

INTRODUCTION the northern United States .which he visited. His first announcement-that the drift or European and American geologists a cen­ diluviurn was the product of glacial action­ tury ago were puzzled by the cover of un­ is dated 1840; his assertion of the geologi- consolidated materials above the bedrock 1:ally 1 cceilt exil>tence of enormous continen­ which clearly was not derived from it by tal ice sheets appeared in 1848. J t took 20 the ordinary process of weathering. Below years of critical observation by a large num­ a zone of surficial alteration by air and ber of investigators, however, to displace the water, the material was largely undecom­ older concepts and bring about a general posed rock debris, and it generally rested acceptance among geologists of his interpre­ on a clean-cut surface of unaltered bed­ tation. rock. In many places abrasional markings occurr.ed on the rock surface. The material One glaciation was all that Agassiz asked was commonly a heterogeneous mixture of for and all that many geologists would ac­ various-sized fragments, from clay to boul­ cept for the next 20 years. Several workers, ders, and many of the fragments were de­ however, insisted that peat beds in the body rived from many kinds of bedrock foreign of the drift, and old soils on drift but be­ to the region. The early geologists called neath a cover of fresh drift, proved that it drift or , for it surely had been there had been at least two such glaciations. moved into the region it covered and, in By 1898, it was clear to most that there moving, had abraded the underlying bed­ had been four stages of continental glacia­ rock. It had been moved along the di rcction tion in 1orth America, separated by stages of the grooves and scratches, either from of deglaciation comparable to the present northerly or southerly regions. Many frag­ postglacial stage. ments were identical with rocks in bedrock­ outcrop areas to the north. Therefore the DRIFT cl rift was explained as the product of some The drift has been differentiated into catacl)rsmic action in northern Europe and that deposited directly as the ice melted and North America which swept debris south­ that modified by the associated meltwater ward halfway across each continent. There into a variety of glacioAuvial (glacial river) was, they thought, no process in operation and glaciolacustrine (glacial lake) deposits. toda)' akin to that action. About this time, Louis Agassiz, a young Swiss naturalist, became interested in the mountain glaciers of the Alps and the changes they were producing. Shortly he conceived the idea that the glaciers he was studying were but shrunken remnants of far larger ones which had covered all the Swiss lowland, had eroded bed rock, and had left their characteristic grooves and scratches beneath a heterogeneous mixture of debris identical with that which existing glaciers deposit. Later he found the same kind of record in Scandinavia and the Fie. 13.-Plancd and �triated bedrock �urface. Quarry of Elmhurst-Chicago Stone Co., Tiritish Isles and, coming to North America, Elmhurst. Scale is shown by the black spot, found it all over those parts of Carrnda and which is r,f inch in diameter. [ .;.2 ) GLA CIOFL UVIAL DEPOSITS 43

TILL streams on earth. Fine material is likely to Till is ice-laid material, a heterogeneous remain in suspension, despite slackening in mixture of fragments of all sizes, with only velocity, and to be carried on down the val­ rarely any suggestion of stratification. The ley. If it is ever deposited by the stream, marginal moraine ridges and the ground­ it will be left where slackening current moraine sheets are till deposits, differen­ could bring no coarse material and could tiated on the basis of topography, and they not transport all the fine. The extreme is, record times when the ice front was either of course, entrance of the stream water into a glacial lake where, with no current at all, maintaining the same position (because the the very finest clay and rock flour will settle rates of advance and of melting were in out. balance ), or was retreating (because the rate of melting exceeded the rate of ad­ Eskers.-Ridged accumulations of glacio­ fluvial sand and gravel-eskers-are fairly vance ). Till is also called , especially in the earlier literature. common in morainic country. They gener­ The till of the Valparaiso and later mo­ ally are oriented approximately at right raines has a very high clay content and a angles to the course of the moraines and paucity of pebbles, cobbles, and boulders, must have had retaining ice walls when de­ whereas the older till, cropping out along posited. They seem to indicate deposition the Sag and the transmorainic DesPlaines in fissures or close to the ice front. valleys, is silty rather than clayey and has An is not necessarily of contempo- an abundance of coarse material. The older • raneous deposition throughout its length ; it till also has an exceptional amount of strati­ is more probable that a superglacial stream, fied material, and in limited outcrops it may or streams, debouching into a fissured re­ look more like a water-laid deposit than a entrant of the ice front, added constantly glacial deposit. In both types of till, many to the proximal end of the ridge as the ice pebbles and larger fragments show glacial front retreated. However, eskers are often scratches (striae ) and planed and beveled interpreted as deposits that surfaces from grinding against each other or record a continuous tunnel at the bottom of against the underlying bedrock, which also the ice. may show abrasion marks. Fairly common in eskers is inclined strati­ fication, due in part to original deposition GLACIOFLUVIAL DEPOSITS (cross-bedding or foreset bedding), and in Glacial ice melted not only at the frontal part to slumping when the ice wall melted margin but over a wide surface zone back away. There may be masses of till in or of that margin. Where crevasses existed, on top of the esker, resulting from ice thrust meltwater penetrated down into the body during or at the close of esker growth. Ice of the marginal zone of ice, perhaps to the thrust may also crumple strata already de­ bottom. Eventually it escaped, from super­ posited. glacial, englacial, and subglacial courses, at Eskers or eskerlike deposits are not com­ the glacier front, constituting extraglacial mon anywhere in the Chicago region. One streams or, if no free drainage was possible, is at Half Day on the Wheeling quadrangle lakes. (map 1), two lie centrally in the northwest Supplied with debris from the melting ice, quarter of the Hinsdale quadrangle (map the streams became overloaded in many 9), there are two on the Sag Bridge quad­ places and deposited part of their load. Such rangle (map 13), one a mile north of Tiedt­ deposits are stratified, the layers dis­ ville, and one near Visitation Boys Camp. tinguished generally by differences in size .-If the gradient of a meltwater of constituent particles. Such layering stream debouching at the edge of the ice is records variation in velocity of the deposit­ notably reduced as it passes from the ice ing stream, which is commonly the result slope to the slope of the moraine, stratified of fluctuating volume, and meltwater washed coarse material may pile up on or streams are as variable in volume as any against the lower ice slopes, located most GLA CIAL GEOLOGY

probably in fissured re-entrants of the gla­ train-in the DesPlaines River Valley on cial front. A superglacial stream falling the Wheeling, Arlington Heights, Park into a near the front may find itself Ridge, and River Forest quadrangles (maps unable to continue to carry the coarser ma­ 1, 3, 4, 7). terial of its load, and the pile of debris will then be built beneath the edge of the ice ; GLACIOLACUSTRINE DEPOSITS melting will constantly enlarge the cavity Deltas.-When standing water is ponded to accommodate the increa.>ing bulk of the along the ice front, meltwater streams on deposit. After retreat of the ice, the piles entering abruptly lose all velocity and con­ are left as hills, called kames. Genetically, sequently build deposits at the debouchures they are closely related to eskers. and contribute fine material to be distri­ Karnes in the Chicago region, like eskers, buted widely in the feebler lake circulation. are limited almost wholly to the V �lparaiso Characteristic of a sand or gravel delta is moraine. There are two kames on the foreset bedding ; the strata dip into the lake Wheeling quadrangle (map 1 ) , 3 miles west at the angle of rest (between 12° and 20°) of the town of Wheeling, and about a dozen and terminate at the top in a uniform hori­ in the northern half of the Sag Bridge zontal plane determined by the lake surface. quadrangle (map 13). The Chicago region has no good showing Kame terraces.-If, as the ice front re­ of sand or gravel deltas. What seems to be treats, a pre-existing valley leading away a fragment of one occurs near Worth (Palos from the glacier is exposed, ice may remain Park quadrangle-map 14), where it is a longer within the protection of its slopes part of the older, buried drift sheet. than on the uplands on either side. Stagnant Offsh ore deposits.-The very fine mud ice masses may thus bt; left behind in the and clay that takes days to settle out of valley bottom and will interfere with escap­ suspension gets wide distribution in a lake ing extraglacial meltwater. The stream is and may make a fairly unifom1 deposit over likely to find the lowest places along one or the whole bottom. This depends, however, both sides of the lingering and on depth and amount of wave agitation. leave its deposits on the lower slopes but Lakes Orland, Tinley, Matteson, and not in the deepest, middle part of the valley. Steger accumulated thick deposits of finely laminated clay during their brief lives ; These deposits are called kame terraces. . They may be somewhat knolly ·but rarely indeed, they became completely filled with are as knolly as kames. Hickory Creek Val­ such material. But in general the big storm ley has a good showing of kame terraces on waves of Lake Chicago dragged bottom on the Mokena and Tinley Park quadrangles the Chicago plain and eroded instead of (maps 17, 18) , and the valleys of Marley depositing. Only in the protected bays did Creek and Long Run possess a few. sediment accumulate under water on the

Valley train .-When no lingering ice Chicago plain. The best showing of this masses obstruct a pre-existing valley which has been in excavation for the North Shore is a route for escaping meltwater, saQd and Channel, in a bay back of the large spits in gravel from the overloaded stream are likely Evanston and the northern part of Chicago. to be deposited as a valley-bottom flat. Beach deposits.-More extensive, and Across the flat the stream makes a series of topographically much more conspicuous channels, which shift location as they be­ than any other deposits left by glacial Lake come aggraded and thus give orie-in to a fill Chicago, are the long ribbons of shore accu­ known as a 'l1alley train. Such a deposit is mulations that stretch for miles across the very similar to what heavily laden streams lake plain. To some extent, the bulkiness in nonglacial regions produce. Valley trains. of each of the three beach accumulations is howtver, head in moraines, and their detri­ a measure of the duration of the stage, tus is readily identifiable as drift relea�ed though other factors were also involved. by melting of the glacial ice. The Chicago In total mileage, most of the deposits are region has one good example of a valley- simple beach ridges on the different shores, THICKNESS OF THE DRIFT 45 their sand and gravel tossed back to the mite and limestone, most of• which is dolo­ storm-wave limit. In volume of deposit, the mite identical with some phase of the im­ large spits at \Vilmette, Evanston (Rose mediately underlying bedrock, the Niagaran Hill) , northern Chicago (Graceland) , group of formations of Silurian age. Fos­ Dolton-Hammond, and Thornton-Dyer sils in the fragments make the identifica­ exceed perhaps all the beach ridges together. tion pos1t1ve. Less common are lime­ In depth of deposit, they are excelled by stone fragments traceable to shores on which the wave-making winds formations that crop out farther north also piled up dunes (Wilmette, Blue Island, along the route of the advancing ice-the and Dolton-Hammond ). In area of unit elongated trough of Lake Michigan. Still deposits, the Evanston (Rose Hill) and less common, but conspicuous because of northern Chicago (Graceland) spits are strongly contrasted lithology and structure, the largest, covering a total of about 4 and are fragments of granite, gneiss, schist, slate, 6 1/4 square miles, respectively. All these quartzite, etc., whose source areas are un­ deposits are composed of the pebble and questionably in the great Laurentian prov­ sand fractions of the erpded glacial till. In ince of Canada, northeast of the Chicago the shallow water offshore or at the foot of region. sea cliffs, the boulders were left where they The drifts of north-central Indiana, were, the sand and gravel were dragged north-central Illinois, and southeastern Wis­ shoreward or along the shore, and the clay consin differ in the types of igneous and and mud fractions were carried off in the metamorphic rocks which they contain. This undertow, to be deposited eventually out in is because the ice which overrode these the basin of the lake. areas travelled different, though subparallel, routes and thus encountered different bed­ EOLIAN DEPOSITS rock:. Distinction is almost universally made The Valparaiso and later tills contain a between two types of eolian deposits-loess vast quantity of finely ground shale derived and dunes, composed of dust and sand, re­ from the bed of Lake Michigan by glacial spectively. The region possesses no loess, erosion. Pebbles of the weak shale which although farther downstate many deposits have survived the grinding clearly are from are recognized as made by the winds of the the shale formations now largely glacial and stages. There are submerged. So are the very abundant, al­ limited examples of dunes on each of the most microscopic, fossilized spores of the Lake Chicago beaches and on the present genus Sporangites, a Devonian type. Much shore. The dunes of the glacial lake shores less sandstone was traversed by the ice­ have already been listed. A tract between sheet than shale or limestone, hence the 71st and 79th streets and a small park at relatively small quantity of sand in the till. the east end of Touhy Avenue, just south HICKNESS OF THE DRIFT of the Chicago-Evanston boundary, en­ T compasses almost the only dunes of the The maximum known thickness of the present lake within the region. They are ghcially deposited debris of the Chicago small and readily obliterated when they are region is 216 feet, in a well on Ridge Road built over. Accounts icdicate that there in the Highmoor district of Highland Park. were similar small dunes south of old Fort The district, on the Blodgett moraine, has Dearborn at the time of the historic mas­ only a moderate altitude, and the thickness sacre of 1812. is caused by an unusually low place in the underlying bedrock: surface. If this surface SOURCE OF DRIFT MATERIALS were a horizontal plane, the uplands would Larger fragments in the drift, whose have the thickest drift, the low lake plain and lithology and structure are apparent, are the deep Sag and transmorainic DesPlaines readily traced to their general source area. valleys the thinnest. We find, however, a Dominant among these fragments are dolo- marked relief in that buried surface and 46 GLA CIAL GEOLOGY little correspot'l.dence between it and the by differences in color, hardness, nature of relief of the drift itself. The average thick­ the fine matrix, and kinds of included ness of the drift is therefore difficult to esti­ pebbles. But the composition of till must mate. Well data show that it averages 60 vary with the kinds of bedrock contributing to 70 feet under the lake plain, 100 feet to it and with the amount of water action at under the western morainic upland, and the time of deposition. Hence no one till 140 feet under the northern morainic area. possesses constancy of all characters, if indeed of any one of them, throughout its DIFFERENTIATION OF DRIFT SHEETS extent. The problem of identifying a till Newberry and Orton, about 1873, argued which cannot be traced continuously is not independently that a "forest bed" (a peat simple. bed with abundant wood) in a body of till The pioneer study of this problem in the recorded a time of deglaciation and refor­ Chicago region1 was made during the prog­ estation interrupting the glacial domination ress of this survey, although it was inde­ of a region. T, Chamberlin in 1882 pendently executed. It was in part an argued that differencesC. in amount of erosion attempt to learn if a till sheet possessed any on horizontally adjacent drift sheets indi­ constancy in textural composition, or any cated differences in age-the more eroded, consistent variations in the composition, the older. Salisbury in 1893 proposed that, along the length of a moraine. A consider­ in a vertical succession, a buried weathered ably larger area was chosen, of which the surface or a buried stream-eroded surface Chicago region was but a part. Valparaiso indicated that the subjacent till had been till was selected because the moraine topo­ long exposed before the superjacent one graphically is identifiable continuously for was deposited. These criteria, with others. many miles through Illinois, Indiana, and have established the Pleistocene succession Michigan. as we now know it. Krumbein's study demonstrated that But Chicagoland is well back from the throughout "a length of forty miles limits reached by the ice sheets which have samples taken at intervals of 1 or 2 miles overrun it. So located, it is not to be ex­ showed only slight changes in composition pected that excavations here will discover from one sample to the next. The study a full Pleistocene stratigraphy, for later indicated that intervals of 10 miles would invasions either destroyed the deposits left not be too great if a considerable length of by earlier ones or eroded their upper por­ moraine was involved." tions. Another phase of this study dealt with Another criterion can be used in some identification of bedrock fragments in the situations. If the ice of two successive till. It was found that along the Valparaiso invasions came from somewhat different moraine from Elgin, Ill., to Benton Harbor, directions, thus passing over different kinds Mich., dolomite and limestone fragments of bedrock, the two drifts will possess cer­ constitute about 80 percent of all pebbles tain lithologic differences. This criterion for the first 30 miles, that the percentage appears to find application in the drift de­ drops to about 10 in the next 13 miles, posits of the Chicago region. and remains there for nearly 100 miles, to Otto's utilization (p. 83 ) of difference in Benton Harbor. Conversely, shale and silt­ water content of till sheets, essentially based stone pebbles average about 10 percent for on the principle that buried till becomes the first 30 miles, then rise in percentage densified because of a later overriding, is as the dolomite and limestone pebbles de­ a related criterion for differentiation of crease, and for the last 100 miles remain drift sheets of successive ages. It is appli­ close to 7 5 percent of the total. This, cable only in situations where the till never Krumbein thinks, is due to the difference subsequently became desiccated. 1Krumbein, W. C., Textural and lithological varia­ Till sheets in vertical sequence in a re­ tions in glacial till : Jour. Geo!., vol. 41, pp. 382-408. 193 3. This paper was a Ph.D. thesis in the Department of gion may be distinguished from each other Geology, l'ninreity of Chicago. CLASSIFICA TION 47

TA BLE 1.-CLASSIFICATION OF THE PLEISTOCENE ErocH

Rock term: Series Group Stage Substage Stages in Time term: Epoch Subepoch .Age subage Europe . Recent

Mankato Eldoran Cary Wisconsin Tazewell Wurm (glacial) Iowan Farmdale 1------1·------Sangamon Riss-Wurm (interglacial) Centralian Illinoian Riss (glacial) Pleistocene Yarmouth Mindel-Riss (interglacial) Ottum wan Kansan Mind el (glacial)

Aftonian Gunz-Mindel (interglacial) Grandi an r.�:· kan � � 1 l __-_ __ un _ -- a ) I _:---_-_-�- __ _ _ in bedrock : Niagaran dolomite underlies It may well be that a gradation can be the till high in dolomite and limestone shown between this older till of the region pebbles, and Devonian shale and siltstone and some morainal till farther west. underlies that portion rich in pebbles of The method should be applied to the shale and siltstone. The change in pebble deeper tills encountered in the clay pits of dominance, however, occurs 40 miles west the region, in the caissons of the Loop dis­ of the bedrock change, probably because trict, and in other excavations. They are the ice moved diagonally across the contact in some places apparently alike though farther north, under Lake Michigan. Krum­ separated by sediments, and may prove to bein warns his readers not to expect too be the same deposit with intra-till strati­ close a correspondence, too uniform a per­ fied members. In other places, they are centage, in any pebble waste from under­ distinctly unlike. lying rock, because portions of older drift sheets covering the rock locally may pro­ CLASSIFICATION duce variations in percentages. Following the most recent revision of the The conclusion of Krumbein's study is Pleistocene2 series and its nomenclature, that "a giYen ice sheet tends to produce we now have the classification presented till having a fairly well-defined frequency in table 1. It is J most applicable in the distribution" of the various grade-sizes of northern part of the United States east of particles. Sedimentological studies may prof­ the Rocky Mountains. itably be made on the region's buried tills. The interglacial intervals following each The silty and stony till beneath the Val­ of the first three glaciations were long, paraiso drift should be studied in this man­ and the exposed part of each drift sheet ner, and for the investigator attracted by was greatly weathered and eroded before the problem, there is on page 68 a list of it was covered by the next younger drift. all localities where, though not shown on 2first used by Lyell, C., Charlesworth's Mag. Nat. the maps, it is known or suspected to exist. Hist., vol. 3, p. 323, footnote, 1839. 48 GLA CIAL GEOLOGY

In contrast is the relatively brief postglacial most ( Shelbyville6) to the Marseilles. 7 The interval of today and the relatively shallow oldest of the Cary8 substage moraines is the ,depth of weathering of the latest drift Minooka/1 the youngest is the Lake Border sheet. A cyclic succession of glacial and system. Ice did not reach this region dur­ nonglacial climates gives rise to the concept ing .Mankato10 time. The change in out­ of four subepochs, each one including line of the Lake Michigan lobe between ':l . complete oscillation of the climatic pendu­ :Marseilles and Minooka time suggests an lum. The record is clear enough, but the unusually marked retreat. On readvancing causes for the climatic rhythms are as yet at the beginning of Cary time, the Minooka little understood. moraine was deposited on top of the Mar­ Each of the Wisconsin3 substages4 has seilles near Elgin, where the two are subdivisions determined by a series of elongated almost at right angles to each marginal moraines built during pauses in other. the general retreat. The ice front often retreated extensively before readvancing STRATIGRAPHY and depositing successive moraines (fig. 14). Beneath the glacial drift lies Niagaran The great lobe of the Wisconsin con­ dolomite of Silurian (mid-Paleozoic) age. tinental ice sheet which spread southward The break between the two involves a vast out of the Lake Michigan basin deposited stretch of geological time. The only record in Illinois the moraine system illustrated in for the region is that of erosion, and the figure 15. The Tazewell5 substage includes 6.'famed for the town of Shelbyville, Ill ., which is all the moraines from the oldest and outer- located at the extreme southwest part of the moraine. Leverett, Frank, The Illinois glacial lobe : U.S. Geo!. 3Named for the state of Wisconsin where drift of Survey Mon. 38, p. 125, 1899. this age is widely distributed. Chamberlin, T. C., in 7Named for the town of Marseilles, Ill., which is Geikie, James, The Great , 3rd ed., pp. 754-774, si"tuated at the place where the Illinois River cuts the 189-1- ; The classification of American glacial deposits : moraine. Leverett, Frank, op. cit., p. 307. Jour. Geo!., vol. 3, pp. 270-277, 1895. 8Named for the village of Cary, Ill., which is lo­ 4These Wisconsin substage names were first published cated on a prominent part of the Valparaiso morainic in : Leighton, M. M., The naming of the subdivisions system. The substage was formerly called "Middle Wis­ of the Wiscons in glacial age : Science, vol. 77, no. 1989, consin." Leighton, M. M., op. cit. p. 168, Feb. 10, 1933. 9Named for the village of Minooka, Ill., which is 5Named for Tazewell County, Ill., in which the situated on its crest. Leverett, Frank, op. cit., p. 319. moraines of this substage are well developed. It was tONamed for Mankato, l\finn. The rnbstage was formerly designated as "Early Wisconsin." Leighton, M. formerly called "Late Wisconsin." Leighton, M. M., op. M., op. cit. cit.

OLDEST MORAINE YOUNGEST MORAINE

; } • · . · · .· : · · · � . �. ·. . · ··. 3 .. ···.;.:· ··."�: :'.:°·. .•1 ::e-::: ...,._...,...,__ · · . · .. .. ·£. ·....·.: •..·. ':"'' . .,·..J ·.·.····..;·.·�..T·�•S.\�· · ·;;_:·•.··.·-, .. . . 3 �"'' -::-".'�G--M'.'.'."i�=.,..,-c,�:.,, _,.•····""".••• "°< ..;�,;;M;,.,1�;,{ ;;.;,..; .:;.,; ..;\ :.,!;·?i,!!Mi-'}?..::;:::.;.,.;. :.:.::::;7�'."' •.'.°"' .. .· · , . · . GlM 2 ·.· . ·:JG�M[·� �:G;i0· · .•.•••• . . �•· ·· . ··· Cross-section of ••.

deposits mode by melting ice

>

Shifting position of ice front

Direction of

ice flow ot TM =

oll stages GM = Ground - moraine

FIG. 14.-Development of successive moraines by minor readvances in general retreat of an ice sheet. MORAINES IN NORTHEASTERN ILLINOIS 49

_

_ __j

i 1�·- r--i ------,J ·-, ---1 ' . ILL/NO/AN I• I -- i DRIFT , _ )- j -- ! _ - I - --,I

__

oI I I i ---� ___ L

LEGEND

D MORAINES KANKAKEE TOR!if:NT § AREAS ILL/NO/AN LAKE CHICAGO � AND OUTLET DRIF T MARGIN OF / WISCONSIN . SCALE 0 IO 15 ?fMI.

FIG. 15.-Moraines and associated features in northeastern Illinois. Compiled by George E. Ekblaw from data furnished by the Survey, January 1, 1942. 50 GLACIAL GEOLOGY

MAXIMUM SUB­ MATERIAL ORIGIN SE.R IE� STAGE UNIT SECTION STAGE THICKNESS 1 ::;11t, c1ay, sand, RECENT 12 oraveL neat ALGONQUIN 6 Sand, 11:ravel Beach denosit

Beach ridges and Sand, gravel LAKE 30 dunes CHICAGO silt, sand, 13 C lay, Offshore lake deposits .----l-�m!.!!5!a�r�l�n�e�a�t�+-��

Till, gravel, Ice deposits, HIGHLAND 70 PARK sand, silt frontal outwash

BLODGETT

deposits DEERFIELD 23 Till Ice z >- tzl Ii: Ill z < Till, sand, Ice deposits, z 27 tzl u PARK RIDGE 0 gravel valley-train u u 0 Ill !-< Ice deposits, Ill Till, sand, ;::: TINLEY 45 frontal outwash, tzl : : gravel, clay ._ : lake deposits �:::W<�· � :.· . ..1 · :' " � . fl. >>· . :

Ice deposits, Till, sand, VALPARAISO 60 kames, eskers, gravel kame terraces

-· � Ice and lake deposits tzl � BLOOMINGTON Till, clay included in you.-i ger tzl � � till -?- ----£-<);:::__

Ice deposits, Till, silt, 60 outwash, LEMONT s nd, a gravel lake deposits, ... delta � 0 ·.....·····..···...... ···..· ··..· � ·.·::::.·.·:.·::.·.·:. 25 ·.·.·.· :.·.·.·.·:: .·.· .· :. Till, clay, Ice deposits, 85 cl ------sand, gravel outwash .· . :::::·::.:·_·. . . .:-_: ::::·_:·.:::: o::���· :O� . :-�o:-:- .o�q · ·.·.·-·.·.·.·.·.· .·.-.·. · · ·o �·:-�; ..�:. ;c;: =·�·>«; ..� §f��) Fm. 16.-Generalized columnar section of the Pleistocene deposits of the Chicago region. contact is a great unconformity. Post-Silu­ eastern corner. Otto (unpublished manu­ rian Paleozoic deposits were laid down here script, Illinois Geological Survey) has shown but they were completely stripped off later, that at least three older tills occur here, but and only fissure fillings in the Niagaran they are nowhere exposed. Our section must dolomite record their former presence. be made by a horizontal traverse of the The Pleistocene sequence of the region region from northeast to west-central, based (fig. 16) is nowhere all present in one on the knowledge that each stratigraphic section. If it were, that section would be unit overlaps westward on an older one located under the youngest moraine of the (fig. 17). Constructed in this way, the sec- region (Highland Park) , whose till covers tion is just a list of the moraines, youngest only 12 to 13 square miles in the north- (Highland Park ) at the top and oldest BEDROCK TOPOGRAPHY 51

Unidentified Tills I Lakes Orland Des Plaines ...

Tinley, etc. valley-train ., . 0.. <> .., .., c . ., ii'. <> .., 0 iii �x

FIG. 17.-Diagrammatic cross section of the Pleistocene deposits of the Chicago region. (Valparaiso) at the bottom. Repeatedly edge of the Silurian formations therefore referred to, however, is a once completely is the highest part and constitutes the di­ buried drift in the western part of the re­ vide between Lake Michigan and Missis­ gion, without surface expression in the sippi drainage approximately as far north as form of marginal moraine and ground mo­ . In the Chicago region, raine. It is the Lemont drift, which is not it coincides with the preglacial and early to be thought of as now underlying all the Pleistocene bedrock divide under the west­ others. It may never have been a complete ern morainic uplands. cover, and if it was it may have been largely Hundreds of wells recording depth to bed­ eroded away during later glacial invasions. rock have made possible the contouring of its Nor should the Valparaiso till sheet be surface. The contour maps (to be published thought of as having continuous contact later) show that the bedrock surface is with bedrock where not underlain by Le­ diversified by a number of stream valleys mont drift. Subway sections, deep caisson with their tributaries and separating divides records, and the sections of the Sanitary and that the direction of valley-bottom and Ship Canal encounter some dense, hard slopes is generally a function of the east­ tills whose correlation is uncertain. The ward bedrock slope (fig. 18) . They show upper till of the lake plain may be Tinley that the Lake Michigan basin must have or one of the Lake Border sheets, depend­ been a free-draining valley at the time the ing on location. Valparaiso till should be valleys were formed, and that they are the beneath them. These densified tills may be eastward headwater drainage of the St. Valparaiso or Lemont, or perhaps some Lawrence-Mississippi divide of that time. other till not yet identified in the region. The master stream to which they flowed was a contemporary of the Mahomet BEDROCK TOPOGRAPHY ( Teays) River, 11 which received the drain­ Silurian dolomite, nearly 500 feet in age westward from the same divide through maximum thickness, underlies all the Chi­ Kempton and Newark valleys (fig. 19). cago region except a small area near Des­ The degree of dissection of the bedrock Plaines. It has a gentle eastward dip that surface indicates a mature stage in the ero­ carries it under the Lake Michigan basin sion cycle. and beneath the Devonian shales that un­ Although we do not know if Nebraskan derlie the lake. The north-south strike ice ever invaded the region, it probably ad­ prevails northward along the entire east vanced far enough from the Labradorean side of Wisconsin, and the dolomite be­ center to interfere with free drainage from comes much more prominent topographi­ what is now the Lake Michigan basin. It cally in Door and Garden Island peninsulas, seems likely, therefore, that these bedrock which separate Green Bay from Lake tributary valleys are largely of preglacial Michigan. In general, the surface of the origin. bedrock slopes with the bedding, descending 11Horberg, Leland, Bedrock topography of Illinois : gradually toward the east. The western Illinois Geo!. Survey Bull. 73, 1950. 52 GLA CIAL GEOLOGY

KEY � 500 Contour showing elevation of bedrock ; interval 50 feet.

•4Jit- Bedrock exposure

SCALE of MILES

41

40

39

38

37

35 N.

10 II

Fm. 18.-Generalized map of bedrock valley system in the Chicago region. After Leland Horber�, Bedrock topography in Illinois : Illinois Geo!. Survey Bull. 73, pl. 1, 1950. PREGLACIAL DRAINAGE 53

· ··· .·· ··· ·· ·1

�Lotz

�� ...... • : • . • ••· 3,·�I . i

Champaign •

Frn. 19.-Preglacial drainage. After Leland Horberg, Bedrock topography in Illinois : Illinois Geol. Survey Bull. 73, pl. 2, 1950. CJl +

� � � Q � � � � a � a � �

UR INTERVAL 10 f'[ET {:�::::�: SEOROCI< OUTCROP MILE� CONTO , L=J SC� 600/

Frn. 20.-Contour map showing bedrock surface in vicinity of Joliet. Af ter Leland Horberg and K. 0. Emery, Buried bedrock valleys east of Joliet and their relation to water supply: Illinois Geo!. Survey Circ. 95, pl. 1, 1943. BEDROCK TOPOGRAPHY 55

SPRING CREEK VA LLEY MARLEY CREEK VA LLEY

--

...... _ Vo1 o """'- P roiso -...... : ......

