Photograph by Chicago Aeria ,Sun.1ey Company "Eastward lies the lake, as great a contrast with the city as night with day." STATE OF ILLINOIS HENRY HORNER, Go:'ernol' DEPARTMENT OF REGISTRATION AND EDUCATfON JOHN HALLIHAN, ]. Direclol'

DIVISION OF THE STATE GEO LOGICA L SURVEY M. M. LEIGHTON, Chief URBANA

B U L L I N N 65 E T 0 .

GEOLOGY OF THE CHICAGO REGION PART I-GENERAL

BY

J HARLEN BRETZ

PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS

URBANA, ILLINOIS

1939 STATE OF ILLINOIS HoN. HENRY HORNER, Governor DEPARTMENT OF REGISTRATION AND EDUCATION HoN. JoHN J. HALLIHAN, Director

BOARD OF NATURAL RESOURCES AND CONSERVATION HoN. JoHN J. HALLIHAN, Chairman EosoN S. BASTIN, Ph.D., Geology HENRY C. CowLEs, Ph.D., D.Sc., WILLIAM A. NOYES, Ph.D., LLD., Forestry Chem.D., D.Sc., Chemistry ARTHUR CuTTS WILLARD, D.Eng r., Loms R. HowsoN, C.E., Engineering LL.D., President of the University WILLIAM TRELEASE, D.Sc., LLD., Biology of ll!inois

STATE GEOLOGICA L SURVEY DIVISION Urbana M. M. LEIGHTON, Ph.D., Chief ENID TOWNLEY, M.S., Assistant to the Chief JANE TITCOMB, M.A., Geological Assistant

GEOLOGICAL RESOURCES GEOCHEMISTRY

Coal FRANK H. REED, Ph.D., Chief Chemist G. H. CADY, Ph.D., Senior Geologist w. F. BRADLEY, Ph.D. L. C. McCABE, Ph.D. G. c. FINGER, Ph.D. JAMES M. ScHOPF, Ph.D. HELEN F. AusTIN, B.S. EARLE F. TAYLOR, M.S. Fuels CHARLES c. BOLEY, M.S. Non-Fuels G. R. YOHE, Ph.D. CARL HARMAN, B.S. J. E. LAMAR, B.S. H. B. WILLMAN, Ph.D. Non-Fuels ROBERT M. GROGAN, M.S. Oil and Gas J. s. MACHIN, Ph.D. A. H. BELL, Ph.D. JAMES F. v ANECEK, M.S. L. CHALMER CooPER, M.S. Analytical G. v. COHEE, Ph.D. FREDERICK SQUIRES, B.S. 0. w. REES, Ph.D. CHARLES w. CARTER, Ph.D. GEORGE w. LAND, B.Ed. JAMES L. CARLTON, B.S. P. w. HENLINE, B.S. RoY B. RALSTON, B.A. MATHEW KALINOWSKI, B.S. //real and Engineering Geology ARNOLD J. VERAGUTH, M.S. GEORGE E. EKBLAW, Ph.D. RICHARD F. FISHER, B.A. MINERAL ECONOMICS Subsutface Geology L. E. WORKMAN, M.S. W. H. VosKuIL, Ph.D., Mineral Economist J. NORMAN PAYNE, Ph.D. GRACE N. OLIVER, A.B. ELWOOD ATHERTON, Ph.D. MERLYN B. BuHLE, M.S. EDUCATIONAL EXTENSION GORDON PRESCOTT, B.S. Stratigraphy and Paleontology DoN L. CARROLL, B.S. J. MARVIN WELLER, Ph.D. Petrography PUBLICATIONS AND RECORDS RALPH E. GRIM, Ph.D. GEORGE E. EKBLAW, Ph.D. RICHARDS A. ROWLAND, Ph.D. CHALMER L. COOPER, M.S. Physics DoROTHY RosE, B.S. R. J. PIERSOL, Ph.D. ALMA R. SWEENY, A.B. M. c. WATSON, Ph.D. M. FRANCES HARPER, M.S. DONALD 0. HOLLAND, M.S. MEREDITH M. CALKINS

Consultants: Ceramics, CULLEN WARNER PARMELEE, M.S., D.Sc., University of Illinois; Pleistocene Invertebrate Paleontology, FRANK CoLLINS BAKER, B.S., University of Illinois.

Topographic Mapping in Cooperation with the United States Geological Survey.

�2 (A4899-9-39) July 1, 1939 PREFATORY NOTE

Part I of this bulletin is intended for the use of schools and the layman. Part II will be more technical in nature and will include the details needed by geologists, engineers, and others interested in the scientific and economic aspects of the geology and mineral resources of the Chicago region. CONTENTS

PAGE Physical setting of greater Chicago. 11 Surveys of the region. 17 Today's geological changes in the Chicago region ..... 19 Weathering ... 19 Work of running water. 21 Palos Park ravines. 22 Maple Lake. 24 North Shore ravines. 26 A rock-walled valley ... 27 Plum Creek and Hart Ditch. 27 Piracy of Sawmill Creek.. 28 Erosion without valleys. 30 Constructional valleys. 31 Inherited valleys .. 31 Deposition by running water .. 31 Organic deposits ...... 32 Groundwater and its work. 34 Work of shore agencies. 37 Wind work...... 42 . Summary. 42 Unconsolidated materials and their topography. 43 Glacial origin of the materials. 43 Valparaiso moraine ...... ·t· ...... : ... 4S Lakes between the Valparaiso and Tinley moraines ... . 49 Tinley moraine...... so Glacial stream deposits...... so Kame-terraces. so Eskers... Sl Karnes... S2 Problem of the pre-Valparaiso valleys .. S2

Mapping of contacts ...... S3 Salt Creek and Flag Creek valleys .. S3 Region east of the Tinely moraine... 5S Lake Border morainic system .. 55 Des Plaines valley-train. 56 Chicago plain ...... 57 Conclusion. 59 Bedrock of the region ... 60 Introduction .. 60 Niagaran formation...... 60 Reefs and klintar. 61 Thorn ton reef. 63 Stony Tsland..... 65 Chicago Heights. 67 McCook ...... 67 Lake shore klintar. 67 Mi nor reef exposures .... 68

Jcin�...... 69 Fissures and fissure fillings. 70 Chert ..... 73 Fossils. 7S Minerals. 83 .... �' ..... General distribution and structure. 83 Well logs and their interpretation... 85

[7] PAGE Artesian wells...... 90 Topography of the bedrock surface...... 91 Geological history of Chicagoland...... 93 Cambrian period...... 94 Ordovician period...... 94 Silurian period...... 98 Post-Devonian pre-Pleistocene interval...... 98 . Pleistocene period...... 99 Niagara Falls as a geological clock...... 100 History of Lake Chicago...... 102 Glenwood stage...... 102 Calumet stage...... 107 Toleston stage...... 108 Later lake stages...... 110 Low-water stages ...... 115 . Recent changes of level in Lake Michigan...... 116 Life of the glacial lake stages...... 116 The coming of Man...... 118 Conclusion...... 118

ILLUSTRATIONS •

PLATE PAGE I. Glacial geology of Chicago and vicinity...... �,�� I I. Brachiopods...... 74 III. Gastropods...... 77 IV. Cephalopods.. 78 V. Trilobites ...... 79 VI. ' Sponge, corals, and bryozoa .. . 80 VII. Crinoids and crystoids ...... 81

FIGURE PAG E Frontispiece-"Eastward lies the lake, as great a contrast with the city as night with day" 1 "Like an unmown lawn of brown and gray spread out around the clustered structures of the

Loop"...... · ·.· · · · · · · · · · · · · · · · · · · · 12 2 North America as it would appear if depressed 600 feet 13 3 Chicago region drainage lines ...... 14 4 Normal drainage pattern in Jo Daviess County 15 5 Township grid system of the Chicago area... 17 6 Index map to topographic maps of Chicago and vicinity 18 7 Road cut along Southwest Highway at Worth showing soil profile. 20 E Typical "badland" erosion ...... 22 9 Map of ravines in the Palos Park region .. 23 10 Ravine developed by stream erosion in Palos Park. 24 11 A ravine developed in an abandoned roadway...... 24 12 Mays lake ...... 25 13 Basin of a former lake...... 25 14 Map of ravines in the North Shore district. 25 15 Profiles across the Highland Park moraine ...... 26 16 A small canyon eroded in thin-bedded limestone.. 26 [8] PAGE 17 Sketch map showing Plum Creek drainage changes ... 27 18 Hart Ditch, the new lower course of Plum Creek ... 28 19 Original lower portion of Plum Creek's valley .. 28 20 Map of Sawmill Creek ...... 29 21 Abandoned portion of Sawmill Creek valley. 30 22 McGinnes slough, near Orland Park .. 32 23 Muck and peat heaved by a highway fill .. 33 24 Diagram showing the position of the water-table. 34 25 Diagram showing conditions necessary for an artesian basin. 35 26 Wave-cut cliff near Lake Bluff. 36 27 Cross-section of a wave-cut cliff and its accompanying cut-and-built terrace ..... 38 28 Diagram illustrating the course of a particle on a beach when waves impinge diagonally upon the land...... 38 29 Groins and resultant beaches protecting the lake bluff along the North Shore. 39 30 Shoreline changes at the mouth of Chicago River...... 40

31 Map of Calumet River and its surroundings...... 41 32 Low dune ridges in Touhy Park...... 42

33 Diagrams showing relation of mantle rock and bedrock...... 43 34 Sharp contact of glacial drift mantle rock and planed-off bedrock in the Chicago region. 43 3S Striated boulders from the Chicago glacial drift...... 44 36 Sketch map showing the North American area covered by ice at t!ie,time of maximum glacia-

ti=...... ·························· 45 37 Lobate distribution of glacial moraines around the southern part of Lake Michigan ... 46 38 Cross-section railroad profiles across the Valparaiso and Tinley moraines 47 39 Cross-section profiles along highways across the Valparaiso and other moraines. 48 40 Profiles across Tinley moraine and some of its associated lake beds. 49 41 Kame-terrace knolls in the valley of Long Run. 51 42 Tiedtville esker. 51 43 Sketch map showing the relationship of Salt Creek, Flag Creek, and Des Plaines River. 54 44 Dipping beds of Niagaran limestone in Moulding-Brownell quarry at Thornton. 61 45 Dipping beds of Niagaran limestone in old quarry at Stony Island...... 61 46 Unstratified core of small reef overlain by dipping stratified rock. 62

47 Asphaltum oozing from a cavity in core-rock...... 62 48 Block diagram of the Thornton Reef...... 63

49 Sketch showing dislodged fragments of reef rock and a "baby" reef...... 65 50 Displaced fragment of reef rock...... 65

51 Map of Stony Island...... 66 52 A glacially smoothed and grooved surface of Niagaran limestone...... 68 53 Traces of two systems of joints...... 69 54 Vertical joints in the Niagaran limestone ...... 69 55 Solution of limestone is concentrated along joints. 70

56 Irregularly weathered surface developed by solution...... 70 57 An irregular fissure filled with brown shale...... 71 58 Shark teeth and limestone fragments in clay filling from a fissure in the Niagaran limestone. 71 59 A fragment of pisolitic (pea-like) limestone from fissure filling...... 71 60 Layers of white chert in the Niagaran limestone ...... 72 61 Cross-section of spheroidal chert nodule in a lime�tone fragment 73 62 Irregular chert nodules in the Niagaran limestone. 73 63 Restoration of a fossil crinoid... 82 64 Outcrop belt of the Niagaran formation in the Great Lakes region .. 84 65 Geological cross-section of lower Michigan and southern Ontario. 85 66 The Niagaran Interior Sea of North America...... 86 67 Relations of Niagaran formation in two wells in the Chicago area... 87 68 Map of northern Illinois showing the general distribution of various rock formations under

the glacial drift...... 88

69 Geological cross-section of northern Illinois...... 89 70 Geological cross-section of Boutheastern vVisconsin and northeastern Illinois ...... 90

[9] FIGURE PAGE

71 Map showing outcrop of Cambrian formations and St. Peter sandstone...... 91 72 Cross-bedding in Cambrian sandstone, Dells of Wisconsin River.. 94 73 Diagrammatic cross-section of LaSalle anticline along the north bluff of Illinois River. 95

74 Starved Rock ...... 96

75 Amphitheater in St. Peter sandstone at head of French Canyon ...... 97

76 The Niagaran escarpment between lakes Erie and Ontario...... 100

77 Diagram illustrating the conditions at Niagara Falls...... 101 78 Sketch map of Glenwood Island and associated features of the Glenwood stage of Lake Chi-

cago...... 102 79 Sketch map of LaGrange spit, Glenwood stage of Lake Chicago 103 80 Sketch map of Oak Park spit, Glenwood stage of Lake Chicago .. 104

81 Sketch map of Wilmette spit, Glenwood stage of Lake Chicago...... 104 82 Sketch map of Blue Island and associated features, various stages of Lake Chicago. 105 83 Wave-cut cliff of the Glenwood stage of Lake Chicago. 106

84 Dune on the west slope of Blue Island...... 106 85 Sketch map of Chicago region during the Glenwood stage of Lake Chicago. 108 86 Sketch map of Chicago region during the Calumet stage of Lake Chicago .. 108 .