Lemont drift

I llinoion (?)

FIG. 21.-Cross section of buried Hadley Valley and its overlying drift.

The maps give no hint that subsequent paraiso Spring Creek Valley. The line of glacial overriding did more to these valleys deep, poorly drained depressions in the than fill them with drift. Divide tops northeastern part of Mokena quadrangle, which here and there form rock outcrops ditched to drain to Spring Creek, also lies in the Chicago region, or are very shallowly along the buried valley's course. The pres­ covered with drift, undoubtedly suffered ent divide, almost on the east edge of the some erosion ; an especially high percentage Mokena quadrangle, determined by drift of dolomite boulders in the drift to their in and above the old valley course, is be­ lee establishes the fact. Yet glacial erosion tween 710 and 715 feet above sea level, largely failed to modify this buried stream­ and bedrock at this place is at 500 feet. carved topography. Certainly the surviving As the bedrock summits on either side of relief and its character indicate that Mar­ the buried valley average 630 to 640 feet, tin's estimate12 of 100 to 200 feet of glacial the bottom of the present valley in drift erosion on the Niagaran of Wisconsin is actually lies higher in general than the top far too great for northeastern Illinois. of the valley in bedrock (fig. 21 ). A remarkable trench, called Hadley Val­ 19, 20), Seven miles northwest of Hadley Val­ ley (figs. across the bedrock divide ley, the DesPlaines Valley, cut into bed­ between the St. Lawrence and Mississippi rock, is a functioning drainage way across drainages is clearly younger than the other the buried divide. The surprising thing bedrock valleys.13 It was discovered by the about the DesPlaines Valley is that its use of earth-resistivity methods, and its floor has an altitude of 585 feet, 45 existence is substantiated by numerous well feet higher than that of Hadley bedrock logs. Instrumental data show that thick un­ valley. Two parallel valleys across a bed­ consolidated deposits buried beneath the rock divide only 7 miles apart seems an Valparaiso till along the valley of Spring extraordinary consequence of glacial de­ Creek (Mokena quadrangle) continue east­ rangement of drainage. That the surviving ward across the present divide to the head­ and functioning one is the shallower makes waters of Mill Creek drainage near Orland it at once evident that the two cannot be Park. Hadley bedrock valley here underlies contemporaneous in origin. The earlier one these deposits, its floor about 540 feet above 7 5 100 must be the Hadley trench, and the later mean sea level, its depth from to DesPlaines Valley could have developed feet, and its course followed by the pre-Val- only if the earlier valley became buried by 12Martin, Lawrence, The physical i>:eography of Wis­ drift which accumulated there until its co nsin : \V isconsin Geo!. and Nat. Hist. Survey Bull. 36, 2nd ed., p. 251. 1932. surface was higher than at the site of 13Horberg. Leland, and Emery. K. 0., Buried bedrock vallevs east of Joliet and their relation to water supply : Lemont. Illinois Geo!. Survey Circ. 95, 1943. Horberg, Bull. 73, p. 44. Both these transections must have been 56 GLACIAL GEOLOGY

initiated by glaciai damming of the Lake valleys to join the Ancient Mississippi south Michigan basin and discharge of ponded of Peoria. After ice covered the region, at water westward to the Mississippi. The least by Kansan time, the drainage from Hadley buried valley has been eroded 7 5 Hadley Valley was westward to Ticona to 100 feet deep in rock, the Des Plaines Valley, 14 joining the Ancient Mississippi trench has been cut about 40 feet into the River southwest of LaSalle (fig. 19). limestone. Both figures suggest a longer Inspection of figure 20 �ill show three occupancy by discharging lake waters than unusual features of the buried Hadley Val­ seems provided by the duration of a glacial ley : ( 1) the altitude of its floor descends dam. both to the southwest, which the interpre­ Hadley Valley may have been made by tation requires, and the northeast, which the discharge from Nebraskan and Kansan interpretation will not explain ; (2) traced "Lake Chicagos" across the divide. The westward, the valley becomes divided into DesPlaines transection may have been made two equally capacious valleys, both of which by a late Illinoian "Lake Chicago" dis­ reach the DesPlaines in the eastern part of charge which may have continued as an Joliet ; ( 3) the bedrock floor of the Des­ ice-free "Lake Michigan" discharge during Plaines at Joliet "hangs" above the floor the following i�terglacial interval ; there of the buried valley at their junction. These was the post-Lemont discharge of a "Lake features require special explanation. Chicago" of that time ; there was the ensu­ For the first, it is suggested that in the ing pre-Minooka substage of stream-valley preglacial cycle two tributaries headed erosion ; and there was the discharge of the nearly opposite each other on the buried post-Tinley Lake Chicago. The postglacial divide-one flowing to the St. Lawrence, DesPlaines has added little if anything to the other to the Mississippi-and that the the sum of valley-deepening and need not be earliest "Lake Chicago" found here the considered. Presumably the pre-l\1inooka oc­ lowest place across which to spill westward. cupancy was also a "Lake Chicago" dis­ The large glacial river widened the twu charge and its duration was probably as opposite-flowing valleys at the time it ini­ long as the other two episodes combined. tiated the steep-walled trench that connects Yet the bedrock valley at Lemont falls them. Subtributary drainage to the north­ 45 feet short of the depth reached by the east-flowing stream is clearly recorded in buried Hadley Valley. The highest place the bedrock contour map. on the floor of the buried valley is 40 feet The second feature, the separation of the lower than the surface of Lake Michigan, trench into two valleys, each as wide at the and were it drift-free today, the three great bottom and as steep-sided as the main trench, lakes, Michigan, Huron, and Superior, is abnormal for a stream valley. It seems would be draining through it to the to demand so great a volume of glacial water Mississippi instead of discharging to the as to overrun one of the existing valley­ St. Lawrence. walls. Here the overflow appears to have It seems a plausible inference that, in found a minor tributary valley, down which some pre-Lemont Pleistocene epoch or it spilled to the head of River Ticona. The epochs, the outlet of these three lakes was demand for extra spillway capacity was through Hadley Valley and thence, by way met by deepening in the overflow route, of the Mississippi, to the Gulf of Mexico. hence the distributary character of Hadley This concept would allow water enough Valley on the extreme western edge of the and time enough for the buried valley's Mokena quadrangle. incision of 7 5 to 100 feet into the late The third noteworthy feature is the alti­ Tertiary and early Pleistocene bedrock tude of bedrock in the DesPlaines valley­ divide. floor at oliet where it is joined by Hadley The first waters diverted across the .T "Willman, H. B., Pregl acial River Ticona : Ill. divide through Hadley Valley flowed b�· Acad. Sci. Tra'l<., vol. 33, po. 172- 175, 1940 ; Illinois Geo!. Survev Circ. 68, pp. 9-12, 1940. way of Kempton and Mahomet (Tears) Horberg, Leland, op. cit., pp. 56-5 7. LEMONT DRIFT 57

Valley. The buried valley's course 1s con­ till is very hard when dry because of the tinued as a trench about 25 feet deeper in high percentage of clay. Some of it is very rock than the floor of the DesPlaines Val­ sandy, and its lumps are soft and crumbly. ley north of the junction. The low rock­ Yet its matrix has so high a percentage of Aoor below the junction belongs to the comminuted shale that its color is dark buried-valley profile; it was cut deeper thari brown instead of gray. One clay member, the DesPlaines rock floor above that junc­ 11 feet thick, has a few· small pebbles scat­ tion. This feature agrees with the age re­ tered through it and some small elliptical lations already pointed out a·nd, indeed, cavities which seem to record gas bubbles is required to make the hypothesis consistent. in the clay when it was being deposited. Spring Creek does not follow either of There is no evidence of weathering or the two distributary valleys in bedrock for groundwater staining in the entire section. their full length. Instead, it crosses the Because it is buried beneath Lemont drift, buried hill between them, uncovering the it can be no younger than that formation, very top of the hill in the bottom of it-; and it is probably of lllinoian age (p. 63). channel in. sec. 6, T. 35 N., R. 11 E., and sec. 1, T. 35 N ., R. 10 E., on the LEMONT1G DRIFT Joliet quadrangle. Similarly, Hickory Cr•�ek The identification of a previously un­ fails to follow its preglacial valley, cutting recognized sheet of drift in the Chicago into buried rock hills on the south side ot region is one of the important additions to the old valley course in four places in thr our knowledge of the Pleistocene that re­ vicinity of New Lenox and in one place sulted from this study of the region. The on the north side, I 1 /.J. miles east of Joliet discovery was possible largely because there city limits. Roth Spring and Hickory Creek was an abundance of fresh highway cuts valleys have normal widths at these places, when the study was undertaken. By the hence arc not to be interpreted as simply time this report is published, these cuts will sags in the surface of the Lemont drift be so largely covered with grass that most because of underlying bedrock valleys. of the exposures will have disappeared. One Their courses were not entirely controlled splendid exposure, however, promises to re­ by such sags; their widths were determined main clean for many years and has been by stream erosion during a post-Lemont, chosen as the type exposure. It lies about a pre-Minooka erosional interval. l\llarley mile west of the town of Lemont (Joliet Creek, with a valley proportionately capa­ quadrangle), just outside the Chicago re­ cious, has no bedrock valley beneath it. gion as defined in this report. fact strengthens the conclusion that it This ":'\amc fi<>< published in Bull. 6;. Port I. 19j9. was stream erosion which made these pre­ V alparaiso valleys of the Mokena quad­ rangle.

ILLJ NO IAN ( ?) ST AGE

Sun-LEi\IONT DRIFT TN BuRrnD HADLEY VALLEY Sub-Lemont drift 85 feet thick nearly or completely fills the buried Hadley Valley as revealed in a test well drilled for the Illinois State Geological Survey. It con­ sists of alternating till and washed ma­ terials, all characterized by the presence of brown shale occu rring as pebbles or as com­ minuted material in the matrix. There are Fie. 22.-Lemont till in ravine wall, one mile probably four till members. Some of the west of Lemont. 58 GLACIAL GEOLOGY

f.10. 24.-Contact between Valparaiso :111d Le­ morit tills, one mile west of Lemont. The older till maintains nearly vertical clifffaces, the gen tier slope in the profile is on the F10. 23.-Lemont till overlain by Valparaiso till, clayey Valparaiso till. one mile west of Lemont. The contact is at the top of the vertical faces of the buttresses <.:HARA<.:TER IN 'l'llE TYPE LOCALITY between gullies. The term drift, instead of till, is used

TYPE J,OCALITY advisedly. Much of it, though undoubtedly of glacial derivation, is not till, but con­ Lemont was formerly the center of an sists of washed products of till-gravel, active quarry industry. The 1iagaran dolo­ sa nd, and silt-very irregularly associated mite here crops out extensively or lies close with each other. The exposures generally to the surface of the DesPaines valley show till ahove the washed sediments, al­ Ooor for several miles. It is unusunlly well though in some places till is intercalated in ded tra n :ire fine textured bed and some s t the stratified material. The till is strikingly and desi rah le for flagstone and building different from Valparaiso till anywhere in stone. Before concrete, hard-burned brick, l llinois. Valparaiso till is clayey, weathers and terra cotta appeared, it was in great brownish, has a starchy fracture in the demand in Chicago, Joliet, Au rorn, and weathered portion, contains very few stones, nearby smaller towns. One quarry or group and has a lime-enriched zone at the proper of quarries, on the south side of the Dcs­ depth in its soil profile. The till of the Plaines and a mile or so "·est of Lemont, Lemont drift is silty, not clayer, is dis­ found desirable stone back in the base of tinctly yellowish rather than brownish in the bluff under a heavy cover of drift. It weathered portions, has a laminated struc· was worth the additional cost of removing ture instead of a starchy fracture, is wcll­ the overburden, and before the industry charged with stones, and shows no lime waned and died, the removal of the glacial enrichment. There are many shale pebbles deposits produced a cliff about a mile long in the Valparaiso till but almost none in and as much as 50 or 60 feet high. Though the Lemont till. this cliff of unconsolidated material has stood untouched by man for fifty years, it still constitutes an excellent exposure. It is the type exposure for the Lemont drift.

THICKN ESS

Debris from ravine erosion and slope­ wash has obliterated the quarries and all but concenled the bedrock at the foot of the cliff. Valparaiso clayey till appears in a few places at the cl iff summits. Other­ wise, the entire section here expose d con­ sists of various phases .of the Lemont drift. Fie. 25.-Coarse gravel beneath till. Lemont Its maximum thickness is about 60 feet. drift one mile west of Lemont. OTHER EXPOSURES 59

Till vanes with source material and OTHER EXPOSURES with conditions at time and place of dep­ A deep ravine in Lemont (Sag Bridge osition. The above-listed contrasts, there­ quadrangle-Map 13) separates two resi­ fore, might exist in well-separated areas of dential districts on the bluffs south of the the same till sheet. But where they occur business district. Only the clayey Valpa­ in the same section, as they do near Lemont; raiso till is exposed in �uts and excavations and the clayey till is sharply separated from on the bluff slopes and summits, but in the the silty till below, they definitely suggest ravine walls the yellow silty Lemont drift two different till sheets. And when the underlies the clayey till, and in one place contrasts are found to be the same in dozens near the mouth the contact of the two is of other exposures in the Mokena (Map shown in the ravine floor. Both the strati­ 17), Sag Bridge (Map 13), Hinsdale fied silt and the very stony silty till are (Map 9), Tinley Park (Map 18), Palos present. A marked descent of the contact Park (Map 14), Joliet, and Wheaton quad­ of Valparaiso till and Lemont drift in rangles, the case for a pre-Valparaiso drift crossing the valley indicates a pre-Valpa­ m the Chicago region becomes much raiso depression here, filled during the later stronger. advance, and now re-excavated. It is ex­ In the type locality, the Lemont drift is actly what would exist if ravines had been highly variable both vertically and hori­ eroded in the Lemont drift during a pre­ zontally, and its glaciofluvial material ap­ Valparaiso interval of deglaciation, and this pears to have been deposited in proximity suggestion is supported by similar evidence to ice, the till being laid down by an ad­ from other places. vance of that ice over the outwash material. The south bluff of the DesPlaines Valley Some of the sand and gravel is sufficiently for a mile and a half west of Sag Bridge cemented to yield boulder-sized fragments village (Sag Bridge quadrangle-Map 13) of sandstone and conglomerate when ex­ is mapped as Lemont drift. It is the most cavated and gullied. extensive outcrop known, except in the The drift is tan to buff in all but one of cliffs west of Lemont, but at present it is the exposures west of Lemont. The excep­ very poorly exposed. Slight cuts have been tion is a blue unoxidized till mass exposed made in the five ravines which here trench in the lower slopes of the easternmost ra­ the bluff, and a good cut was made at the vines in the quarried area west of Lemont. east end of the exposure when Archer Above it is buff till. A dolomite slab 18 Avenue was graded and paved. At a height inches in maximum dimension was found of 80 or 90 feet above the adjacent valley standing edgewise at the sharp contact, half floor, 4 feet of brownish clayey till is shown in the blue till, half in the overlying buff overlying 8 feet of yellowish very stony till, till. The blue till was wetter at the time with some silt or clay layers in it. The most of observation, suggesting less-ready escape marked difference between the two tills is of seepage from the bluff through it and, in the clay content. The yellow lower till, therefore, less permeability, although both though damp, will not make a slippery sur­ are clear�y parts of the same till mass. The face between thumb and forefinger, nor most interesting feature is a bright orange will it pinch out into a wafer without sand immediately beneath the blue till, grad­ crumbling. The upper till will do this ing downward into a yellow sand, which in readily. Indeed, the upper till's damp starch­ about 2 feet grades into the normal tan or like fragments are slightly adhesive even buff sand. The strongly colored sand is when lightly touched. incipiently cemented with iron oxide. Lo­ Several hundred feet downhill along cally the sand has been deformed by ice , actually 30 feet lower in thrust ; blue till and yellow-to-orange sand altitude, 4 feet of clayey Valparaiso till are interfingered. Only groundwater can overlies 15 feet of stratified silt. Most of be the cause of the coloration of the sand. the silt is dark reddish-brown, but the basal 60 GLACIAL GEOLOGY few inches is yellow or orange-yellow, and two tills in section. The pit has been un­ the intervening few inches is bluish. Be­ used for twenty-five years, the cut bank low the silt is 1 foot of very stony yellow­ has become obscured by slumping, and the ish till resting on Niagaran limestone. The sections are so poor that considerable dig­ brownish silt effervesced moderately under ging with a spade was necessary. There is acid, the blue silt vigorously, and the basal a body of cemented gravel beneath the lower yellow silt faintly. Neither the color dif­ till, which is no longer exposed, but aban­ ferences nor the responses to acid are dis­ doned masses of it lie on the pit floor. tributed vertically, as they would be in a Swallow Cliffs, along the south side of soil profile ; groundwater changes, rather Sag Valley in the Palos Forest Preserve than weathering down from the surface, (Palos Park quadrangle-Map 14), are must have been responsible. These sections composed almost wholly of Lemont drift, along the Archer Avenue grade, from val­ although Valparaiso till covers the forested ley Aoor to upland, show that the Valparaiso upland and comes to the cliff edge in some till was deposited as a thin veneer on a pre­ places. The exposures in general are poor, existing valley �lope. The Sag-DesPlaines the best ones occurring in the ravine just Valley was here before the Valparaiso gla­ west of 96th Avenue. One of these is ciation. "Swallow Bank," a small cliff of yellowish Highway cuts along 107th Street west silt and very fine sand fenced off to allow of 109th Avenue exposed Lemont drift at bank swallows to nest in it undisturbed. the base of the north bluff of Sag Valley Another is the very active gully, described (Sag Bridge quadrangle-Map 13). A in Part I of this bulletin ( p. 24), which ravine eroded in the south slope of Mt. has developed on the site of a former farm­ Forest Island, a mile west of Palos Golf road down the bluff. It shows Valparaiso Club, also shows Lemont drift and will do till above the very fine sand. The 96th so long after the highway cuts are ob­ Avenue cuts, before they were planted, also scured. showed Valparaiso clayey till above Lemont The best exposure in the ravine 1s Just drift, which here consists of till, gravel, below the common junction point of three and fine sand. Several other cut banks in tributary gullies. Six feet of clayey till, ravines of the Palos Forest Preserve show crumbling into hard starchy lumps that Lemont drift, chieAy the fine buff or yel­ resist crushing in the fingers when dry, low sand. overlies a reddish-to-yellowish sand, beneath For years, this silt and fine sand has which is 15 feet of a stony till which con­ been interpreted as a loess, although appar­ tains so little clay that it does not smear ently there is no published statement to that or stick to the fingers when damp. I ts effect. Its fineness and evenness of grain, color, however, is bluish gray, not yellow­ its lack of pebbles through considerable ish. The section is in the lower wall of the ravine, hence is much farther below the upland level than the thickness of the Val­ paraiso till here might suggest. The l 07 th Street cuts, which are still lower, displayed only Lemont drift in which the predominant constituent was yellow silt. Borings slwwed that this silt was bluish 5 to 10 feet below the road grade. The yellow color is due to oxidation, just as is the brown color of Val­ paraiso till. An old pit along the Santa Fe Railroad, about a mile southwest of Byrneville (Sag Fie. 26.-Swallow Bank, Palos Park Forest .Pre­ serve. An exposure of silt of the Lemont Bridge quadrangle-Map 13), in the north drift. Clayey Valparaiso till overlies this slope of the DesPlaines Valley shows the silt farther back up the slope. OTHER EXPOSURES 61 thicknesses of the deposit, and its ability Nearly 20 feet of Valparaiso till was found to maintain steep faces in cuts, seemed to in the top of the section, underlain by a 3- substantiate the hypothesis. There is a deli­ foot "boulder stratum," this in turn resting cate cross-bedding in some exposures of the on 2 feet of washed gravel. Under the fine sand, interpreted as eolian in origin. gravel was 10 feet of the silt (the so-called If this is correct, the deposit should be con� loess), and beneath that was a till. The sidered as fine dune sand rather than as Valparaiso till was br�wn except for the loess. basal portion, which was an unoxidized Since cross-bedding is also produced by blue. The boulder stratum was a hetero­ streams and shore currents, it is necessary geneous unstratified mixture of clay, sand, to examine this structure critically. The pebbles, and striated cobbles and boulders. cross-bedding is on a minute scale, the It very probably was till. The matrix had lenses or unit groups of inclined laminae an oxidized brown color and, whatever the being rarely more than an inch thick. The origin of the deposit, an explanation for this foresets of associated units all dip in the oxidation beneath unoxidized basal Val­ same direction. The assemblage is that of paraiso till is needed. The 10 feet of silt horizontal beds made up of the lenses of dip­ is described as "typically buffish-yellow" ex­ ping laminae. In some places definite layers cept in the lowest part, which is bluish. of clay are present, most of them thin, but From memory of the cut when freshly some are as much as 2 inches thick. Rarely made, only four characteristics of this sec­ also pebble layers are found in the sand. tion can apply in general to the entire cut : Vertical gradation from cross-bedded mem­ (I) the brown clayey Valparaiso till every­ bers to evenly bedded ones is common. No where was the uppermost member, (2) unconformities of the sort that cross-bedded the yellow silt was a large constituent of dune sand commonly possesses have been the material exposed, ( 3) gravelly members found in the deposit. It seems clear that the occurred, and ( 4) in a few places a stony surface of the deposit remained flat at all till was associated with the silt and gravel. times during its growth. The texture of the There was no constant order of succession material is everywhere much finerthan dune of the members below the uppermost till. sand, so fine that if wind-whipped it would There was great irregularity of thickness be more likely to rise in the air like dust of the members except for the uppermost than to drift close to the ground like dune clayey till. There were notable contrasts sand. Yet the cross-bedding shows that it of color, ranging from unoxidized blue to was rolled along. The most satisfactory oxidized yellow-orange. There was consid­ interpretation of the silt and fine sand in erable deformation of the stratified mem­ Swallow Cliffs and vicinity is that it was bers of the Lemont drift, caused probably carried by gentle currents of water over a by thrusts from overriding Valparaiso ice. wide flat of aggradation. It is outwash silt Three features will need more attention associated with the silty till and is a part of when the remaining sections of Lemont the Lemont drift. drift have been described : (I ) the marked oxidation in certain portions beneath un­ Excellent exposures of the Lemont drift oxidized Valparaiso till. (2) the silty char­ were made when the Wabash Railroad re­ acter of the till, and 3) the occurrence of located its right-of-way through Palos Park. silt as the only well-washed( product from However, before this study was undertaken the till. there was much slumping at the exposures The Southwest Highway, when newly and many details were lost. A vertical sec­ graded, afforded an interesting cut a few tion at one place was cleaned of its slump hundred feet north of I 19th Street in the debris and described in a Master's thes!s16 Palos district. Almost all the material ex­ written a few years after the cut was made. posed was yellow silt ; in a few places, at 16Bolyard, G. L., Pleistocene features of the Palos the base of the cut, the silt was bluish or Park region : unpublished Master's thesis, Dept. Geology, Univ. of Chicago, 1923. bluish gray. It was stratified, though rather 62 GLACIAL GEOLOGY indistinctly so, and showed no cross-bed­ there obliterated by the advance of Lemont ding. The most interesting feature of this ice. section was the great distortion of the silt. Lemont drift is well exposed in the south­ 1 n some places the stratification was verti­ western part of the village of vVorth, along cal ; almost everywhere it departed from the Southwest Highway, and in a gravel the horizontal. The blue silt appeared only pit east of the highway and south of 111th where there had been up-squeezing, and in Street. The highway cut ,,;as studied dur­ one place a mass of blue silt with vertical ing its excavation. Lt revealed irregular beds was entirely wrapped around by the bodies of yellow silt, coarse gravel, and yP.l lowish :ind hrownish distortP

Fie:. 27.-Gravcl-fillcd channel in T .cmonr silr. Fw. 28.-Dclra forcsct bedding in Lemont drift Southwc�t Highway, south of Sag Canal. near Worch. OTHER EXPOSURES 63

ley ice, constituted a maturely developed B zone. A large but shallow borrow pit, worked when I 19th Street was graded and paved, lies a few hundred feet southwest of the intersection of l 19th and Harlem Avenue (Palos Park quadrangle-Map 1-t). A foot or so of clayey til 1 O\'erlies 5 or 6 feet of gravel with depositional dip west\\·ard. Beneath the gravel is finely laminated gray silt, nowhere more than 6 or 8 feet from Fie. 29.-Forcset bedding in Lemont drift near the surface. Except in color, this silt is Worth. Two delta lobes are recorded, the identical \\'ith that of the Lemont drift, one to the left younger and overlapping on the one to the right. and almost nowhere is silt known in asso­ ciation with the Valparaiso till. If it is of heel� of the gra vcl and sand (figs. 28 and Lemont age, its lack of oxidation so near 29). The deposit is part of a delta, prob­ the surface indicates that the yellow color ably recording a glacial river that debouched is pre-Valparaiso in age and that in the here in a lake. The silt is the offshore lake later overriding the weathered zone was �edimcnt, laid down beyond the delta edge. entirely removed. If this interpretation is The topography is not now that of a delta, correct, one might expect to find masses of for the Valparaiso ice sheet has overridden stained Lemont drift embedded in Valpa­ it, and there may have been other altera­ raiso ti! I. tions in form after its deposition and before Three low gravelly knolls on the lake­ the Valparaiso glaciation. Rut the forcset bottom plain cast of Ridgeland Avenue and beds shown in figure 29 dip toward each north of 127th Street are mapped as Lemont other, and also toward the photographer drift. All have gravel pits in them. Two (which docs not show in the photograph ); of the knolls are composed chiefly of Aoury, these relations can only mean that a delta velvety yellow silt, associated with gravel lobe at the right was later encroached on which has west-dipping beds. In one, the by one at the left. washed gravel grades into a verr poorly Beneath the cover of Valparaiso till the washed phase in which ycllO\\- silty material gravels in one place are oxidized for a depth is a prominent constituent. This is taken to of several inches, and the limestone pebbles be modified Lemont till. Over the till, are etched and softened, suggesting the rem­ gravel, and silt is the Valp;1raiso clayey nant of a weathered zone developed after till, and above that is beach sand of the the Lemont glaciation and before the Val­ Calumet stage of Lake Chicago. paraiso till was deposited. But the same \i\lashed gravel is commonly associated result might be produced by groundwater with the Lemont till-much more com­ in the porous gravel while the dense clayey monly than with the Valparaiso till. It till immediately above remained unaffected. has been noted al ready in the exposures Recent excavations in this pit, since the in the old Santa Fe pit (p. 60). A ledge field work for this report was completed, of cemented gravel crops out in the mouth have exposed Lemont drift so decomposed of the ravine just west of the ski jump in that Leland Horberg, who found it, is fairly Palos Park Forest Preserve. The large pit confident that it is a surface-weathering at \i\l'orth is in similarly associated gravel. product. Depth of leaching reaches a maxi­ From these relations, it is a fair inference mum of -tO inches, a figure strongly sug­ that beds of clean gravel which lie beneath gesting that the Lemont drift may be Illi­ Valparaiso till in the general region of the noian in age. instead of early "'i,consin. outcrops of Lemont drift belong to the The upper part of thi� weathered material. earlier deposit. Two such bodies of gravel although cfoturbed by the overriding Tin- are to be noted here as probably of Lemont 64 GLACIAL GEOLOGY age, though the exposure5 do not show the characteristic yellow, silty, stony till or the commonly associated yellow silt. One of these gravel deposits underlies a terrace on the north side of Sag Valley where it is crossed by Kean Avenue (Palos Park quad rangle-Map 1-1-). A large spring discharges from it, there are many seepages from it, and shallow wells in it yield abundant supplies of water. It is not mapped as Lemont drift because its age has not been definitely established and because Fie. 30.- Mass of cemented gravel in pit near the surface is covered by gravel of the Lake Willow Springs. Chicago outlet river. Indeed, it may all be related to that river and not Lemont in clay 7 or 8 feet thick is reported to underlie age. . the gravel, beneath which is said to be an What may be the same gravel underlies even cleaner gravel. The gravel is well the Tinley moraine just north of the ter­ above the nearby Flag Creek morainic sag, race. \Vells near the intersection of Kean hence must be a pre-Valparaiso deposit. and 107th Street it at about feet find 625 In a pit south of Fifth Avenue, half a above sea level, 5 to I 0 feet higher than the mi!e farther northeast (Hinsdale quad­ terrace top. Its thickness is unknown, and rangle-Map 9). there is no gravel, but 5 its maximum kno"·n horizontal extent be­ feet of yellow silty stony till underlies a neath the till is only half a mile. It mar cover of clayey till and is underlain by be related to an earlier Valparaiso glacial dean sand, part of it current-bedded, with river along the Sag, before the Tinley re­ westward dip. Here apparently are both advance occurred and before Lake Chicago Valparaiso and Lemont tills, the Lemont began .11 It may also be outwash deposited again associated with material reworked by during the Tinley readvance and overridden glacial water. I ndced, it is the writer's be­ by Tinley ice shortly afterward. lief that essentially all the well-sorted sand The other gravel deposit suspected of and gravel bodies below Valparaiso till belonging to the Lemont drift is in the along both Sag and DesPJaines valleys above north bluff of the DesPlaines transmo­ their junction belong to the Lemont drift. rainic valley a mile north of \ Villow Springs (Sag Bridge and Hinsdale quadrangles­ LEMONT DRJFT JN YOUNGER TILLS Maps 13, 9). This area was extensively The miles of fresh highway cuts avail­ excavated years ago, but subsequently the able when this study was made afforded a cuts have become greatly obscured. At leagt 25 feet of dominantly limestone gravel is overlain by 12 to I 5 feet of clayey till. The contact is sharp, and the gravel for a few inches below the till is so solidly cemented that it resembles concrete. Here and there cementation sufficient to make boulder-like masses (fig. 30) has occurred deeper in the gravel. There is a slight brownish stain locally in the upper few inches of the gravel ; otherwise its only alteration is the partial cementation. Rlue

t'Thi1' possible Lemont gr:n·el i! oot to be _confused with the J:!r:l\'Cl �hown on the P:ilos P:ark J:toloi:ical map on both sind •outh ol 107th St.rec•. Fie. 31.-Cross-bedded sand in Lemont drift definitely outw3sh dep�ittd when 1hc Tmley which j5 near Willow Springs. mouinc was being bu'.lt. LEMONT DRIFT IN YOUNGER TILLS 65 short-lived opportunity to search for masses silt 3 l /2 feet thick and 10 feet long is of older drift embedded in Valparaiso till. completely surrounded by clayey Tinley till, l t ·was suspected that the Lemont drift had the layers of the silt much distorted. Asso­ undergone much weathering before the Val­ ciated with it are half a dozen smaller paraiso glaciation, but none of the sections masses of red-stained silty gravel, their really proved this; a complete profile of stratification also distorted, and one of them weathering could not be found. Two con­ partly in the silt and partly in the clayey Aicting interpretations were possible: ( 1) till. the Valparaiso ice had removed the upper Figure 32 shows enough of the weather­ part of a normal weathered zone, and (2) ing pr.ofile in the Valparaiso till to make it the Lemont drift had oxidized beneath the clear that the masses of red gravel are dis­ Valparaiso till, exceeding the oxidation of tinct from the till and are blocks incor­ the clayey till because of greater porosit11• porated from an older deposit, already If masses of Lemont drift could be found stained at the tirne they were embedded in in the Valparaiso and Tinley tills, sealed the till. The iron-stained horizon of the by the dense clay from air and water except till itself lies above two .of the gravel masses what the tills contained in their own inter­ and largely above a third. Three small stices, and if such masses were definitely blocks are in the most heavily stained till leached and oxidized, the concept of pre­ but, like all these fragments, are consider­ Valparaiso weathering would be greatly ably darker than the till. Further evidence strengthened. here is afforded by two small stringers of A cut near the intersection of Harlem unweathered clay penetrating from the sur­ Avenue and 135th Street, 2 miles southea>t rounding till for 6 and 18 inches respec­ of Palos Station, 3 miles south of Worth tively into the oxidized silt block. They do (Palos Park quadrangle-Map 14), is not show in the photograph. A similar fea­ typical of many of its kind. It is on the ture from another cut nearby is illustrated east side of Harlem Avenue, 400 feet north in figure 33. of the intersection ; it is illustrated in figure A highway exposure showing a mass of 32. An irregular mass of stratified yellow older and more weathered drift enclosed in

Fie. 32.-Masses of Lemont drift included in Tinley till. The large mass is composed of yellow silt, the smaller and darker masses are of reddish gravel. East side of Harlem Avenue, north of I 35th Street (Palos Park quadrangle). Photograph by Paul MacClintock. 66 GLACIAL GEOLOGY

Top of rood - cut

Ye llow silt with

distorted bedding Gray Tinley till

---�--�-Stringers of unwe athered clayey till

Gray Tinley till

Fro. 33.-Sketch showing masses of Lemont drift included in Tinley till. Corner of Harlem Avenue and 135th Street.

Valparaiso till was found in the cut through Only one other highway section showing the hill on 143rd Street, a mile west of older drift incorporated in the Valparaiso Orland Park and just east of the junction till will be described, although there are of 108th Avenue (Sag Bridge quadrangle several others known in the southern part of -Map 13). Six feet of typical Valparaiso the region. It was exposed in grading for till, leached to a depth of 4 feet, overlies the 26th Street crossing of Thorn Creek a foot of dark fine gravel, beneath which Valley just west of Chicago Heights is a foot of unleached clayey till, and below (Steger quadrangle-Map 23). Tinley till that 6 feet of silt and fine sand, brownish constitutes the material, but when cuts were to yellowish in places but gray in large part, fresh, several blocks of older drift were to the bottom of the cut. The silt and sand recognizable, the largest 6 feet across. Some is leached for 3 or 4 feet down. Four feet of these were of sandy yellowish till, dis­ to the side of this vertical sequence, the tinctly unlike the matrix till ; some were of Valparaiso till extends down to the silt and sand and gravel, with distorted bedding. sand. There is no dark-stained gravel with The included fragments effervesced with unleached till above and below. The gravel acid but none as vigorously as the enclosing therefore is a mass of older drift included clayey till. Furthermore, in the largest in­ in the Valparaiso till. A third vertical sec­ cluded mass, which has nearly horizontal tion, a dozen feet distant, shows the clayey bedding, the least effervescence was found till to extend below the level of the bottom in the lower part, the most in the upper. of the first section. Therefore, the silt and It seems logical to interpret this block as fine sand probably is a fragment of the now upside down in its matrix. older drift enclosed inalso the Valparaiso till. Complete outlines of fragments were im­ LEMONT DRIFT IN THE BURIED HADLEY possible to obtain because the cut had al­ VALLEY ready slumped considerably at the time of A test-well drilled to bedrock in the examination. middle of Spring Creek Valley, above th� CORRELATION 67 buried Hadley Valley, showed 27 1 /2 feet It may be that the Lemont drift was de­ of clayey Valparaiso till, 51 feet of Lemont posited during the pause at the end of a drift, and 85 feet of gravel, sand, clay, and retreat from one of the Wisconsin mo­ till beneath the Lemont materials. Identi­ raines farther west and before a readvance fication of the Lemont drift was based on occurred. Its survival under such condi­ the silty character of its till and the ab­ tions would be no more remarkable than sence of shale pebbles and of finely ground its survival from the Valparaiso overriding. shale in the matrix. Both the overlying Val­ ( 4) It may be that the Lemont ice never paraiso till and the 85 feet of drift beneath advanced beyond the present known limits the Lemont contained shale, so abundantly -that this drift is the record of an early in some samples from the lower drift that Wisconsin advance which later was ex­ the material was dark brown and gave a ceeded by those which built the moraines marked brown smudge on white paper. farther west. Three till members were found in the The notable differences between the Le­ Lemont part of the section, separated by mont till and the other Wisconsin tills is two sand ·and gravel members. The upper another problem. Three interpretations are member was tan, whereas the remainder of open to us at present : ( 1) it may be that the Lemont drift was gray. an excess of escaping water removed clayey constituents and left the till silty and stony ; CORRELATION (2) it may be that an earlier "Lake Chi­ Considering the preceding data, it is cago" left quantities of beach sand and clear that there is a body of drift beneath gravel, dune sand, and lacustrine sand, the Valparaiso till in the region of the Sag which became incorporated in the till of the and DesPlaines transmorainic valleys which advancing Lemont ice and thus gave it the differs markedly from that till. The evi­ stony and silty character repeatedly noted ; dence strongly suggests that considerable or (3) it may be that a somewhat different time intervened between the two glacial route was followed by the Lemont ice in overridings, though nowhere was a true soil reaching the region, and thus debris from horizon or a true loess found separating the different kinds of bedrock gave a different drift sheets. lithological aspect to the deposit. The position of the Lemont drift in the The first of these tentative explanations Pleistocene succession has not yet been seems the least probable for it requires al­ positively determined, for no facts now in most complete removal of a dominant con­ our possession seem to be conclusive. Sev­ stituent of the till while leaving it a till. eral possibilities exist : ( 1) The Lemont The second suggestion requires that a clayey drift may be older than Wisconsin, and till, from being dragged over a few miles of the recent discovery of a weathered zone sand-, silt-, and gravel-covered country, be­ in Lemont drift at Worth ( p. 63 ) supports came a completely different material. The its identification as Illinoian in age. (2) third interpretation is supported by the It may be the ground-moraine correlative fact that the silty Lemont till has very few of some earlier Wisconsin moraine farther shale pebbles in it whereas the clayey Val­ west, although its material is unlike the till paraiso till has an abundance of them. in any of them, at least along the line of Spores of Sporangites huronensis are in both glacial movement across and beyond the the clay matrix and the shale pebbles and Chicago region. They are all more clayey indicate that the Devonian black shales in till moraines, while the Lemont is a more the glacially eroded bed of Lake Michigan silty till with an abundance of stones at supplied at least some of the pebbles and almost every exposure. Further objection clay. If the Lemont ice which traversed to this interpretation is that much of the this region had come more nearly from the Lemont drift was deposited by free-flowing north than northeast, it would not have extrag:lacial water, therefore is not a sub­ crossed the shale outcrops. Accessory evi­ glacial ground-moraine accumulation. ( 3) dence would be glacial striae on bedrock GLA CIAL GE OLOGY 68 beneath Lemont till. The only place where of these cemented gravels are clearly older these are known is in Sawmill Creek Val­ than the valleys in whose lower slopes they ley, Sag Bridge quadrangle ; but here the now outcrop and therefore older than the striae strike N .55 ° E., a course which if valley train gravel in the valleys. A sug­ projected far enough back to the northeast gested correlation of the Joliet outwash will intersect the black-shale outcrop be­ plain with the Algonquin gravels along neath the lake. The explanation therefore Fox River northwest of the Chicago re­ must be emended or discarded. A possible gion is considered under a later heading. emendation is that the local Le�ont ice travelled southward along the western edge ADDITION AL LOCALITIES of the lake basin and had turned southwest­ Localities where Lemont till is known or ward before it reached the bedrock now believed to be present, but which are not exposed in Sawmill Creek bed. shown on the geological maps, are as fol­ lows : JOLIET OUTWASH PLAIN AND LEMONT Mokena Quadrangle ( Map 17) : DRIFT Hickory Creek Valley. Tributary flow­ The type exposure of the Lemont drift ing from Cleveland School, sec. 20, ex­ lies just outside the mapped limits of the treme SE corner of quadrangle. In hill Chicago region, a mile or so in the Joliet spur projecting from the south, northeast quadrangle. The Illinois State Geological of the schoolhouse. Also in bluff on south Survey Bulletin 51 on the Joliet quad­ side of ravine, almost directly north of the rangle18 describes cemented gravels at this schoolhouse. place but makes no mention of a pre-Val­ Hickory Creek Valley. North side, in SE paraiso till here. The cemented gravel of 1/4 sec. 13. the Lemont drift is correlated in Bulletin Intersection of Bell Road and 151st 51 with other exposures of cemented gravel Street, cornering of secs. 11, 12, 13, 14, in the quadrangle and environs. The in­ northern part of quadrangle, 4 1 /2 miles terpretation is that after the Minooka mo­ north of Marley, in road cut. raine (8 to 10 miles west of Joliet) was Maple Street Road. Near the western deposited, the ice withdrew to a position edge of the quadrangle in several road cuts. east of the present Valparaiso moraine, Sag Bridge Quadrangle (Map 13) : while an extensive sheet of outwash sand Intersection of Archer and Highway 4A, and gravel was deposited in front of it, 1 1 /2 miles south of Lemont, on west edge later to be overridden when the ice ad­ of quadrangle, in road cut. vanced at the Valparaiso moraine-building Sawmill Creek Valley, in west bluff a stage. This gravel Fisher called the "Joliet little upstream from the place of the piracy. outwash plain."19 He clearly thought the Hinsdale Quadrangle (Map 9) : indurated gravel and sand to be older than Flag Creek Valley, west bluff, extreme Valparaiso. southeastern part of Hinsdale city limits, Although Fisher specifically refrained in road cut. from correlating all the cemented sand and Tinley Park Quadrangle (Map 18) : gravel of the Joliet quadrangle with that Hickory Creek Valley, along Lincoln near Lemont, it now appears that most of Highway south of Gatter School, in road the sub-till gravels he reported may well cut. belong to the Lemont drift. They appear Frankfort, northern part, 200 feet south to have been deposited beyond a moraine of Lincoln Highway, along 96th Avenue, whose outer margin slightly overlapped the in road cut. eastern edge of the Joliet quadrangle. Most Palos Park Quadrangle (Map 14) :

lSfisher, D. J., The geology and mineral resources Southwest Highway, 3/8 mile south of of the Joliet quadrangle : lllinois Geo!. Survey Bull. 51, 1925. Southmoor Country Club, in road cut. 19J. W. Golclthwait had earlier called it the "Joliet Southwest Highway, 1 mile northeast of conitlomerate." Su Phvsical features of the De

Southwest Highway, about 1/10 mile ish Tinley ground moraine, in the lower southeast of Southmoor Country Club, in part of the oxidized zone and below the road cut. leached zone. The largest was 3 feet in maximum diameter. All were irregular in WISCONSIN STAGE shape and several fingers of yellow till were thrust into the pink or red till. TAZEWELL SUBSTAGE Excavations for a grade separation of BLOOMINGTON20 ? ) DRIFT and , almost on ( Well known to glacialists of the north­ the county line in the northeastern part of central states is the pink-to-red color of Elmhurst, showed several masses of pink much of the Bloomington drift, the hue till, harder and more pebbly than the en­ being deeper when the material is moist. closing gray Tinley till. The largest mass One recognizes it in highway cuts west of was close to the bottom of the cut, perhaps Chicago, as soon as one has crossed the 18 feet below the surface. In the dump younger moraines. It is also found in places from this excavation, there were manv· pieces of pink till. beneath the younger drift sheets, the nearest occurrence probably being in the southwest Two fragments of pink till were cut corner of the Joliet quadrangle,21 where through in an auger boring in the Tinley "there is a two-foot section of highly cal­ ground moraine at the Lake Street subway careous pink till underlying about 4 feet beneath the Chicago and Northwestern of laminated lake-clays, which are overlain Railroad tracks, less than half a mile south­ by till of Minooka age." This till is very east of the intersection of Lake Street and sandy, its pink color mottled with yellow, North Avenue. They were 7 and 10 feet and the yellowish parts are apparently more below the surface, embedded in bluish-gray sandy than the pink. In its sandiness it unweathered till. Neither was more than 4 resembles the pink Bloomington till along inches thick. This and the Buffalo Grove the upper Illinois Valley. 22 Bloomington occurrence are about 30 and 17 miles re­ till is also known in the eastern part of the spectively, southeast and east of k�own Elgin quadrangle, west of the northern part Bloomington till in place in the Fox River of the region. There it is beneath the West Valley on the Elgin quadrangle. Fragments of an unctuous red clay, which Chicago moraine, the outermost member of . the Valparaiso system. might be a derivative of the Bloomington Fragments of pink-to-red drift, incorp­ drift, were found in the Bohnsack Brick orated in the clayey till of the Valparaiso, Company's pit along the Soo Line tracks Tinley, and Lake Border drift sheets, have three blocks south of Irving Park Boule­ been found in six quadrangles. In another vard in the southeast part of the River quadrangle, pink till has been reported in Forest quadrangle. They were small (the sewer trenches and in a well. In another, largest only 2 inches in diameter) and were a pinkish till is known in situ beneath two �ound within 6 feet of the surface. Similarly, other tills. :Most of the incorporated frag­ m both the Illinois Brick Company's pits ments are small and owe their discovery near Bernice, Calumet City quadrangle, entirely to a notable contrast in color. small fragments of red clay are embedded The largest fragments known were ob­ in till. Workmen report them as 1 foot in served in a cut along the McHenry road maximum dimensions, generally elongated half a mile southeast of Buffalo Grove, horizontally, but none that large was seen 'Vheeling quadrangle. Five differentmasses at the time of examination. They appear to of de ink till were embedded in yellow- be limited to a lower clay till, 18 feet or � more below the surface. A third occurrence 20Named for Bloomington, Ill., which stands on a of small bits of the red clay in unweathered orominent portion of the moraine. Leverett ' USG · · · S · Mon. 38. p. 240. bluish till is south of Burnside, Calumet 21Fi

where they have been found is the Illinois to penetrate a pink or red drift. Sewer Brick Company's pit south of Deerfield and trenches in Homewood and Chicago Heights just north of County Line Road, Highland (Harvey quadrangle), dug a few years be­ Park quadrangle, in ground moraine of the fore this study was undertaken, entered a Lake Border system. pinkish clayey till unlike anything in ex­ During excavation for the Chicago sub­ cavations made after 1930 in these towns. way, numerous bits and one large fragment There was an overlying gray or bluish-gray of unctuous red clay were found in the till in both places. Future deep digging in soft gray clayey Lake Border till underlying this quadrangle may add to our knowledge. the downtown district. The large mass had A peculiar section along the Chicago an estimated volume of 2 cubic yards. They Drainage Canal, which includes three tills were not till and none possessed any laminae of notably different characters, should be such as a lake clay might be expected to mentioned. The lowest till, definitely in have. Many pieces showed outlines of in­ place, is itself slightly pinkish in color (see terfingering stringers of red and gray and p. 77). undergone kneading and squeez­ clearly had PRE-VALPARAISO TOPOGRAPHY ing while being plowed up by the ice and incorporated into the gray till. In some Previous writers on the geology of the places the red clay fragments were so Chicago region have described the upland numerous that they constituted a breccia. west and south of the lake plain as a termi­ The large mass possessed a unique fea­ nal moraine built at the Valparaiso stage ture, so far as Chicago geology goes. The of the Wisconsin retreat. 23 Back of it, ac­ red clay enclosed many fragments of dark cording to their interpretation, the ponded greenish-gray clay, from a quarter of an waters accumulated as the ice sheet with­ inch to an inch in diameter, fully as soft drew and over it in two places the dis­ and unctuous as the enclosing red clay and charge spilled westward into Mississippi certainly not bits of the surrounding gray drainage. They thought that both dis­ clay or fragments of Devonian shale. charge ways were simultaneously deepened The red and pink till fragments may, 40 feet or more, through the Valparaiso as suggested, be Bloomington, and the red terminal moraine to bedrock. Subsequent clay may be a lake sediment derived from drainage of a large part of the lake plain Bloomington till before any of the later has continued to use both these outlet tills were deposited. This interpretation channels. Similarly, earlier writers consid­ best fits the meager evidence but is only ered that the irregularities of the upland tentative. It would be strengthened if belt were due to irregula·r deposition of the masses of red clayey till occurred in the Valparaiso drift, and to subsequent stream Lemont drift, but none has been observed. eros10n. Pinkish and reddish areas a few inches There are remarks in the early studies to a few feet in diameter, but without def­ on the probability of pre-Valparaiso drift inite outlines, in many exposures of un­ existing in the region. A "brown hardpan" weathered Valparaiso and Lake Border till found in wells and caissons, a very dense till in the Chicago region suggest that older exposed in the Drainage Canal a mile east reddish drift has been mixed enough to of Summit, and the gravel beneath till a obliterate all fragment outlines. The source mile north of Willow Springs are the only of this incorporated material must be either deposits specifically referred to as perhaps beneath the younger tills of the region or pre-Valparaiso. The Lemont sections are somewhere to the northeast beneath Lake noted in two of the early papers, but no

Michigan. It seems a fair inference that 2�Leverett, Frank, The Pleistocene features and de­ Bloomington drift may locally exist in situ posits of the Chicago area: Chicago Acad. Sci., Geol. and Nat. Hi

(') t-o ::i:.. � ::i:.. t-o (') t'tl a t-o a (') '-<

0 Y2 I Mile

Fie. 34.-Pre-\"alparaiso valler� triburary to Sag \"all.:y. \'isication csker shown in pattern. (Sag Bridge quadrangle.) PRE-VALPARAISO TOPOGRAPHY 73 a drainage system down the west slope of Hickory Creek, Marley Creek, Spring the upland before the Valparaiso glaciation Creek, Fraction Run, and Long Run val­ seems by far the most probable explanation. leys, differing only in size and orientation. They are recognizable here because they They lead to the deep Sag Valley and could were more deeply eroded than contemporary have developed only when such a valley valleys elsewhere in the region. Deeper existed. Since they are pre-Valparaiso, the erosion and better development were con­ Sag must be pre-Valparaiso. sequent on steeper slopes of the Lemont Another unnamed creek enters the Sag drift accumulation. The necessary gradients from Mt. Forest Island, crossing 107th were provided by a higher piling up of the Street between 96th and lOOth Avenues drift and the existence of a nearby Des­ (Palos Park quadrangle). I ts course has Plaines trunk valley. several peculiarities. It drains half a dozen Earlier writers26 report low rock bluffs swamps in the center of the "island," flows and a glaciated bedrock floor in the Des­ in a fairly narrow valley southeastward as Plaines Valley near Lemont, and comment far as Kean Avenue, and there makes a hair­ on the probable existence of a river valley pin turn southwestward. It flowsfor a mile here before the Valparaiso glaciation. No across a tract with mild morainic topog­ one, however, argued that the pre-Valpa­ raphy which has a· marked bluff about 50 raiso valley extended northeastward along feet high overlooking it on the north but no its present course to the Chicago plain. That corresponding bluff on the south. The it did so has been concluded from the field topographic map clearly shows this bluff to studies for this report. Three kinds of evi­ be fairly straight and very definite, yet it dence are found along both the Sag and is not a bluff of the post-Valparaiso dis­ DesPlaines valleys east of the rockbound charge of Lake Chicago. Traced northeast­ part at Lemont. One consists of modified ward, it runs into the Tinley moraine tributaries to main valleys and surviving ridge just east of Kean Avenue, the trends bluffs of the main valleys, all overridden of bluff and ridge outlining an angle of by the Valparaiso ice and partially obliter­ about 45°. A similarly oriented bluff half ated by its drift. Another is pre-Valparaiso a mile southeast, eroded by post-Valparaiso gravel deposits near the two ­ drainage and cutting into the wuth side of heads, requiring for their .origin open val­ the Tinley moraine, is entirely distinct from leys in pre-Valparaiso time. The third is the one in question (fig. 35 ). There seems the presence of eskerine ridges of Valpa­ to be good topographic evidence that the raiso age on the main valley slopes. eastern end of a bluff of an older Sag chan­ Two unnamed valleys on the south side nel here has been overridden and obliterated of Sag Valley (Sag Bridge quadrangle ) in the Tinley moraine-building and that a may be taken as examples of the first kind portion of the Tinley moraine-dam across of evidence. One discharges to the Sag this channel still remains on the north. The through a little canyon (Cowles Canyon) post-Tinley Sag channel here appears to be in bedrock less than half a mile east of Sag a little farther south than its predecessor, Bridge village ; the mouth of the other is and Swallow Cliffs owe their prominence a mile west of the Palos toboggan slide. and their youthful ravines to post-Tinley Both are far larger and more capacious undercutting in this southward shift. than the post-Valparaiso ravines of Swallow If the above interpretation is correct, the Cliffs and both have tributary valleys. Yet old bluffs on Mt. Forest Island west of the in both there are morainic knolls and ridges, Tinley moraine should contain Lemont undrained depressions, and even lakelets. drift. Exposures are poor in the ravine Running water has done litt!e to this mo­ where the creek makes a hairpin turn, but rainic topography. It certainly has not spade and soil auger show that the silty eroded the valleys since the Valparaiso gla­ yellowish Lemont till is present, under a ciation. They belong . in the category of cover of clayey Valparai�o till. The Lemont 261.everett, Salisbury, Alden, Goldthwait, and blEk aw. till occurs in the bluff and ravine wa1ls 74 GLACIAL GEOLOGY up to 680 or 685 feet, 45 to 60 feet above levels. For westward escape of the vigorous the mildly morainic flat south of them. The streams, there must have been a pre-Val­ Valparaiso ground-moraine deposit did not paraiso "Sag channel" and a pre-Valparaiso greatly change the character of the old "DesPlaines channel" fully as deep as to­ bluff, though it put its own mark on the day's channels. flattish summit and base. The thicker Tinley In the Sag Bridge qua�rangle several marginal-moraine deposit cast of Kean ridges, or elongated mounds, of Valparaiso Avenue completely obliterated the bluff in moraine gravel lie on the northern bluffs that direction. The hairpin turn · of the of the DesPlaines channel and there is one creek ma�' be compounded of a pre-Val­ suc:h rlP.pnsit on thP. southern hl11ff of the paraiso stream course above the turn and a Sag channel (see fig. 35). These ridges post-Tinley course below it. are definitely eskerlike and kamelike. They The well-washed gravel deposit at Worth owe their form to the fact that the}' were ( p. 62), associated with other phases of partially enclosed by glacial ice when the Lemont drift, and the one a mile north of deposits were made. They antedate the Willow Springs (p. 64) are beneath Val­ discharge of Lake Chicago water across the paraiso till and record glacial rivers escap­ Valparaiso moraine. Became most of them ing westward. Excavations in both deposits lie on the bluff slopes and the longer ones have gone below the higher Lake Chicago reach almost from upland to valley bottom,

Fie. 35.-Pre-Valparaiso bluffs, Tinley moraine, and "Hairpin" Creek near head of Sag Valley (Palos Park quacrangle). PRE-//ALPARllISO TOPOGRAPHY 75

the Sag and transmorainic DesPlaines val­ paraiso valleys here, there must have been leys must have existed beneath the Valpa­ two most extraordinary transverse morainic raiso ice sheet during its retreat. Lake Chi­ sags. To. be low enough for Lake Chicago's cago's outlet waters cleaned out what ti ll initial discharge, they would have had to and outwash still obstructed the outlet, the · be lower than outcrops of Lemont drift in Tinley moraine being the major deposit. almost every place it is known along these · On the north side of the DesPlaines channel "channel" walls. That they existed as ero­ the largest eskerine ridge comes down from sional valleys before the Valparaiso gla­ 675 to about 610 feet above sea· level. This ciation seems an almost undeniable conclu­ " ridge is 1 1/2 miles west of the Tinley sion. Goldthwait27 says that no precise moraine; on the east side of the ravine near reason can be given for the presence of the the center of the N 1/2 of sec. 6, T. 37 N., two initial sags in the moraine." That R. 12 E. (Sag Bridge quadrangle-Map problem of his day is believed now to be 13). The valley floor here, therefore, was at solved. least 25 feet lower than the highest stage Part l of this bulletin contains a brief of the lake and only 3 miles distant. From statement regarding the pre-Valparaiso, 625 feet to 610, this eskerine ridge has been post-Lemont stream erosion. Since the pub­ eroded by the lake's outlet river and is very lication of Part I in 1939, a study of the cobbly and bouldery on the surface. Only Grays Lake quadrangle has appeared which the Tinley moraine could have been the contains significant contributions to the Lake Chicago dam in this channel. problem.28 The Grays Lake quadrangle Similarly, on the north side of Sag Val­ is northwest of the Chicago region, mostly in Lake County, and lies within the Val­ ley (Palos. Park quadrangle), gravel con­ . stituting a terrace of Tinley outwash paraiso moraine belt. The moraine here is (crossed by 96th Avenue) extends down resolvable into five subordinate members. at least to 615 feet above sea level just west It buries older drift, both till and out­ of the Tinley crossing (fig. 35 ), and, on wash, as it does in much of the Chicago the south side of the Sag Valley, the esker­ region, and the buried relief, greater than ine ridge 2 miles >vest of the Tinley (fig. that of the moraine itself, was made in part 34) begins at 61 S or 620 feet and ascends by stream erosion. Fox River Valley is the to 685 or 690 feet above sea level. Thus major pre-Valparaiso streamway on the the valley slope through that range in alti­ Grays Lake and Barrington quadrangles. tude was in existence while the Tinley It transects the west of moraine was being built. the Valparaiso moraine, hence is adjudged younger. The later Minooka ice front ap­ North-south profiles along the Valparai:;o pears to have displaced the earlier Fox and Tinley moraines, across the two chan­ River near Elgin for a time, forming a nels, show that if there were no pre-Val- broad lake (Lake \.Yauconda) whose clays were later overridden by the Valparaiso ice. Fox Valley was therefore in existence be­ fore the Minooka advance. The \iVest Chi­ cago mornine, oldest of the Valparaiso ridges, crosses the Fox Valley near Algon­ quin (Barrin�ton quadrangle), modifying the 100- to 150-foot valley walls at the crossing even more strikingly than the Val­ paraiso moraine modifies the slopes of Long Run and Spring Creek valleys in the Chi­ cago region.