87 Sketch map of the Chicago region during the Toleston stage of Lake Chicago . . 109 88 The Great Lakes region during the Toleston stage of Lake Chicago... .. 111 89 Lake Algonquin with three outlets ... 112

90 Nipissing Great Lakes ...... 113 91 Beachlets of post-Toleston lake stages between Hammond and Gary, Indiana ... 114

[10] GEOLOGY OF THE CHICAGO RFGION

PART I-GENERAL

J HARLEN BRETZ

PHYSICAL SETTIN G OF GREATER CHICAGO

UPWARD by express elevator, we zon is as primeval as the day white men first HOTstep out on the observation platform entered the region. Man has done his bit ofS the Tribune Tower. A clear sky and a to the lake, of course, but it is trifling. The wind off the lake gives maximum visibility. shores have been changed a little and a Half of our expansive horizon is the primi­ subsidiary outlet has been made, in part by tive lake, half is dominated by the works of reversing the sluggish river. The lake re­ man. North, west, and south, an irregu­ mains, however, the one unalterable prim­ lar checkerboard of buildings and streets itive feature of Chicagoland. reaches out farther than we can see. The In but one long lifetime, the second kings of the checkerboard, closely crowded greatest metropolis of the western hemi­ in the Loop district and along the river, sphere has grown up in the immense central make a city in themselves, an Arabian lowland of the continent. Some of the Nights city unlike anything in the Universe physical reasons for its location and growth a hundred years ago. The monotony of the are well known. It could not have de­ lower buildings is like an unmown lawn of veloped away from the lake ; it needed the brown and gray, spread out around the advantage of head-of-lake navigation and a clustered structures of the Loop (fig. 1). harbor ; it had to have a productive hinter­ The haze which limits the view westward land ; it required a suitable topography for is man-made also, the dust and smoke of this its spread and favorable conditions for the great site of human activity. were we blind growth of a great railroad center. Some and on this tower, we could hardly mistake factors were important in determining loca­ our location. The world had no sounds like tion and early growth ; others became more these a hundred years ago and our eyrie significant as the growth progressed. All had only the sounds of wind and waves. of them, in their turn, are only results of Nor are man's constructions all above the earlier causes. ground within our horizon. The feet of The unmatched history of Chicago's this steel-boned structure are planted on metropolitan development is therefore a bedrock, a fifth as far below street level as consequence of earlier history, even pre­ its capstone is above. I ts fellows stand like­ human history. We wish to look into that wise, their great weight carried on concrete pre-history. We shall read the story of the legs to bedrock. Basements, sub-basements, Great Lakes, of the prairie soil and subsoil, tunnels, innumerable conduits, all are vital of the hills and plains of the region, of the parts of the great city. Even if the entire bedrock which crops out here and there or structural aggregate above ground were is revealed in quarries, reached by caissons, swept away, the underground structures re·· and penetrated by wells. To do this, we maining would record its former greatness. must interpret a record unlike any written Eastward lies the lake, as great a con­ language. There is only one authentic trast with the city as night with day. A source-the geological features of Chicago­ smudge or so on the horizon, moving boats land. These we must observe, map and in­ inside. the curved dome that brings sky and terpret as the results of former conditions water together, the intake cribs a few miles and changes. The geology of this region is out-aside from these, this half of our hori- not a distinct separate unit in itself ; it is [ 11 ] l'-.l

"-;:: ::r:: '"'< (;".) ...... CJ :::... t-<

(/) � '-3 �

CJ�

Photograph by Chicago Aerial Survey Company Frc. 1.-"Like an unmown lawn of brown and gray spread out around the clustered structures of the Loop." PHYSICAL SETTING 13

This picture of great thin sheets of marine water ( epicontinental seas) spreading far into the interior of a continent is drawn for a purpose. Relatively slight changes of level in land or sea are competent to make great changes in the areas of both. Know­ ing in a general way that the earth has passed through many vicissitudes, we may ask here if this vast low interior, of which Chicagoland is a part, ever has experienced such a widespread flooding by the sea. The answer, given in advance of the evidence. is affirmative. It is not enough to say that Chicago might have been a seaport, had it been built some millions of years ago--it would have been a submarine city. The waves of shallow seas rolled completely across the region and the top of a modern FIG. 2.-North America as it would appear if skyscraper, had one stood here at that time, depressed 600 feet. The lightly shaded areas would not have reached the water surface. would then be shallow sea. (Reprinted by "There where the long street roars hath permission from "Historical Geology," by Schuchert and Dunbar, published by John been the stillness of the central sea." Wiley and Sons, Inc.) The record of those epicontinental seas is in the bedrock. The whole interior of intimately a part of the geology of the the country carries this record-layers piled Great Lakes country and of the upper on layers of sediments now consolidated to Mississippi Valley country. thicknesses of thousands of feet. In our Chicagoland is near the geographical region, these old stratified sea deposits are center of North America, in the midst of a almost entirely concealed beneath surface great plain that stretches from the Arctic materials, and our information about them Ocean to the Gulf of Mexico. Highlands comes from deep well borings. A maximum border the plain on the east (Appalachian of 2500 feet has been penetrated in the Mountains and plateaus) and on the west deepest boring in the region. At many (Rocky Mountains). A large embayment places in Illinois and neighboring states, of Arctic water (Hudson Bay) reaches these stratified rocks crop out. At Starved southward on the plain, shalloyvly sub­ Rock Park and Deer Park near LaSalle, merging an area nearly ten times as large Illinois, at White Pine State Park and along as the state of Illinois. Were Hudson Bay Rock River near Oregon, Illinois, at Turkey added to the north side of the Gulf of Run State Park near Marshall, Indiana, Mexico, it would reach northward from along the upper Wabash Valley in Indiana, New Orleans to Chicago, which would be in the Dells of Wisconsin River, and all only 600 feet above it, the great Loop along the upper Mississippi Valley, there towers rising as high again. Or in other are good showings of these old deposits. words, if the great central plain of the Most of the mineral industries within 200 United States sank 600 feet (or if sea-level miles of Chicago are based on them, with rose that amount), another shallow Hudson mines and quarries exhibiting the stratified Bay would be formed on it (fig. 2). Av­ erage oceanic depth is between 12,000 and character of these former sands, muds, lime, 13,000 feet, about 2)/:2 miles. Hudson Bay's and peat, now changed to sandstone, shale, greatest depth is 600 feet and its average is limestone, and coal. 420 feet, one-thirtieth of the average ocean Thus the broad plain country in which depth. The new Hudson Bay we imagined Chicagoland lies is a great interior basin, would be very similar. The ordinary map now undergoing erosion but having been tells us nothing of a very significant thing­ for ages beneath shallow seas, some of which the depth of the water. reached completely across the continent. 14 PHYSICAL SETTING

LAKE MICHIGAN

I

� 6 7MILES '\ SCALE

FIG. 3.-Chicago region drainage lines. Note the parallelism of many streams to the lake and the large areas that are undrained. Compare with Figure 4. PHYSICAL SETTING 15

FIG. 4.-Normal drainage pattern in Jo Daviess County, northwestern Illinois. The streams are uniformly distributed, the smaller streams converge towarrl larger streams, and there are neither lakes nor large undrained areas. 16 PHYSICAL SETTING

Coal, though a stratified deposit, is not of of the United States. The divide between marine origin, and we alter our picture a these two systems is a major water-parting, bit when considering it. Vast lowland though it is inconspicuous and hardly swamps, lying close to sea-level, are visual­ seems to deserve the name of continental ized. Limestone beds between the coal divide. It lies subparallel to the shore of seams record encroachment of marine the lake, not more than five miles distant waters which destroyed the swamps repeat­ in the latitude of Fort Sheridan and Lake edly and were as often withdrawn and re­ Forest· but at a distance increasing to 20 placed by swamps again during this time. miles south of Hammond, Indiana. Today we are a thousand miles from the Before man began to tamper with na­ nearest sea and 600 to 800 feet above sea­ ture's drainage ways here, almost all the level. No notable deposition of any kind is St. Lawrence drainage, from Lake Forest occurring in the vast plain, and no marine to Hammond, was brought together into deposition at all. Instead, the former de­ two streams before entering the lake­ posits are being destroyed, and the debris Chicago River with four named headwater is being carried away by streams to make portions, and Calumet River with half a new stratified deposits, either in Lake dozen named headwaters. These streams Michigan or in the Gulf of Mexico. The are curiously parallel to the lake shore surface of the plain is being etched out in (fig. 3). In the southern part of the area, tree-like patterns of main river valleys and several streams flow directly toward the their branching tributaries. It is this etch­ lake but are intercepted by Calumet River, ing of valleys by stream work that has and their waters are carried parallel to the exposed the bedrock, the old marine deposits, shore for many miles before entering the in the state parks and river valleys just lake. Of the streams flovving to the Missis­ listed. As valleys are deepened by the erod­ ing streams, the hills between them become sippi and the Gulf, the upper part of the relatively higher, more tributary valleys DesPlaines possesses the same parallelism develop, and the land surface becomes with the shore line, although when it turns rougher. In the Chicago region this work it flows away from the lake instead of to­ has only begun and there is much more for ward it. Salt Creek is similarly parallel. the streams to do than they have yet ac­ Some streams flowing toward the lake are complished. The whole sequence of erosion­ intercepted by the DesPlaines, and their al changes is very, very slow. One's life­ waters are carried off to the Mississippi. time is far too short a measure. The life­ This parallel drainage pattern, as shown in time of a nation is too short. The history figure 3, is quite unlike the pattern created of the human race on this planet is short, by normal valley development (fig. 4). The compared with these changes. Through the larger streams of our region almost all whole story of geological change outlined, found pre-existing lowlands in which to time beyond our experience, almost beyond flow between pre-existing higher tracts. our comprehension, is an essential factor. Though streams have done some work here The Chicago region is not richly endowed and are still working, they have modified with streamways. Many square miles have but little an inherited topography that was no drainage courses at all. But stream not of stream origin. The parallelism of water which does flow off the Chicago area valleys and divides with the lake shore, ab­ goes in two nearly opposite directions to normal for a stream pattern, is perfectly two great drainage systems of the continent. natural when the mode of origin of these We are in a headwaters region where every features is explained. The broad low inter­ stream can be traced to a source in or very stream ridges were built up to stand higher near the metropolitan area. All streams than their surroundings, some by glacial ice entering the lake belong to the St. Lawrence and others by lake waves and shore currents. River system. Their waters reach the At­ These agents habitually contruct ridges of lantic Ocean north of the United States. their deposits and almost invariably leave Streams flowing to the Mississippi River, other tokens of their presence. A wealth like the DesPlaines, the DuPage and, a of evidence in support of this interpretation little farther away, the Fox and the Kanka­ of Chicagoland's parallel streams and di­ kee rivers, drain to the gulf of Mexico south vides is submitted in later chapters. SURVEYS OF THE REGION 17

SURVEYS OF THE REGION The sparse aboriginal population, found here by the early explorers, held the region chiefly for hunting. Metes and bounds of land were of little significance to them. In the wake of the explorers finally came men who stayed, who built habitations, culti­ vated the soil, dug ditches, and built roads, harbors, canals, and railroads. Land meas­ urement and accurate boundary locations became a prime requisite. Squatter's meth­ ods of demarking land units were inade­ quate and the Federal Government's rec­ tangular grid pattern of townships and sections was laid out, a little more than a hundred years ago. The public domain of the young nation was surveyed in various large parcels as demands arose at different times. Settle­ ment of Illinois progressed northward from the Ohio and Wabash waterways. The first Federal land survey in the state was made long before the Blackhawk \Var had ex· tinguished Indian claims west of the Illinois River. That area between the Illinois and Mississippi rivers was surveyed later and from a different base line and meridian. The Third Principal Meridian of the Federal land survey lies in the center of Illinois, running the entire length of the state. Rockford, Bloomington, Centralia, and Cairo are almost on the line. The base line selected was a parallel of latitude lying a little south of Centralia and East St. Louis. The rectangular pattern of town­ ships, each with 36 square miles, was num­ Fie. 5.-Township grid system of the Chicago bered from the intersection of these lines. area covered by this report. Thus in the Chicago region, which is north and east of this intersection, the townships and beyond the region. Rogers Avenue are numbered from T. 35 N. ( 35th tier, marks the east end of this line. The other east-west row of townships north of the line is nearly parallel with and twenty miles base line) to T. 44 N ., and from R. 11 E. south of the first. It begins near the mouth (11th range, north-south row of townships of Calumet River and is marked by offsets east of the principal meridian) to R. 14 E. in many roads crossing it. Both lines bear (fig. 5). That part of Indiana on the maps the name "Old Indian Boundary." They of this report has different range numbers mark a strip of territory ceded in 1816 by since it was surveyed from the Second Prin­ the Sacs and Foxes when Fort Dearborn cipal Meridian, located in that state. Errors was re-established, four years after the his­ in the two surveys show in the failure of toric massacre. This gave the United States the two tiers of townships to coincide along possession of a strip of land extending as the state line. far west as Ottawa and including most of There are two surveyed lines in the Chi­ the present site of Chicago. It was intended cago region, however, that are older than for protection of the Chicago portage and any township and section lines. One ex­ the canal route already proposed to connect tends from the lake shore near the Evans­ the St. Lawrence and Mississippi navigable ton-Chicago boundary southwestward across waters. The township and section survey 18 SURVEYS OF THE REGION

was made later and when this ceded tract a ° e 87 45' e7''30' was subdivided the section lines failed to 0 42°15•,.----..,.--,----,------;,---- 42° 5' meet on the two sides of the southern 1 boundary. The consequent road offsets v!f �� probably will always record that old survey l LAKE CO line. -cooK. co. The next Federal survey of the Chicago EVANSTON area, begun in 1889 and completed a few years later, was made by the United States Geological Survey. In addition to the con­ ventional data of land-lines, drainage, and culture, the maps showed the topography of the region by means of contours. Ac­ curate triangulation and leveling, carried across from the Atlantic seaboard, gave the necessary control. Following the procedure of the United States Geological Survey, the boundaries used were longitude and latitude lines, none of them coinciding with state, county, township, or section lines. Six quadrangles were mapped, each 15 minutes of latitude in length and 15 minutes of longitude wide. The region covered by the maps extended from Lake Forest on the north to Chicago Heights on the south, a distance of 53 miles, and from a meridian 1 Yz miles east of the Illinois-Indiana line to the longitude of Lemont, about 26 miles to the west. The maps were printed on a scale of an inch to the mile and the con­ 4 tours on five of them were drawn at vertical 4 30 0 1 1030, 1 1 BRISBANE FRANKF�RT STEGER OYER intervals of 10 feet. The remaining map, e ______I_ e1 5•______j_87° a 0 ° coox. _19?.:-__ 0' which included the flattest and most densely 4 3 built up region, had 5-foot contour inter­ FIG. 6.-Index map to topographic maps of vals. In 1898 the U. S. Geological Survey Chicago and vicinity. completed the geological mapping of the four southern quadrangles, publishing it as the drainage, topography, and geology was the Chicago Folio.1 Geology was shown by a crymg one. overprinting patterns and colors on the The new survey was begun in 1925, the contour maps. United States Geological Survey and thr For nearly forty years this folio was the Illinois State Geological Survey cooperat­ chief source book of geological information ing. A 5-foot contour interval was adopted, regarding the region. During this time, and the larger scale of one inch to 2,000 Chicago grew from one and a half million feet. Map sheets of the same size therefore to three and a half million, and its suburban covered considerably smaller areas. Each of towns kept pace. The era of hard roads the six original quadrangles was subdivided came, and more grading was done through­ into four but because the lake occupies large out the region than ever before. Swamps areas of two of the original maps, the total and lakes were drained, ditches and canals number of new quadrangles is twenty in­ were dug, and the lake shore was altered. stead of twenty-four (fig. 6). The north­ The cultural changes were so great that ern portions of four other quadrangles, the old maps, long out of print, would have lying immediately south of the group above been useless if reprinted. The need for new described, were also surveyed in order that maps which would show more accurately all of that part of Cook County should be included. Approximately 1,100 square miles !Alden, W. C., U. S. Geo!. Survey Geo!. Atlas, Chicago of territory is included in these new maps. folio (No. 81), 1902. WEA THERING 19

Some data were supplied by the Chicago The Illinois State Geological Survey un­ Department of Public Works and Sewer dertook in 1930 to re-map the geology of Department, by the Cook County Highway fifteen of the new quad�angles and to make Department and Map Department, by the the first geological maps of five new quad­ rangles to the north and> he portions of Sanitary District, and by the Chief Engi­ ) neers of each railroad in the region. The four to the south. This",;tonsumed three Army Air Corps made vertical airplane consecutive summers of Held· work. The photographs of the entire area. This new results are presented briefly in this volume. mapping was completed in 1927 and pub­ The work was placed ,in the charge of the lication of maps followed as soon as possible, present author who was ably assisted by George H. Otto and Edward H. Stevens. providing the metropolitan district with as fine a group of topographic maps as has ever 2An interesting account of this survey is found in the ] ournal of the Western Society of Engineers, Vol . 33, No. 1, been made.2 1-32, 1928. pp.

TODAY'S GEOLOGICAL CHANGES IN THE CHICAGO REGION No one has ever found an authentic in­ basal part is the original color. The rusty scription on a rock ledge recording its origin colors of the upper part of the section are, in such and such a vear B. C. Nature's precisely as the adjective implies, the prod­ structures carry no c�rnerstone dates. Yet uct of actual rusting in the material. In­ geologists constantly ask us to think in completely oxidized compounds containing terms of a hundred thousand, five hundred iron have yielded to the attack of water thousand, a million years. These figures and air, m�st of the change occuring near­ must be understood to be approximations, est the surface where exposure is greatest. indicating only the order of magnitude of The black top soil contains added carbon time in earth history, and not precisely from plant debris. measured intervals. But the geology of a Another important change in the upper region is no more a thing of the past than few feet of the cut, unrevealed by color are its human activities. For both, there differences, is readily shown by a simple is a recorded past and a living present, and chemical test. A few drops of dilute hydro­ for both these are intimately related. chloric acid poured on the lower part of the

.\i\TEATHERING slope produces a vigorous foaming or effer­ vescence. Calcium carbonate, the chief con­ Drive out of the city along some ne·w stituent of limestone, is breaking down and highway. Somewhere in any few miles the yielding carbon dioxide gas to make the highway grade has been cut into the brow foam. But in the upper two feet or so of of a hill. The cut need be only 4 or 5 feet the cut, where the rusty colors are strongest, deep to show what we are looking for, a there will be no response to the acid because color contrast between the upper and lower calcium carbonate is lacking here. Closer parts of the cut bank (fig. 7) . The surface inspection of a clean new cut may show material is generally dark brownish to black. irregular gray seams in the upper part of This is the true soil, the cultivated horizon, the light brownish zone just below the the sustainer of most food plants. Below darkest part of the rusty zone. Foaming the few inches of soil is a yellowish to rusty under acid on these seams will be more reddish zone 2 or 3 feet thick, conforming than vigorous, it will be violent. like the dark soil to the undulations of the surface. Below this, probably extending to Calcium carbonate is slowly soluble in the bottom of the cut, the material is lighter rain-water and water that percolated down brown to brownish-gray in color with some through decaying organic matter in the top irregular gray seams. If the cut is 10 feet soil. For centuries this slow process has or more in depth, the lowest part exposed been removing the "lime" and carrying it is generally gray or bluish gray, especially downward. At the zone of the gray seams when wet. The bluish-gray color of the the process has been reversed in part and 20 TODAY'S GEOLOGICAL CHANGES

FIG. 7.-Road cut along Southwest Highway at Worth showing soil profile typical of the Chicago region. The uppermost zone of a few inches is ash-colored (forest soil) and has lost its lime and most of its iron. The underlying dark zone is reddish colored owing to a concen­ tration of iron oxide. Below the rusty iron oxide zone is gray unweathered glacial till in about the same condition as at the time of its deposition. some of the mineral has been redeposited. Thus all surficial rock material is suffer­ The rest of it has gone on with the down­ ing destructive alteration by several chemi­ ward percolating water and has been en­ cal and mechanical means. The sum of all tirely removed by the escaping water. these changes is called weathering and the Leaching and oxidation are the two most product is an oxidized, leached, hydrated, conspicuous changes wrought by water and and finely comminuted material, commonly air in rock near the surface. (The un­ termed residual soil. indurated material in the highway cut is The making of a residual soil mantle rock, even though it is unconsolidated. ) from unweathered rock is much more com­ If there are boulders or cobbles in the plex than outlined above, too complex to upper part of the cut, they may show a consider in detail here. It is a series of crumbling exterior, a tendency to fracture chemical and physical changes, some occur­ more readily in the outer part, perhaps ring simultaneously, others in a definite se­ a fracturing and crumbling of their entire quence, some conditioned by the character mass. Often this fragmentation is due to of the original material, others by the char­ water entering into chemical combination acter of the climate. The soil has a begin­ with the rock material. This third process, ning, it grows through an infancy and a or hydration, increases the volume of the youth to a maturity as the thickening soil rock minerals and the resulting expansion mantle becomes a protection against the produces stresses that may finally cause attack of weathering. All changes begin at disruption. Once cracks exist in the boulder, the surface and gradually extend down­ water may freeze in them or plant-roots ward. Oxidation proceeds more rapidly than grow in them, both aiding fragmentation. leaching. Thus the zone of brownish rusty WORK OF RUNNING WATER 21 earth in our road cut is thicker than the of rolling higher country beyond the limits zone which gives no response to acid. of the plain to find the highway cuts, almost Chemical decomposition of silicate minerals any one of which, if ungrassed, will show is slower than either oxidation or leaching. the material described. This hill land is In Chicagoland it has hardly begun, and essentially built up of the unconsolidated we have therefore a young soil profile. In material deposited on and almost completely other parts of Illinois, weathering has been burying the bedrock. There is a large pro­ longer at work and there both the oxidized portion of unweathered local bedrock debris and leached zones are thicker, and the in it but there is also much material from slowest change of all-complete chemical beneath the lake and some which has come decomposition into a colloidal clay-shows even from Canadian territory. The deeply in the upper part of the sections.1 Three scratched pebbles, cobbles, and boulders in waves of alteration, which have progressed it indicate a method of transportation un­ downward at three different rates, are familiar to most of us. Almost complete therefore spaced out in the mature soil absence of stratification tells of a method profile. Our region's youthful soil profile of deposition quite different from that which shows clearly only the two more rapid ones. made the well-stratified bedrock beneath. The Chicago region possesses no true Anticipating a more ample discussion, let residual soil as yet ; what we have examined us now accept this thick unweathered is only an initial stage in its development. blanket of rock debris above the limestone Time, an essential item, has been too brief foundation as a glacial deposit, the ice-sheet since the weathering started. In other which left it having spread southward into words, the material exposed in the cut has this region from Canada. Climatic condi­ lain out-of-doors only a relatively short tions then differed sufficiently from those while, as geological changes go. of the present to allow such an episode. Most land is covered with residual soil The deposit is henceforth to be called glacial from the weathering of consolidated rocks, drift. The ice-sheet ground most of the or bedrock. In our region, as over much of drift so fine that it may be termed rock the northern United States, the weathering fiour. Larger fragments which escaped com­ processes are attacking an unconsolidated plete reduction carry marks of the abrasion deposit which overlies and protects the bed­ they suffered. Coarse and fine, all mixed rock, which contains debris from the bed­ together, were left on the final melting of rock, yet which is essentially fresh rock the ice, mechanically changed but chemi­ material and is therefore not a product of cally like the parent rock. Thus the glacial weathering. Because of the slight amount drift is fresh, and thus the slight amount of of weathering already accomplished, the de­ position of the unconsolidated material must weathering on its surface is evidence that have been geologically recent. it was deposited in geologically recent times. No directions for finding the highway WORK OF RUNNING WATER cut were given except that one drive out of In the few millenia since the glacial drift the city. The city lies on a plain along the was piled on top of the bedrock, rain has If lake but does not completely cover it. fallen on its somewhat hummocky surface, one drives southward, he will find the plain has accumulated in closed hollows to make extending as far as Dyer, Chicago Heights, Homewood, Oak Forest, and Palos Park. lakes and swamps, or has flowed off free­ If he goes westward, he will find the plain draining slopes to become concentrated as as far as Justice Park, LaGrange, and Hill­ streams. Rain also has soaked into the drift side, the towns of Hinsdale and Elmhurst and kept it saturated to within a few tens being on the higher rolling country beyond of feet of the top. Winds have whipped its limits. Northwestward, the plain has a across the surface. In the northern part very irregular boundary but northward it of the area, where the hill lands of glacial is recognizable along the lake as far as drift extend eastward to the lake, waves Winnetka. One must drive into the belt and shore currents have operated on it. All these agencies have modified the original 'Leighton. M. M. and MacClintock, Paul, Weathered deposit, in ways which, conspicuous or not, zones of the drift sheets of Illinois: Jour, Geo!., vol. 38, . 28-53, 1930. are significant. pp. 22 TODAY'S GEOLOGICAL CHANGES

Most rock is consolidated and running water alone is relatively ineffective in wear­ ing it away, but a stream of water rolling fragments of rock along with it or carrying sand or silt in suspension, is an effective agent of mechanical wear and so will deepen and widen its channel, even in rock. Rain­ wash crossing soil-covered surfaces on its way to a stream brings the debris for tools. In so doing, it removes that much of the soil. When brought to a stream by rain­ wash, the soil detritus is carried away as on a belt conveyor. Continued weathering replenishes the lost soil, and continued rain­ wash in turn removes the replacement. On FIG. 8.-Typical "badland" erosion developed on steep slopes the bedrock may retain no soil spoil heaps of glacial till along the Chicago cover at all, but generally in natural situ­ drainage canal south of Cicero (Berwyn quadrangle ). ations weathering can maintain a soil blanket of debris despite constant surface removal. relatively gentle slopes and its cover of The surficial zone of disintegration is vegetation. The effect of rainwash and ever migrating downward as material is rivulet erosion on steep unvegetated slopes taken away and thus the hills between the is strikingly shown on the spoil heaps piled streams are lowered. up alongside the Sanitary Canal where it Man, however, upsets this balance of was excavated in glacial drift. This erosion nature. His food comes largely from the has occurred in less than 40 years (fig. 8) . soil, most of it by the sweat of the plow­ Other badly eroded areas are those laid bare man's brow. Agriculture absolutely de­ by excavation for fill material for the new mands interference with nature's balanced highways. soil-making and soil-destroying forces and Prairie sod or forest growth originally rarely is that interference other than inimi­ covered the entire region and gave a large cal. Man is the greatest destroyer of the measure of protection from the attack of soil mantle. He may return, in fertilizers, running water. But in some tracts the the plant food that he removed by cropping, steepness of the original slopes more than but he cannot return the soil itself after his offsets this factor and many ravine valleys careless cultivation has allowed, even in­ have been eroded. Especially marked are vited, its removal by rainwash and gullying. the ravines tributary to Lake Michigan He cannot return soil blown away by the north of Winnetka (Highland Park quad­ wind after he has destroyed the protective rangle) and those tributary to Sag Valley prairie sod of sub-humid regions. Only by and Des Plaines Valley west of the longi­ an intelligent recognition of the usually in­ tude of Willow Springs (Sag Bridge and conspicuous damage that his cultivation has Palos Park quadrangles). In both areas, done year after year, and a thorough under­ the run-off waters have relatively high standing of how he has done the damage, gradients, descending a hundred feet or will he be able to conserve this most vital so in a mile or less, so that the velocity of resource, the arable soil. 2 flow has more than compensated for small Most consolidated rock goes through the volume. Stream erosion is better illustrated weathering mill before it is ready for trans­ in these small valleys than along the rivers portation, but in our region preparation by of the reg10n. weathering is unnecessary before eros10n,_ because the drift has never become con­ PALOS PARK RAVINES solidated and the impact and friction of The ravines in Palos Park (fig. 9) are running water alone will erode it. Its chief easily accessible and show valley-making protection from the attack of run-off is its in rapid progress. The ski slide there is on the brink of the original steep slope, 2Bennett, H. H., The problem of soil erosion: Assoc. Am. Geographers Annals. vol. 21, pp. 147-170, 1931. about a hundred feet above the Sag Channel Soil erosion and its prevention in "Our Natural Resources and their Conservation". Chap. 4. Wiley and Sons, 1936. flat. U ngullied at first, this slope has now �a � � a � ?::I c:::: <

c;j� � l:'>1..., �

Y2 I Mile

Fie. 9.-Map of ravines in the Palos Park region. The tract marked with X was formerly a lakelet or swamp which has been drained by overflow and by headward erosion of the ravine to the northeast. Note swampy tracts yet to be drained by headward lengthening of ravines. (Part of Palos Park topographic map.)