"Golclthwai1. Bull. 11, p. 52. ''llPowcrs. W. E. . :tnd Ekblaw, G. E. . Glaciation of Fie. 36.-Section in kame near Byrneville. f

Is it justifiable to correlate the pre-Val­ and Fox. But the Chicago region also has paraiso Sag and DesPlaines valleys of the well-developed tributary valleys of the same Chicago region with the pre-Minooka Fox erosional interval. Because the growth of Valley ? All of them are main stream val­ tributary valleys always lags behind that of leys eroded during pre-Minooka time. If the main ones, the post-Marseilles, pre­ they were eroded during the post-Marseilles Minooka interval could not have been brief. interval of deglaciation, the Lemont drift An alternative interpretation considers would be post-Marseilles, perhaps record­ that all these pre-Valparaiso valleys may ing the pause in Marseilles retreat before be pre-Wisconsin in age, that they may the Minooka advance began. record stream erosion during the long Sanga­ The Fox River Valley on the Barrington mon interglacial age. The deep weathering quadrangle is eroded in a widespread sheet profile Horberg found in Lemont drift at of pre-Valparaiso gravel recognized in out­ Worth seems to demand a much longer crops and wells in the Grays Lake, Barring­ interval of exposure than the preceding esti­ ton, Elgin, and Geneva quadrangles. Since mate of the post-Marseilles, pre-Valparaiso to the west of the Valparaiso moraine this period allows. The tributary valleys (Long gravel sheet (Algonquin gravel forma­ Run, Fraction Run, Spring Valley, Hickory tion29) is overlain by the Minooka moraine, Creek, etc. ), which definitely are pre-Val­ it must be older than that glacial advance. paraiso in age, also seem to require a longer The Algonquin gravel appears to have been time for development than allowed by the spread as a great outwash plain in front of preceding estimate. the Lake Michigan glacial lobe during a long pause after retreat from a moraine to TILLS EXPOSED IN THE SANITARY AND the west. It has been presumed to be inter­ SHIP CANAL mediate in age between the Marseilles and Leverett in 189731 commented on the Minooka moraine-building advances. i\o exposure of "very hard, partially cemented till deposited during this pause is recognized till apparentlya of early glacial age" be­ in the Grays Lake or adjacent quadrangles. neath a soft clayey till in the then newly But if the Lemont gravel, the Joliet "out­ made sections of the Sanitary and Ship wash plain" gravel along the DesPlaines, Canal a mile or so east of Summit (Berwyn and the Algonquin gravel along the Fox30 quadrangle). Alden in 190232 added a are contemporaneous, then the Lemont till comment on stratified deposits beneath till is probably the record of this pause. in the same sections between Summit and By this interpretation, the margin of the Willow Springs. No other mention of these Lake Michigan lobe must have withdrawn sections has ever appeared in the literature still farther north and east after deposition although they have remained fairly clean of the Lemont drift, freeing the streams of and are readily acces�ible. the excess load recorded by the outwash In the present investigation, the sections gravels and allowing them to trench into were studied from Kedzie Avenue bridge the newly made deposits. This interval of (Englewood quadrangle) to 96th Avenue erosion was long enough for main drainage bridge (Berwyn quadrangle), a distance of lines, with adequate volume and gradient nearly ten miles. The eastern half of this and with only glacial drift to deal with, to distance has a monotonously similar se­ trench such valleys as the Sag, DesPlaines, quence of 2 or 3 feet of lake clay above

29Leighton, M. M., Powers, W. E., and MacClintock, till ; the middle of the stretch has three Paul, Geology and mineral resources of the Elgin, Geneva, and Barrington quadrangles : Illinois Geol. Survey, un­ distinct tills in vertical sequence without published manuscript. Earlier called CryJtal Lake gravel>, separating sediments ; and the western part in Leighton, M. M., The glacial history of the EJi,·in region : Trans. III. Acad. Sci., vol. 1:,. pp. 69-70. 1924. has till with sediments both below and 30Fisher found no gravel beneath the Minooka moraine in the western part of the Joliet quadrangle, but this above. is only negative evidence. It may be that ground-moraine in that particular district stood high enough to escape The eastern half of the section extends being g'ravel-covered. Fi

be readily obtained from many hundreds north to allow a lake to form in the south­ of well and boring records. The thickness ern portion of the basin. Clay deposited in of the superimposed Lake Border tills has the lake was then incorporated in the till been obtained by using compaction data of the next advance. fr.om test borings for foundations in Chi­ Krumbein also collected a series of 12 cago, but comparable data are not available samples, equally spaced through a vertical for the Valparaiso and Tinley till sheets. range of 60 feet, on the slopes of a valley Till.-Krumbein's study34 of variations cut across the Bloomington moraine. in the texture and lithology of glacial till Though there was no visual evidence of included 24 samples taken near the outer two till sheets here (the Bloomington above margin of the Valparaiso moraine at aver­ an older one), mechanical analyses showed age intervals of 7 miles throughout 165 a "break" in composition between samples miles of the moraine. The line of samples 1 to 8 and samples 9 to 12. Thus the began northeast of Elgin, Ill., swung south­ thickness of the Bloomington till was eastward toward the Indiana line, then figured from the top of sample 9 to the top eastward and northeastward around the of the moraine. As post-Tinley valleys in lake, ending near Benton Harbor, Mich. the Chicago region are not deep enough to The Valparaiso drift was found to be a provide data for this method of determining clayey till as far as Valparaiso, Ind., and thickness of Valparaiso or Tinley tills, the dominantly a sandy till east of there. The method can be used only when samples can difference in texture is ascribed by Krum­ be secured from properly located bore holes. bein to differences in the amount of wash­ Eskers.-ln the north-central part of the ing the till received from escaping melt­ Hinsdale quadrangle (Map 9) are two water and to differences in character of the eskerine-ridged tracts, the better developed older material (bedrock and pre-Valpa­ standing on the "island" already noted (p. raiso sand dunes and drift) which was over­ 31), in the SE 1/+ sec. 23, T. 39 N., R. 11 ridden, eroded, and incorporated in the till. E. The ridge is about 20 feet high and half The most important of these causes he a mile long. I ts sides are steep, and it is thought to be the loading of the Valpa­ margined by a trough on each side, a com­ raiso ice with "surficial unconsolidated ma­ mon esker feature. Two old pits afforded terials in the path of the ice." an imperfect exposure of its composition at Another line of samples, 23 in number, the time of examination. Cobble and pebble began in the Tinley moraine and extended gravel and coarse and fine sand make up southward from the Chicago region across the bulk of the sections. One section the entire assemblage of Wisconsin mo­ showed 4 feet of unwashed till at the top, raines, a distance of about 125 miles. The overlying clean fine sand. The other esker­ spacing in this line was determined by the like ridge, along the south line at the NW intervals between the moraines. The rela­ 1/4 sec. 27, 39 N., R. 11 E., has no tive proportions of clay, silt, and sand and exposures andT. is mapped on the basis of its gravel in the samples from thirteen succes­ unusually knolly topography and steep sides. sive moraines showed that dominantly Perhaps it could as well be considered to clayey till occurs as far south as the Chats­ be a row of kames. worth moraine, 35 next older than the Mar­ The Tiedtville esker, half a mile north seilles moraine. Less clayey till was found of Tiedtville in the northeastern part of in the moraines farther downstate. Krum­ the Sag Bridge quadrangle (Map 13), is bein suggested that the heavy loading with mapped as a little more than half a mile clay in the northern seven moraines may long. I ts highest point is 25 feet above a mean that, between the building of each, little lake in the more western of two the Lake Michigan lobe receded far enough margining troughs. The surface material

MKrumbein, Jour. GeoL vol. 41, 1933. is till on most of the ridge, and there are 35Named for the village of Chatsworth, which is on only two exposures of gravel in it, and both the moraine. in southeastern Livingston County, Ill. Leverett, U.S.G.S. Mon. 38, p. 259. are poor. It margins the top of the Des- 80 GLA CIAL GEOLOGY

Plaines valley wall ; toward its distal end, The bottom of the valley parallel to and it descends from 650 to 615 feet, its tip immediately east of the esker is diversified thus reaching below the higher levels of with morainic hillocks. If, as is confi­ the Lake Chicago outlet river. Here it is dently believed, this gravel ridge was de­ very cobbly and bouldery below 625 feet, posited by the retreating Valparaiso ice, the apparently from erosion by the outlet river. high end is the distal end, the reverse of Its steep slopes and sharp ridges are quite the relations at the Tiedtville esker. out of harmony with the till slopes of the "Till eskers" is a field term used to de­ Valparaiso moraine. With nearly ·a dozen scribe two unusual drift ridges in the Chi­ kame piles on this same valley wall in the cago region. One is on the Valparaiso next 3 miles to the southwest, the Tiedt­ moraine just west of Orland Park, in the ville esker is a part of the evidence for the NW 1/4 NE 1/4 sec. 8, T. 36 N., R. existence of a pre-Valparaiso DesPlaines 12 E., Sag Bridge quadrangle (Map 13), valley. and the other is on the Tinley moraine in Another, smaller gravel ridge lies about Mt. Forest Island, largely in the NW 1/4 a third of a mile north of the Tiedtvillc sec. 2, T. 37 N., R. 12 E., Palos Park quad­ esker along the same nearly north-south rangle (Map 14). In dimension, propor­ line. Traced southward, the little ridge tion, and orientation, these ridges are strik­ ascends the western slope of Flag Creek ingly eskerlike. No excavations existed ; Valley for about 30 feet, indicating an auger borings showed only till in the upper older slope here under the Valparaiso ice. four-fifths of the ridge. In one ridge sand An old pit showed cobbly and pebbly gravel and gravel was encountered below the till, in it. Between it and the larger Tiedtville but auger penetration into this was impos­ esker to the south, a cut along 83rd Street sible, and the amount of washed material showed about 8 feet of washed gravel on could not be ascertained. If they are eskers, the line connecting the two ridges. The they are more than veneered with till­ two may well be interpreted as one inter­ they are buried in it. Yet the form has per­ rupted esker. sisted and it is both incorrectly oriented and The Visitation esker, on the southern much too vigorously expressed to be a slope of the Sag Valley, largely in the west normal morainic ridge. half of sec. 20, T. 37 N., R. 12 E. (Sag Kames.-As with eskers, most of the Bridge quadrangle-Map 13), is three­ kames of the region on Valparaiso drift fourths of a mile long, interrupted in two or are in close association with pre-Valparaiso three places, narrow and sharply expressed, valley courses and most of them are par­ but not very high. An abandoned pit at the tially or completely covered with till. The north end showed about 8 feet of silt and kames of the DesPlaines transmorainic val­ coarse sand with scattered pebbles. Reject ley, already noted, all lie on the valley material on the pit floor, hm.vever, con­ slope, the bases standing above the valley tained hundreds of boulders a foot or so in floor and probably above the highest levels diameter, more than 90 percent of them of the outlet river. One of the kames, half composed of Silurian dolomite. This is a mile southeast of the Byrneville school, much higher than the percentage of Silurian in the SW 1/4 NE 1/4 sec. 11, T. 37 N., dolomite boulders among the rejects on the R. 11 E., Sag Bridge quadrangle (Map floors of brick-plant pits in the Chicago 13), has been extensively opened for gravel, region, excavated in till. There are no and its composition and structure are very other exposures in the ridge, but there are well shown for a depth of 25 feet. It is boulders lying on the surface. Among these, poorly sorted material-cobbles, pebbles, igneous and metamorphic rocks are more and sand mixed together in many places­ numerous than limestone and dolomite. Like although in some places there is clean gravel the Tiedtville esker, the ridge diagonally with open interstices. Irregular stratiform traverses a pre-Valparaiso valley slope till masses are fairly common in the gravel, through a vertical range of 60 feet or so. but none of them are horizontally continu::. TINLEY DRIFT 81

ous for mor.e than 20 feet. The till cover and the Chicago region in some places is 10 feet thick ; in others it has established a positive correlation. Con­ is wholly lacking. The dominant structure sidered in its vertical range, Valparaiso is inclined bedding, the dip being southwest­ drift includes all the clayey till underlaid ward along the valley wall rather than by silty Lemont drift. Elsewhere its base southeastward down the slope. Clearly, the may be uncertain, for reasons already set DesPlaines Valley, when this kame was forth. built, contained a lingering tongue of the In our latitude it is difficult to differen­ receding Valparaiso ice when the upper val­ tiate the broad Valparaiso morainic belt ley slopes had already emerged and, with into ridges of subordinate rank. Studies the ice, constituted the two sides of the made by the Illinois State Geological Sur­ meltwater course. The tabular till masses vey in the McHenry, Grays Lake, Barring­ indicate minor advances during an oscilla­ ton, Elgin, and Harvard quadrangles, north tory retreat past this plact. The kame and west of Chicagoland., have shown that gravel was deposited at the very edge of the Valparaiso moraine there consists of the ice. Noteworthy cementation of the five successive ridges or elongate groups of gravel has since occurred in the central and morainic hills. From west to .east, they are highest part of the deposit. the \Vest Chicago, the Monee, the Fox Most of the DesPlaines Valley kames are Lake, the Zurich, and the Palatine mo­ elongated subparallel with the valley wall, raines. 36 but they are not aligned sufficiently to allow The best evidence in the region for this grouping them as an interrupted esker. succession of Valparaiso units is probably Kame terraces.-Only the Valparaiso the constricted places already noted along drift bears any kame-terrace gravels in the the pre-Valparaiso valleys of Fraction Run, Chicago region, and they are found only Long Run, Spring Valley, Marley Creek, in valleys of the pre-Valparaiso topography and Hickory Creek on the Sag Bridge and where free westward drainage was possible. Mokena quadrangles. M. M. Leighton37 is Hickory Creek Valley's assemblage of kame inclined to think that another unit, the terraces is more than 11 miles long, the sum Clarendon, is identifiable, which is younger of intervals between deposits being about than the Palatine but distinctly older than twice the aggregate length of the gravel the Tinley moraine. mounds themselves. The largest kame­ 38 terrace unit, near the junction of Hickory TINLEY DRIFT and Marley creeks, in the Mokena quad­ Thickness.-Determination of the thick­ rangle (Map 1 7), is 1 3 / 4 miles long, and ness of the Tinley drift is impossible from its highest part is 25 feet above the stream. data now at hand. To the eye and hand, All have rolling, even knolly, surfaces, but the Valparaiso till is indistinguishable from slopes are gentler and heights less than the Tinley, and it certainly underlies much among the true kames. Almost all are on of the Tinley. It is possible that mechanical valley bottoms, some cause notable constric­ analysis may someday show differences be­ tions in width of valley floor, and very few tween the two and that sufficient excava­ overlap up on the middle slopes of their tions may be so located as to give an aver­ containing valleys. Exposures of their struc­ age figure for the thickness of the Tinley ture are rare, for the streams are not drift. actively undercutting them and few excava­ 36Powers and Ekblaw, Geo!. Soc. Am. Bull., vol. 51, tions have been made in them. They appear p. 1331, 1940. The name Monu moraine is proposed by M. M. Leighton (personal communication, 1953) for the largely to lack the cobble-sized fragments name Cary moraine used by Powers and Ekblaw. The name Cary is pre-empted by its use as a substage name. of kames and eskers. Some have yielded 31J>ersonal communication. gravel in commercial quantities, but there 38Name first published in Bull. 65, Part I, p. 50, 1939. Named for the town of Tinley Park, which is just have been no active pits in them for years. west of the front of the moraine in the Tinley Park quad­ rangle (Map 18). Earlier called Arlington Heights Correlation.-Direct tracing of the Val­ moraine and Tinley Park moraine. Su Leighton, M. M., and Ekblaw, G. E., Annotated Guide across Illinois : in paraiso drift between the type locality in Guidebook 26, 16th Internat. Geo!. Congress, p . 15.' 193 3. 82 GL1JCllJL GEOLOGY

The approximate thickness of the Tinley north side of Sag Valley, Palos Park quad­ drift can be determined from the height rangle ( lVIap 1-1-),just west of the southern of the Tinley moraine ridge. Twelve cross tip of the Tinley moraine on Mt. Forest sections, distributed among the seven topo­ Island; 96th Avenue crosses it north of graphic maps that show the full width of 111th Street. Its surface is about 630 feet the Tinley moraine, show that high points above sea level, nearly I 0 feet lower than on the crest average 30 feet above the the highest shoreline of Lake Chicngo, about western toe of the moraine and -1-5 feet 2 miles distant. Its steep descent to the above ground moraine immediately to the Sag valley bottom is an erosional product cast. The Tinley till sheet in these cross of the glacial lake's outlet river, but its sections is at least 30 feet thick. surface bears no record of having been 7'i//.-The clayey till of the Tinley end swept by that stream. moraine and ground moraine is uniform in An active gravel pit east of 96th Avenue texture, color, degree of compaction, and has provided a series of sections in the ter­ lack of washing throughout the Chicago race. The excavations have revealed that region. the enstern part of the deposit, at least the upper 15 feet, consists of poorly sorted Eskers.-The only true esker of Tinley . gravel, some of it very cobbly and bouldery, age in the region is on the north side of and abundant till balls, till masses that have Indian Creek in the village of Half Day, centrally located in the vVheeling quad­ not been rolled since deposition, and a par­ tial till cover. vVestward-dipping bedding rangle (Map I). lt is about half a mile is common, although no true delta forcsets long and no more than 20 feet high. The have been seen. Deformed bedding, the gravel in it is uniformly sorted and contains gravel strata wrapped halfway around a no large cobbles or boulders. It is to be mass of superjacent till 20 feet in diameter, distinguished from gravel mounds lying has been exposed. Channel unconformities, on the DesPlaines valley train in the vicin­ with very coarse gravel in the filled channel�, ity of Half Day. The esker Ji.es wholly on are common. There are many shale pebbles ground-moraine slopes above and west of in the gravel and in the included nnd over­ the DcsPlaines valley Aoor and was de­ lying clnyey till. posited before the retreating Tinley ice had In the western part of the pit, the gravel uncovered the valley. '¥a ter that deposited is cleaner, more uniformly stratified, nnd the gravel of the esker escaped westward, boulders, lnrge cobbles, till balls, and till whereas the low mounds on the valley masses are largely lacking. There is no till train were built by south-Rowing water above the gravel here. after the ice front had receded to the Lake All characteristics and all gradations in Border moraines. character indicate this terrace to be a stream A "till csker" lies on the back slope of deposit made at and just beyond the edge the Tinley moraine on Mt. Forest Island (p. 80). Kr111":s.-On the crest of the Tinley mo­ raine in the southwest part of the Wheeling quadrangle (Map I) nrc two knmcs, one on ench side of Nichols Road, in sec. 6, T. 42 N., R. 11 E. The larger one stands 25 to 30 feet above its surroundings, and in it arc two gravel pits. The material is poorly washed ; clayey gravel predominates nlthQugh there are many cobbles nnd some boulders. Fie. 37.-Till masses in poorly sorted gravel. Frontal outwash.-A prominent grnvel Frontal outwash of Tinley moraine, Sng terrace about half n mile wide lies on the Vnlley. LAKE BORDER DRIFT 83 of the Tinley ice in a wide valley whose sand rather than clay, and its very gently floor was no higher than 610 feet and whose sloping surface descends from the toe of drainage escaped westward along Sag Val­ the moraine to the level of the adjacent fiat. ley. The bluff of the pre-Tinley valley is Correlatio11.-The Tinley moraine has about half a mile north of 107th Street. been traced directly northward into the The northern extension of the terrace to vVaukegan quadrangle where it is over­ the foot of the bluff has minor morainic ridden by the Park Ridge moraine.30 East­ forms on it and a till cover over sand and ward the Tinley moraine has been identi­ gravel. This till lies half a mile and more fied for about �O miles beyond the limits in front of the Tinley moraine and should of the Chicago region. be Valparaiso ground moraine. 1f it is so considered, the underlying sand and gravel LAKE BORDER�o DRIFf are not a part of the outwash above de­ The till sheets of the Lake Border system scribed but more probably belong to the will be discussed in a later publication by extcnsi�c sheet of gravel underlying, and Otto, and therefore they will not be de­ older than, the Tinley moraine to the east scribed here. To the eye and touch alone, (sec p. 64), and arc considered to be there arc no consistent differences among Lemont in age. them ; they are all clayey tiJls. And the Glaciolacustrine deposits.-Fronting the differences Otto has found arc limited Tinley moraine from the latitude of Orland largely to a certain constituent seldom Park to the southern boundary of the Chi­ thought of as a part of the composition of cago region is a series of lake fiatsaggraded a till. Mechanical analysis would never when the ice front stood on the moraine and detect it; neither would mineralogical nor blocked eastward drainage. The flats arc lithological analysis. It is an impermanent primarily underlain by laminated clays constituent, for it is decreased by repeated which cover a total of more than 16 square overridings of glacial ice and by subsequent miles to probably rather slight depths. The exposure to groundwater drainage. It is maximum thickness exposed in valleys cut the original water contained in the till­ in the fiats is 12 feet. A fair presumption the connate water that is actually the melted is that the lamination is varving, but sec­ glacial ice of Pleistocene time. Only a tions have been too poor to establish this. clayey tiJI so buried that groundwater cir­ Only one deltaic tract associated with culation has never affected it could retain the lake flats is known. It is about 2 miles the connate water and make possible the west of Flossmoor (largely in sec. 10, T. differentiating criterion Otto has found. 35 N., R. 13 E., Harvey quadrangle-Map ValleJ• train.-Although the four Lake 19) and is mapped as different from the Border moraines in the Chicago region lake flat because its material is silt and (sec p. 28) do not have eskers, kames, and kamc terraces, the system possesses the only valley train of the entire region. It occu­ pies �he DcsPlaines Valley west of the Park Ridge moraine and reaches almost as far south as the tip of that moraine (fig. 5). The material is a well-sorted gravel, coarsest at the north and decreasing until, near its southern end, it is only granule gravel and sand. The river that deposited this valley-train gravel was largely supplied from regions farther north and presumably continued to Aow during much of the Lake

:li1Jo:kblnw. G. E .. personal communit:ntion. ••Nome firot use

FIG. 39.-Glacial river bars on the DesPlaines valley train near Wheeling.

Border moraine-building stage. Little addi­ Traced northward from the Chicago re­ tion to its volume was made from ice on gion, the valley train is identifiable as far as the Park Ridge moraine in the Chicago Wadsworth. A large pit has been excavated region, and none was possible from the three in it at Libertyville. Around Gurnee in younger moraines farther east. particular, there are numerous kames both LAKE BORDER DRIF1' 85 on the va!ley slopes and in·the valley. They ing of their material far le:;s advanced than appear to record vigorous drainage off the in the mounds. Till balls and till masses ice when the Park Ridge moraine was being occur in them. built. \,.Yater that deposited them had no There is no basis for considering the escape other than the DesPlaines valley mounds in the Chicago area as kame piles. train. The DesPlaines River north of Nor can the mounds be satisfactorily ex­ Gurnee flows along the east side of the Park plained as erosion remnants, for they are Ridge moraine and crosses to the west side not akin to terraces in position or in topog­ near that place. In this northern region raphy. Long stretches of the valley have water probably continued to reach the val­ no mounds, whereas in one place (at \Vheel­ ley train as the ice front retreated from ing) where the valley in all other ways the Park Ridge moraine past the younger appea rs identical, about half the width of units of the system. the valley floor is covered by mounded This valley train appears to have escaped gravel. There certainly are channels in the notice of all earlier students of tt:e this Wheeling group, but not the simple region. It possesses one unusual feature kind that a shifting postglacial DesPlaines which deserves fu;·ther attention. Through­ nver would make. Instead, the channels out 15 miles of its length in the Chicago unite and divide, deepen and shoal along region its plane surface is interrupted by their length, and arc genetically like the broad, low mounds of gravel, all elongated linear closed depressions that exist also with the valley length, most of them ne;;r among the mound units of a compound the middle of the valley and none in con­ group. tact with the valley-train margins. Fifteen The interpretation that has proved most of them are shown on the vVheeling, Ar­ satisfactory is that the mounds arc gravel lington Heights, Park Ridge, and River accumulations on the bottom .of the glacial Forest quadrangles ( Maps 1, 3, 4, and 7). river and contemporaneous with the re�t Some of these mounds arc three times as of the valley train. This conclusion is not long as wide, others nearly ten times. None arrived at wholly by elimination of other of them rise higher than 15 feet above the possibilities. Gravel bars in streams have surface of the valley train. Generally they peculiar structures of their own, one of arc simp!e in outline and topography, but which, a convexity of the bedding parallel some are aggregates of coalesced mounds with the bar slopes, is shown in some of the which have lobed outline$ and which may mounds. The detritus that goes into the be almost as wide as long. accretion of :i bar is the bottom load, which V\1hcn these mounds were first encoun­ is rolled along by traction and cl roppelnines are much steeper and higher, their strati­ valle)' train. Corner of Milwaukee Avenue fication is much less perfect, and the sort- and Deerfield Road (V\lheeling quadrangle). 86 GLA CIAL GEOLOGY

place. This means that stratification in the Glaciolacustrine deposits.-Three of the mounded deposit parallels the growing bays of the Glenwood stage of Lake Chi­ slopes. Figure 40 shows a section in a bar cago received glaciolacustrine deposits from at the corner of Milwaukee Avenue and the Lake Border ice. These deposits are Deerfield Road, Wheeling quadrangle mostly silts that cover the ground-moraine (Map 1 ) . The excavation is near the floor of the bays and have not been differ­ western edge of the bar and the observer entiated on the maps. The fourth bay, be­ is looking north. The slight westward in­ tween the outermost Park Ridge and the clination of the bedding is obvious though Tinley moraine, contains the lower deltaic its parallelism with the surface slope could end of the DesPlaines valley train. No pits not be shown in the photograph. The uni­ in this terminal portion, however, show formity of bedding and the well-sorted con­ delta foreset-bedding. The water appar­ dition of the gravel, shown in the illustra­ ently was too shallow. tion, are characteristic of all the bars. Correlation.-The Lake Border moraines The most serious objection to the river­ were first recognized and described by bar hypothesis is the absence of other evi­ Leverett41 in 1897. Their type locality, dence for a torrential stream. There are like that of the Tinley moraine, is within no boulder-strewn and cobble-covered flats, the limits of the Chicago region. Leverett and no channel walls eroded in the marginal recognized only three moraines, which he morainic slopes. The gravel in many places called Outer or West, Middle, and East fails to reach the adjacent margins, grading ridges. Apparently he grouped the Deer­ into sand and even silt along the valley­ field and Blodgett together as one moraine. train margins. Yet if the mounds are bars, Leverett also thought that Blue Island a river at least 15 feet deep flowed south­ ridge was an isolated portion of the Middle ward down this stretch of the DesPlaines member, whereas in this report it is con­ Valley, and its current would seem to have sidered as a portion of the Park Ridge been vigorous across the entire cross section (Outer) moraine. of the valley flat. The sand and silt tell, OFFSHORE DEPOSITS ON THE FLOOR OF however, of a marked slackening of current LAKE CHICAGO along the margins. With the maximum known depth of the valley train 15 feet, the In the Chicago folio, the lake plain was total thickness of the gravel under the mapped largely as "glacial drift chiefly higher bars should be at least 30 feet. ground moraine," and nowhere else was The Lake Border morainic system ground moraine shown on the four original possesses three other outwash deposits, one quadrangles. The present survey reverses this procedure, showing large areas of on the west slope 0£ the Deerfield moraine and crossed bv Willow Road on the Park ground moraine above the lake's highest Ridge quadrangle, and two on the west slope level and none below. Ground moraine is of the Highland Park moraine (Highland here defined in terms of its original topogra­ Park quadrangle-Map 2)-one in the phy. The lake waters submerged extensive western part of Highwood and one in Lake areas of it and so remade the surface that Forest. The one on the Deerfield moraine, it is mapped as "lake bottom," even where in the center N 1/2 sec. 23, T. 42 N., R. 12 it does not carry a lacustrine sedimentary E. (Park Ridge quadrangle-Map 4) , is cover. thought to be a small deltaic deposit of the The Chicago folio also mapped consider­ Glenwood level of Lake Chicago. The two able areas of the plain as "sandy soil," which others, in the east part of sec. 32, T. 44 is chiefly lacustrine sand. The sand is N., R. 12 E., and in the W 1/2 sec. 15, rather thin and patchy in distribution, and T. 43 N., R. 12 E., are mapped as small in many built-up areas its remapping is outwash plains above the lake plain. In no longer possible. For these reasons it none of them is there much gravel ; their has been omitted as a depositional unit on material is mostly sand and silt. HLeverett, Chicago Acad. Sci. Bull. 2. OFFSHORE DEPOSITS IN LAKE CHICA GO 87

the new maps. The principal fact of its do not attempt to indicate abundance of distribution-prevalence · below and paucity boulders. The present study was under­ above the Toleston shoreline-is shown, taken too late for such mapping, for boulders however. are useful, ornamental, and free-for-the­ The ground-moraine knolls and swells taking. The writer's observation over the submerged by Lake Chicago were beveled years on the distribution of boulders on the off by wave erosion, and the detritus was Lake Chicago floor is that they occurred transferred elsewhere. The gravel and most abundantly at the foot of the Glen­ coarser sand was tractionally carried shore­ wood-stage sea cliffs. Alden thought those ward to the beaches and spits, while the in the heads of the out!et channels had been fine sand, silt, and clay was carried in berg-carried or ice-rafted to present posi­ suspension in the opposite direction, most tions ; the writer believes them to be residual of it beyond the present shoreline. La­ from erosion of till. Leverett, Alden, and custrine sand occurs to depths, locally, of the writer agree that those on the lake 15 feet inside the Toleston shoreline but, floor record erosion of till, but Alden except in beach accumulations, nothing ap­ thought sea-cliff recession more probable proaching such thicknesses of sand are than bottom-dragging by open-water waves. known above this level. The Lake Chicago If this idea is correct, and if there were no plain is largely a clean, wave-swept till great variations in the original abundance floor. Calumet Lake, Wolf Lake, and Lake of boulders in the till, then there has been George occupy incompletely erased depres­ but little wave erosion in making the till sions of the former ground-moraine surface. floor which so largely characterizes the lake These statements are more easily made plain. than proved. The till floor of Lake Chicago Leverett described42 a boulder belt ex­ seems remarkably smooth for a wave-eroded tending north from the north end of .Blue tract made over from a ground-moraine Island to the North Branch of the Chicago surface. Even if that ground moraine v:eis River, saying that south of 63rd Street to itself unusually smooth, there perhaps Blue Island the boulders "remain in about should be faint linear elevations recording their patural abundance." He thought this the ridges across it. boulder belt was a record of a former low Yet nothing other than Blue Island can till ridge connecting Blue Island and the be pointed to, and it was never submerged. Middle Ridge moraine. Alden mapped this Boulders.-The numerous clay pits scat­ area in 1896, and his depiction is of five tered over the Lake Chicago flat contain boulder patches with so little elongation large numbers of reject boulders en­ of the group that if they are interpreted as countered in excavating the clayey till for remnants of a former till ridge, the connec­ brick-making material. The pits may aver­ tion can as well be made with Leverett's age 25 feet in depth. It would seem that a West ridge as with his Middle ridge. Of like abundance of surface boulders should that portion of Leverett's belt of boulders occur on the lake plain, where a comparable north of 63rd Street, Alden said, "Their thickness of ridged till was removed by number becomes so small as hardly to war­ Lake Chicago waves. Boulder belts thus rant more than a suggestion of such corre­ might be expected to mark the course of lation." the Lake Border moraines. It is interesting to find that a similar The floor of Lake Chicago does have, or glacial till or boulder-clay floor exists over has had, a few boulder-strewn areas. They large areas about lakes Winnipeg, Winni­ are shown by Alden on the Chicago folio pegosis, and Manitoba, the successors of maps. The most remarkable ones are in the glacial in southern Manitoba. outlet-channel heads and are due to scour Such surfaces lie below the beaches of the of the underlying till by stream erosion. glacial lake, and though they may be rolling The boulders of the lake floor, as mapped or gently sloping they have stony soils by Alden, are not in belts. The folio maps 42Leverett, U.S.G.S. Mon. 38, p. 383. 88 GLA CIAL GEOLOGY

FIG. 41.-Glaciated pebbles dredged from lake bottom near Indiana Harbor buoy. Photograph by J. L. Hough.