N w 24 TODAY'S GEOLOGICAL CHANGES

FIG. 10.--,--Ravine developed by stream erosion FIG. 11.-A ravine 20 feet deep that within a in Palos Park. year developed in an abandoned roadway. (Palos Park Forest Preserve, near Swallow been gashed with numerous short ravines Cliffs, Palos Park quadrangle.) which carry water only after thaws or heavy rains (fig. 10). How much forest and undulatory, as is that of almost all glacially grass retard this work was strikingly shown deposited material, and numerous closed here a few years ago. Gullying began in basins contain swamps, lakelets, or standing a farm road down the slope of the first water after rains (fig. 12). Most of these ravine east of the ski slide. The roadway basins do not overflow, but lose their water was abandoned but nothing was done to by evaporation and by percolation into the protect the slope and Nature was unable drift. An overflowing basin discharges the to spread her defensive cover in time. Ero­ concentrated run-off from its entire drain­ sion twenty feet deep occurred within a age area across the lowest place in its rim. year where the road had been (fig. 11). Ravine lengthening, accomplished by water The Forest Preserve administration, taking entering the head of the ravine from the over the property at this time, dumped unscarred upland, follows back toward the brush and boulders in the young ravine and greater supply. Thus ravines tend to head also attempted to prevent run-off from the toward basins which overflow. In this way upper slope from entering it, but the scar the western arm of the ravine east of the will remain for many years to come. ski slide has lengthened headward until it Deepening and widening of these ravines has cut through the low rim of an upland is evidenced after every heavy rain. An­ basin and drained it (fig. 13). A flat of other change, less conspicuous but fully as mucky soil records the former bottom of significant, is their lengthening. The pre­ a swamp or lake. cipitation that falls on a considerable up­ MAPLE LAKE land tract south of the Palos Park ravines drains into them, either as direct run-off Another instance of basin drainage by or as slowly percolating groundwater. As headward lengthening of ravines is on yet, this upland bears almost no marks of l.VIount Forest Island, the upland area lying erosion by running water. The surface is between the Sag and DesPlaines valleys WORK OF RUNNING WA TER 25

FIG. 12.-Mays Lake, one of the small lakes that FIG. 13.-The basin of a former lake (fore­ occupy depressions on the uneven surface of ground ) which was drained by the normal the glaci al drift (Hinsdale quadrangle ). development of a ravine. The effect is that of a basin, the rim of which has been notched (background). McCarthy Road, near Bell Road crossing (Sag Bridge quadrangle ).

FIG. 14.-Map of ravines in the North Shore District showing their position on the northeast side of the Highland Park moraine that runs through Highwood and Highland Park. (Part of Highland Park topographic map.) 26 TODAY'S GEOLOGICAL CHANGES

(Sag Bridge and Palos Park quadrangles). the lake bluff which was cut by the waves The drainage occurred at the corner of 95th of Lake Michigan after the ridge of drift Street and Wolf Road. Two ravines once (the Highland Park moraine) was built. notched the lower rim of the basin. The Here are the steepest slopes of the Chicago Forest Preserve administration has blocked area, therefore the steepest gradients for them by concrete dams, restoring the basin run-off, and hence the greatest changes by which now, filled with water, constitutes stream erosion. Tuma or Maple Lake, a popular bathing Some of the North Shore ravines show place in the Preserve. (Compare fig. 13.) an interesting tributary system with the tree-like or dendritic pattern already re­ NORTH SHORE RAVINES ferred to. As they lengthen and increase in The most and longest ravines in the Chi­ number, the eastern slope of the drift ridge cago area are in the "North Shore" district will become more dissected in future cen­ which extends from Winnetka northward turies and the remnants of the original along the lake. Sheridan Road crosses about slopes will be reduced. A struggle for exist­ twenty of them south of Lake Forest. The ence is going on here among the ravines, the competition being for water - supply. Ravine nature is somewhat like human na­ ture-the more it gets, the more it reaches out for, with scant respect for consequent loss to others. Thus many short ravines entering the lake never can extend back to the divide-the spreading branches of the longer, more successful ravines have already captured the run-off from the uplands which formerly went to the losers.

------�---RAVllJIA-

------�------.....__5',Q,, <( COUNTRHLUB

-- - •• _

- -=---'f-------J"•LE \ - --·'Z_���--� 'J------.. Frc. 15.-Profiles across the Highland Park mo­ raine from Skokie Valley on the west to Lake Michigan on the east at localities indi­ cated. The dashed lines extending beyond the lake bluff indicate the approximate original eastward slope.

district, however, is so largely built up, fenced, and posted against trespass that one can see but little topography. The topo­ graphic map (Highland Park quadrangle) shows that all of these ravines lie on the east slope (fig. 14) of a long ridge of the constructional topography (glacial drift de­ posit) that is parallel to the lake shore. The Chicago and North Western Rail­ road and the North Shore Electric Rail­ road follow the divide summit. Although the west side, descending to the Skokie Valley, had steeper original slopes (fig. 15), FIG. 16.-A small canyon eroded in thin-bedded limestone. The canyon is crossed by lllth it has no ravines. This ravine system of the Street half a mile east of Sag Bridge (Sag North Shore district is a consequence of Bridge quadrangle ). WORK OF RUNNING WA TER 27

A ROCK-WALLED VALLEY has low ledges of limestone on either side Very few streams in the Chicago region but they are not steep walled. The river have encountered bedrock in deepening their either has eroded 5 to 8 feet in rock here valleys, and only one has eroded into it or has reexcavated a channel-like low place deeply enough to have limestone walls. It in the surface of the limestone beneath the is an unnamed tributary on the south side drift. Sawmill Creek (Sag Bridge quad­ of Sag Channel, crossed by 111th Street rangle) flows on limestone for nearly 1,300 about half a mile east of Sag Bridge (fig. feet in its lower course and in one place has 16). The stream is hardly two miles long cut 5 feet deep into it. and only the last 1,10 0 feet of its valley PLUM CREEK AND HART DITCH length is cut in rock. Though only 15 feet deep, it is a canyon in form, its walls verti­ The most remarkable instance of rapid cal and its width no greater than its depth. stream erosion in the area is Hart Ditch, The stream entering Sag Channel discov­ the lower course of Plum Creek (Calumet ered a ledge of rock, shallowly buried be­ City quadrangle). When this part of Indi­ neath the drift, over which it descended ana was first settled, and indeed within the steeply to the main valley bottom. The memory of living man, the fertile plain high gradient thus provided has been re­ north of Dyer, Indiana, was a swamp sponsible for the development of the little throughout the year, a duck-hunter's para­ canyon. The limestone is thin-bedded and dise in season. Plum Creek entered this breaks into pieces small enough to be carried swamp from the south, about three-fourths away by the stream when it is in flood. of a mile north of Dyer. Discharge from Deepening therefore has been more rapid the swamp was westward through North than it would have been if thick-bedded Creek, thence northward through Thorn limestone had been encountered. Creek to Calumet River. By stream course Other larger streams of the region flow it was thirteen and a half miles from the over bedrock in places but none has eroded swamp to the river, and the fall in that into it to a comparable extent. Desplaines distance was a little more than 30 feet River east of Lyons (Berwyn quadrangle) (fig. 17). About 1850, Mr. Aaron Hart,

Fie. 17.-Sketch map showing Plum Creek drainage changes. 28 TODAY'S GEOLOGICAL CHANGES

FIG. Fie. 18.-Hart Ditch, the new lower course of 19.-0riginal lower portion of Plum Creek's Plum Creek. This valley has been eroded in valley, abandoned when intercepted by Hart about 80 years. Comp are with figure 19. Ditch. The man is standing in the bottom of the old stream-bed. owner of the swamp, dug a ditch north from it through a sand ridge (on which eroded. There would have been a shallow stands the town of Highland, Indiana) to valley, three or four feet deep, like the Calumet River, shortening the discharge abandoned course of Plum Creek in the route to about a mile and a half and pro­ southeastern corner of the Calumet City viding a fall of nearly 30 feet in that dis­ quadrangle (fig. 19). tance. The swamp water, formerly with PIRACY OF SAWM ILL CREEK a discharge gradient of less than 2Vz feet to the mile, thus obtained a gradient of This shifting of stream courses to cross nearly 20 feet to the mile. Nature's prin­ a former water-parting, thus obtaining a ciples worked with Mr. Hart. The new higher gradient and a shorter course, may high-gradient ditch route was rapidly deep­ occur without man's intervention. An in­ ened by erosion and the head of the ditch, stance of the kind is afforded by Sawmill now become a ravine head, was extended Creek (Sag Bridge quadrangle), a tribu­ southward into the swamp. Guided by tary from the north entering DesPlaines shallow ditching, it lengthened completely River nearly two miles southwest of Byrne­ across the swamp until it reached the place ville (fig. 20) . The stream is unnamed on where Plum Creek entered and thereupon the government map but by some is called became the uninterrupted course of thr Warden's Creek. It has eroded a beauti­ creek (fig. 18). The new gradient had been ful little valley about 50 feet in maximum decreased by half through this lengthening depth along the last half mile of its course across the flat swamp but still was adequate before entering the broad river valley. The to cause rapid deepening ; a deepening which creek valley has a bottom width of a few has now extended up Plum Creek south of hundred feet, produced by lateral shifting Dyer for several miles. The ditch, reported of the stream and consequent undercutting to have been but a plow furrow originally of its valley walls. It is more advanced in (except through the sand ridge), is today development than are the ravines already a ravine 15 to 20 feet deep and 4Vz miles discussed. Figure 20 shows another flat­ long. Unlike any other ravine of the region, floored valley, semi-circular in ground plan, there is no slope to the surface across which immediately to the west, entering the Des­ it flows. The gradient responsible for its Plaines Valley 2,000 feet farther west and growth all lay north of the sand ridge, be­ heading (here is the significant item) in tween that ridge and the river, and arti­ the west wall of Sawmill Creek valley but ficial piercing of this divide was essential about 30 feet above that stream. Except to its development. If man had not altered for a tributary which enters and uses the the drainage, the head of North Creek, the west part of this semi-circular valley, it is outlet of the swamp, presumably would dry. Yet on the dry floor are two small have been extended eastward as centuries crescentic swamps such as are formed when passed and the standing water would have streams abandon meander loops (fig. 21). disappeared in time. But no deep trench And beneath the alluvial soil of its floor like Hart Ditch ever could have been is a deposit of coarse cobbly gravel, 6 feet WORK OF RUNNING WA TER 29

Fie. 20.-Map of Sawmill Creek. The dashed line shows the course form­ erly followed by Sawmill Creek before "stream piracy" gave it a shorter steeper course. Another case of stream piracy may occur in the center of sec. 10 between Sawmill Creek and the creek to the east. (Part of Sag Bridge topographic map.) 30 TODAY'S GEOLOGICAL CHANGES

FrG. 21.-Looking southeast across the abandoned portion of Sawmill Creek valley. The present valley of the creek is marked by the woods to the left (east) and is thirty feet lower. The former meandering course of the creek is shown by the dashed line. in maximum thickness, identical in texture Sawmill Creek has not yet completed the with the gravel that Sawmill Creek is now deepening of the new route. A very heavy carrying. Limestone cobbles in it have rain in June of 1929 produced a flood in 3 been softened on the exterior from weather­ the creek that swept cobbles and pebbles ing since they were deposited. into large bars and up above the ordinary Let us start with the justifiable assump­ channel margins in striking fashion. In one tion that Sawmill Creek has made its own place the flood eroded a basin in the channel valley. If we could put back into it the to a depth of 6 feet and piled up boulders last 30 feet of debris removed in the deep­ and cobbles on its down-stream margin to ening and then could add 10 feet more at a height of 4 feet. Flood time is work time the place where it now enters the Des­ for streams. Plaines Valley, the stream would have to Figure 20 also shows a case of piracy, flow around through the semi-circular aban­ imminent but not yet accomplished, close to doned valley, and would enter the Des­ the middle of section 10. The reader may Plaines 2,000 feet farther downstream. The here test his understanding of a contour map creek would make a sharp turn in entering and of the mechanics of piracy. The prob­ the abandoned valley. Swinging to the out­ lem is to determine whether Sawmill Creek side of this sharp turn, it would erode lat­ or the creek immediately to the east will erally into the 10-foot earthen dam that lose by the piracy. we built in imagination and, before long, would by this process cut it entirely away. EROSION \V ITHOUT VALLEYS A shorter and considerably steeper route One learns shortly to recognize the pat­ would then be available and the semi-circu­ tern of contour lines that represents a lar lower half mile of its course would be stream-dissected topography. The North abandoned. This is precisely what is thought Shore district (fig. 14) is our best Chicago­ to have happened at an early stage in the land example. The topographic maps of the creek's history, 30 feet of down-cutting hav­ Chicago area, however, consistently show ing occurred since the diversion. If a short very little such topography in the area as a ravine descending the DesPlaines · Valley whole. Slopes exist almost everywhere out­ wall where Sawmill Creek now enters had side the lake border plain, but they belong existed before the shift, its headward erosion to the original sag-and-swell topography of would have facilitated the lowering of the the glacial deposits. These slopes have been old water-parting here and the change somewhat eroded by rainwash, but the run­ would justify the term "stream piracy." Do­ off has not been concentrated and therefore mestic stream piracy would be an even more has not produced gullies and ravines. The definitiveterm, since both pirate and pirated evidence for their erosion is best seen, not streams belong to the same system. on the slopes, but in the basins enclosed by

3This gravel is not to be confused with cobbles and the higher tracts. Many of these are mapped boulders which have been picked up in the field in the as "basin fill," for they contain varying abandoned valley and dumped over the edge into Sawmill Creek valley. depths of silt and clay material, in many WORK OF RUNNING WA TER 31 cases with traces of decayed vegetable mat­ DEPOSITION BY RUNNING WATER ter. Some of them have been filled until It was stated earlier in this chapter that they are no longer closed basins. All this the debris carried away by streams of this records the inconspicuous work of rainwash, region goes either to Lake Michigan or to while in more favorably situated places the the Gulf of Mexico. It is now time to concentration of run-off has produced gul­ qualify this statement. Some detritus is lies, ravines, and valleys. Rainwash is being deposited by streams within the con­ simply the muddy water that runs down fines of Chicagoland. Deposition by run­ slopes, without gullying those slopes, during ning water occurs whenever the current is and immediately after rain storms. I ts rills sufficiently checked ; the larger the load be­ are too minute to threaten seriously a hill­ ing carried, the less the decrease in velocity side mantled with vegetation. In fields needed to cause deposition. Small, high­ plowed up and down the slope, gullying is gradient streams on steep slopes may de­ very likely to develop from rainwash. Culti­ bouch on more nearly level surfaces at the vation across the slope (along the contours) base and there leave much of the debris tends to destroy incipient gullies and to removed in cutting the gully above. Such a check the work of the rainwash itself. Prob­ deposit is commonly fan-shaped or semi­ ably as much material has been moved circular in outline, sloping downward and downgrade by the inconspicuous rainwash outward from its center at the mouth of the as by the streams since the ice-sheet aban­ gully. Some fans are readily recognized doned the region. because of the radial slope from apex to margin (the Palos Park ravines have many CONSTRUCTIONAL VALLEYS good examples), others may be so nearly flat that to the eye they are only a part of For the reader who notes the capacious the general plain. The carefully surveyed valleys of the upper DesPlaines River, Salt contour maps show many of them. Alluvial Creek, Skokie Creek, and the forks of the fan deposits are most common in the Sag North Branch of Chicago River, it should Valley and along the landward margin of be repeated that these valleys are construc­ the lake-border plain. tional, just as are the undrained basins. The largest fan in the region, not now They have been inherited by their streams growing, has been built at Dyer, Indiana, and only the valley bottoms have been modi­ where Plum Creek leaves the hilly glacial fied subsequently. moraine country and enters the lake-border plain. Though too flat to be recognized as INHERITED VALLEYS a topographic feature, it is shown by the Another group of large valleys of the northward looping of the 620 and 625-foot region also needs explanation. It lies in the contours on the Calumet City topographic southwest quadrangle and includes, from map and the 625-foot contour on the Dyer map. Borings on the fan also show an north to south, the valleys of DesPlaines alluvial deposit with a maximum thickness River west of Argo or Justice Park, Sag of 9 feet above the stratified sand of the Channel, Long Run, Fraction Run, Spring plain. Layers of vegetable matter occur in Creek, Marley Creek, and Hickory Creek. the fan deposit, indicating swampy condi­ Although they are stream-eroded valleys, tions at times during its aggradation. Plum they all antedate the late�t glaciation of the Creek is a relatively low-gradient stream, region and two of them, DesPlaines and and it might well be assumed that 9 feet of Sag, were also used by great volumes of aggradation on the plain at its mouth would water discharged from the basin of Lake result in damming which would go on Michigan before the Strait of Mackinac slowly while the fan grew, thereby causing gave the Great Lakes an outlet to the east. deposition on the valley floor farther up­ Special attention is given their history in a stream. The assumption is borne out by later section. They all carry good evidence the field evidence. To an average depth of of having been over-ridden by glacial ice 8 feet, an irregularly interbedded deposit of but they were not filled with glacial drift gravel, sand, silt and peat has accumulated and subsequently they have undergone but in the lower part of this valley south of little modification by their present streams. Dyer. Shells, deer antlers, and mammoth 32 TODAY'S GEOLOGICAL CHANGES

Photo by Chicago Aerial Survey Company

Frc. 22.-McGinnes Slough, near Orland Park (Palos Park quadrangle ). bones and teeth have been found in it, to­ after the retreat of the ice-sheet but subse­ gether with numerous fragments of drift­ quently became so filled with peat that no wood and even entire tree trunks. Some of open water remained. The outlet valley has the logs can be seen from the Steger Road a very low gradient, a complete lack of bridge two miles south of Dyer. ravine characteristics, and contains two more swamps, indicating that the former ORGANIC DEPOSITS lake has not been drained by headward We have reviewed the function of vege­ erosion of young and vigorous streams. The tation in weathering and erosion. It remains swamp probably could not be drained arti­ to note that deposits of vegetable debris may ficially except by a deep trench more than a accumulate and be partially preserved un­ mile in length. The Izaak Walton League der favorable conditions. The prime condi­ has proposed a reverse procedure ; the build­ tion is partial protection of the material ing of a dam across the outlet to restore the from decay. This occurs in bogs and swamps lake, or rather to raise the water level and where the debris, submerged in water, is make a new lake, higher and more extensive protected from the rapid bacterial decom­ than the original. The marsh is the breed­ position that requires free oxygen of the air. ing place of many waterfowl, and bird Swamp deposits of peat generally occur in lovers, taking up arms against the fish undrained hollows of the glacial drift topog­ lovers, secured an injunction preventing raphy. this. The owner of the slough at present The largest existing swamp of this sort floods the eastern part of the marsh by a in Chicagoland is McGinnes Slough (fig. dam across the lower part of the culvert 22) (southwest corner of Palos Park beneath Kean (96th) Avenue. quadrangle), half a square mile in area. It Skokie Marsh, west of Winnetka and probably was a shallow lake immediately Glencoe (Park Ridge and Highland Park ORGANIC DEPOSITS 33

FIG. 23.-Muck and peat heaved by a highway fill across a swamp along 104th Avenue (Flavin Road) just south of 95th Street. quadrangles), lies in an elongated construc­ too little water and the Calumet Feeder tional valley between two broad ridges of was dug along the Sag Channel. The glacial drift. Though the topographer swamp was completely drained when the found a total length of five miles of marsh Sanitary District constructed the Calumet­ land, and the botanist knows it to possess a Sag Canal, a much deeper and more capa­ typical hydrophytic flora, the geologist is cious waterway. So great was the effect of unable to map all of it as a peat deposit. this canal in lowering the groundwater Skokie Valley is not completely enclosed level that many wells in the vicinity went and the marsh exists simply because the dry when it was opened. The swamp has gradient of the valley floor is too gentle for entirely disappeared and the peat is so dry adequate drainage. Borings show that the that fires occur in it almost every summer. peat that does exist in the northern part of The depth of the peat deposit is variable, the marsh is only a foot or so thick, glacial depending largely on the surface of the drift or fine sand immediately underlying it. substratum which is chiefly bedrock scoured Marshes in the vicinity of Calumet and clean of drift by the discharge from the Wolf Lakes (Calumet Lake quadrangle) Lake Michigan basin. Ten feet of peat is are similarly without peat accumulations known in places. adequate to justify mapping them as such. The contiguous towns of Hinsdale, Glacial drift has been found close to the Clarendon Hills, Westmont, and Downers surface in every boring made. Grove (Hinsdale quadrangle) are built on The most extensive peat deposit in the an exceptionally irregular surface of the region occurs in the valley of Sag Channel glacial moraine. Undrained depressions con­ (Palos Park and Sag Bridge quadrangles). taining peat are numerous and the deposit It is nine miles long and three-fourths of a in some is unusually thick, a maximum of mile in greatest width. On the topographic 26 feet being known. When sewers were maps the area is shown almost wholly installed in the first three towns, peat-filled without the symbol for swamp or marsh basins had to be crossed and the pipes were land. It is a drained swamp lying on the supported on piles to prevent them from floor of one of the two great abandoned sinking in the peat and were also weighted spillways out of the Lake Michigan basin. down to keep them from rising. Even after Artificial drainage was begun about 1870 the sewers had lowered the water level, when the Illinois and Michigan Canal houses inadvisedly built in some of these along the DesPlaines Valley proved to have basins have settled and cracked. 34 TOD;J Y'S GfiOLOGIC!lL CH!lNG/iS

FIG. 24.-Diagram showing the position of the water-table or surface of the groundwater (a-b) in a region of undulatory topography and homogene­ ous materials. The heavily dotted portion is completely saturated.

Some concrete pavements have been laid porous bed to provide water throughout the on earthen fills made in peat-filled swamps year. In rolling country, hill-top wells are of the region. Many such pavements have deeper than those in valley bottoms, though cracked and sagged badly, some of them the additional depth is not as great as the being unrepairable and necessitating new height of the hills. The water-table (the paving. Good engineering requires either upper limit of the saturated zone) under a adequate time between making the fill and hill may be many feet higher than it is in pouring the concrete so that complete the adjacent valley. The water-table, there­ settling can occur and be rectified by a final fore, has a relief of its own, corresponding grading, or for removal of the weak bog to but less than the relief of the land (fig. deposit before the highway fillis made. (See 24). During droughts wells in higher land fig. 23.) may go dry because, without replenishment, A striking illustration of the weakness of the water-table is lowered and the zone of peat was afforded when the Calumet-Sag aeration becomes deeper. Gravity moves Canal was dug. A spoil heap was made on the groundwater, just as it does the stream the east side of 104th Avenue (west edge water. This means that groundwater is of Palos Park quadrangle.) Its weight slowly moving down and out. Ordinarily squeezed the peat out from beneath and its circulation is very slow, the water perco­ forced it up into large wrinkles encircling lating rather than flowing through the the dump. At the time of construction, it minute spaces it finds. looked much as though a huge stone had Stream-cut valleys may intersect the been dropped into shallow water, remaining water-table, offering escape in seepages and partly above the water, the peat wrinkles springs, and providing themselves with a simulating waves just beginning to spread water supply during dry weather. Most of away on all sides. the springs in Chicagoland are in stream The map legend uses the compound term valleys. Generally their occurrence is in "peat and muck." There is no sharp dis­ the outcrop of some particularly large-pored tinction between the two. Muck contains deposit, like gravel or sand, which affords more earthy material, largely contributed free movement of water. by rainwash from higher slopes, and its The largest spring in the Chicago region vegetal content is more altered by decom­ is three miles south of Elmhurst and 3Vz position. Muck is likely to occur in the miles north of Hinsdale, on Spring Road shallower basins which dry out in the sum­ mer and along the margins of peat-filled just west of Salt Creek (Hinsdale quad­ depressions. rangle). It is almost in the center of section 23, T. 39 N., R. 11 E. Its unusual size GROUNDWATER AND ITs WoRK seems due to subdrainage from an aban­ Rain which soaks downward into the doned part of the creek valley west of the drift and bedrock is known as groundwater. present route. The old valley contains It produces a permanently saturated condi­ basin-fill which is saturated nearly to the tion at sufficient depth in accessible perme­ surface. Elmhurst secured its municipal able materials. Above that depth the ground water supply from this spring until the is saturated only after long-continued rain. population of the town exceeded 5,000. On In ordinary weather its pores are partially the Chicago Folio map ( 1902) it is called filled with air. Wells must penetrate Mammoth Springs, but the new map, through this zone of aeration to a saturated though showing it, gives it no name. GROUND WA 'f'HR /IND ITS WORK 35

���\\������������,�f""'""'§i�����'C:-������-=;::;����i����Bt���l?s��3_: ������§0§����� �--�-����������������� ..� ..�. ��e a FIG. 25.-Diagram showing conditions necessary for an artesian basin ; is a porous layer, is a b an impervious layer that traps water in and and are flowing wells. a, c d

Perhaps the next largest spring in the entering here, moves southeastward down region is on the south slope of Mt. Forest the gently inclined strata at least as far as Island, 1000 feet southeast of the inter­ the Chicago region. It is as though a long section of 107th Street and Kean Avenue. water pipe were laid on a gentle incline, the The specially favoring circumstance here lower end (Chicago area) closed, and water is that the water which falls as rain on the (rainfall) poured into the upper end (south­ adjacent Mt. Forest upland to the north central Wisconsin) until the pipe is full. A emerges from the lower slope of a gravel hole drilled into the lower end of the in­ terrace along the north side of Sag Channel. clined pipe and a small pipe fixed vertically The gravel seems nearly saturated with in it represents the artesian well. Water water, for there are seepages elsewhere along will rise in the small pipe until it is as high the basal slope and a well at the Greager as the water in the open end of the main greenhouse on Kean Avenue obtains an "in­ pipe. Should the small vertical pipe be exhaustible" supply at a depth of only ten shorter (the land surface lower) than the feet. height to which the water can rise, a flovv vV ells of the Chicago region are of two will result. Should it be longer (the land classes-those dug in the drift to a depth surface higher) pumping will be necessary. below the water-table, and those drilled far In Nature, the flow is much restricted by deeper, penetrating even thousands of feet the small openings in the sandstone and by into the bedrock. Wells of the first class the consequent frictional resistance, and de­ may become contaminated from barnyards, mands on the well may be greater than the earthen toilets, leaking cesspools, etc., and subterranean flow can supply. This is par­ furthermore they do not commonly yield ticularly" true of the artesian wells in the large quantities of water. For industrial Stockyards district where heavy demands on plants and small municipalities, deep wells a number of closely spaced wells have nota­ with large yield of "safe" water may be bly lowered the level to which the water drilled. An interesting item regarding such originally rose. wells in Chicagoland is that the water, en­ The topographic effects of groundwater countered in porous sandstone far below in the Chicago region are very slight. Lime­ the limestone of our outcrops and quarries, stone is a relatively soluble rock and many rises after the water-bearing layers are pene­ regions underlain with it possess caves in the trated and has even flowed from the well rock and sinkholes in its surface. both the mouth. Obviously somewhat different con­ product of long - continued solution by ditions control the movement of this ground­ groundwater descending and migrating lat­ erally along vertical cracks (joints). Chi­ water though it still is true that gravity cagoland has neither caves nor sinkholes. causes its flow. In many regions springs have built up The deeper wells of Chicago reach an deposits of calcium carbonate (calcareous artesian water supply. The sandstone for­ tufa) at their mouths. None of our springs mations containing the water extend north­ has done this. ward and northwestward into Wisconsin. Loose material lying on steep slopes, be­ gradually rising in that direction, with coming heavy and lubricated with ground­ therefore a decreasing thickness of impervi­ water, may slip down hill in large masses, ous stratified rock above until they crop out constituting landslides. Features of this in south-central Wisconsin. This outcrop character are not uncommon on our ravine area is higher than the land surface in the walls, especially where the streams are un­ Chicago region (fig. 25). Wisconsin ram, dercutting, or in deep highway cuts, but 36 TODAY'S GEOLOGICAL CHANGES