because "wave action during the existence taken by Hough, one of which is illustrated of the lake washed away the fine particles in figure 42. The pebble concentrate is and left the stones and boulders on the thin, and the core consists mostly of a surface."43 In contrast are the boulder­ pebbly sandy clay, undoubtedly glacial till. clay areas above the level of Lake Agassiz, Such a thin pebble concentrate does not unmodified by subsequent wave action, indicate any considerable removal of the where the soils contain few stones or finer constituents, but it does indicate the boulders. occurrence today of erosion, instead of dep­ It is also interesting that Hough'sH osition, at these depths. A pebbly veneer bottom-sampling of Lake Michigan off the of this thickness would hardly remain after Chicago shoreline revealed extensive areas the lake water had been drained off and of gravel or gravel-veneered till, miles out weathering and soil-making had gone on in the lake and at depths as great as 60 for several thousand years. We therefore feet. Hough interpreted the gravel as "a do not ask, in substantiation of the theory, lag concentrate of the coarser constituents that the carry a gravel cover. The of glacial till, resulting from wave and scattered boulders on the smooth plain are current action on the bottom under present all we may now expect. conditions." The pebbles are subangular Our topic is lacustrine sedimentation in and some are striated ; hence they are not Lake Chicago, and thus far we have been beach pebbles, either from the present shore endeavoring to show how little of it there or of some earlier and lower shoreline now was. In the clay pits, canals, and other 'ubmerged. Some core samples also were excavations examined during this study, 4:1.Toh n:-ton, "' · A . . Surface depo�its and ground-water i;;uppl}r of \V innipeg map arc.:t, 1'Vf an1tob.1: Canada Geo! . there is so little offshore lacustrine sediment Survev Mem. 174. 1934. above the till that glacial Lake Chicago 44'f-TouJ?h. Jack L .. The bottom d!posits ,. of s.outh rn � Lake Michigan : Jour. Sed. Pet., vol. >, pp. > 7 - 8 0, 19J 5 . never could be mapped from its distribution OFFSHORE DEPOSITS IN LAKE CHICA GO 89

sections of this clay deposit, made when U.S. Highway No. 6 was graded, have largely disappeared, but the deepest and best section, in the National Fireproofing Company's clay pit at Hobart, about 14 miles east of the state line, probably will remain available for years. Further study of the deposit is needed, for this lake sediment is not a con­ ventional glaciolacustrine deposit. Thickness of the Hobart clay exceeds 40 feet in the pit. I ts surface constitutes a smooth plain, except for some sharply trenched V-shaped valleys cut into it and some beach and dune ridges of Calumet age built on it. So far as is known, it all lies east and northeast of Hobart Island, a low till island of the Glenwood stage in Lake County, Ind.45 The island surface carried a few boulders, no more than any ground­ moraine surface of the region, but none was found on the plain, in contrast with the old lake bottom across the line in Illinois. The Toleston topographic map shows the plain to lie between 630 and about 645 feet, but the map is an old one, sketchy and undependable for this purpose. o precise altitudes have been obtained in this study, for the tract lies well to the east of the Chicago region. The pit section 1s as follows : Thickness in feet

Stratified yellow clay ... . 12 Stratified blue clay ...... 32 Gr�vel-largest pebbles about walnut size ...... Stratified clay, sand, and pea-sized pebbles; more sand and gravel than clay...... 20

A clean section 27 1/2 feet in height was made in the north wall of the pit, extend­ ing from the bottom of the oxidized zone Fie. 42.-Core sample from lake bottom near to the base of the cut. It showed throughout Indiana Harbor buoy, taken about six miles an alternation of clay layers and sand layers, offshore, in 50 feet of water. Photograph by 127 J. L. Hough. of each in the section. One might think of them as varves, except that there are and probably could not even be proved to other facts which deny that hypothesis have existed. or at least demand additional causes for Hobart sectio11s.-One of the few areas the stratification. of lacustrine deposits of Lake Chicago The clay layers are four to ten times as known in the general region is some miles thick as the sand layers and are more dis- east of the mapped area, in Lake and �:;See map ·in Cressey. George, Indiana sand dunes :111d shorel ines of 1hc Lake l\IJichigan basin : Chicago Geog. Porter counties, Ind. The numerous good Soc. Bull. 8. 1928. 90 GLACIAL GEOLOGY crete units. Whereas very thin seams of cession may well have allowed ponding in clay occur in some of the sand layers, no front of the ice, earlier than Lake Chicago's sand seams occur in the clay layers. The beach-recorded history, and in such early thicknesses of the couples are highly vari­ ponds, with the edge of the glacier close able, ranging from half an inch to 6 inches by, much of the clay and sand might have in immediately adjacent layers. accumulated. The thin, discontinuous till The alternation of thick clay units with sheet would, by this hypothesis, record the thin sand units clearly records some alter­ Tinley readvance, the clay beneath being nation of conditions of sedimentation, but pre-Tinley but post-Valparaiso. Or a it does not indicate seasonal varving. A clue similar sequence, immediately preceding and may lie in the fact that some of the inter­ contemporaneous with the Park Ridge mo­ leaved very thin clay members of the fine raine-building, might have left the inter­ sand units aggregate more than the sand calated till, in which case Glenwood sedi­ itself. Storms or stormy seasons may be ments would underlie as well as overlie the recorded by the sandy material, and longer supposed till. periods of quiet by the clay. A detailed Other Indiana sections.-Another tract study of the deposit is necessary before it of lacustrine sediments between the Glen­ can be explained satisfactorily. wood and Calumet shores is found in Another problem afforded by the Hobart Porter County, Ind., exposed along U.S. pit sections is a 30-inch layer of pebbly clay Highway 6 and the banks of Salt Creek 15 feet below the surface in the west wall. Valley. The McCool landing field is on It looks like an unusually clayey till. There this deposit. The silt and clay here are at are striated stones in it, and its flat sha!ey least 25 feet thick, the upper 10 feet oxi­ pebbles are oriented at all angles. It con­ dized, the lower portion bluish. There is tains very thin discontinuous laminae of fine no till and no true varves in the section. sand, visible only when the material is At the bottom of the zone of oxidation, broken horizontally. It does not occur in there is an abundance of calcareous con­ the north wall where the 27 1 /2 feet of cretions, thin, very irregularly branched, stratified clay and sand was examined, nor and lobed in the plane of stratification (fig. was any evidence of an interruption in sedi­ 43 ). Concretions in Pleistocene deposits mentation found there. are exceedingly rare in the Chicago region Because the entire deposit goes beneath and, except for these, are small and with­ the Calumet beach and dunes, it would out noteworthy features. These concretions, seem to be a record of the Glenwood stage however, are characterized by a peculiar only. There is a possibility, however, that ridge along the middle of the arms and this particular Calumet beach grew first branches, always at the bottom of the con- as an offshore bar which later accumulated a beach on offshore sediments of the same stage and shifted the shore north from the original Calumet land-and-water contact. Cressey seems to believe this though his statement was not explicit. In this case, the upper part of the clay deposit could be Calumet in age. If the 30-inch layer of pebbly clay is till, there is a possible place for it in the sequence of events known from the moraines beyond the lake plain. The Tinley moraine prob­ ably records a minor readvance of the ice Fie. 43.-Calcareous concretions from lacustrine front to the position marked by it, which sediments near McCool, Ind. The longest specimen measures 77;1 inches. Specimens followed a greater recession after the main in next to top row show upper side; all others Valparaiso system was built. Such a re- show bottom side. OFFSHORE DEPOSITS IN LAKE CHICA GO 91 cretion. In proportions and size, it re­ highway cuts is 10 feet. Beneath the till sembles a ripple-mark ridge, though there is 6 feet of clean, pebbleless, unstained surely is no genetic relationship. The re­ sand, as light in color as sand on the lake striction of the concretions to one horizon, Michigan beaches today. The bottom of their surprising abundance at that horizon, the sand was not reached in cutting the and the median ridge on the bottom of each highway grade. I ts top constitutes a broad are worthy of further study. In steeply mound, buried by the till. Also buried by tilted strata, such concretions would afford the till, and lapping up on the eastern slope a clue to upper and lower sides· of beds. of the sand mound, are stratified silt and A little east of the Salt Creek crossing clay with some interbedded very fine sand. on U.S. Highway 6 and 13 miles east of Another till member lies beneath the silt of Broadway in south Gary, till appears in and clay and apparently goes beneath the the section. I ts maximum thickness in the sand mound also.

Fw. 44.-Baker's station 33 along North Shore Channel. 500 feet south of Devon Ave. Fr om Baker, Frank Collins, The life of the Pleistocene or as recorded in the deposits laid down by the great ice sheets: Univ. of lllinois Bull., vol. 17, no. 41, plate XVII, 1920.

Material Thickness in inches

Silt and loam . 20 Silt ...... 32 A­ Peat, interstratified with thin beds of sand ...... 38 B­ Occasional sand pockets, rarely 12 inches thick. Gray sand ...... C­ Silt. Anodonta (clam) and wood on top of this layer ...... 6 D­ Gray sand, with wood and Sphaerium (clam) ...... 4 E­ Silt ...... 4 F­ Gray sand...... 2� G­ Silt ...... · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2� H- Silt and sand ...... 11 K- Wood, solid layer...... I Sand and gravel ...... , ..•...... 8 Wood with spruce cones...... 1� Sand with shells, wood, anrl spruce cones . 4 Sand with some gravel ...... 4 Boulder clay...... 44+

Total thickness .. 180 inches GLA CIAL GE OLOGY 92 The upper till of this section is inter­ pelecypod shells. Crayfish burrows and a preted as Tinley or possibly Lake Border duck humerus were also found. in age. The clean sand is a small dune Baker generalized the succession of de­ built close to a glacial lake in the southern posits in all the sections and, from his sum­ part of the Michigan basin. The level of mary,47 we may make a composite column this lake rose as the advancing ice front of the stratigraphic units of the North altered discharge routes ; the overlapping Shore Channel. silt and clay were then deposited ; and finally 7. Sandy silt and peat beds. Average thickness the overriding ice buried everything beneath 20 inches. Shallow-water molluscs in lower the upper till. When Lake Chicago came layers. into existence after the recession of the 6. Silt and peat beds, 15 to 52 inches thick. Oxidized zone and crayfish burrows in upper last ice advance, this till floor in Indiana part. was too shallowly submerged for sediments 5. Silt, sand, peat, and marl; 19 to 59 inche� thick. Lower layers generally without ; to lodge on it, and it was wave-swept as upper layers filled with shells and fish re­ was most of the lake bottom now exposed mains, representative of shallow-water types. in the Chicago region. Oxidized zone and crayfish burrows in upper part. 4. Unios North Shore Channel sections.-Exca­ "Heavy" bed of shells, mostly (clams). 3. Gravel and sand, 2 to 19 inches thick. No vations for the three canals across the lake record of life except in upper part where plain of the Chicago region afforded un­ Unios begin to appear. paralleled opportunities for observation of 2. Silty, carbonaceous, and peaty materi al; 1 to 40 inches thick. Shells of shallow-water lacustrine sediments, opportunities which molluscs, spruce cones, oak leaves. promptly ended when the canals were com­ 1. Sand or sand with pebbles. From a fraction pleted and their upper slopes slumped or of an inch to 12 inches thick. No evidences life. became covered with vegetation. The geo­ of logical literature on the Chicago region Baker reviewed all earlier literature bear­ contains one outstanding study based on ing on the history of Lake Chicago and such observations. In 1911, F. C. Baker46 attempted to correlate the sedimentary "was fortunate in being able to follow the record he found with a more complicated excavation of [the North Shore Channel] success10n of events than has so far been foot by foot and thus to secure fresh ex­ presented in this bulletin. A correlation posures." This canal, more than 8 miles will be discussed in Chapter IV. It will long, was dug in the bed of a long bay of be sufficient here to say that unit 1 was the later stages of Lake Chicago, a bay pro­ considered Glenwood in age, unit 3 Calu­ tected behind the great spits in Evanston met, and units 4 and 5 Toleston ; unit 2 and North Chicago ; it could hardly have was interpreted as a record of a low-water been better located for our purpose. Sixty­ stage ( Bowmanville) between the Glen­ three sections were measured and de­ wood and Calumet stages ; and the oxi­ scribed, all cutting through the bay sedi­ dized zones of units 5 and 6 were believed ments into underlying till. The till surface to record a complete emergence and weath­ was highest in the northern part of the cut ering of those sedimentary units before the and was, in general, more undulatory than next overlying deposits were laid down. the wave-cut lake flat. Sediments over the Evidences of aquatic life in Lake Chicago till were 1 foot to 12 2/3 feet thick and had been known before Baker's study ; Ban­ were composed of clay, silt, sand, gravel, nister in 1868 mentioned shells, wood frag­ peat, and marl, the sections varying con­ ments, and "vegetable mould" (probably siderably in kind and amount of the con­ peat ) beneath lake sediments on the Chicago stituents. Fifty-four sections yielded some plain. But no one ever announced any organic relics, ranging from peat and marl record of Glenwood life until 1929 when to scattered rootlets, leaves of oak, spruce Ball and Powers48 briefly described the cones, twigs, sticks, logs, and gastropod and 47Baker, F. C., op. cit., pp. 65-67. •SBall. J. R., and Powers, W. E . , Evidence of 46Baker, F. C., The life of the Pleistocene or glacial aquatic life from the Glenwood stage of Lake Chicago : period : Univ. Illinois Bull., vol. 17, no. 41, 1920. Science, n.s., vol. 70, p. 284, 1929. MANKA TO SUBSTAGE 93 discovery of the fauna of minute molluscan The northern channel around the island shells from lake silts and clays in Skokie also has at least seven mounded aggregates Valley above the Calumet level of the gla­ of pebbles and cobbles on the outlet-river cial lake. Baker identified ten species in bottom, none more than 10 or 12 feet high the collection. Only a meager biota is to and all elongated with the channel length. be expected in the cold waters of this early The largest, a mile in length, has three lobes stage of the lake.49 As the ice retreated pointing down-channel. It is crossed by northward, more and varied forms entered Harlem Avenue a mile northwest of Chi­ its waters and lived on its shores, as Baker cago Ridge (Palos Park quadrangle-Map has shown. 1-1-). One other is also compound, from par­ Lake Chicago took origin in Cary time tial coalescence of narrow parallel ridges. and glacial lake waters continued to over­ Old pits show a little of the composition lap some of the Chicago plain until the end but nothing of structure. These channel­ of Mankato time. In this region there is no floor bars are composed of coarse material, precise marker for the break between the including even boulders. The definite chan­ two substagcs. Field evidence along the nel walls and the boulder-strewn floor agree Wisconsin lake shore indicates that the with the coarse detritus in recording a vig­ Bowmanville low-water stage immediately orous current here, a current which eroded preceded the rcadvance of the Lake Michi­ 10 to 15 feet deep in the till and, removing gan lobe at the beginning of Mankato time the finer constituents, left the scattered (sec "Causes for the Lake Chicago Stages," boulders and the cobble bars. Some of the p. 109) . For convenience in the absence boulders, of course, may have been con­ of definite indications of substage position, tributed by floating ice, although at the the Lake Chicago deposits are all considered Toleston or Hammond stage the ice front here under the Cary substage and the out­ was far to the north and bergs probably let-channel bars under the Mankato sub­ rarely reached the outlet. stage. DesPlaines outlet channel.-In a similar MANKATO S uBSTAGE way, the head of the DesPlaines outlet GLACIAL RIVER BARS channel contains bars of coarse gravel for a stretch of 5 miles on both sides of the Sag outlet channel.-During the Calu­ Tinley moraine transection. The village of met stage of Lake Chicago, a low island, Hodgkins (Berwyn quadrangle-Map 10) Worth Island (Palos Park and Blue Island stands on the easternmost bar, Tiedtville quadrangles�Maps 14, 15), stood just east post office (Sag Bridge quadrangle-Map of the Tinley moraine crossing, in the 13) on the westernmost. A trench dug middle of a bay leading from the lake to through some of the bars for a 24-inch the Sag outlet. A current capable of erod­ natural gas pipeline at the time this study ing the bay bottom seems to have flowed was undertaken showed an amazing coarse­ westward along both the north and south ness of the mounded debris on the old sides of the island during this stage. When glacial river floor. The material is almost the lake was lowered to the Toleston or wholly cobbles and boulders, most only Hammond level, the two parts of the bay slightly worn, some slabby, and 99 percent became definite river channels, the dis­ Niagaran dolomite. In the Hodgkins bar, charge dividing to pass around the island upstream from the Tinley moraine, the and reuniting before entering the deeper, dolomite debris apparently came chiefly older part of the Sag outlet. The till be­ from the southern slope of the bedrock hill came considerably scoured then, definite which outcrops near McCook. The pipe­ channel walls were cut, and a boulder­ line trench sho,ved also that till immediately strewn floor was produced. underlies the bars and constitutes the chan­ 49Subsequent to the field work on which this report is based. excavations in a spit-like extension of the Glen­ nel floor around and among them. wood beach, a mile we"t of Dyer, Ind. (Dyer quad­ The most interesting of the three large rangle) . have reve1led W.'.l\·e-worn fragmeni:s of drift­ wood in the deposit. mapped bars of this channel lies at· the 94 GLACIAL GE OLOGY mouth of Flag Creek Valley, more largely ing out from the river-cut bluff across the in the valley mouth than in the DesPlaines embayment like a bay-mouth spit from an channel. It covers most of the NW 1 / + adjacent cliffed headland. sec. 32, T. 38 N., R. 12 E. (Sag Bridge It is interesting to compare this bar with quadrangle-Map 13) but extends into ad­ the gravel terrace deposit in the Sag Chan­ jacent areas. It is exceptionally prominent nel, crossed by 96th Avenue, also imme­ topographically, descending 30 feet from diately downstream from the Tinley tran­ its summit to the floor of the channel on section ( p. 82). There are no mounded bar the southeast and more than 10 feet to the forms on the terrace ; the material is only alluvial flat of the tributary, Flag Creek, poorly washed and there are many till to the north. It nearly blocks Flag Creek, balls, till masses, and soft shale pebbles in which is detoured over to the west side and it. Although the top of the deposit is 630 there confined in a narrow "inner" valley feet above sea level, 10 feet below the high­ with steep bluffs on both sides, three to ten est Glenwood level, it is apparently not a times as high as any other place along the river bar. It is a poorly differentiated out­ creek. The summit of the bar is 635 feet wash deposit made when the Tinley moraine above sea level, approximately the altitude was being built. Glenwood waters, pouring of the Glenwood shoreline of Lake Chi­ over the Tinley moraine after it was aban­ cago. The southern base is 605 to 610 doned by the ice, eroded away that part of feet, the floor of the Toleston outlet. the original terrace where the channel floor Apparently the whole mass is a bar, or now is and left this portion back of the compound group of bars, the surface ma­ moraine projection just high enough to terial cobbly on the channel side and pebbly prevent flooding by the glacial river. and sandy on the much gentler northern An alternative interpretation for this bar slope, and apparently it is all of Glenwood at the mouth of Flag Creek Valley, with age. The steeper southern slope is erosional less supporting evidence known, is never­ and dates from the Calumet and Toleston theless worthy of consideration. Future ex­ lake stages. The bar was built in the cavations may show that, although the sur­ morainic sag between the main Valparaiso ficial gravel is truly a bar deposit, the body moraine and the younger Tinley ridge, not of the deposit contains till balls, poorly in the channel proper. The low altitude of sorted gravel, irregular stratification, chan­ the base of the deposit (almost equally low nel unconformities, ice-push deformations, on the west side along the creek) means that etc., like the outwash in front of the Tinley a free escape for Glenwood water beyond moraine in Sag Channel. The Tinley mo­ the Tinley moraine existed when the bar raine lies immediately to the east. Possibly was initiated, that the DesPlaines channel the Tiedtville bar is also a modified rem­ was essentially as deep west of the Tinley nant of a Tinley valley train in the Des­ moraine then as it is now, and therefore Plaines transmorainic channel. If the Tin­ that the Tinley moraine alone was the Lake ley moraine and outwash constituted the Chicago dam. dam for Lake Chicago, as argued in this The interpretation of the mounded gravel report, some outwash remnants are to be deposit as a river bar considers that the bar expected in the DesPlaines channel. owes its location to an embayment along the GLACIAL RIVER BARS NEAR THE CHICAGO river channel afforded by the Flag Creek REGION morainic sag. The deposit was a complete barrier to the sag at first, and silts were Another tract of glacial river bars, just deposited on its back slope in a small lake. outside the Chicago region, is on the valley Debris came largely from destruction of trains of the DuPage River system, on the the Tinley moraine dam and differs cor­ "\Vheaton and Joliet quadrangles. When respondingly from the slabby material of the mounds of the DesPlaines valley train the Hodgkins bar east of the moraine. The were being studied, this district was ex­ bar is a dependency of the moraine, extend- amined briefly to test the theory that glaciar RECENT STAGE 95

rivers in the region built bars. The outwash various deposits have been made by the is closely associated with the Valparaiso agencies of wind, running water, standing moraine, part of it in a valley within the water, waves, and organisms. They record moraine, part lying just in front of it. a regimen identical with that of the present, Mounds of gravel with all the features and generally such deposits are still accu­ and relations of those in the DesPlaines mulating. valley train are found on the East Branch CHARACTER valley train, from a point about 2 miles Floodplains.-Alluvial deposits of silt, north of Lisle downstream to the junction sand, and gravel characterize most flood­ of the two branches and thence over a much plain accumulations chiefly in floodtime and, wider valley train, or more properly an geological maps. Str eams add to their flood­ outwash plain, as far as Plainfield. The 15 plain accumulations chiefly in floodtime mounds are 5 to feet higher than the and, because the locus of currents across the surrounding gravel flats, elongated with flats may change considerably from flood direction of current flow, and none are to flood, the deposits vary from place to found along the margins of the gravel fill. place and show marked differences in ver­ As in the DesPlaines Valley, kames are tical sequences of materials. No one stratum built on the slopes or uplands but none out is likely to be very extensive laterally. in the flat. The mounds are not kames. Floodplain deposits of low-gradient streams, The area covered by the mounds on the however, are unlikely to contain coarse East Branch valley train is much less than material. that of the channel floor. But farther down­ Organic material commonly enters into stream and out on the broad gravel plain, the composition of floodplain deposits, the the channels become less prominent and the most striking example in the Chicago region bar mounds predominate. From Plainfield being the buried peat, marl, and driftwood southward, the bars are so much broader of Plum Creek (see p. 40 ). and more numerous that their tops consti­ Alluvial fans.-When a tributary stream tute the plain, the channel-floor plain dis­ of relatively high gradient enters on the appearing in the narrowing and decreasing floodplain of a larger stream, the abrupt number of channels. This is in perfect har­ decrease in velocity commonly causes local mony with the concept argued for, because deposition in the form of an alluvial fan. here the river current spread most widely, If coarse material is thus deposited, the and its ability to transport was reduced to resultant fan has an easily recognizable a minimum. Only certain routes carried slope, even though finer materials also enter currents of sufficient vigor to keep them into its composition. The silt fan at Dyer open. (see p. 40 ) has so gentle a slope that the Four miles north of Plainfield, pits in a eye fails to detect it, and the material in it bar just east of the DuPage River show is indistinguishable from that in the flood­ gently dipping strata parallel with the plain of the creek farther upstream. original surface slope, the common structure Slope-wash deposits.-Similar in genesis in river bars. River bars are rarely de­ to alluvial fans are the deposits of silt and scribed in the literature on Pleistocene sand at the foot of steeper slopes by un­ glaciation. There is no reason why this concentrated slope wash. They do not con­ region should be exceptional in possessing stitute topographic forms, but their incon­ them. They probably exist on many valley spicuousness is no indication of unim­ trains but, being minor topographic features, portance. Largely, these slope-wash deposits have been overlooked. consist of material from the A-zone of the hillside soil, agriculturally by far the most RECENT STAGE valuable part of the soil.

Since subsidence of lake waters and Swamp deposits.-Enclosed depressions emergence of the present Chicago plain, in morainic country, among the abandoned 96 GLA CIAL GE OLOGY beach ridges and old dunes or in abandoned Shore deposits.-A continuous beach-sand glacial-river channels, are favored sites for accumulation marked the lakeward edge of dense growths of hydrophytic vegetation, most of the Chicago plain before the city and the carbonaceous material is largely began to grow. It \Vas the product of wave preserved by the constantly high level of and shore-current work of postglacial Lake the groundwater. The largest deposit of Michigan. Some of its material appears to peat in the region is in the Sag channel, of have travelled southward with the prevail­ Toleston age (Sag Bridge and Palos Park ing currents from the sea cliffs north of quadrangles-Maps 13, 14). It is 9 miles \V innetka, and some probably was dragged long, three-fourths of a mile in average inshore by storm waves. The comparison width, and 10 feet in maximum thickness. of the bulk of this Recent beach material The original swamp in which it accumu­ with that of the glacial lake shores con­ lated was largely drained when the Calumet stituted the theme of the first outstanding feeder ditch was dug in 1870. Another large geological research in the Chicago region. peat deposit is in the morainic sag between Salt Creek and the head of Flag Creek, in CORRELATION the western part of Western Springs (Hins­ The end of the \Visconsin age (glacial) dale quadrangle-Map 9), and a third is and the beginning of the Recent age (post­ in the semicircular depression partially en­ glacial ) is generally accepted as marked by closing the "island" in the north-central the disappearance of all ice barriers to part of the Hinsdale quadrangle ( p. 31). drainage from the Great Lakes basins. This The latter two deposits contain some is only a marker of convenience in classi­ surface wash and are mapped as basin-fills. fication, for geological processes now in op­ Many other peat deposits are mapped in eration began in the Chicago region before the Valparaiso and Tinley moraine country. that time, and glacial conditions prevailed Shell marl below the peat in many deposits in northern for some time after­ records an earlier lake or pond in the de­ ward. The oldest "postglacial" deposits of pression. the region are on the Valparaiso moraine, There is no sharp line between peat and where deposition has been continuous in muck, although the two, if typically de­ the swampy depressions ever since the ice veloped, are readily distinguished. The mix­ withdrew and plants first reinvaded the ture of mineral matter brought from nearby region. The Lake Michigan shore accumu­ hillsides by slope wash and of accumulated lations have the shortest "postglacial" his­ vegetal material in a depression is classified tory, save only where strictly local con­ as muck. ditions have initiated deposition later. Thus the bogs on Cary drift, which give us a Groundwater deposits.-Calcareous ce­ continuous pollen record, the beach mentation of some gravel deposits of the of the last great storm, and floodplain de­ region has been produced by groundwater posits of the last great flood, perhaps only work in Recent time. Perhaps some of the a year ago, are all classified as Recent. cementation shown by the "Joliet con­ glomerate" and other Lemont gravels is of intraglacial origin, although degree of ce­ GEOLOGIC ASPECTS OF SOILS mentation is not a criterion of age. Most geologists describe the alteration Tf/ ind deposits.-The two small areas of product of the agencies of weathering as dune sand along the lake shore (see p. mantle rock. It generally grades downward 45 ) are probably of Recent age. Much into unaltered subjacent material, maximum larger wind deposits lie a little to the east change having occurred at the surface. Be­ of the Chicago region, along the Indiana cause time is one factor in its production, shore of Lake Michigan. None of the Lake mantle rock generally becomes deeper with Chicago dune sand appears to have been increasing age. Soil is a more common term reworked during Recent time. than mantle rock and, although not strictly GEOLOGIC ASPECTS OF SOILS 97 synonymous, is used here as meaning the processes in soil-making. One is oxidation, same thing. another is leaching of calcium carbonate, Soil covers all the varied surficial de­ and the third is development of colloids and posits of Chicagoland, save where streams their downward migration. These changes are eroding and where man has excavated go on at different rates, hence their depths or filled. As the deposits are not all of the of penetration into the subjacent material same age, weathering must have begun on are different. Oxidation proceeds the most the oldest before it could have attacked rapidly and the lower limit of iron-staining younger deposits. But soil-making is so gives the maximum depth of what we are slow a process that no detectably greater here calling soil. Leaching of calcium car­ weathering has occurred on the Valparaiso bonate by downward-percolating water is till than on the Highland Park: till or the slower, hence its depth of penetration is still more recently exposed till floor of less, rarely exceeding 2 feet in the region. Lake Chicago. There are differences in the Above that depth, there is no effervescence soils in the region, to be sure, but they are when acid is dropped on the soil, below it traceable to other factors, chiefly differ­ effervescence is likely to be brisk. The mak­ ences in parent materials. The greater age ing of soil colloids has hardly begun, and of the Valparaiso drift could never be the drift sheets have nothing to compare established from a comparison of depths of with the sticky gumbotil which character­ the altered zones on it and on the younger izes the shallower depths of the weathered tills. Duration of Valparaiso exposure over Nebraskan, Kansan, and Illinoian drifts. and above that of Highland Park: is clearly In the soil classification of the University a small fraction of all postglacial time. of Illinois Agricultural Experiment Sta­ Thickness.-Soils of the Chicago region tion, stress is laid on the effect native are deeper in the more porous sands and vegetation has had in determining the ex­ gravels than in clayey deposits of the same isting soil types. On this basis, the three age. Depths of the soil vary also in the same large categories of soils in Illinois are parent material because of differences in , forest, and marsh or swamp. "Forest slope of the surface and in depth to ground­ vegetation produces a thin accumulation water. Varying degrees of slope-wash re­ of leaf and twig litter on the surface where moval mak:e important differences in thick­ it is exposed to the air ; and being, there­ ness of the soil remaining. All the variables fore, subject to rather rapid and complete render impossible any precise figure of the decay, it supplies little organic matter for thickness of soil in Chicagoland. Oxidation the soil. Moreover, the roots of trees are of the iron, recognized by yellowish or red­ coarse, penetrate deeply, and are relatively dish staining, has occurred to depths of 10 few in number. As compared with grass feet in some of the Lak:e Chicago dunes roots, they add little to the organic matter where favored by high permeability and a supply when they decay. . . . The grass low water table. In clayey till, the zone of vegetation of the , on the other oxidation may average not more than 2 to 3 hand, produces enormous quantities of feet deep. These figures pertain to situa­ fibrous roots which are mostly concentrated tions where neither removal of the topsoil in the surface 12 to 18 inches of the soil. on steep slopes nor additional deposition at Because air does not move freely through the foot of such slopes has occurred. the soil, these roots decay slowly, and when Character.-Chicagoland soils are young decomposed the resulting organic residue compared with most soils of the earth. They tends to be preserved for a long period. are young compared with soils on the drift­ Since the incorporation of organic matter sheets of the pre-Wisconsin glaciations. in the soil produces a dark color, the grass­ Their shallowness is one expression of their land soils have brownish-colored surface youthfulness ; another is the very slight de­ strata. Marsh or swamp vegetation also velopment of zonation. produces large quantities of fibrous roots ; Soil zones result from three simultaneous but the low-lying pond-like nature of a 98 GLA CIAL GE OLOGY swamp area is conducive to a more or less added in varying quant1t1es during post­ permanent high water table which pro­ glacial time (the Recent age). The lack of hibits the entrance of oxygen and so prac­ a definite age contrast between soils on the tically prevents complete decomposition. oldest and the youngest till surfaces of the Thus immense accumulations of organic region is a consequence to two factors, time matter were preserved in the wet areas of and climate. The time interval between the the lowlands and the soils became dark building of the Valparaiso moraine and the brown to black in color."50 disappearance of Lake Chicago appears to . Corre/ation.-Essentially all soils of the have been a relatively small fraction of all region have been developed on parent ma­ post-Valparaiso time. The climate since terials of Cary (Wisconsin) age. Organic the ice sheet withdrew from the lake basin matter and wind-transported dust have been has been warmer, and the chemical and biologic activities concerned in soil-making "'Wascher, Herman, Smith, R. S., and Smith, L. H., correspondingly greater, than during the Boone County soils : Univ. Illinois .Agr. Expt. Sta. Soil Rept. 65, p. 10, 1939. Valparaiso-Lake Chicago interval. CHAPTER IV - GLACIAL HISTORY