Courtesy of George D. Fuller

FIG. 26.-Wave-cut cliff near Lake Bluff (Highland Park quadrangle ). WORK OF SHORE AGENCIES 37 groundwater in such places is an important terial down the cliff faces is a common conditioning factor, and artificial drainage, phenomenon. Once at the bottom, a few executed with a knowledge of geological storms generally will disperse the material conditions, often proves corrective. and waves will again steepen the profile for All spring water and well water of the more sliding to occur. The summit area, region is hard, the hardness being due to high above the attacking waves, is wasting dissolved mineral matter secured as the away by this attack as surely as though the water moved slowly through the calcareous waves were dashing over it. Greater ex­ glacial drift or the limestone bedrock. Es­ posure of the cliffdetermines greater retreat caping groundwater joins the streams, and locally, as also does weaker material in the thus rock material in solution is removed cliff. Higher lake stages, as in 1929, have from the region. The average river load of caused greater annual recession all along dissolved material, contributed largely by the shore. The level of Lake Michigan groundwater, is about one-third as large as varies from time to time, largely because of the load carried in suspension (clay, silt, and variations in rainfall and evaporation. In sand). Hard water is objectionable for 1927 the elevation of its surface averaged many industrial uses as well as for domestic 578.96 feet above sea-level. By April 1929 purposes. Lake Michigan water is less hard it had risen to 582.34 feet, more than 40 than our groundwater, a fact well known to inches higher. Obviously the waves of 1929 commuters living in suburban towns whose were capable of doing far more damage to water supply comes from wells. It is inter­ the shore than waves of a low lake-level. esting to note in passing that the drainage The rate of shore recession north of area of Lake Superior has very little lime­ Evanston, as estimated by old residents, has stone in it and the lake water there is almost been about 5 feet a year. Measurements as soft as rainwater. made at different times and places give WORK OF SHORE AGENCIES rates varying from 1 Yz to 16)/z feet an­ nually. These were all made before any North of the city of Chicago, the coast attempts to check the recession had been line is cliffed to and beyond the limits of undertaken. the area but the city waterfront itself has no cliffs. The North Shore cliffs nearly co­ For some years after 1845 a small village incide with the extent of the glacial moraine called St. Johns stood close to the edge of along the shore and the uncliffed coast is the cliff in the southeastern part of the wholly in the lake border plain. The north present Fort Sheridan grounds. It appears part of the plain, however, in Evanston, to have grown up around a brick plant, for Wilmette, Kenilworth, and Winnetka, is a part of the old pit and the grade of an old higher than elsewhere along the waterfront railroad spur to it still remain. In 1907 the and is itself cliffed for a few miles. only surviving traces of the village itself The origin of the lake cliffs is no puzzle were two orchard trees and the remnants to one who has seen the waves of a "north­ of an old foundation which at that time were easter" attack this shore. It is no mystery on the very edge of the cliff although orig­ to property owners who have seen their land, inally they were in the westernmost part undercut by the waves, slide piecemeal into of the village.4 Today even these traces the lake from year to year. There is no have vanished, the prey of the attacking district of more rapid geological change in waves. The amount of recession thus re­ the region. corded was estimated in 1907 to have been The cliff (or bluff) ranging in height from 100 to 400 feet. In 1930 Ball5 re­ from 15 feet in Evanston to 85 feet in ported observations of shoreline recession Highland Park, has been retreating before north of Kenosha which he had made in the onslaught of storm waves ever since the 1918, 1921, and 1929. He found that be­ lake was formed (fig. 26). The unconsoli­ tween 1918 and 1921, when the lake was dated glacial drift yields somewhat as it does to vigorous stream erosion. Boulders 4Atwood, W. W., and Goldthwait, J. W., Physical geography of the Evanston-Waukegan region: Illinois and cobbles from the drift, once in the grasp Geo!. Sun•ey Bull. 7, p. 92, 1908. of the waves, are used as tools in the attack. 5Ball, J. R., and Powers, W. E., Shore recession in southeastern Wisco.nsin: Illinois Acad. Sci. Trans. vol. 22 Sliding and slumping of water-soaked ma- 1930. • • 38 TODAY'S GEOLOGICAL CHANGES

t

�/ 7\ Open Water t .. c/ � \

Fw. 27.--Cross-section of a wave-cut cliff and its accompanying cut-and-built terrace.

(Illinois Geo!. Survey Bull. 7, fig. 20, 1908). Land high, the average annual recession at the measured places had been 12.33 feet with ---'\ a maximum of 15 feet. The lake then -�-- Widll1 of&ad1 --- dropped steadily until 1927 and, despite another rise before he again measured, the FIG. 28.-Diagram illustrating the course of a particle on a beach when waves impinge average recession was found to have de­ diagonally upon the land. creased to less than a foot a year. At first thought, the simplest and best out as the breakers in heavy storms. ln solution to the problem of checking this waves that reach the beach, the debris tossed encroachment of the lake would be the back and forth as they break on and recede construction of a sea-wall. On many shores from the shore will tend to be shifted along a sea-wall is the only feasible method, the shore a little as each oncoming wave though very costly. But the method usually carries it shoreward. The sum of many such adopted by North Shore property owners zigzag to-and-fro trips means transportation has been to build piers or groins extending alongshore on the beach itself. across the beach and out into the shallow Now examine the Highland Park topo­ water for 100 to 250 feet or more. The graphic map, or that portion of it shown in structure does not take the brunt of the figure 14, and also figure 29, an airplane attack, it does not stand between the waves view of the shoreline, and note the greater and the cliff, and the reason for its effective­ width of beach on the north side of each ness may not be apparent at first. Other groin. The alongshore current on the Chi­ shore processes, thus far undescribed, under­ cago region coast is southward, determined lie its success in checking, although not com­ by the dominant northeaster waves. The pletely stopping, the cliff recession. Let us groins check this drift, retain a portion of approach the problem by means of diagrams. the debris, widen the beach zone, and thus In figure 27 a shelf-like shoal is shown provide a buffer more or less adequate to off shore, partly an eroded platform left by absorb the energy of the wave attack. In cliff retreat but also partly depositional, this way, the cliffbases are less energetically built from detritus dragged out by the un­ undercut, vegetation gets a hold, and gully­ dertow and deposited below the effect of ing and slumping are checked. even great storm waves. Not all the debris The ravines of the North Shore have all stops here ; the fine rock flour settles on the added their debris to the shore drift. Not lake bottom well beyond the terrace. Sig­ one has been able to build a delta in the nificant for our problem, however, is the fa7:e of the wave attack. They have also fact that not all the debris from cliffdestruc­ suffered a constant shortening in their lower tion comes out across the wave-cut platform portions as the cliff has receded. This has to the depositional terrace. There is another maintained in them a steeper gradient than dimension to be considered-along the shore. they would otherwise have and is un­ The diagram (fig. 27) implies wave at­ doubtedly a factor in their marked develop­ tack at right angles to the shore. It is far ment. more probable that the average direction of As the shore drift is southward past this wave approach is diagonal to the shore (fig. source of supply, one might expect to find 28). Successive diagonally approaching somewhere in that direction a region where waves will produce a current along the shore deposition is occurring, or at least was shore, the effect of which will be felt as far occurring before man took charge of the WORK OF SHORE AGENCIES 39

Pier. This beach accumulation was a tri­ angular area, identical in character with those against the north sides of groins in the North Shore area. Still more striking was the course of Calumet River before man began his exten­ sive alterations (fig. 31). The complete history goes bac� to the later high-level glacial lake stages and involves the develop­ ment of the old beach ·ridges about Wolf Lake and Lake George, Indiana. Stated briefly here (the section on unconsolidated material contains a more ample account), the mouth of Calumet River was originally near Riverdale. Had there been no along­ shore movement of sand while the lake was being lowered to its present stand, the river mouth would have been approximately at the intersection of the lake shore and the eastern edge of the Calmuet Lake quad­ rangle. But this southeastward drift of

Photograph by Chicago Aerial Survey Company sand and the building of beach ridges suc­ FIG. 29.-Groins and resultant beaches protecting cessively farther out as the accumulation the lake bluff along the North Shore. grew, shifted the river mouth southeastward until, by the time the first maps were made, it was entering the lake east of Millers, 14 shoreline configuration. An enlightening miles over in Indiana. This was in the area fact relates to the mouth of Chicago River of active dune development and about 1870 before harbor improvements were begun the river was seriously embarrassed by dune in 1833. The river, two blocks east of growth at its mouth. Dredging from Hege­ Michigan Avenue, turned a right angle to wisch to South Chicago, along a canoe the south and flowed behind a sand barrier waterway used by the Indians, has given us as far as Madison Street, half a mile, before the present lower course and mouth of Calu­ entering the open lake (fig. 30). This sand met River, 20 miles west of the abandoned barrier was a continuation of the sandy mouth at Millers. beach at Evanston and clearly was a product The entire waterfront from about 53rd of the alongshore current. After the present Street south to the Indiana dunes was being river mouth was dredged and protected by built out by accretion of shore drift prior to piers, sand accumulated on the north side the growth of the city and its need for of the north pier until by 1864 the shore­ "made land" additions. The two piers in line had been extended, without further aid Jackson Park, protecting lagoon mouths, of man, half way out from Michigan Av­ show today a constant accretion of sand on enue to the foot of the present Municipal their north sides. 40 TODAY'S GTWLOGJCAL CHANGES

�����------���= =� --- � ����� _3L== r - I 1I I ____J ____ ------I CHICAGO- L - - - : ;-AVE-i [ \------__J L ___ , ____J, -- - - - SUPERIOR ,- -ST ------r::�-- �::J - ��r.- ---;'\�� - -������- -c�- �---i] i--i -'\------i---: � � -\ - -sr -\- . ------.:::::: __J - tNJ�io' 1 _ _JiL � �� � - - \en��6�\��-\-,,-�� :.:.1------__JL__ _iL __ ""'--\""'- -\:: it;i it;��..._ _ - __ it;i0H10- - -ST __J ;�L :Z..------i :- - : ; - : 'o7�- L - �- -��"%:\�- '\------____J ,o;l-"' __J; L __2 J � - _ -::_-::_-::_-::_-::_-::_-::_- -1 ... - __ _ - _\'t__\,_��- -__ Q.l_A� w l T I �-�\f"Y\ -\-\---\ --��: � �' I l � ______J��---\�I ------= - "" \- � ---: iJ,bl!'()_I� 1 i = === __Jo ;-2T_i�---=-� \�\ � ��\ �\ - __ l___ _J I W,.'\__:;: -_:: ��- -:-=--�-0 .}_· M���� l ::, ... -���-3'-�-x-\----' _J _Jl "' -:' --J ��u.1_::.B--r rr -1- -y --\-y-- -

l-� ------1

r- L " =·=·=· "'' " · c _::-- : i I i -- I i:•�::J:T�L-� -�:���-�-i ------I ! HA1RBOR INLET 183011 1 l �- l...J\ I !It-.. '11::,I" 11� I II110: � 1: � i{1�111f II" �:::.:; "' i1 1 1 'I : �A���� ii I I ii: . i I 1 1 I ',,l);;f:· II I\ ·Hb�',f ��{�SQ�. i! :: 1 1 I I: I � - L i ___ _J i! - ;0!'!.fil'I.!_[� \ 1 : l :: FIG. 30.-Shoreline changes at the mouth of Chicago River. (U. S. Geo!. Survey, Geologic Atlas of the United States, Chicago Folio [No. 81], Fig. 13, p. 11, 1902.) Mil u...LLJ._____L�-'-----'---'------'1 o 2 3 4 s es

111 111 o 2 3\ 4 5l Kilometers

<. �a ,..q � A' ,A £ I I G � M c H a "':l V'.J ::r: a � � ::,., () � �

� V'.JQ

Fie. 31.-Map of Calumet River and its surroundings. (U. S. Geo!. Survey Geologic Atlas of the United States, Chicago Folio [No. 81], fig. 14, p. 11, 1902. )

+ ...... 42 TODAY'S GEOLOGICAL CHANGES

WIND WORK Every Chicagoan with a love for out-of­ doors knows the Indiana dunes and recog­ nizes these huge sand hills as accumulations of beach sand blown inland by on-shore winds. Much of the Michigan shore of the lake also has dunes, formed in the same way. But there are almost no dunes on the west shore of Lake Michigan, although sandy beaches, low shoreland, and on-shore winds exist here also and about as many miles of wind per year come off the water as off the land. It is a weather proverb that east winds Frc. 32.-Low dune ridges in Touhy Park (Evanston quadrangle). bring rain. Meteorologists find the reason in the cyclonic and anticyclonic circulations, The accounts of the Fort Dearborn mas­ so largely responsible for our variable sacre tell of Indian ambush behind low weather. Chicago's on-shore winds are east­ dunes along the lake shore a mile or less erly winds which are usually accompanied south of the present Loop, but these dunes by rain so that the beach sand is damp, in have long since disappeared. which condition it will not drift. Northerly The Chicago region has much more dune winds and most westerly winds are fair sand, piled up in considerably larger masses, weather winds. Beach sands then dry out than in those areas just described. They are and in Indiana and Michigan are blown not, however, along the present lake shore inland to form the magnificent display of but lie some distance inland and their for­ dunes extending eastward from Gary com­ mation dates back to the higher lake levels pletely along the Indiana shore and far when discharge was across the present re­ north of the Michigan line. The virtual gional divide to the Mississippi. They are absence of dunes along the Chicago shore described in the historical section. therefore seems largely attributable to un­ SUMMARY favorable weather conditions when wind directions are right. Geological changes now in progress in the However, two dune areas large enough Chicago region were inaugurated with the final retreat of the ice-sheet and the emer­ to map occur along the Chicago portion of gence of the plain by lowering of the lake the lake shore. One is at the lakeward end level. These changes are largely destruc­ of 79th Street and extends with an inter­ tional. By chemical and mechanical means ruption north to 7 lst Street (Jackson Park present-day agents are removing surficial quadrangle). The dune features are hardly material and, where concentrated in their recognizable today because of building, grad­ action, the land slopes are becoming steeper ing, and park development. The other area and the land forms more varied and sceni­ is at the east end of Touhy Avenue (7200 cally interesting. These new land forms are north, Evanston quadrangle) where two being etched or carved from materials de­ blocks of park land on the lake shore remain posited during an earlier regime under con­ with original topography and vegetation ditions very different from those of the (fig. 32). The sand is heaped into several present. Locally the relief is being decreased parallel ridges 10 to 15 feet high, the ridges by redeposition of material which has failed being successively younger nearer the lake. to travel on beyond the region. GLACIAL ORIGIN 43

UNCONSOLIDATED MATERIALS AND THEIR TOPOGRAPHY A superficial mantle of unconsolidated rock surface shows marks of tremendous material, spread over hilltop and valley bot­ abrasion-planed-off surfaces that are tom, across upland and lowland, is the rule grooved, scratched (striated), perhaps pol­ throughout the earth. It is like a blanket ished, the grooves and scratches parallel thrown over the topography. I ts removal with each other and in the Chicago area would make little difference with the major directed very nearly northeast-southwest. relief features except that they then would Fragments of the local bedrock, themselves consist wholly of bare consolidated rock. bearing similar marks (fig. 35), constitute This cover, known as the mantle rock, is a large proportion of the mantle rock and generally the product of weathering, and as indicate that the unconsolidated debris was it thickens, it serves to protect the deeper obtained by the same agent which planed rock from weathering (fig. 33). and scratched the bedrock surface. The overlying material seems, therefore, to be the actual abrasive, left in place when the work was completed. The abrading agent has disappeared and its nature must be learned from the clues it left behind. The problem is a kind of detective story, lacking only the elements of "guilt" or "innocence" and of human interest in motives. The striae in the underlying bedrock in­ dicate that the agent moved either from the northeast or from the southwest. Fragments of rock foreign to the region, but traceable

FIG. 33.-Diagrams showing relation of mantle rock and bedrock. Above-mantle rock is residual soil de­ rived by weathering of the bedrock. B elo�..v-mantle rock is glacial drift depos­ ited on the bedrock.