The glacial and genetically associated strata existed in the region, stream, lake, and wind deposits of the and the rock removed to expose the Silurian Chicago region have been described, and strata may have been hundreds of feet thick. their relationships discussed, in the preced­ The peneplain referred to, the Central ing chapters. It remains nmv to "\veave Illinois, is the third known to have eroded these facts and interpretations into a co­ in Illinois bedrock. The earliest, the Dodge­ ordinated history of the region during the ville,4 was first recognized in the Driftless Pleistocene. Because depositional records of area of southwestern Wisconsin. Opinion the earlier part of the Pleistocene, known has varied as to its age, and indeed as to its from other regions in the upper Mississippi very existence,5 but conviction has grown drainage area, are lacking here, the history that the uplands of the type area6 are rem­ will largely be of the latter part of the nants of a former erosional lowland of Pleistocene. Tertiary age, now standing more than 1400 feet above sea level near Sparta· and Tomah, PRE-PLEISTOCENE EROSION Wis., and sloping gently down to about 1000 feet in extreme northwestern Illinois. For more than a geological era before the The second peneplain, the Lancaster, bevels first ice sheet invaded Chicagoland, the re­ several tilted formations in the LaSalle gion was a land area. The lithified marine anticline, but apparently all traces of both sediments which, as bedrock, underlie the earlier ones were destroyed in the Chicago glacial deposits today were weathered and region during the Central Illinois erosion eroded. From features of north-central cycle. Illinois, we know that an essentially com­ plete cycle of erosion occurred late in this The Silurian surface beneath the Lemont interval, and that the peneplain thus pro­ and Valparaiso drift a little east of Joliet has a fairly uniform altitude of 630 and duced (the Central Illinois peneplain) 1 was then uplifted a few hundred feet and 640 feet above sea level. This surface, cor­ slightly tilted, inaugurating a new cycle of related with the Central Illinois peneplain, erosion early in the Pleistocene. bevels the Silurian formations, whose strata How great a thickness of rock material have a gentle eastward dip. The surface was removed during the preglacial erosional itself descends westward 30 to 40 feet m attack is unknown. From fossils found in the 50 miles to the Ottawa region. clay fillings of fissures in the Silurian dolo­ 4Trowbridge, A. C., The erosional history of the : Univ. Studies in Kat. Hist., vol. 9, mite in the region, we know that younger no. 3, 1921. Silurian strata, 2 and probably Devonian 5�lartin, Lawrence, of Wisconsin : Wisconsin Geo!. and Nat. Hist. Survey Bull. 36, 2nd ed., and strata,3 once overlay the 1932. 6Bretz, J Harlen, Geology and mineral resources of the Silurian rocks. In most of Illinois and much Kings quadrangle: Illinois Geo! . Survey Bull. 43, pp. 27'-277, 1923. of the southern peninsula of Michigan, Knappen, R. S., Geology and mineral resources of the Pennsylvanian strata are found above the Dixon quadrangle: Illinois Geol. Survey Bull. 49, pp. 90-92. 1926. Mississippian, and the northeastern edge of Bevan, Arthur, Geology and mineral resources of the Oregon quadrangle: Illinois Geol. Survey, unpublished the Illinois Pennsylvanian is only 20 miles manuscript. Thwaites, F. T., in Guidebook Ninth Annual Field distant from the southwest corner of the Conference, Geol. Soc., 1935. Chicago region. Probably, therefore, even Bates, R. E., Geomorphic history of the Kickapoo region. \V isconsin: Geol. Soc. Amer. Bull., vol. 50, pp. 819-850. 1939. 1Horberg. Leland, Preglacial erosion surface<: in Illi­ noie : Jour. Geo! ., vol. 54. pp. 179-192. 1946. Reprinted Willman, H. B., and Payne, J. N., Geology and as Illinois Geo!. Survey Rept. Inv. 118. mineral resources of the Marseilles, Ottawa, and Streator %Carey Croneis, personal communication. quadrangles : Illinois Geo! . Survey Bull. 66, pp. 204-205, 3Wcllcr, Stuart, A peculiar Devonian deposit in north­ 1942. eastern Illinois : Jour. Geo! ., vol. 7, pp. 483-88, 1899. Horberg, Leland, Pregia:::ial erosion surfaces in Illi­ Ea:'tman, C. R., Description of new species of Dip­ nois : Jour. Geo! ., vol . 54, pp. 179-192, 1946. lodus teeth from the Devonian of northeastern Illinois : Herberg, Lel and, Bedrock topography of Illinois : Jour. Geo! ., vol. 7, pp. 489-93, 1899. Illinois Geo!. Survey Bull. 73, pp. 87-96, 1950. [ 99 J 100 GLACIA L HIS TORY

EARLY PLEISTOCENE EROSION PLEISTOCENE EPOCH Uplift and slight warping of the Central CHARACTER OF THE PLEISTOCENE EPOCH Illinois peneplain occurred in late Plio­ The Pleistocene, or "Glacial," epoch is cene time, and stream entrenchment con­ not unique in earth history. There were sequent on this rejuvenation continued into several much earlier great ice sheets which the early Pleistocene. Westward across the grew and waned and left their record in plain a major river, the Mahomet (Teays), striated rock surfaces, till ( tillite), and flowed from , , and varved lake clays (banded slate). The Indiana to the ancestral Mississippi. Its northern Central Lowlands, however, have course across Illinois was held during Ne­ no known earlier record of the experience braskan and Aftonian ages, but the Kansan that came to them late in the Cenozoic era, ice sheet, coming from the northeast, oblit­ a million years or so ago, and was repeated erated its valley and a new drainage system three times, the fourth glaciation ending formed. One trunk stream was the River only about 10,000 years ago. During these Ticona, ancestral to the Illinois River of glaciations the northern half of North today.7 America must have resembled the interior The stream-carved surface of the Ni­ of Greenland or today, a vast agaran dolomite beneath the drift of Chi­ 51 monotonous expanse of snow and glacial cagoland (see p. ) was made during the ice, completely deserted by living forms. Mahomet (Teays ) cycle by the local head­ water drainage of a main river that initi­ CENTERS OF ACCUMULATION ated the Lake Michigan depression. Theo­ The glaciers invading the Chicago region retical reconstruction of this major drainage came from far to the northeast. Ice from system east of the divide is much less ad­ a center in the Labrador peninsula (fig. vanced than is that of the Mahomet 45) spread out in all directions, particularly (Teays). The main valley undoubtedly to the south, covering the New England occupied part, if not all, of the elongated states and and invading northern basin, but glacial erosion in the soft under­ New Jersey and Pennsylvania. Most of lying Devonian rocks has so greatly altered Ohio was covered by this ice sheet, five­ it, and glacial deposition in southern Michi­ sixths of Indiana, and all but 400 square gan and northern Indiana has so masked miles of Illinois. the bedrock valleys, that until much more Another great center of ice accumulation, is learned from well-log data, reconstruc­ the Keewatin, existed at the same time west tion will remain uncertain. It is not even of Hudson Bay, its southward expansion known yet whether this pre-Lake Michigan reaching into the United States all along river belonged to the St. Lawrence or the the Canadian border on the Great Plains Ohio drainage. A connection between the and spreading down along the Central south end of the Lake Michigan basin and Lowlands west of the Mississippi nearly the deeply buried Mahomet (Teays) val­ half-way across and into north­ ley in the general region of Lafayette, Ind., eastern Kansas. Although the Labradorean believed to be the trunk valley of what is and Keewatin ice sheets coalesced, the Chi­ now the Ohio drainage,8 may be found cago region appears never to have received when more is known of the drift-covered any glacial ice from the Keewatin center. bedrock topography of extreme northwest­ Direction of movement is read from bed­ ern Indiana. rock striae, from ground plans of moraines, In all likelihood stream occupancy of the from lithological features of the drift, and Michio-an° basin ended and lake occupancy from comparisons of preglacial drainage began with the coming of the earliest ice systems with glacial derangements of drain­ �heet. age and with modern drainage patterns. •Horberg. Bull. 73. pp. 56-57, 99. From such data we know of several smaller 8fidlar, ?-.if. -:\I. . The nreglactal Teays valley in In­ diana : Jour. Geo! ., vol . 51, pp. 411-418, 1943. centers of glacial growth and radiation in THICKNESS 1JND MOPEMENT OF THE ICE SHEETS 101

..

•

..

..

..

...... ; ...

... " ...

F10. 45.-Northern part of the Northern Hemisp here showing areas glaciated during Pleistocene time. Af ter Encyclopaedia Britannica, vol. 10, p. 375, "Glacial Epoch or Pleistocene Ice Age," 1949.

North America, probably contempo­ affected by the slopes of the land beneath raneously developing and wasting away them. They were more like the icecap of through the four Pleistocene epochs along Greenland today, which is 8800 feet thick with the two great ice sheets. at the thickest known places; its average may be about 3000 feet. Surface gradients, THICKNESS AND MOVEMENT OF THE except near the margin of the icecap, are ICE SHEETS too low to be detected by the eye alone. Unlike mountain glaciers, which move vVhether the upper ice Aows over the lower downgrade for the same reason that streams ice on low gradients or the lower ice ii; Aow downhill, the enormous Pleistocene squeezed out laterally by the weight of the ice sheets moved radially out from thick upper part is a matter as yet undetermined. central dome-like accumulations, largely un- The important point here is that the Pleisto- 102 GLACIAL HISTORY cene ice sheets of North America were in LENGTH OF THE PLEISTOCENE EPOCH only a general way responsive to under­ Again we must deal with estimates. The lying topography, that they overrode most glacial lake varves give us definite annual hills and valleys in their way without units, but they bridge only fractions of the changes of course, that they eroded deep glacial retreats. Depth to which the oldest basins like that of Lake Michigan, and that exposed drift has been leached is an ex­ the bottom ice successfully rode up out of pression of elapsed time, but it cannot be those basins with the debris it had abstracted formulated in precise numbers of centuries from them. The thickness of the ice in the or millenia. Development of stream-erosion Chicago region probably was at least a mile. patterns on drift sheets affords another ap­ If the ice sheets were like Greenland's, proach, but it too is incapable of precise the Pleistocene ice moved very slowly, prob­ evaluation. The retreat of is ably only a few feet a day. Since advance of widely used to measure a part of late Wis­ an ice front is the rate of movement of the consin and all of postglacial time, but that ice body minus the amount of marginal is all it can measure. The figure that has melting, our estimate of the time required been generally accepted during the past few for a glacial invasion from Labrador must decades is 25,000 years. A notable and again be lengthened. sweeping revision of the duration of the If the rate of invasion was comparable Pleistocene and post-Pleistocene time is dis­ to that of retreat (in which excess melting cussed on page 128. over the still-continuing forward flowage Because the Mankato drift in Iowa is determines the rate), we may have some­ thought to have been deposited essentially thing better than estimates. By counting contemporaneously with the opening of the and correlating annual layers of silt and Niagara route, depth of leaching in that clay ( varves) deposited in glacial lakes, young drift is a yardstick for estimating the the retreat of the Wisconsin ice sheet is time required for the deeper leaching on estimated to have been at the rate of less older drifts. Thus one authority arrives at than half a mile a year across a stretch of a figure of a million years for the duration 745 miles and at the rate of about 250 of all Pleistocene time.11 But in the next feet a year across another stretch of 185 paragraph he admits that it may have been miles.9 two million years. Since publication of CAUSES OF GLACIATION Part I of this bulletin ( 1939), the "yard­ No one cause for glaciation ever pro­ stick" has been shortened by half (see page posed has satisfied all geologists. Many 128). theories have been urged, the more plaus­ ible ones including : ( 1) higher altitude of LIFE OF THE PLEISTOCENE EPOCH the land, (2) decrease in percentage of As geologists measure earth history, a atmospheric carbon dioxide, ( 3) shifting of million years back in the past was only an ocean currents and wind belts, ( 4) climatic hour ago. No great extinctions, like that consequence of sunspot cycles, ( 5) preces­ of the Mesozoic dinosaurs, mark the tran­ sion of the equinoxes, ( 6) shifting of the sition from Pleistocene life to that of the earth's axis, ( 7) variations in solar radia­ present. Some conspicuous species, like the tion, and ( 8) effects of great quantities of mastodon, mammoth, sabre-toothed tiger, volcanic dust in the atmosphere. Opinion dire wolf, cave bear, giant sloth, and giant today10 is that favorable and simultaneous beaver, have disappeared from the earth, and combinations of several of these influences the ranges of many surviving species have on terrestrial climates probably gave the changed greatly. Mammoth teeth and bones earth its Pleistocene epoch. - have been found in several places in the e . Ernst, The last glaciation, with special ref­ _ Chicago region, buried in late glacial and erence---;A_;.. to � the ice retreat in northeastern North1 Amenca : Am Geog . Soc. Res. Ser. 17. 1928. · 1osee pages 105-1 10 of F. T. Thwaites' Outline of 11Kay, G. F., Classification and duration of the . glacial gtology (193 7) for a good summary of vanous Pleistocene neriod : Geol. Soc. Am. Bull., vol. 42, pp.• theories. 425-466, 193 1. KANSAN AGE 103

early postglacial swamp deposits. Associated san ice from the same center appears to remains are deer antlers and the shells of have reached as far as the Nebraskan, bivalves and snails, the latter so abundant hence Nebraskan drift is to be seen only that they constitute marly layers in the where streams have cut through the younger sediments of Lake Chicago.12 Logs, sticks, drift cover. twigs, leaves, and pollen grains13 give a The rough, stream-eroded topography of fairly good picture of the late glacial and the Driftless area is believed by Trow­ early postglacial flora. Although no inter­ bridge16 to be post-Nebraskan, pre-Kansan glacial faunal or floral relics' have been in age. But if Nebraskan ice invaded the identified in the Chicago region, they are Lake Michigan area far enough to block known from Aftonian (first interglacial ), the preglacial river that is believed to have Yarmouth (second interglacial ), and San­ initiated the depression (later occupied by gamon (third interglacial ) deposits else­ the lake), the bedrock valleys beneath Chi­ where in Illinois and in adjacent states. cagoland are probably pre-Nebraskan. Some northern conifer species show, by growing in these latitudes, the effect of the AFTONIAN AGE glacial stage which has just passed or fore­ A deep weathered zone on the surface of tell the approach of the ice of the next the Nebraskan till sheet and beneath the glaciation. Biota of the middle of the unweathered basal Kansan till overlying it, interglaciaJ stages record a climate as mild found widely west of the Mississippi Val­ as that of the present. ley, clearly records a long period of ex­ Man was a member of the European posure between the two glaciations. The Pleistocene fauna ; his tools and bones have soil profile, where undisturbed by overrid­ been found in gravels whose stratigraphic ing Kansan ice, shows the three zones well position is definitely determinable. For a developed. The colloidally enriched upper long time, the search for Pleistocene man part is a typical gumbotil-a dense clayey in North America was fruitless, but much material entirely the product of weathering new evidence on early man in the continent of the till. In addition, peat and silt de­ has recently been found. We now know posits are found in undrained places on the that our species lived in Colorado,14 Texas,15 Nebraskan topography. and elsewhere during early postglacial time and perhaps during some of the later Pleisto­ KANSAN AGE cene epochs. Any drift of Kansan age in the Chicago region was deposited by Labradorean ice. NEBRASKAN AGE Kansan drift of Labradorean origin has If the Nebraskan ice sheet ever invaded been identified in the Marseilles-Ottawa­ the Chicago region or adjacent territory, Streator area.11 There is no conclusive all evidence of the invasion has been obliter­ evidence, however, that any of the undated ated by erosion or concealed by complete tills of Chicagoland are of this age. burial. Ice from the Labradorean center Most of the known Kansan drift in the apparently thrust farther south in New Upper Mississippi Valley lies largely west Jersey at this time than did any later ice, of the Mississippi, and was deposited by ice but most of the known Nebraskan drift from the Keewatin center. The eastern mar­ lies west of the Mississippi River and was gin of this ice sheet crowded across the deposited by Keewatin ice. The later Kan- Mississippi into Illinois. Thus Illinois has

"Baker, F. C., The life of the Pleistocene or Glacial Kansan drift (buried by younger tills) period : Univ. of Illinois Bull., vol. 17, no. 41, 1920. 13Voss, John, Comparative study of bogs on Cary and from both centers. Tazewell drift (abst.) : III. Acad. Sci . Trans., vol. 29, no. 2, p. 81, 1936. It is probable that advancing Kansan ice "Bryan, Kirk, and Ray, L. L., Geologic antiquity of Lindenmeier site in Colorado : Smithsonian Misc. Coll ., made a "Lake Chicago" in the southern ml. 99, no. 2, 1940. 15Sellards, E. H., Artifacts associated with 18'frowbridge, Univ. Iowa Studies in Nat. Hist., vol. elephant : Geo!. Soc. Am. Bull., vol. 49, pp. 999-1010, 9, no. 3. 1921. 1938. 11Willman and Payne, Bull. 66, p. 151. 104 GLACIAL HISTORY part of the Lake Michigan basin and that Chicago region, some of the undated tills this was repeated during its retreat. Dis­ may be of that age. The weathered drift charge of such a lake across the bedrock at the Dolese and Shepard quarry ( p. 78) divide might, at this time, have initiated appears to be at least as old as lllinoian. the erosion of the Hadley bedrock valley. The Lemont drift may have been deposited by the Illinoian ice sheet but, if so, the YARMOUTH AGE deeply weathered zone which developed dur­ The longest interglacial interval of the ing the Sangamon interglacial age and which Pleistocene followed the Kansan glaciation. generally separates Illinoian drift from Gumbotil on Kansan drift west of the Chi­ Wisconsin deposits west of the Chicago re­ cago region has a maximum thickness of 15 gion was almost entirely eroded by the ad­ feet, an average of 11 feet. Local peat vancing Wisconsin glacier. Of scores of deposits are found above the gumbotil. exposures, only the one recently found at Yarmouth time encompasses the interval of Worth ( p. 63 ) shows part of a weathered formation of these deposits and includes zone which may be comparable to the San­ considerable erosion of the underlying gamon profile of weathering. deeply weathered Kansan till before the With each succeeding glaciation, glacial Illinoian glaciation. It has been suggested scour doubtless increased the depth of the that the long Yarmouth age might well Lake Michigan basin, and a late Illinoian justify a bipartition of the Pleistocene. glacial "Lake Chicago" is therefore even The lowest 85 feet of fill in the Hadley more probable than one during Kansan buried valley is an undated drift below the retreat or Yarmouth time. But if the low­ typical Lemont drift. If Lemont drift is est drift in the buried Hadley Valley is Illinoian in age, then the subjacent fill is Illinoian, the outlet of any such late Illi­ Kansan, and the buried valley must have noian glacial lake probably was the Des­ been completely developed during Aftonian Plaines Valley at Lemont. time and ceased functioning as a lake outlet with the Kansan advance. A corollary of SANGAMON AGE this conclusion is that the rock-bottomed Like the Yarmouth age, the Sangamon DesPlaines Valley at Lemont was initiated interglacial age records a long time of during the Kansan retreat. weathering, during which 2 to 5 feet of If, however, Lemont drift is Tazewell gumbotil was formed and peat and humus (Wisconsin) in age, the lowest drift in the were accumulated in low places. None of Spring Creek buried valley is probably Illi­ its history is decipherable from the Chicago noian, and the valley presumably functioned region. as an outlet for a late Kansan "Lake Chi­ The Hadley buried valley may conceiv­ cago" and perhaps for a Yarmouth "Lake ably have operated during Sangamon time Michigan," possibly even for a Yarmouth if Illinoian drift had so filled the Ticona "Michigan-Huron-Superior'' lake. Valley that the gradients across the divide were low. The sand and fine gravel below ILLINOIAN AGE the Lemont drift in the test well indicate The Labradorean ice made its maximum only gentle currents. It is probably glacial advance during Illinoian time, nearly reach­ outwash, not the bottom deposit of a Sanga­ ing the southern end of Illinois and ad­ mon river. The favored interpretation of vancing westward a short distance across the the buried valley's history calls for final Mississippi River into Iowa. Illinoian till blocking during the Illinoian retreat. lies farther south in Illinois than any other till left by the great ice sheets of North WISCONSIN AGE America. In· contrast, drift of Illinoian age On the eastern seaboard, in New England from the Keewatin center has not yet been and New Jersey, the Wisconsin ice sheet identified in Illinois. reached or almost reached the limits at­ Since Illinoian ice must have covered the tained in earlier glaciations. Also in places TA ZETFELL SUBA GE 105

in the northwestern states, Wisconsin ice 15 is largely a record of the oscillation of reached and probably exceeded previously the Tazewell ice lobe that deployed out of attained limits. In the Great Lakes and the Lake Michigan basin from the much Upper Mississippi Valley states, this latest larger Labradorean ice sheet of this time. glaciation, despite vigorous moraine-build­ Closer to Lake Michigan, the Tazewell ing, fell considerably short of the southern drift was overlapped by Cary ice, which extensions attained by Kansan ice west of built the Minooka and all later moraines. the Mississippi and of Illinoian ice east of it. Although there are no moraines of T aze­ The in the Missis­ well age in the Chicago region, there prob­ sippi and St. Lawrence drainages involved ably is buried Tazewell drift. oscillations of the ice front not recorded Bloomington (?) glaciation.-The oldest during any of the earlier glaciations. There were five definite advances separated by drift of Chicagoland to which a tentative four retreats. The earliest advance was Tazewell age can yet be assigned consists of generally overridden by the later advances the inclusions of pink and red till and red clay and is recognized principally by a deposit in Valparaiso, Tinley, and Lake Border tills. of loess which shows the presence of valley If these inclusions have been derived from trains. During the remainder of the Wis­ Bloomington drift, as the color suggests, consin age each succeeding advance gener­ then remnants of that drift should underlie ally fell short of the limits reached by the the younger deposits somewhere in the re­ immediately earlier one. The retreats were gion. If the suggestion is correct, the Lake of unknown extent and duration but were Michigan lobe, which built the Blooming­ much less than those during the interglacial ton moraine in early Tazewell time, must ages. In the region of the Great Lakes, the have retreated until its margin was back ice front may have retreated each time to somewhere in the lake basin. In the north­ stand within the limits of the Lake Mich­ ern part of Chicagoland the Bloomington igan basin. moraine lies only 40 miles west of the lake shore, and its red till is known in situ within The five advances are the basis for the subdivisions of Wisconsin time. The source 30 miles of the lake. Farther south, Bloom­ ington retreat would have to be at least and extent of the ice during the earliest 75 to 80 miles to account for the Burnside, subage, the Farmdale, is not known, but its Bernice, Chicago Heights, and Homewood associated loess is widely recognized in the pink-to-red till. Mississippi, Missouri, and Ohio valleys. The second, or Iowan, subage is recorded Lemont glaciation.-Labradorean ice un­ by Keewatin ice mainly in east-central and doubtedly deposited the Lemont drift in western Iowa ; the third, or Tazewell, by close association with a west-facing ice ice mainly from the Labradorean center; front. If it is of late Tazewell age, it prob­ the fourth, or Cary, presumably by ice from ably records a pause (or minor readvance) a secondary center, the Patrician, lying south during retreat from the Marseilles, the of Hudson Bay ; and the fifth, or Mankato, youngest of the mapped Tazewell moraines, by ice again from the Keewatin center. As 40 miles from the Lemont drift along the a consequence of these differences in ex­ direction of glacial striae. Thickness of the pansion from the differentcenters of growth, ice-laid drift and abundance of the asso­ the outlines of the ice front changed so ciated coarse washed drift indicate that it greatly that some later Wisconsin moraines is part of a once strongly marked marginal actually overrode earlier ones at consider­ moraine. I ts silty character and almost total able angles. lack of shale pebbles argue that the trans­ porting ice did not cross the Devonian shales TAZEWELL SUBAGE in the bottom of the Lake Michigan basin Tazewell drift covers about 20 counties but probably traversed the western part of in northeastern Illinois and portions of a the basin and the extreme eastern part of dozen more. The moraine pattern on figure Wisconsin. If this is a correct view, drift 106 GLA CIAL HIS TORY of Lemont age m northern Indiana, if it outwash18 was eroded away during this in­ exists there, will never be identified by terval by the re-established Illinois River. extreme siltiness and a lack of shale pebbles. If, however, pre-Lemont ponding in the CARY SUBAGE Lake Michigan basin had accumulated great The change in outlines of the Cary mo­ quantities of shore sand and gravel and raines is taken to mean that the Patrician offshore silt, and if their later incorporation center, somewhat farther west than the in the Lemont drift gave rise to the char­ Labradorean center, dominated in supply­ acteristic sandy and silty texture, then this ing ice for northeastern Illinois and adja­ drift in northern Indiana, if it exists there, cent \V isconsin during this time. All the will closely resemble in composition the type moraines of the Chicago region are of Cary exposures. subage.

Post-Lemont, pre-Minooka interval.­ .- alparaiso glaciation Three Cary mo­ The ice front retreated from the Lemont raines// lie west of the Valparaiso moraine­ "moraine" for an unknown distance, prob­ the Minooka, Rockdale, and Manhattan­ ably not entirely from the Lake Michigan all composed of clayey till indistinguishable basin. Discharge from a post-Lemont "Lake at present from Valparaiso till. Hence all Chicago" used the new west-draining valley the clayey till, rich in shale pebbles, that across the bedrock divide (the present Des­ overlies the Lemont drift is treated as Plaines and Sag transmorainic valleys), Valparaiso till. locally cutting down into bedrock beneath The Valparaiso ice, probably of Patrician that drift but failing to attain either the derivation, built a wide moraine belt en­ depth in rock or the low altitude above sea­ circling the southern end of the Lake level of the floor of Hadley buried valley. Michigan basin. Excavation of the basin Total depth of this major valley was of was now almost complete, and the shape of the order of a hundred feet. High gradients the ice lobe clearly reflects the basin's con­ were thus afforded for drainage into it from trol of its spread. A neighboring lobe in adjacent surfaces. The silty Lemont drift Wisconsin, the Green Bay lobe, underwent was eroded more rapidly, probably, than a greater expansion, causing the Valparaiso a clayey till would have been, yet the tribu­ moraine near the state line to overlap the tary-valley development during this time is north end of the Minooka just as the so extensive that a long interval is required. Minooka had overlapped the north end of Much of the oxidation of the Lemont drift the Marseilles moraine. Five minor oscil­ occurred at this time, perhaps largely caused lations of the ice front occurred during Val­ by circulating groundwater in the porous paraiso time, well recorded farther north 19 drift below the soil zones instead of by but less pronounced in the Chicago region's downward-moving soil water but neverthe­ record. less it required a long interval. The Valparaiso moraine stands higher This interval may coincide with the time than any other in the Chicago region be­ of the "break" between the Tazewell and came it was built on high bedrock and Cary subages. The separation was origi­ thick Lemont drift. The same relative nally established on the basis of notable thinness of Valparaiso drift over buried re­ changes in alignment of the ice front on its lief much greater than that of the moraine return to build the Minooka moraine. The itself is found north of the region.20 extent of tributary-valley growth during The pre-Valparaiso tributary valleys on the Lemont, pre-Valparaiso interval argues the Mokena and Sag Bridge quadrangles for a longer exposure than this "break" were little modified by Valparaiso erosion would provide and suggests that the Lemont or deposition. The major DesPlaines and drift may be Illinoian in age. 18Toliet outwash plain of Bull. 51 (pp. 79-87) . Lake Illinois disappeared before the be­ lDPowers, W. E., and Ekblaw, G. E., Glaciation of the Grays Lake, Illinois, quadrangle: Geo! . Soc. Am. ginning of Cary time, its valley again be­ Bull., vol. 51, 1940. Reprinted as Illinois Geo!. Survey Circ. 63 . coming a streamway. Much of the Lemont 20Ibid. LAKE BORDER GLACIA TION 107

Sag valleys emerged from beneath the wast­ of which (Lake Wauponsee) was the slack ing Valparaiso ice essentially as capaciou� water which terminated the Valparaiso Des­ as today and nearly as capacious as before Plaines valley train. the Valparaiso overriding. Karnesand eskers Tinley gla ciation.-Neither the time nor were built in positions that only the pre­ the distance of the retreat from the Val­ existing valleys could have determined. paraiso moraine and the readvance to the Parts of the bedrock floor still carry the Tinley moraine position are known. The glacial striae21 left by Minooka, Rockdale, Tinley moraine was built across the heads Manhattan, and Valparaiso ice. The striae of the Sag and DesPlaines transmorainic were protected from the later Lake Chicago valleys, and Tinley meltwater found the discharge by their higher marginal position valleys open westward with floors at the along the channel or by a cover of till or head not higher than 610 feet. A post­ outwash. Valparaiso, pre-Tinley "Lake Chicago" is Valparaiso valley trains were built of argued from this, the discharge being large outwash gravels in the Dupage and Dcs­ enough and the interval long enough for Plaines valleys beyond the moraine front.22 eroding the Valparaiso drift to the level of They were subsequently eroded greatly, but 610 feet. There is no other known evidence remnants indicate that the glacial rivers for this pre-Tinley lake. entered standing or slack water near the The Tinley is a slender moraine, com­ present junction of the DesPlaines and parable with the units of the Valparaiso Kankakee rivers, about 15 miles below north of the Chicago region. But the Tin­ Joliet. If the DesPlaines valley train west ley's distance from them and the marked of the Valparaiso moraine ever was ex­ morainic sags between it and the Valparaiso tended back upstream as the ice retreated clearly establish it as a separate moraine. across the wide moraine belt, it has been Furthermore, the Tinley moraine projects entirely removed by the post-Tinley Lake somewhat out into the transmorainic val­ Chicago outlet river. leys, unlike the Valparaiso moraine. It Much water flowed down Fox River seems clear that the Tinley moraine was Valley during the Valparaiso glaciation ; built as a continuous ridge across the head the valley-train gravelS deposited there over­ of each valley. lie and are distinct from the older Algon­ In the Sag Valley, a terrace remnant of quin gravels of possible Lemont age. outwash gravel in front of the Tinley mo­ In the Kankakee River Valley, relatively raine (see p. 82 ) indicates that a valley enormous quantities of meltwater were dis­ train was built down along the Sag from charged at this time. The meltwater came this crossing. All but this remnant was ( 1) from the eastern and southern margins removed during the post-Tinley lake dis­ of the Lake Michigan lobe, ( 2) from the charges. It may well be that the two bars entire free margin of the Saginaw lobe in in the head of the DesPlaines transmorainic south-, and ( 3) from the valley, at Tiedtville and in the mouth of western side of the Erie lobe in southern Flag Creek Valley (see p. 93 ), will prove Michigan and northeastern Indiana.23 The to be largely only eroded remnants of a great volume of water made extensive pond­ similar valley train on the north side of Mt. ings among the Tazewell moraines, 24 one Forest Island. The question will be settled 21Guthrie, Ossian, The Lake Michigan glacier and glacial only when adequate excavations are made channels aero% the Chicago divide : Geo!. Soc. Chicago, p. 9, Oct. 30, 1890. in the gravel deposits. Leverett, Frank, The Illinois glacial lobe : U.S. Geo!. Survey Mon. 38, 1899. Lake Border glaciation. -The four Lake Goldthwait, J. W., Physical features of the DeePlaines Vallev : Illinois Geo!. Survey Bull. II. 1909. Border moraines are probably as closely Fisher, D. J .. The geology and mineral re0ources of the Joliet quadrangle : Illinois Geo!. Survey Bull. 51, related as are the five Valparaiso units 1925. 22Leverett, U.S.G.S. Mon. 3 8, pp. 3 75-3 78. north of the region, and consistency re­ 23Ekbl aw, G. E., and Athy, L. F., Glacial Kankakee Lake Border system torrent in northeastern Illinois : Geo!. Soc. Amer. Bull ., quires that the term vol. 38. np. 417-428. 1925. be matched by the term Valparaiso system. 24Willman and Payne, Bull. 66, pp. 167-1 70 and 222-225. All the oscillatory shiftings of ice front' that 108 GLACIAL HISTORY produced these four moraines were minor. combined basins of Superior, Huron, and All four of the moraines date from the Michigan late in this episode of glacial and Glenwood stage of Lake Chicago. Otto's early postglacial Great Lakes. work supports the early suggestion25 that, The history of Lake Chicago26 includes south of Winnetka, the Highland Park ice­ the thr.ee highest well-recorded water levels, front did not reach as far west as the adjusted to successive lowerings of a west­ present shoreline. The Blodgett and Deer­ ward outlet. There are no other known field moraines were not built in sufficient drainage routes for the lake, although it is strength across the floor of Lake Chicago well established that at least one low-water to survive the wave drag of later lake stage occurred during its history, too low to stages and, of the Park Ridge moraine, discharge westward. only Blue Island survives. Standing water The highest recorded stage of Lake Chi­ up to about 640 feet above sea level lapped cago27 is the Glenwood28 level, 635 to 640 against the ice front of these four stages, feet above sea level. During this time the providing most unfavorable conditions for ice front built the Lake Border moraines building ridge accumulations of the highly and meltwater deposited the DesPlaines water-charged clayey till. valley train. How far northeast of the During the deposition of at least the region the ice withdrew can be approxi­ earlier of the Lake Border moraines, a mated by tracing the Glenwood shoreline glacial river drained southward along mo­ northward into Wisconsin and Michigan. rainic sags to enter the Glenwood stage of Alden29 found it as far north as Racine, Lake Chicago at the head of a long bay Wis. Beyond Milwaukee, he thought it between the Tinley and Park Ridge mo­ had once been developed but had later been raines. It is recorded by the only well-de­ overridden by a post-Glenwood readvance veloped valley train of the region, now tra­ of the ice front. Lev.erett30 believed that it versed by the DesPlaines River as far south could be identified in Michigan as far as River Grove. By the time the glacial north as Ludington, nearly 150 miles north river ceased to flow, the advancing deltaic of the Michigan-Indiana line. There is front of the valley train had almost obliter­ weak development of the old shoreline in ated the bay. This Lake Border DesPlaines several places because of unfavorable con­ valley train is to be distinguished from the ditions for its formation, and there is dis­ possible Tinley valley train farther down­ continuity in other places because of en­ stream in the transmorainic DesPlaines Val­ croachment of the modern shoreline or ley. burial under modern dune-sand accumula­ Lake Chicago time.-Immediately after tions. If these facts are coupled with the glacial retreat from the Tinley moraine, fact that, in its northern part, any possible ponded water accumulated over the lower Glenwood shore (in common with all later ground moraine in front of the ice, con­ glacial-lake shorelines) has been warped by fined between morainic highlands on one crustal movements, the identification this side and the great ice sheet on the other. far north becomes uncertain. Overflow had to go across the morainic 29Named for the city of Chicago. Leverett, Chicago Acad. Sci. Bull . 2, p. 65. dam, and the already-existing Sag and Des­ 2Tfhere have been suggestions of pre-Glenwood Lake Chicago stages, but the field evidence supporting them is Plaines valleys localized the discharge. This unconvincing. See Atwood, W. W., and Goldthwait, J. W., Physical geography of the Evanston-Waukegan region : condition persisted throughout the re­ Tllinoi< Geol . Survey Bull. 7, p. 60, 1908; Cressey, G. E., and all Mankato The Indiana sand dunes and shorelines of the Lake mainder of Cary time Michigan bacin : Geog. Soc. Chicago Bull. 8, pp. 54-55, time. The area of Lake Chicago expanded 1928; and Ekblaw, G. E., Some evidences of incipient stages of Lake Chicago : Ill. Acad. Sci. Trans., vol. 23, as the ice receded, and its level lowered no. 3. pp. 387-390, 193 1. 28Named for the village of Glenwood where this as the outlet was deepened, until it finally shoreline is well developed. Leverett, Chicago Acad. Sci. Bull. 2, p. 66. merged into the much more extensive lakes 29Alden, W. C., geology of southeastern i nsin : U.S. Geol. Survey Prof. Paper 106, p. 328, Algonquin and Nipissing, which flooded the {;;jg� roLeverett, Frank, and Tavlor. F. B.. The Pleistocene 2:1Cooley, L. E., in Leverett, U.S.G.S. Mon. 38, p. nf Indiana and Michigan and the historv of the Great 384. Lakes : U.S. Geol. Survey Mon. 53, p. 354, 1915. CA USES OF THE LAKE CHICA GO STAGES 109

To these limitations on earlier identifica­ of flat and featureless lake-bottom topog­ tions must be added the fact that an inten­ raphy, should find their explanation in the sive search by the writer and colleagues31 detailed . history of erosional destruction of has completely failed to find any Glenwood the dam. shorelines north of Milwaukee, Wis., and Leverett, who named the lake and the Muskegon, Mich. three shorelines (Glenwood, Calumet, Since the front of the ice lobe doubtless Toleston ), did not write on this problem. bulged southward in the middle of Lake Alden, Goldthwait, and Wright34 have Chicago, the areal extent of the Glenwood argued that there was an abrupt descent stage should not be visualized as approxi­ in the outlet river as it crossed the Val­ mating the southern half of present Lake paraiso moraine that gave rise to rapids Michigan. It was doubtless a crescent­ which, by stoping, retreated upstream until shaped lake throughout the entire Glenwood the dam was breached. Detailed knowledge stage. The area of Lake Chicago increased of the outlet region acquired subsequent to during Calumet32 and Toleston33 times, the their writings35 shows this idea to have been shorelines of these stages being identified based on inadequate knowledge and in­ farther north on slopes of moraines which correct assumptions. themselves are younger than Glenwood. It The interpretation here presented differs may be that ice had entirely abandoned the from those of earlier students ( 1) in recog­ basin by early Toleston time. nizing the Valparaiso moraine in the outlet After many thousand years of exposure, region as only a veneer over a body of the three Lake Chicago shorelines can Lemont drift, ( 2) in identifying the outlet hardly be expected to yield precise altitudes valleys as pre-Valparaiso in age, ( 3) in for the lake stages. Indeed, with Lake making the Tinley the moraine dam (earlier Michigan's fluctuations in mind, it may be writers did not know of the existence of a justly suspected that every Lake Chicago Tinley moraine) , ( 4) in using the concept stage had variations in level of a few feet that erosion-resistant boulder pavements on both sides of its average. The figures checked moraine incision and thus caused 635 640 generally cited are to feet above stillstands, and ( 5) in utilizing ll greatly sea level for the Glenwood stage, 615 to 620 increased discharge contributed by glacial feet for the Calumet, and 600 feet for the lakes in Ontario, southeastern Michigan, Toleston. and western Ohio to explain the removing Causes of the Lake Chicago stages.­ of these boulder pavements and re-establish­ The three definite shorelines left by this ing of the erosional deepening across the glacial lake, about 60, 40, and 20 feet above Tinley dam. the level of its lineal descendant, Lake The pavement of boulders in many mod­ Michigan, appear to record three stillstands ern streams flowing on glacial till repre­ in the lowering from 635 or 640 feet above sents the coarsest fraction of the till, which sea level to Michigan's present average level the stream has been unable to remove. It of 579 feet. The level was lowered largely is an effective protection against further while the retreating glacial front still deepening. The Chicago outlet channels blocked discharge from the basin to the St. seem to have developed such pavements dur­ Lawrence and while escaping water crossed ing discharge through them of Lake Chicago the Tinley moraine-and-outwash dam to alone, and then to have had the boulders enter the Mississippi drainage. The succes­ swept away when the erosive and trans­ sive shorelines, interrupting wide expanses porting abi1 ity increased because of increased

31Bretz, J H., The stages of Lake Chicago : their discharge from the east. The top of Worth causes and correlations : Am. Jour. Sci., vol. 249, pp. 401-429, 1951. 34Alden, W. C., The Chicago folio (no. 81) : U.S. "Named for the Calumet River, whose course is de­ Geol. Survey, 1902. Goldthwait, Bull. 1 I. termined largely by the beach built at this stage. Leverett, Wright. G. F., Explanation of the abandoned beaches Chica�o Acad. Sci. Bull . 2, p. 72. about the head of Lake Michigan : Geol . Soc. Am. Bull ., 33Named for the former village of Toleston, which vol. 29. po. 23 5-244. 1918. stood on the bearh of this stage, and which i• now a part 35Bretz. J H., Geolo11v of the Chicago region : 11li­ of the city of Gary, Ind. Leverett, Chicago Acad. Sci . nois Geol. Survey Bull. 65, Part 1. 1939. Bull. 2, p. 74. Bretz, Am. Jour. Sci., vol. 249. 110 GLACIAL HISTORY

: . _. ..-:. • . ., .L.�M Fie. 48.-Another view of boulder pavement near F10. 46.-Boulders from the bed f the glacial � . Willow Springs. river in the DesPlaines transmora1111c valley.

A boulder pavement increases in volume (Lanes) Island originally carried a boulder and therefore in effect iveness as a channel pavement dating back to the highest (Glen­ is deepened, and it should eventually put Chicago wood) stage. Alden says in the an end to deepening. Thus the discharge f o/io that there were as many as a thousand across the Tinley dam finally ceased erod­ boulders to the acre. vVhen the rate of ing because of the growth of channel-bot­ erosion increased, the channel became di­ tom armor, and the lake back of the outlet vided as it was deepened, and the boulder ceased lowering. This determined the G!en­ accumulation on Worth Island was spared. wood stage of Lake Chicago, which per­ Spoil heaps of the Sanitary and Ship Canal sisted until a new factor appeared : greatly contain so many boulders that a boulder increased volume of the outlet river. pavement beneath postglacial deposit, in The interpretation of this study takes the DesPlaines transmorainic valley seems account of the succession of pondings in the indicated. The trench for the natural-gas Saginaw, Huron, and Erie basins, contempo­ pipeline north of Willow Springs was dug raneous with that in the Lake Michigan through a boulder accumulation on the basin.'w Twice during the history of the Toleston �hannel Aoor, the upper part of eastern lakes the discharge Aowed westward which can be seen in the boulder-strewn across southern Michigan by way of Grand fields in the vicinity. Stony Creek is a River and entered Lake Chicago. Glacial small, low-gradient stream in the Toleston lakes Maumee, Arkona, and Whittlesey channel north of \11/orth Island. This stream contributed the fi rst discharge, glacial Lake never could have carried the large number Warren the second. During the interven­ of boulders that litter the channel bottom ing time the levels of the eastern lak�s in places. If, however, another maximum . were lower because retreat of the ice Ill discharge were to be turned into the Stony western New York had afforded a tempo­ Creek channel, these houlderg would un­ rarv escapeway to the Mohawk and Hudson douhtedl�' start travelling. riv�rs, lower than the channel. Because the ice front which blocked the eastern lakes from draining to the St. Lawrence was larger than that holding Lake Chicago, their levels were higher. and when their discharge wag added to Lake Chicago its discharge acro�s the Tin!ey dam more than doubled. l ncreased volume alone, with­ out changes in load of debris, channel shape, gradient, and roughness of channel, will ,;roduce increased velocity in a stream. Doublin� the discharge may cause as much 1'10. 47.-Boulder pavement in De�Plainc.s out­ let channel near Willow Springs. :MIJ.c\•erelt :uid Tnylor. 05>. cir. CA USES OF THE LAKE CHICA GO STAGES 111

QU EBE C

\ KEY \

Areot coY!red by lakes. CJ '1' ! ,_.,and c0Mectin9 ��!���· ------' Correlative ice border. I l EdQe� of�"Y ice sheet.

FIG. 49.-Glacial lakes Whittlesey, Saginaw, and Chicago. Af ter Leverett, Frank, and Taylor, F. B. The Pleistocene of Indiana and Michigan and the history of the Great Lakes : U.S.G.S. Mon. 53, pl. 16, 1915. as a 20 percent increase. 37 Because erosive the Two Creeks, Wis. , forest bed.39 The ability of running water varies as the square forest grew on till exposed by Cary retreat of the velocity, a small increase in velocity and became buried later beneath the red might produce a noteworthy increase in a Valders (Mankato) till. The low-water stream's erosive work:. The two episodes period preceding Lake Chicago's Calumet of channel deepening which lowered Lake stage is also correlated with the Chicago about 20 feet each time are there­ low stage of the eastern glacial lakes, when fore ascribed to the two times when the their overflow abandoned Grand River and eastern lakes were discharging their over­ escaped eastward down the Mohawk.40 flow westward. Because there is no Glenwood shore on Excavation of the North Shore Channel the Valders till sheet and only a weak about 1911 (see p. 92) revealed a ne\v Calumet beach on the southern portion of chapter in Lake Chicago's history, a chapter the till sheet, it is believed that this Bow­ dealing with a low-water level intervening manville-Two Creeks-Lake Wayne stage between the Glenwood and Calumet high­ coincided with a marked retreat after the level stages. The outlet channels went dry Cary moraines had been built and before at this time because a recessional shifting the readvance which deposited the Valders of the ice border far to the east of the drift as far south in the Lake Michigan Chicago region exposed a lower discharge­ basin as Milwaukee and Muskegon. At this way eastward for all glacial lakes in the time the Strait of Mackinac probably was Great Lakes basins. Baker named this low­ the outlet of Lake Chicago to Lake Wayne water stage the Bowmanville stage. 38 The in the Huron and Erie basins. present writer has correlated the Bowman­ 39Bretz, Am. Jour. Sci., vol. 249. ville with a low-water stage recorded in Wilson, L. R., The Two Creeks forest bed : Wiscon­ sin Acad. Sri . Trans., vol. 27, pp. 31-46, 1932. 37Einstein. H. A., personal communication. Thwaites, Outlines of glacial geology. 38Baker, Univ. of Illinois Bull., vol. 17, no. 41, 1920. 40Bretz, Am. Jour. Sci., vol. 249. 112 GLACIAL HISTORY

SHEBOYGAN

� WHITEHALL • PT. " "� \.'"" MUSKE�ON '"'"" "-..J. ""��� � '">:;Lt-ij-...;:

Fm. 50.-Moraine correlation across Lake Michigan. From Bretz, J Harlen, The stages of Lake Chicago: their causes and correlations: Am. Jour. Sci., vol. 219, fig. 1, June 1951. GLENWOOD STAGE 113

With the l\!I ankato readvance there was ievel does not record a long stillstand be­ considerable realignment of the Lake Mich­ cause, with discharge shortly augmented igan ice front and a marked change in the from the eastern , larger than character of the till deposited over the any earlier glacial lake, any boulder armor earlier Cary drift. The change in till indi­ on the channel floor was swept away and cates a notable recession, adequate to use erosional deepening was promptly re-estab­ as a Cary-Mankato break. If Glenwood lished. shores had ever been made north of Mil­ Lake Chicago at once began dropping waukee and Muskegon, they became obliter­ from the second-attained Calumet level to­ ated by this Mankato advance. The weak ward the Toleston, its lowest level de­ Calumet beach on the Valders till near Port termined by the western outlet. This low­ Washington, Wis., indicates that a lake at est level with Mississippi connections marks the Calumet level existed during at least the final attainment of a bedrock bottom the early part of Mankato retreat. in both the Sag and DesPlaines channels. The idea that the Bowmanville-Two On the resistant floor, even the maximum Creeks-Lake Wayne low-water stage came discharge from Lake Chicago had little before Calumet time requires that we visual­ effect. Bedrock instead of boulder armor ize the Chicago outlets as already deepened determined the Toleston level. to the Calumet level by the time the eastern Another factor that entered into the outlet initiated the low-water level in the complex of the glacial Great Lakes history entire group of basins. It is possible that was the differential uplift that occurred dur­ the first-attained Calumet level was not a ing the changing scenes of these lakes. stillstand of Lake Chicago and that no North of the "hinge line," all glacial lake Calumet shoreline had yet been made when shorelines depart from the horizontal and the lake began dropping to the Bowman­ become higher toward the northeast ; the ville level and the western dischargeways older and higher ones depart most, the went dry. It is also possible that a boulder younger and lower ones, least. It is possible armor had already checked the downcutting that the Bowman ville low-water stage (for of the outlets and the lowering of the lake, which we have no shorelines) was termi­ in which case a Calumet shoreline would nated and the level of Lake Chicago was have been left. raised 30 feet back to the abandoned west­ The Mankato advance which buried the ern outlet by the uplift of the eastern or Two Creeks forest and closed the eastern northeastern region where the Bowmanville spillway returned all eastern lake discharge outlet must have been. A slow rise in lake (Lake Warren) to Grand River and thence level caused in this way would be more to Lake Chicago. The lowered lake began likely to drive the beach materials forward, rising, eventually to spill back through the instead of submerging them, than would the Chicago outlet and again to enter the Missis­ more rapid rise caused by an ice advance. sippi drainage. As it flooded up on the Probably, however, the uplift was too slow nearly level lake bottom that had become to have accomplished this before readvance exposed during the low-water stage, waves of the lobes produced the same effect on tossed beach materials before them in an the lake level. Stanley believed that "hinge aggregate that constantly increased as it line" warping did not begin until long after was shifted across the flat. Bowmanville time, a conclusion supported Thus by the time the flooding basin's by Hough's later researches (1953). water level had reached the level of the The Glenwood stage.-Several earlier abandoned outlet, the beach had been car­ students of the region have stated that the ried up the slope with the rising strandline Glenwood shores vary somewhat in alti­ to the outlet's altitude, here to be added to tude and have attributed the variations to any beach that might have been left when minor fluctuations of lake level. The total the water fell to the Bowmanville level. range seems to have been little more than The beach of the second-attained Calumet Lake Michigan has shown during the past l> - en :+ - C1I C1I en 0 +. 0 UI C1I - 0 0 c 0 0 Q. Cl>

Glenwood stage. Initial spill over Tinley dam at 640 fe et. Little erosion in out­ let-channe ls.

Addition of Maume e, Arkona. , Whittle sey dischar ge , deepening outlets and lower­ ing lake to Calumet level, 620 feet. Port Huron moraine.

.... Pause in deepening of outlets when retreat of Huron and Erie lobes opens eastern L outlet, lowers Whittlesey, and deprive s Lake Chicago of lal"ge influx from the east. First-attained Calumet level.

Further retreat of eastern lobes opens still lower outlet, location unknown. Re­ c;J t°"" corded only by Bowmanville stage in Michigan ba sin. Lake Chicago outlets go � dry. � t°"" Bowmanville low -water stage at 590. I• I ::i:: -Bowmanville outlet closed by readvance of eastern lobe s. � 1-.3 1_ a � Lake Chicago rises to 620 feet and drains we stward. Wave s sweep sand and � gravel up the slope of the Chicago plain to make the Calumet shor e.

Calumet stage. Lake Wayne dis charging to Mohawk and only Lake Chicago water using western channe ls. Little erosion in outlets.

Additional readvance of Huron and Erie lobes, closing Mohawk outlet and forming Lake Warren with discharge to Lake Chicago. Readvance of Michigan lobe to deposit Valders red drift. Beginning of Mankato substage.

Deepening of outlet-channels and lowering of Lake Chicago.

Bedrock reached in outlet-channel floors, deepening ceases. Lake Chicago at first-attained Toleston level. Ice retreat in the east again opens Mohawk outlet . Lake Lundy Dana succeeds • ( } Lake Warren; western outlets again carry only Lake Chicago discharge. Fur ­ ther ice retreat creates Lake Algonquin of both Kirkfield ci.nd two-outlet stage s. Hammond shore built. / / ("'.) ::r:: / ::-...... � c;J Lake Algonquin lowered by opening of unknown low outlets fr om Huron basin. � c;J Water in Michigan basin falls to 480 fe et and drains eastward through Mackinac � Strait Fiver to lowe st Algonquin or Taylor Lake s stage in Hur on basin. Sag � ( } � low-water stage. � V:l� not shown in diagram ...... ( } ,-____ � --- r------L__ Final withdrawal of ice barrier opens North Bay outlet to create early Lake � Nipissing. >::t... � � Differential uplift raises North Bay outlet and causes water-level in Michigan ' � basin to rise to Englewood shore, fe et. " 590 ' ("'.) spills south through Port Huron outlet. � ' ------c;J Erosion of Port Huron outlet lowers Nipissing to present levels of Lake Michigan >::t... and . � b::l �>::t...

51.-Changing levels in the Lake Michigan basin from the Glenwood stage to the !:: FIG. (JI (JI en .... present time. No attempt is made in this diagram to express relative duration of 0 (JI (JI - - (/ g c the different stages. 0 0 0 - Q. 111 (.J\ 116 GLA CIAL HIS TORY century (see p. 25),41 and the Glenwood shore is here considered a unit. The Glenwoodshoreline, where definitely marked in the Chicago region, consists of alternating sea cliffs and beach deposits in almost equal proportions, there being a total of nearly 30 miles of each. Nineteen of the 30 miles of beach deposits are measured on spits that grew during the stage� not on original contacts of land and water. Glen­ wood waves had opportunities for ero­ sional attack unequalled in the later stages when, except in one place, waves could reach and work only on the floor abandoned by Glenwood water. The exception is the east face of the Highland Park moraine, in the Highland Park and Evanston quad­ ran�;les (Maps 2, 5), where the record shows that the waves encroached on the land through all Lake Chicago and subse­ quent time. A vanished Glenwood sea cliff is recorded by the Wilmette spit, whose debris, derived from cliff-undercutting, was carried southward past the tip of the mo­ raine and deposited on the shallow lake­ floor in the Park Ridge and Evanston quad­ rangles (Maps 4, 5) to make the most intricate spit of the region. The spit is 5 miles long and has nine definite "fingers" built successively from north to south. The Glenwood cliff later was undercut and destroyed by Calumet waves, whose own sea cliff, recorded by the Rose Hill spit, was in turn destroyed by Toleston waves. The Toleston sea cliff, similarly recorded FIG. 52.-Sketch map of the Chicago region dur­ by the Graceland spit, was undercut and ing the Glenwood stage of Lake Chicago. destroyed during later lake stages. The From Bretz, J Harlen, Geology of the Chi­ cago region. Part I. General : Illinois Geo\. vanished cliffs probably were much more Survey Bull. 65, fig. 85, 1940. striking features than any which have sur­ vived from Lake Chicago time (fig. 57). mals to enter the region as the ice receded.42 The growth of the Wilmette spit largely The remains are minute molluscan shells, closed off the shallow Glenwood bay in ten species having been identified by F. C. Skokie Valley ; in the wanner waters thus Baker. "All the species, with one exception, made possible lived the earliest-known ani- are fresh-water shells," the exception by inference being a land form. Baker said 41Alden (Quaternary geology of southeastern Wiscon­ sin : U.S. Geo!. Survey Prof. Paper 106, p. 331, 1918) that all are known in older (Pleistocene) gave the largest range, 15 feet, although Goldthwait (The abandoned shorelines of eastern Wisconsin : Wisconsin deposits in middle Illinois. Geo!. and Nat. Hist. Survey Bull. 17, p. 44, 1907) spoke Glenwood waves reached the southern of beach "ridges at many places which mark successive lowerings of the lake while the Chicago outlet was being end of the Park Ridge moraine with suffi­ cut down ; and these extend the Glenwood series down to about 627 feet . . . only a few feet higher than the cient strength to cut a low sea cliff in its Calumet stage." Such ridges properly are not of Glen­ wood age : they belong to the interval of increa

be a record of waves in the bay between the MANKATO SUBAGE two large beaches, or it may be a product of The second Calumet stage.-Readvance the earliest Calumet waves before the Lan­ of the Lake Michigan lobe with altered sing-Munster bar had grown beyond its outlines and flow lines and deposition of Glenwood dimensions. East of Dyer for the Valders red drift are here accepted as several miles the Glenwood dunes have a marking the inauguration of the Mankato steep, straight northern front, as though subage. Because the southern part of this they had been trimmed by good-sized Calu­ drift sheet in the lake basin carries a weak met waves. This feature favors the second Calumet beach but no trace of a Glenwood explanation above. shoreline, it is believed that eastern glacial Rising Calumet water did not surround lake water (Lake Warren ) had risen from Blue Island, although a group of beach the Lake Wayne low level and was dis­ ridges of this age was built a little out from charging again into Lake Chicago. This the foot of the Glenwood sea cliff on the east side. On the west, Glenwood lake bottom had become land all the way from Blue Island to Mt. Forest Island ; the Blue Island tract was the blunt end of a large peninsula projecting southeastward into the lake. A similarly aligned bay along the southern side of the peninsula extended northwestward to the head of the Sag outlet a little west of . Worth. In the middle of the bay, another high area of about two square miles in the Glenwood lake bottom emerged to constitute Worth (Lanes) Island. A hairpin-shaped beach ridge outlines the larger portion of this Calumet island. The island was originally thickly strewn with boulders left behind by scour of the outlet stream before the Bowmanville stage. The growth of the Rose Hill spit gave rise to a protected bay between it and the Calumet shore about 3 miles to the west. This was the Wilmette Bay43 of Calumet time, larger than, and covering the site of, the Bowmanville bay. The shallow-water biota living in the Bowmanville bay was destroyed by the deepening Calumet lake, and not until the lake lowered considerably toward the Toleston level were shallow­ water conditions restored. A fauna char­ acterized by the "heavy Mississippi River type of mussels"44 migrated into Wilmette Bay by the time it had shoaled to depths of 5 to 20 feet. Of 35 species, 30 are clams. Baker thought that larval forms (glochidia) attached themselves to fish and thus mi­ e:rated uo the lake outlet. FIG. 54.-Sketch map of the Chicago region dur­ ing the Toleston stage of Lake Chicago. •aNamed by Goldthwait for the to"'.n of Wilmette, From Bretz, J Harlen, Geology of the Chi­ which is bu ilt largely on the floor of this bay. Atwood cago region. Part I. General: Illinois 'Geol. and Goldthwait, Bull . 7, p. 62. "Baker, op. cit., p. 32. Survey Bull. 65, fig. 87, 1940. 120 GLACIAL HISTORY

ICE SHEET

HINCE

Niagara

-----

·------�-- ---� ------

Fw. 55.-Lake Algonquin with three outlets. From Bretz, J Harlen, Geology of the Chicago region. Part I. General : Illinois Geol. Survey Bull. 65, fig. 89, 1940.

lake regained the level necessary for west­ the Toleston outlet level was attained. ward discharge before the Valders (Man­ Again, the complexity is caused by factors kato ) ice had more than begun to retreat operating far to the east and northeast of from its maximum advance. Deepening of the Chicago region and, because of them, the western outlets came promptly on re­ it is not certain that the existing Toleston newal of their functioning, and Lake Chi­ shoreline dates back to the original attain­ cago as promptly began dropping from the ment of that outlet level. second-attained Calumet level to the Toles­ Research, chiefly by Taylor, has shown ton. There is no one stage in the lake's that Lake Warren fell to the Lake Lundy history to use as a marker for the opening (Dana) level when retreat of the ice in the of Mankato time. That geological moment Huron and Erie basins again opened a dis­ came at some time between the Bowmanville charge route to the Mohawk. After Lake low-water stage and the second-attained Lundy's time, still further recession of the Calumet level. Deepening of the outlet and ice front allow,ed a great expansion of gla­ consequent lowering of the lake to the Tol­ cial-lake water, which formed Lake Algon­ eston level are Mankato events. quin, bringing to a close the Lake Chicago The Toleston stage.-The Toleston episode. According to Leverett and Taylor, stage of Lake Chicago has been thus far Lake Algonquin spread over the three com­ presented as a simple consequence of a bined basins of Superior, Huron , and simple cause : rock floors in the outlets de­ Michigan, but recent research by Hough in­ termined a fixed low level of ponded water. dicates that the Superior basin was still In reality, the least understood part of the occupied by glacial ice and did not share in history of Lake Chicago took place after the Algonquin level. Discharge from this TOLESTON STAGE 121 one large lake escaped from the southeast Mackinac Straits49 suggests that Lake Al­ end of by way of Trent gonquin's level probably sank so low that River (Kirkfield or Fenelon Falls outlet ) the Michigan basin became dismembered to a glacial lake (Iroquois ) then occupying and had its own outlet river to the Huron the Ontario basin. basin through the remainder of Algonquin

The Trent River discharge so lowered time. Water in the Lake Michigan basin the lake level that the western outlets went at the time of this lowest Algonquin level dry again. Baker thought the Sag low­ stood "about 100 feet"50 lower than it does water stage45 may have been lower at Chi­ today. cago than the present surface of Lake Hough, in extensive coring of Lake Michi­ Michigan. Stanley46 believed that if the gan sediments,51 found that cores from less combined lakes discharged through Trent than 350 feet of water all had a layer of Valley, this stage was "very considerably sand or sand with shells that was lacking in lower." cores from deeper water. The shells were Differential northeastern uplift during of gastropods and pelecypods that inhabit the waning of the great ice sheet, because water from 1 to 15 feet 'deep. From this he of the reduction of load on the crust, pro­ concluded that Lake Michigan had had a gressively raised the Trent outlet on the low-water stage after Algonquin time but east. This caused Algonquin water to rise before the next (Nipissing) high level. He higher on all shores. Eventually it found correlated this low-water stage with Stan­ another low place across which escape was ley's Mackinac Straits River, and named possible, at Port Huron, down the St. Clair the shrunken remnant in the Lake Michi­ River. Opinion is general that this rise in gan basin Lake Chippewa, and that in the water level also brought a return discharge Lake Huron basin . to the Chicago outlet, which operated simul­ If a low-water level endured long enough taneously with the initial Port Huron dis­ and if the newly exposed bottom had suffi­ charge. Thus, water in the Lake l\!I ichigan cient slope, streams entering the lowered basin was now back to the Toleston level, lake would erode valleys across the emerged and the existing Toleston beaches were floor and would deepen their pre-existing added to or "overwhelmed and worked over valleys. The ensuing rise of water would entirely by Lake Algonquin waters."47 The then cause drowning of the valleys and Port Huron spillway, however, was on gla­ deposition in the drowned valleys. Several cial drift, and relatively rapid erosion there earlier writers52 have discussed the filled soon gave it all of Algonquin's discharge. channels and ponded lower courses of sev­ The two-outlet48 stage came to an end, and eral Michigan rivers entering the lake, the rock-floored Chicago outlet probably inclining to the view that a low-water stage has not been used since that time. is recorded but failing to date it closely. The ice barrier still lingering in the Stanley53 more recently has cited borings northeastern part of Georgian Bay covered in the channel near the low country which, when it finally became mouth, through fine sand and peaty ma­ exposed by continued shrinkage of the ice, terials, to depths of 85 feet below lake- offered still lower escapeways eastward, 49Stanley, G. M., The submerged valley through probably to the Ottawa Valley ; this caused Mackinac Straits : Jour. Geo! ., vol. 46, pp. 966-974. 1938. 5

I. GLENWOOD STAGE. 640. Z. Maumee. Arkona, Whittlesey discharge deepens outlets. 3. First -attained Calumet level. 2� 4. Opening of unknown eastern outlet lowers lake. 3 5. BOWMANVILLE LOW-WATER STAGE. 590. 6. Rea.dvance of ice closes eastern outlet.