GLACIAL ORIGIN OF THE MATERIALS In the northern states, however, the blanket of unconsolidated material is itself unweathered and generally is much thicker than a mantle produced by weathering. Were it removed, the bedrock topography would seldom correspond to the hills and valleys of the mantle itself. This is particu­ larly true in Chicagoland. There are two differenttopographies here, one of the buried bedrock and one of the superficial material. The metaphor of "blanket" applies here better than in regions where weathering has made the cover, for here a clean-cut separation exists, a sharp contact that is essentially absent under a weather-made blanket (figs. 33 and 34). Once the cover of mantle rock is removed, FIG. 34.-Sharp contact of glacial drift mantle as it has been over local areas, another con­ rock and planed-off bedrock in the Chicago trast becomes apparent. Much of the bed- region. 44 UNCONSOLIDATED MA TERIALS

force, that agent must have had a general downhill movement. The only "downhill" possible was its own surface. Great thick­ ness or depth is again implied. The items above listed rule out every agent now operating in the region. The features are so peculiar that early attempts to explain the origin of "drift" called for purely fanciful catastrophes. One, for ex­ ample, postulated a tremendous earthquake beneath the Arctic Ocean, producing an inconceivably enormous wave which swept southward across half the continent. Ice­ bergs carried in this debacle, dragging bot­ tom, made the records of great abrasion. As late as 1873, a report of the Illinois Geolog­ ical Survey1 indicates the origin of the "drift" to be unsolved and perhaps an un­ Fie. 3 5.-Striated boulders from the Chicago solvable problem. glacial drift. Arctic and alpine explorations since have made us familiar with thick masses of land to outcrops about Lake Superior and farther ice, or glaciers, slowly moving under gravi­ northeast, eliminate the possibility of deriva­ tative pull. They originate where snowfall tion from the opposite direction. The un­ is in excess of melting and evaporation, so weathered nature of the deposit suggests that each year sees an additional thickness that the work was done either too rapidly of snow. Compaction under its own weight for weathering to occur or else under a and from partial melting and refreezing cover which prevented atmospheric attack. during the accumulation changes this snow The irregular surface of the deposit, par­ into ice, and when thick enough, movement ticularly its enclosed basins, proves it to be of the mass begins. Some western mountains a "dump" deposit, not sorted and aggraded in the United States possess glaciers today bit by bit as are stream and shore deposits. although they are simply ice streams in the The complete lack of assortment, boulders valleys. The continent of Antarctica, how­ and clay occurring together, is further evi­ ever, carries an almost complete cover of ice dence for this conclusion. The thickness of and snow, estimated at about four million the debris (a maximum of 216 feet being square miles in area. Greenland has the known in a well on Ridge Road in the largest single expanse of ice and snow in the Highmoor district of Highland Park) northern hemisphere, covering more than argues for ability of the causal agent to move enormous weight. One square mile of half a million square miles. On both these the material, 10 feet thick, weighs more large land areas, the ice moves radially out­ than 20 million tons, yet it assuredly has ward from central higher tracts. The been moved in much greater thick­ Greenland ice is especially instructive be­ nesses than this.en masse The uninterrupted spread cause it moves in terms of its own surface of debris shows that the agent covered the slope. The land is known to be actually entire region. The broad north-south ridges lower under the central part of the ice than of the material indicate successive marginal along the margin. The maximum known accumulations. Their parallelism with the thickness of the Greenland ice 250 miles in edge of the lake basin suggests that this from the edge is 8800 feet (about 1 315 basin determined the outline of the agent miles). The surface of the ice, on the other responsible. The existence of an upgrade hand, rises inland to an altitude of nearly out of the basin, in the direction of move­ 10,000 feet above sea-level in this distance. ment, proves that this agent was able to If we did not actually know that such move up regional slopes. The agent was so enormous accumulations of ice-from-snow do thick or deep that the relief of the under­ •Shaw. James. The geology of Winnebago Co in lying bedrock surface was of trifling conse­ . .• "Geological Survey of Illinois . by A. H. Worthen. and . quence. Yet if gravity were the moving others. vol. V, 1873. VALPARAISO MORAINE 45 exist, or did not know that the existing ones spread slowly outward because of their own weight, we might still be saying as James Shaw said in 1873, "we shall never perhaps positively know" how the drift in the north­ ern states was formed. But now we know that it was formed by an ice-sheet or glacier of enormous thickness and weight, covering very large regions, moving slowly but resist­ lessly across the ups and downs of a buried land surface, and carrying a great load of detritus which it used as tools to abrade the rock mechanically. We know that the posi­ tion of the terminus of valley glaciers and ice-sheets on land is caused by a balance between rates of advance and rate of melt­ ing that at such places the vanishing ice dro s its load along its margin, and that in a few� decades or centuries, great ridges or moraines accumulate whose topography, composition, and relationship to the under­ lying planed-off rock closely resembles those of the Chicagoland drift deposits. The back slopes of the marginal moraines descend to surfaces with less relief but with unsorted Fie. 36.-Sketch map showing the North Ameri­ glacial drift beneath them and with un­ can area covered by ice at the time of maxi­ drained hollows on them. They are almost mum glaciation. as definitely ice-made as the marginal ridges themselves. This lower and more softly the basin of Lake Michigan) considerably moulded drift topography is called "ground­ influenced the shape of the margin and the moraine," being largely deposited while the direction of flow. In Michigan, Indiana, ice edge was retreating from the marginal Illinois, and Wisconsin (fig. 37) the mo­ deposit. All but one of the six marginal raines near the lake form roughly concentric moraine ridges of Chicagoland have an area loops about the southern end of the basin of ground-moraine behind them (on the and this patte.rn records a pronounced loba­ lakeward side). Such lower surfaces of tion of this part of the ice margin. The ground-moraine are especially subject to outermost of the concentric moraines is the odification by water from the melting ice. oldest. The inner ones are successively ;; younger. The areas of ground-moraines be­ Geologists no longer differ on the problem tween the moraines record stages of fairly -most of the unconsolidated deposits of the rapid retreat of the lobate glacial margin northern states are now accepted as glacial (melting more rapid than feeding forward in origin. Running water from the melting of the ice). Amelioration of the climate, by ice made some modifications in the surface which the ice was being cleared from the deposits at the time, as also did ponded water reg10n, obviously had pauses in its progress. in front of the ice. These are but details, however, of the general process. Study of VALPARAISO MORAINE the glacial drift and glacial striae in the The largest and highest of these con­ northern United States and Canada has centric moraines in Chicagoland can be shown that the ancient ice-sheet had two traced southeastward from our area (Pl. I) principal centers of growth, one east and into Indiana, thence eastward and northeast­ one west of Hudson Bay, and that ice ward into Michigan, nowhere being more radiated from these centers (fig. 36) much than 20 miles from the lake. It is known as it does from the Greenland and Antarctic as the Valparaiso moraine because of its ice-sheet of today. In its southward spread marked expression in the region of that into the Great Lakes region, marked longi­ Indiana citv.- The outer border of this tudinal depressions (like that which is now moraine is a few miles to the west and south 46 UN CONSOLIDA TED MA TERIALS

I I I I I

I I I I I I I I \ I I I � I "" I \ II \ � / " / '-' ...... _ _ ......

Fm. 37.-Lobate distribution of glacial moraines around the southern part of Lake Michigan. (After Leverett, Alden, and Weidman, U. S. Geo!. Survey Prof. Paper 106, Pl. XXIII, 1918.) of the Chicago area (fig. 3 7) . The inner The width of the Valparaiso moraine is border is indefinite, the upland descending generally 10 to 12 miles. Its highest point eastward with very gradual diminution of within the twenty quadrangles of the Chi­ relief into the ground-moraine plain. cago area is near the head of Fraction Run between Lemont and New Lenox (in the The Valparaiso moraine is not a simple western part of the Mokena quadrangle) , broad ridge but a complex arrangement of and is 800 feet above sea-level, 219 feet hills and depressions, the sum total of which above Lake Michigan, and 100 to 125 feet constitutes several parallel broad ridges and above the plain at the base of the moraine. elongated hills, basins, and valleys. Its char­ Farther northwest toward Barrington, it acter is perhaps best shown by the series of is more than 900 feet above sea-level. profiles across the Valparaiso and Tinley The moraine in our area lies almost moraines (figs. 38, 39). wholly within the Mississippi River drain- VALPARAISO MORA/NF 47

8 , 0 «

FIG. 38.-Cross-section railroad profiles across the Valparaiso and Tinley moraines. The th ird profile is that of both the Atchison, Topeka, and Santa Fe and the Alton railroads. 48 UNCONSOLIDATED MA TERIALS

FIG. 39.-Cross-section profiles along highways across the Val- paraiso and other moraines. 1. East-west profile along Dundee Road. 2. East-west profile along Central Road. 3. East-west profile along Ogden Avenue. 4. East-west profile along 95th Street. 5. Northeast-southwest profile along southern Old Indian Boundary. 6. Approximately east-west profile across the country trav­ ersed by 151st and 159th streets.

age system, only a few square miles of its Tinley moraines. Sag Channel and Des­ southern part draining to Lake Michigan. Plaines Valley west of Argo are cut entirely DesPlaines River as far downstream as across the two moraines, and for much of Riverside and Lyons, flows east of both the the way, each has been eroded down to bed­ Valparaiso and Tinley moraines and parallel rock. l\1t. Forest Island, a part of the with them. Salt Creek, except for the last moraines, has thus become completely iso­ few miles, flowsbetween the Valparaiso and lated from the rest of them. GLACIAL LAKES 49

w. E.

- ,... ,...,. Edge Jee Sheet restored of

Tinley Moraine Ground-Morame

w. E.

Edge or Ice Sheet restored

Sediments of Lake Steger

Tinley Moraine

Ground-Moraine

------� S. E. N.W. "' - of » ,.. - - Cross-section small Jobe of Ice Sheet restored o� ____ t J"lo_or_ Sediments of Lake Matteson Proiect1on of Tinley Morame if!� of Lake Steger

Fie. 40.-Profiles across Tinley moraine and some of its associated lake beds. Upper-Along 183rd Street, Tinley Park and Harvey quadrangles. Middle-Along Sauk Trail and Old Lincoln Highway, Steger and Dyer quad rangles. Lower-From Lake Matteson to Lake Steger.

LAKES BETWEEN THE VALPARAlSO AND has been filled up to the level of that outlet TINLEY MORAINES with clay and silt. None of the outlet routes had sufficient gradient to suffer trenching, In the south part of the region, particu­ and none of the four lakes disappeared by larly in the Tinley Park quadrangle, the being drained out westward. Each of the Valparaiso ground-moraine includes exten­ four shallow basins now has free drainage sive flat or very gently undulatory areas to the east through youthful valleys that are underlain by stratified pebbleless clay and trenching through the Tinley moraine. silt. Four such separate areas are mapped These lakes, named Orland, Tinley, Mat­ (Pl. I) in the Palos Park, Tinley Park, teson, and Steger, first appeared when the Harvey, Steger, and Dyer quadrangles, ice was building the Tinley moraine. Its comprising a belt of lowland between the irregular crest is generally lower than these Valparaiso and Tinley moraines and elon­ flats. Four low places in it have been oc­ gated with their trend. The margins of the cupied by postglacial streams and eroded flats as drawn are very irregular and cannot considerably lower. But even if there were be identified bv topographic features. The no stream-cut valleys across the Tinley d areas of groun -moraine which separate and moraine ridge, no lakes could exist there interrupt the stratified clay flats are them­ todav. It follows, therefore, that these four selves almost as featureless, but they differ lake� existed when, and only when, the ice in being composed of unstratified glacial front rested on the Tinley moraine and material (till), in having a few boulders made an effective dam. In figure 40 only scattered about on the surface, and in pos­ the middle profile is so located that a lower sessing shallow undrained depressions. surface of the moraine to the east is shown. This belt of flatlowland was once a string There is further evidence that these lakes of shallow lakes. Each of the four separate disappeared when the Lake Michigan lobe lakes had its own outlet to the west and each of the ice-sheet withdrew from the Tinley 50 UNCONSOLIDA TED MATERIALS moraine. No cut or boring in the stratified east in the Dyer quadrangle, however, the deposits has shown a trace of organic ma­ mapping of the moraine is more conjectural terial, although such traces are common in than in any other place in the region. all postglacial lake sediments. In a few places along the contact of lake flat and GLACIAL STREAM DEPOSITS Tinley moraine, glacial till actually overlies The ice-sheet that once covered the Chi­ the lake clay. It appears from this that a cago area disappeared largely by melting as slight readvance of the ice front occurred the climate became warmer. Melted ice after the lake history began. must be disposed of either as water-vapor Streams from melting glacial ice are about or as running water, and such running the muddiest streams on earth. Certainly water can escape only by flowing away from the ice which deposited the clayey drift of the wasting ice-sheet across the debris-cov­ Chicagoland must have yielded very dirty ered country the ice has already abandoned. water. This seems to have been the source If the sheet of debris (ground-moraine and of the sand, silt, and clay which filled up marginal moraine) is not thick enough to these shallow basins of the Valparaiso obliterate the pre-existing topography, the ground-moraine south of Sag Channel. The escaping meltwater will very likely follow lakes probably were huge mud puddles, un­ the larger preglacial valleys. This is what attractive to anyone but a geologist. happened on parts of the Valparaiso moraine in our area. The evidence for it, however, TINLEY MORAINE is not of the character that one would at first expect. The Tinley moraine, mapped by a sep­ arate pattern, is distinct from the Valparaiso Streams born of glaciers are commonly morainic system because it was built after overladen. They deposit their excess load, the ice had retreated an unknown distance consisting of the coarser debris, in their and then readvanced, encroaching upon the channels. With channel capacity thus de­ Valparaiso moraine. I ts position back from creased, they overflow to less aggraded the main part of the Valparaiso moraine in places in the valley bottom, in turn aban­ the southern quadrangles not only allowed doning them as the deposition continues. room for but created Orland, Tinley, Thus a uniform sheet of gravel and sand is Matteson, and Steger lakes on an area that spread from side to side, making a relatively would be otherwise all Valparaiso ground­ flat-surfaced fill (valley-train) perhaps moraine. Farther north (Hinsdale and many feet thick and extending down valley Elmhurst quadrangles) the sag between the many miles beyond the ice. After the glacial two moraines is narrow and looks, with Salt episode is closed the streams of normal run­ Creek flowing along it, somewhat like a offtake possession of the valley and, far less stream valley. The intermorainic sag here embarrassed by load, may trench into the had free drainage southward and no lakes glacial river deposit, perhaps eroding away a are known to have existed. good share of it and leaving only terraces or benches of gravel along the valley sides The southeastern portion of the Tinley to record the originally continuous fill. moraine is least well differentiated. It fails These are common relationships of glacial to continue south of Flossmoor and Olympia streams to preglacial valleys and of post­ Fields (Harvey quadrangle) as a ridge or glacial streams to the glacial stream deposits. belt of hill-land. Lakes Matteson and Steger were separated by some barrier other than KAME TERRACES the land surface between them as it is too low to serve the purpose. A protuberance of Now many westward-draining valleys of the Tinley ice-front seems to be the only the Valparaiso moraine do contain deposits explanation, and the Tinley moraine is of stream gravel, too extensive and too high therefore drawn to include the region of up on the slopes to have been deposited by Richton Park. (Pl. I. See also the third present streams. But this gravel is not in cross section in fig. 40.) In South Chicago terraces. It occurs in mounded and ridged Heights and Steger (Dyer quadrangle) the forms, heaped up 10 to 40 feet high, the Tinley moraine is again a definite upland hillocks and hills enclosing originally un­ separating Lake Steger flaton the west from drained depressions, the accumulations Deer Creek Valley on the east. Farther patchy instead of continuous, and essentially KAME TERRACES 51