7. CALUMET STAGE. 6ZO. 8. Addition of Warren discharge deepens outlets to bedrock.

9. TOLESTON STAGE. 600.

10. ALGONQUIN TWO-OUTLET STAGE. Hammond shore. 11. Ice retreat opens unknown Algonquin low outlets. ll. SAG LOW-WATER STAGE. 480+. Algonquin's lowest level. Mackinac Strait RiVer.

13. LAKE CHIPPEWA. 2.30+. Mackinac Strait River. 14. Differential uplift raises outlet of lake. North Bay outlet.

15. ENGLEWOOD STACE. 590.

16. NIPISSINC STACE. 17. Deepening of Port Huron outlet.

18. LAKE MICHIGAN. 580.

FIG. 56.-Diagrammatic cross section showing oscillations of the shoreline across the Chicago plain. The detached part of the diagram shows the relative position of Hough's Lake Chippewa. level, and is convinced that "the river ex­ In the Chicago region there are at least cavated its bed to this depth after the gla­ two minor filled stream valleys on the lake cier withdrew from the region and during plain, both completely obliterated by beach a period when its base level [Lake Michi­ sand at the Toleston level and known only gan] was at least 7 5 or 80 feet lower than from borings and excavations. One was 40 now." The writer would correlate this feet wide and had been eroded 16 feet deep deep valley with the functioning of the in till before being buried in the beach sand. Mackinac Straits River. But these datings are all subject to A low-water stage of Lake Chicago that cnt1c1sm. If Taylor is right in thinking followed the Calumet and preceded the that Lake Algonquin's two-outlet stage saw Toleston stage has been argued by Leverett, a remaking of the Toleston beaches, the Goldthwait, and Alden. Leverett's evi­ evidence submitted for a low level by dence54 is the deep valley-fill along Black Leverett and Goldthwait may be used to River near Holland, Mich., apparently support Baker's post-Toleston Sag low­ younger than the Calumet beach and older water stage and Stanley's Mackinac Straits than the Toleston beach at that place. A low-water level, which were also post­ lowering of at least 50 feet below the T oles ton and appear to have been the same present lake level is reQuired for the .erosion episode. If the writer is correct in dating of this now-filled valley. Goldthwait's evi­ the red drift as late Calumet or as post­ dence55 is peaty material beneath the gravel Calumet but pre-Toleston ( p. 111), Al­ of a Toleston bar in Evanston. Alden's den's low-water stage also is best dated as evidence is the occurrence of marsh deposits post-Toleston. The data now in our posses­ as much as 53 feet below Lake Michigan sion are not adequate to justify asserting or level, discovered in borings in Milwaukee denying a post-Calumet, pre-Toleston low­ River Valley. He dates the low-water in­ water stage. It is not included in the dia­ terval necessary for the erosion of this deep grams of figures 51 and 56. Future investi­ valley as subsequent to the deposition of gations may clear up this doubtful point. the red drift (i.e. post-Mankato). The Toleston shoreline is nowhere more than 6 miles back from the present shore, 54Leverett, U.S.G.S. Mon. 38, pp. 446 and 499. 65Atwood and Goldthwait, Bull. 7, p. 63. and in places in its northern stretches only POST-TOLESTON, PRE-MICHIGAN TIME 123 a few blocks separate it and the lake today. Stony Island appeared in Lake Chicago It varies considerably in strength of de­ at the Toleston stage and is unique in that velopment, being especially bulky in the it was the only island of bedrock in this northern and southern parts of the plain region. Like Blue Island, it still is a suffi­ and almost completely lacking in the central ciently marked eminence in the Chicago part. The lack of well-marked beach ridges plain to carry the popular designation of between the heavy shore accumulations may "island." Stony Island is in the north­ be related to the fact that the currents central part of the Calumet Lake quad­ swept the beach-making materials into the rangle (Map 16), about 1 1 / + miles long, outlets. one-third of a mile wide, and 15 to 20 feet The largest spit of Lake Chicago in the higher than its surroundings. Like Worth region, the Graceland spit in the Evanston Island, its surface originally carried an un­ and Chicago Loop quadrangles (Maps 5, usually large number of boulders, which 8), grew southward from the sea cliffs here must be ascribed to wave erosion dur­ on the Highland Park quadrangle at the ing earlier stages, to stranded icebergs, or Toleston level, its surviving length being both. A gravel beach ridge at Toleston 12 miles and its greatest width nearly 1 1/2 level almost encircles the island. miles. Its northern half is a gravel ridge The only Toleston cut-bank shore that only two or three b!ocks wide, the great deserves the name of sea cliff is traceable widening farther south strongly supporting through Roseland and Kensington, south the view that it is -a spit rather than a from about 103rd Street to 127th Street. simple beach ridge. Some of the debris eroded from it was In the three high-water stages of Lake moved southward and accumulated as a Chicago, three spits were built in the Evan­ short, blunt spit at the south end, almost ston region almost alongside each other, suc­ in the head of the Toleston outlet channel cessively lower and younger nearer the lake. that led to the Sag. It has been exploited Their material is believed to have come as a source of sand and is now largely re­ from the erosion of sea cliffs north of moved. Kenilworth and Winnetka. Each spit was With the drop in lake level to the Toles­ built after a drop of about 20 feet in water ton stage, the outlet channels necessarily level, which shifted the new shore farther lengthened eastward across emerged Glen­ east. It is as though a fulcrum point had wood and Calumet lake bottom. The Sag existed in the Kenilworth district, the suc­ channel was lengthened 10 miles ; its new cessive spits shifting eastward as the suc­ head was shifted as far east as Riverdale. cessive sea cliffs were driven westward. Worth Island became more definitely out­ Extensive sand accumulations on the lined because the two Calumet channels strong southern, or Dolton-Hammond divided by it were deepened by Toleston Toleston beach (Calumet Lake and Calu­ discharge. met City quadrangles-Maps 16, 20), pro­ Post-Toleston, pre-Michigan time.- In duced the largest area of dunes in the Chi­ the Chicago region the Toleston shoreline cago region. They appear to have continued is roughly paralleled by other , somewhat to grow during the following Algonquin, lower beach ridges closer to Lake Michigan and perhaps still later, lake stages. About and at two different levels. They have 2 miles south of this beach, the Lansing­ been variously called the lower Toleston M unster Calumet beach has a small sea beaches, the second and third Toleston, and cliff cut at the northern foot, at the Toles­ the Hammond and Englewood beaches. It ton level. The cliff is probably an early is not certain that the Toleston outlet Toleston feature, although it might be the functioned for these lower levels, although result of waves generated on the bay be­ they are not records of any of the late tween the two larger features. By either Algonquin low-water levels above noted. interpretation, the Dolton-Hammond beach To approach an understanding of con­ must have grown up on an offshore bar. ditions at these times, the entirety of· the 124 GLA CIAL HISTORY

GUL F

IRVING PARK BLVD.

Fie. 57 .-Reconstruction of the vanished sea cliffs and spit connections of the North Shore district. POST-TOLESTON, PRE-MICHIGAN TIME 125

FIG. 58.-. From Bretz, J Harlen, Geology of the Chicago region. Part I. General: Illinois Geol. Survey Bull. 65, fig. 90, 1940.

upper three lake basins again must be briefly formed, occupying most of the three upper considered. lake basins. The formation of Lake Nipis­ Lake Algonquin levels, well recorded in sing marks the close of glacial history and the Georgian Bay region, must have made the opening of post-glacial time. Lake correlative shorelines in the southern part Nipissing was entirely surrounded by land ; of the Lake Michigan basin. But today it had no glacial ice margin. they are all superimposed on or built against The initial North Bay-Mattawa-Ottawa the lakeward slope of the Toleston beaches. spillway appears to have determined an Reduction of the load on the depressed early Lake Nipissing level that later rose crust of the region as the ice sheet retreated as tilting continued to uplift the new outlet back into Ontario was causing continued and added to the deformation of the Al­ uplift. The Algonquin beaches north of gonquin shores. Stanley56 has found Nipis­ the hinge line are strik.ingly deformed, the sing marl overlying lower Algonquin beach amount of deformation increasing toward gravels, proving that in the southern part the northeast to a maximum of 6 feet to of the Huron basin, the Nipissing level, the mile. This warping must have occurred because of the continuing uplift, eventually after the lake had constructed the shore­ submerged some of the lower Algonquin levels. line, yet much of it had occurred before Finally, the rising level of Lake Nipissing the ice front to the northeast ceased acting brought the Port Huron outlet into action as a dam. The last stand of an ice dam again, the discharge out of North Bay appears to have been in th e North Bay ceased, and the stage was set for develop­ district of northeastern Georgian Bay. ment of the modern lakes. Antevs57 be- \Vhen the ice retreated from the North 56Stanley, G. M., Lower Algonquin beaches of Pene­ Bay district, the lowest pass to the Mat­ tanguishene Peninsula : Geo!. Soc. Am. Bull., vol. 47, pp. 1933-60, 1936. tawa- was opened and Lake 57Antevs, Ernst, Late Quaternary unwarpings of northeastern North America : Jour. Geo!., vol. 57, .pp. Nipissing (or Nipissing Great Lakes) was 707-720, 1939. 126 GLA CIAL HIS TORY

lieved that there was a pause in uplift at Above this land surface lie silt and peat this time and that North Bay and Port beds of the Hammond stage, the two-out­ Huron long functioned simultaneously, con­ let stage of Lake Algonquin. Wilmette stituting a two-outlet stage for Lake Nipis­ Bay was very shallow at this time, partly sing. because of the low level of the lake, partly In the southern and undeformed parts because it was filled with these stratified of Lake Algonquin, the main shoreline deposits. The upper surface of the silt and stands at about 607 feet above sea level, 58 peat beds, in turn, carries the same record which is not far from the Toleston level. of exposure (oxidized yellow color and The undeformed Nipissing shoreline, ad­ crayfish burrows), dating from a low level justed to the Port Huron outlet, is at about following Lake Algonquin and preceding 596 feet, 59 and this stage may be repre­ Lake Nipissing. At this time, Lake Michi­ sented by the Englewood60 beach in the gan basin (containing Lake Chippewa) Chicago region. was drained by a river through Mackinac Since the Port Huron discharge was re­ Straits. stored the North Bav outlet of Lake Nipis­ Lifting of the North Bay outlet of Lake sing h�s been raised by continuing differen­ Nipissing brought the water level in the tial uplift until it now stands 100 feet above Chicago region back up as far as the Engle­ the level of Lake Huron. Similarly, the wood level, about 690 to 695 feet, and silt Nipissing shoreline in the northern part of and peat were deposited over the Hammond the Lake Michigan basin rises toward the sediments in Wilmette Bay. Shallow-water northeast. , being entirely molluscs characterize these deposits. When north of the hinge line, has all its glacial the Port Huron outlet was deepened, the lake shorelines deformed. The bottom of bay was drained-just as it was when the the strait which in Nipissing time connected first Europeans found it. Superior with the rest of the three-basined There was formerly a definite shoreline lake has emerged entirely, making Superior recording the Englewood stage, but it was a separate body of water 20 feet higher than faint and has largely disappeared beneath Michigan and Huron and giving origin to the city. Alden mapped it, and the Chicago the rapids in St. Marys River at Sault Ste. region geological maps reproduce Alden's Marie. delineation with dotted outlines. It was a The Hammond shoreline, according to long beach ridge that reached originally Baker, is the same as the Toleston or is from the tip of the Graceland spit ( 800 built up against it. In later Toleston time, block North, West ) south Wilmette Bay received silt, sand, peat, and to 87 th Street (Chicago Loop, Jackson marl deposits above the heavy clam bed Park, and Calumet Lake quadrangles­ which marks the early Toleston bay, the Maps 8, 12, 16), where it joined the Toles­ deposits totalling a maximum of 6 feet. ton beach. In its growth it blocked any The upper part of the late Toleston sedi­ possible drainage westward into the head ments is crowded with shells which record of the DesPlaines outlet, and its existence a shallow-water environment. The upper is further evidence that the Chicago dis­ surface of this stratigraphic unit has a yel­ chargeway was then dry. low oxidized color with traces of crayfish East of the Toleston and Englewood burrows. Both the yellow color and the bur­ beaches, the nearly flat plain carries a rows record draining of the bay during the number of sand ridges on the Calumet Lake Sag low-water stage ( Kirkfield stage of quadrangle (Map 16) that differ very little Lake Algonquin ), an interval when the in altitude and that determine the outlines bay bottom became land. - of Wolf Lake and Lake George. There ''"Goldthwait, J. W., An instrumental survey of the shorelines of the extinct lakes Algonquin and Nipissing were even more of them on the Jackson in southwestern Ontario: Canada Geol. Survey Mem. 10. 1910. Park quadrangle, but they are no longer 59Goldthwait. Bu ll. 11. traceable. The ridges record the lowering OOBaker, Univ. of Illinois Bull ., rnL 17, no. 41, p. 93, 1920 . from the Nipissing level to that of the POST-TOLESTON, PRE-MICH/GAS TIME 127

Fie. 60.-Water-worn grooves in floor of Toleston channel near Lemont. Fie. 59.-Potholes in floor of Toleston channel, near Lemont. varied as, the late glacial and the post­ present lake. Alden counted 90 of them, glacial history of the Great Lakes. The falls and figure 91 in Part l of this bulletin originated with the first emergence of the shows 68 in one photograph. above the lowering Quarrying in the D.esPlaines valley bot­ water levels of glacial lakes in the Ontario tom near Lemont has for many years pro­ basin, in early Lake Algonquin time. The vided almost continuous exposures of water­ cataract has retreated 7 l /2 miles back worn grooves and potholes in the bedrock from its first position at the escarpment. Aoor. The marked elongation of the grooves Variations in the width of the gorge in early prompted the idea that they were ice­ different portions along the 7 1/2 miles arc worn, but Leverett's statement that "they ascribed to variations in volume of dis­ may be the product of the waters of the charge. \iVhen the Port Huron outlet was Chicago outlet"'11 suggests the correct ex­ pouring the overAow of the l\llichigan, planation. Apparently the circular type Huron, and Superior basins into Lake Eric shown in figure 59 was not exposed in the the discharge was at its maximum ; when earlier quarrying. Some of the potholes Trent River or outlets are worn into cherty limestone, and the were functioning and only Erie discharge chert nodules are as cleanly cut as the lime­ was going over the falls it was at its stone. Their production hy the early post­ m1111mum. glacial DesPlaines seems out of the ques­ The correlation between Niagara Falls tion ; it is more likely that they were pro­ history and lake historv. which has been duced during the latest occupancy of the generally accepted for three decades11� is valley by glacial-lake discharge. based on the presence below the falls of Deepening of stream valleys is likely to three stretches of relatively wide gorge, leave remnants of the valley floor of earlier $eparated by two stretches of narrow gorge. stages as terraces on the lower slopes. But The wide stretch farthest upstream is being in the Lake Chicago outlet valley, the lengthened today by recession under the volume of discharge seems to have occupied combined disd1arge of all four upper lakes. the full width of the vallev at all times and r ts inception is dated back to the closing of thus no terraces were built. Onlv one the North Bay outlet. The narrow :>tretch definite terrace is known, a remnant �f the downstream from it was formed during the life of early Lake Nipissing, which drained Tinley valley train (sec p. 82), and it is protected in part by the pro.iection of the out of North Rav. to the l\IIattawa and Tinley moraine into the Sag Valley. Ottawa rivers and allowed onlr Eric water to go over Niagara. The wide middle The history of Niagara Falls is inti­ !'trctch is correlated with the Algonquin matelv interwoven with, and almost as ••K indlc. F.. �!.. "'"' Torlor. F. n.. The �iopiro •1Lc\'cro11. Chicoso ..\rod. Sci. Bull. 2. p. 53. folio (No. 1?0). U.S. Ceol. Sun-ci•. 191 L 128 GLA CIAL HIS TORY

Port Huron discharge. The narrow stretch atoms are broken up by such bombardment next downstream is a record of Erie dis­ to form carbon and hydrogen, the resulting charge during the Trent River outlet stage carbon atom being radioactive with a half­ of Lake Algonquin. The wide stretch at life period of about 5600 years. These car­ the lower end of the gorge is believed to bon atoms shortly combine with atmos­ record an early stage of Lake Algonquin, pheric oxygen to form carbon dioxide and not previously referred to in this bulletin. to become a small part of the atmosphere's It endured until the Trent River outlet total amount of carbon dioxide. Because was opened, and its discharge necessarily plants build their structures largely from went into the Erie basin and thence over carbon dioxide, all vegetable tissue, when the falls. fon1:1ed, must contain the same proportion Some refinements and revisions of this of radioactive carbon 14 and nonradioactive correlation are proposed by Antevs.63 His carbon 12. revisions include a new estimate of 22,000 Assuming a constancy of cosmic-ray re­ years for Niagara's total age, instead of ception by the earth during the recent geo­ Kindle and Taylor's figure of 25,000 to logical past, there must now be a balance 30,000 years. between the rate of disintegration of radio­ active carbon and that of assimilation of RADIOCARBON DATING new radiocarbon in all living matter. In­ put ceases when an organism dies, and the In Part I the recession of Niagara Falls amount of carbon 14 begins to decline, be­ was called a "geological clock," and the coming reduced to half its original amount Tay!or and Kindle estimate of the age of in peat, wood, bone, or shell material m the gorge, 25,000 to 30,000 years, was about 5600 years. presented. This estimate is found in virtu­ ally every textbook on historical geology Because the proportion of carbon 14 to now in use, but it is more than twice the other carbon atoms in living organic ma­ recent measurements made by a wholly terial is known, it follows that buried different and far more precise method. wood or charcoal whose original carbon Working with geological material, but using content has undergone no other alteration the laboratory methods and principles of subsequent to burial may carry a record of physics and chemistry, we have been getting time elapsed since the plant was alive.64 some surprising figures, in terms of years, Using this method of approach, determina­ for the age of the rocks in the geological tions of the age of numerous samples of record. wood and peat of late glacial age65 have given a correctly proportioned chronology The amount of radioactive decomposition back as far as about 20,000 years, which is of uranium and thorium minerals in igneous the present limit of laboratory determina­ rock has moved our estimate of the earth's tion. The highest figure is for some wood beginning back in time more than two bil­ buried in the loess of the earliest Wis­ lion years. More recently, the amount of consin glaciation, more than a hundred radioactive decomposition of an isotope of miles southwest of Chicagoland (Fann carbon, carbon 14, in wood and peat of Creek). There were 15 or more moraine­ late glacial age has demanded that we move building episodes after the radiocarbon con­ these late events much nearer the present tent of that wood began to decrease and than the Taylor and Kindle estimates for before Lake Chicago's history began. Ni­ Niagara. agara Falls, born after Lake Chicago had The principles on which radiocarbon dat­ ceased to exist, obviously cannot date back ing is based may be briefly outlined as follows. Cosmic ray neutrons, with very "'Some scientists doubt that the only alteration in Cl4 content since burial has been radioactive decay. high specific energy, are constantly bom­ Antev>, in Geochronology of the deglacial and neothermal ages, Tour. Geo! ., vol. 61, pp. 195-230, 1953, lists a con­ barding; the earth's atmosphere. Nitrogen siderable number of cames possible for other alterations. MLibbv, W. F., Radiocarbon dating : Univ. Chicagd' 83Antevs, Jour. Geo! ., vol. 47, pp. 719, 720, 1939. Press, 1952. RADIOCARBON DA TING 129

25,000 years if the radiocarbon method of to be altogether too young for Toleston. It dating is correct. may be Algonquin or Nipissing. The discovery of wood buried in Lake Recent studies by Hough67 indicate that Chicago deposits has made possible an ap­ in disagreement with some earlier interpre­ proximate carbon 14 dating of some events tations of Nipissing history, Nipissing levels in the lake's history. Wood has been found : rose in the south end of Lake Michigan ( 1) in and under the Dyer spit, itself un­ basin to the Algonquin level. Arnold and doubtedly of G�enwood age ; (2) in an ex­ Libby in 1951 reported that peat from the cavation on the campus of the ·University Nipissing beach at Sand Island, Bayfield of Chicago, made in sand probably of Co., Wis., is 3656 -+- 640 years old. Toleston age ; ( 3) in an aggregate of beach The Plum Creek deposit was interpreted ridges near Dolton that range from Toles­ in Part I (p. 117) as at least post-Calumet, ton to Algonquin and perhaps Nipissing and accumulated because of the growth of in age ; and ( 4) in Plum Creek alluvial an alluvial fan farther downstream after deposits, of indeterminate post-Calumet age. Lake Chicago was lowered from its Calu­ met shoreline. The wood is only 1850 -+- A deposit of peaty debris, driftwood, 480 years old-younger than any glacial­ and a few ice-rafted bpulders underlies the lake stages of the Lake Michigan basin. sand and gravel of the Dyer spit, which The North Shore Channel sections itself can be no younger than latest Glen­ studied by Baker are no longer exposed. wood. The site of the deposit was exposed Baker reported peaty and woody material in early Glenwood time to waves from the of Bowmanville, Calumet, and Toleston open lake while a beach ridge was built on ages, but, until new excavations are made the landward side. Later growth of a bar­ on the floor of the bay, the age of these rier beach and of another spit (see p. 117) lake deposits cannot be determined by the made the site a protected bay. Into this radiocarbon method. quiet water, plant debris was floated by a The writer has correlated the Bowman­ littoral current that still later brought in ville low-water stage with the Two Creeks the sand and gravel of the spit. The or­ forest bed north of Manitowoc, Wis. Wood ganic material is indubitably of Glenwood and peat from the deposit have been found age. Carbon 14 determinations made by to be 11,400 -+- 350 years old, this figure two different laboratories have not yielded being an average of several samples.68 The the same age in years, but both agree that rise to the second-attained Calumet level the Dyer material is older than the Two occurred because of the Valders (Mankato) Creeks buried forest. advance, and a weak Calumet beach on the In excavations on the University of Chi­ southern portion of the Valders red till cago campll's, wood was found buried 14 sheet indicates that this lake level flooded feet deep in lake bottom sand below the back briefly when the Valders ice was be­ level of the Toleston beach. It seems prob­ ginning to retreat. The Calumet stage, able that this sand and the driftwood are of therefore, did not persist much later than Toleston or later age. Its age was found to 11,000 years ago. Niagara Falls, dating be 8,200 ± 480 years. from early Algonquin time, must be The driftwood log found under beach younger than this-younger even than the sand near Dolton was interpreted in Part wood found in the excavations on the I (p. 117) as probably Toleston in age. campus of the University of Chicago. But the wide belt of beach ridges here must Final retreat of Wisconsin ice from any include Algonquin deposits and perhaps in­ locality marks the beginning of that re- cludes Nipissing deposits. The log was 67Hough, J. L., Pleistocene chronolol!y of the Great under the lakeward edge of the sand belt. Lakes re,,ion : Office of Nani Re,earch, Project l'\R 018- 122, 1953. I ts age, 3469 230 years, seems by com­ 68fn an elaborate study of glacial-lake varves and ± their correl ative moraines in both North America and parison with the :-pecimen from the excava­ F.urone, Antevs (loc. cit.) holds that the Two Creeks depo

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Fw. 61.-Changes in level in the Great Lakes region in centimeters per century. Af ter Gutenberg, 1943. Arrows point in direction of uplift; lines of equal uplift from 10 to 80 cm. 132 GLACIAL HISTORY that the balsam fir (Abies ) was a promi­ region, his presence had little influence on nent member of the earliest forests that re­ the biological and geological regimen. The possessed the land in our region, and that early Indians exterminated no animal species it disappeared after something like 5000 to and introduced few if any plant species that 6000 years. The spruce ( Picea) was a con­ have since become established in nature. temporary of the fir and held its own for They made no alterations of the natural a somewhat longer time. Disappearance of drainage routes. They did very little that both genera was gradual and coincided with altered nature's rates of slope-wash erosion. a similarly gradual increase in oak · ( Quer­ Their only interest in mineral resources was cus ) and hickory ( Carya ). These changes to secure hard stones for tools and clay for were doubtless climatically determined. pottery. Cooper,81 reviewing a considerable liter­ White man's arrival was the signal for a ature on fossil pollen-grain stratigraphy of series of notable changes in the equilibrium. a larger area of glaciated North America, Streams have been dredged or dammed or finds spruce and fir reported from all the diverted. New waterways have been con­ lowest layers of postglacial peat, oak and structed and the drainage divide has been pine ( Pinus) in the middle layers, and so shifted that the Mississippi has gained spruce and fir again in the upper layers. and the St. Lawrence has lost nearly 1200 It is a record of a mid-postglacial warm, square miles of contributing territory. In­ dry time, followed by a return toward cool, dustrial and other wastes have polluted the moist conditions. larger streams and made great changes in Matthes,82 working with the records of their biota. Artificial draining has made alpine glaciers in the Cascades and Sierras, many wet areas arable and has lowered the believes that these glaciers completely dis­ water table. Energy taken from stream appeared in a mid-postglacial warm, dry in­ flow, at Lockport, has been transformed terval (comparable to that found by the into light and heat and mechanical work. botanists ), and were formed again with Every geological deposit of the region has the coming of cooler and more moist con­ yielded raw material for man's use. Soil ditions some 4000 years ago. Since glacial erosion has increased from clearing the shrinkage and retreat is now going on, the forests and breaking the prairie sod for climate is judged to be shifting again, in a agriculture, and unwise cultivation has in rhythmic fashion, toward another warm, many places unnecessarily damaged the soil. dry interval. Matthes calls the time of Many mammalian species have been forced regrowth of the Sierra and Cascade glaciers to abandon the country and far too many the "." It did not reach the undesirable plant species have entered. The extremes necessary to initiate regrowth of lake-shore regimen has been extensively al­ the continental ice sheets. tered with construction of protecting walls, The appearance of man in the local fauna dredging of sand from offshore shallows, is, for the Chicago region, an undated event. accumulation of "pocket" bathing beaches, Although evidence strongly suggests that he anrl construction of harbors. was a pre-,Visconsin arrival in North Some of man's changes have been par­ America, there are no indications that he ti:llly detrimental because of uninformed in­ inhabited Chicagoland before the present terference with, and manipulation of, climate and biota were well established. nature's forces. An understanding of the For many centuries after man entered the region's geological development should help S1Cooper, W. S.. Contributions of botanical science to guide man into wiser cooperation with to the knowledge of postglacial climates : Jour. Geo!., vol. 50, pp. 981-994. 1942. existing geological agencies and wiser utili­ 82Matthes, F. E., Recent variations of glaciers viewed in their relation to the Pleistocene ice age ; pp. 190-215 zation of those resources nature has been of Chao. 5, , vol. 9. Physics of the earth : 1'\ational Research Council. 1942. so long in accumulating. ILLINOIS STATE GEOLOGICAL SURVEY, BULLETIN 65, PART II 132 p., 61 figs., 1955