FIG. 41.-Kame-terrace knolls in the valley of Long Run (Sag Bridge quadrangle). FIG. 42.-Tiedtville esker (Sag Bridge quadrangle). piled up on the glacial till of the valley slope. by some of these deposits. As the present Glacial stream gravel ( outwash) it surely streams have only begun to remove these is, but with equal certainty it never was a obstructions, they clearly did not make the part of a uniform valley-train fill. valleys. The obstructions, of glacial age, To explain these irregular piles of glacial prove the valleys to be older than the stream gravel on the slopes of pre-Valparaiso moraine building. These conclusions are valleys, we invoke the presence of ice in the supported by the occurrence of other con­ valleys at the time of their deposition. The strictions, due to moraine hills instead of front of the retreating ice-sheet was not uni­ kame terraces, and by incongruous widen­ form-the ice melted more rapidly on the ings, some of them swamp-filled completely exposed hilltops, it lingered long in the across the valley. protected valleys. Thus water escaping westward found either elongated projections ESKERS of the ice-sheet or, more probably, aban­ Glacial stream deposits along the north­ doned ice masses in these valleys, stagnant west wall of DesPlaines valley and south­ and separated from the main mass. Over, west of Willow Springs have several around, and among these wasting remnants, significant features. Most of them are ridges the glacial water flowed. Greater melting either elongated parallel with the valley along contact with valley slopes located wall or gradually descending that wall to­ channels prevailingly along the valley mar­ ward the southwest (downstream). They gins. Deposits from these excessively loaded are not compos.ed wholly of gravel ; the up­ streams occurred in favorable places between valley, higher ends of the ridges commonly the ice masses and the land. By the time the consist of clayey till which grades into ice blocks had melted out, the glacial streams stratified gravel toward the lower or south­ had ceased to flow and the gravelly debris western ends. The largest of these ridges is was left as low hills and ridges where the half a mile long. It lies 1 �2 miles southwest hollows had been. Such deposits are called of Willow Springs and half a mile north of kame terraces (fig. 41). The places that Tiedtville (Sag Bridge quadrangle). A were occupied by the ice blocks are now part of its crest is shown in figure 42. Its depressions. 2• highest point, near the north end, is nearly The maps show kame terraces (symbol 7 5 feet above the floorof DesPlaines Valley, for kames and eskers) in Hickory Creek its south end is only 10 to 15 feet above. valley (Tinley Park quadrangle), Hickory, The high part apparently is all till and Marley, and Spring valleys (Mokena quad­ except for having steep slopes and a marked rangle ) , and Long Run and DesPlaines ridge form, it seems to be simply a part of River valleys (Sag Bridge quadrangle). In the general moraine topography. all except the DesPlaines valley striking con­ All of these ridges are apparently the strictions of the alluvial flats are produced product of combined glacial ice and glacial

'Another explanation for these gravelly knolls is that water. They may owe their form to the the preglacial valleys were subglacial drainage lines along existence of major cracks or fissures ( cre­ which glacial waters concentrated, due to suoglacial slope and crevassing, and that there was rapid melting of the ice. vasses) determined by the pre-existing steep 52 UNCONSOLIDA TED MA TERIALS

valley-slope here beneath the thin edge of action of glacial water greatly reduced the the waning ice-sheet. Glacial debris collect­ percentage of clay in the normal till, thereby ing in these cracks was partially sorted over concentrating the coarser debris, but not by · water which utilized the crevasses as washing it clean. Another example of this channels. The ridges appear to have been type of glacial stream deposit is half a mile . successively formed, the youngest being south of Joliet Road (State Highway No. farthest northeast. 66) in the northwest quarter of Sag Bridge Ridges of morainic gravel also occur on quadrangle, two miles north of DesPlaines the Valparaiso moraine where no buried River. Topographically it is not to be dis­ tdpography appears to have determined their tinguished from the rest of the moraine by location. One such ridge is a quarter of a steeper slopes or greater height, but two pits mile from Mammoth Springs (Hinsdale show that the hill is composed of gravel, quadrangle), or about 1 Vz miles south of nearly or quite to the surface. In one place, Villa Park business district. Another is at 5 feet or so of till overlies the gravel. Halfday, on Milwaukee Avenue (Wheeling Hills like these, not notably elongated quadrangle), and a third is on the south side into ridges yet surely recording the work of of Sag Channel, about two miles east of meltwater escaping from the ice, are thought Sag Bridge (Sag Bridge quadrangle). All to have been built up where streams emerged have gravel pits in them, the material show­ from the fissured and irregular edge of the ing that glacial stream water was a factor retreating ice-sheet. The essential condi­ in their origin. Yet all have till also, the tions for their origin are discharge of the first having in one place 4 feet of unwashed stream into a marked re-entrant of the ice till on top of the gravel. Ice certainly was edge (probably an enlarged crevasse) and a present when they were deposited. Only ice notable decrease in gradient at the point of in motion or overlying ice which had been escape. The hills are called kames and are in motion, would put till on top of the more closely related to alluvial fans than to gravel. The last ridge is elongated almost any other normal stream deposit. at right angles to the valley wall instead of Where streams of meltwater plunge from being nearly parallel like those north of the glacier's surface into crevasses before DesPlaines valley and its southwest end is reaching the margin, great well-like tubes 65 feet higher than the valleyward end. It become melted out by the falling water. In is composed of gravel at the lower end, the bottoms of these, water-washed material though most of it consists either of till or of may accumulate to considerable depth. After gravel with a deep cover of till. the ice has vanished, such fillingswill be left These sharply ridged forms, containing as sharply conical hills of sand and gravel, considerable glacial stream gravel, seem to called moulin kames. belong to a class of deposits called eskers. Typical eskers are composed largely or PROBLEM OF T·HE PRE-VALPARAISO wholly of gravel. They are generally con­ VALLEYS sidered to be the product of streams flowing An interesting question concerns the at or close to the bottom of the ice-sheet, in tunnels that started in crevasses which stream-made valleys that are definitely older than the kame terraces and esker ridges on became enlarged by melting as the somewhat their slopes. In what material were these warmer water flowed through them. partially obscured pre-Valparaiso valleys KAMES eroded ? One thinks immediately of the un­ derlying limestone but finds on examination Still another type of morainic gravel de­ that bedrock .is only rarely exposed in the posit is to be considered before the subject stream floors and is seldom found in upland is closed. Two good examples lie 4Vz miles wells, even those as deep as adjacent valleys. west of Wheeling (Wheeling quadrangle) The bedrock has no relief features corre­ and half a mile north of Dundee Road. Each sponding to these pre-Valparaiso valleys and is a hill of gravel standing from 25 to 40 their divides. One finds, however, in high­ feet above the surrounding undulatory way cuts and stream-eroded bluffs, that the moraine surface. Two pits opened in the clayey Valparaiso till (the direct deposit of northern hill expose gravel containing much the ice) is surprisingly thin, on hilltops and clay and fine sand, showing that the sorting on valley slopes alike. The till is essentially PRE-VALPARAISO VALLEYS 53 only a veneer, in many places not more than For example, the Tinley moraine bounda­ 10 feet thick, and under it is a distinctly ries are indefinite contacts even though lines different kind of glacial drift. It is in the have been used. The endeavor has been to underlying drift that the pre-Valparaiso include the higher and more steeply sloped valleys have been eroded. morainic topography in the marginal mo­ The best exposures of this lower drift are raine. In places this makes the outline in the abandoned quarries a mile or so west very irregular. Elsewhere, there is complete of Lemont, just outside the Chicago area3 gradation, with no change in slope from the but there are numerous good ones along and highest part of the marginal moraine to the near Sag Channel and along DesPlaines lowest part of the ground-moraine, and here Valley west of Argo (Sag Bridge and Palos the location is simply a matter of opinion. Park quadrangles). For the gradations of nature, we choose This older drift beneath the Valparaiso to use lines which show our ideas of genesis till is strikingly free from clay, its finest and relationship. A geological map cannot material being a silt or very fine sand. Its have the precision of a photograph. The oxidized parts are distinctly lighter in hue reader who checks over any part of these and yellowish rather than brownish. It has maps in the field must permit the geologist a large percentage of stratified materialin it, one of the privileges of an artist. The map so much that one hesitates to call it a till. is a picture in which interpretations as well Yet typically unstratified till with an abun­ as objects are shown. dance of ice-marked pebbles is intimately associated in many exposures with the water­ SALT CREEK AND FLAG CREEK VALLEYS handled, stratified material. The till itself One peculiar drainage feature of the Val­ is far more stony than the overlying Val­ paraiso and Tinley moraines in our area is paraiso till, although almost entirely lacking the course of Salt Creek. It has already been in the pebbles of shale (consolidated mud­ described as following an intermorainic sag, stone) that are abundant in the Valparaiso not a stream-eroded valley. This it does till. From the excellent exposures near from its head near the northwest corner of Lemont, this glacial and aqueo-glacial de­ our area, southward across the Elmhurst posit is named the Lemont drift. It is a quadrangle to the. middle of the Hinsdale record of a pre-Valparaiso glaciation. Fol­ quadrangle. About a mile north of the busi­ lowing this was an interval of stream erosion ness district of Hinsdale, the creek turns before the Valparaiso glaciation occurred. abruptly eastward, leaves the sag, crosses The Valparaiso ice over-rode the Lemont the Tinley moraine, and joins DesPlaines drift much as though it had been bedrock, River some miles farther east near River­ and the · height of the Valparaiso moraine side and Lyons (fig. 43). But the morainic (at least in the Sag Bridge quadrangle) is sag, largely occupied by Flag Creek, con­ mainly an expression of the thickness of the tinues southward for six miles to join the Lemont and not the Valparaiso till. DesPlaines valley north of Mt. Forest MAPPING OF CONTACTS Island. If Salt Creek had followed this sag Perhaps the reader, while scanning the direct to DesPlaines River, its route would maps referred to in this report, has won­ have been 13 miles shorter. In this detour dered at the apparent precision with which to the east and back again as a part of the the boundaries between different formations DesPlaines, its waters flow three times as and deposits have been drawn. The author far as appears to have been necessary. If the has similarly wondered how he dared show sa:; were followed all the way, the creek some of these contacts by lines. On the map would have a fall of nearly seven feet per they look as definite as fence lines. Many mile from the moraine transection to the of them are just that definite in nature but river. The gradient of its waters now be­ many others are simply gradations. Particu­ tween these two points is actually about larly is the latter true of the contact between two feet per mile. marginal moraine and ground-moraine. Did Salt Creek ever use the shorter route,

3The exposures may be located by reference to the old the Flag Creek part of the morainic sag, and quarry dumps on the south side of DesPlaines Valley, has there been a shift to a longer and less eastern part of Joliet quadrangle, shown in red on Plate Bulletin 51 of the Illinois State Geological Survey, ''GeologyI, steep gradient ? Piracy certainly has. not and Mineral Resources of the Joliet Quadrangle," by D. ]. Fisher. occurred here, for that procedure always 5-l- UNCONSOLIDATED MA TERIALS

water way across the moraine north of Western Springs was not then possible. And glacial water there was, for the ice certain­ ly did not all disappear by evaporation. One may ask therefore if a glacial river ever occupied the full length of the sag north of the DesPlaines River. The sag contains no kame terraces like those in the valleys of the Mokena and Sag Bridge quadrangles. Is there a valley-train, an aggraded "flood plain'', of a glacial Salt Creek ? There are three stretches along this valley where record of a valley-train may be sought. One part is the upper Salt Creek valley portion where postglacial erosion might be expected to have removed part of it; the second is the streamless tract between Salt and Flag creeks where it should be present essentially as deposited; and the third is Flag Creek valley where postglacial deposition might have buried it under peat, muck, clay, and silt. Dozens of borings along the Salt Creek portion have shown only glacial drift out­ side the present floodplain. Within the limits of this narrow, crooked meander belt, the upper three to six feet of material Fie. 43.-Sketch map showing the relationship of Salt Creek, Flag Creek, and Des Plaines consists of alluvial clay, sand, and fine River. gravel, with many fragments of woody ma­ terial-clearly a postglacial deposit. Below gives steeper grades and generally makes this in some places is a poorly sorted fine shorter courses. gravel that may be. considered either as an The moraine is extraordinarily low at earlier deposit of Salt Creek or as glacial Salt Creek crossing. A dam here, as high river gravel. It certainly does not record as the valley is deep, would not divert the a large stream. The Salt Creek portion has creek along the shorter Flag Creek route no mappable valley-train. without the aid of a ditch at least five feet deep and a mile long. The floor of the On the sag floor between Salt Creek and Flag Creek sag is actually higher here than the marsh at the head of Flag Creek, no the summit of the moraine. Furthermore, gravel has been found. The floor is gently the topography in the sag is itself morainic, rolling, the underlying material is till alone the material in the low knolls is glacial till or is till beneath basin deposit. There is no and in the depressions among the knolls it valley-train here. is clay and muck resting on glacial till. The head of the Flag Creek valley was There is no abandoned channel across the trenched for three miles at the time of this tract to record its use by the creek. It seems study, the trench being made for the sewer obvious that Salt Creek never has used the system of Hinsdale, Clarendon Hills, and shorter route which appears, on first inspec­ Westmont. The excellent exposures showed tion, to be so invitingly open. two to five feet of alluvium and swamp Defeated in this attempt to find the material resting in some places on till and plausible looking valley a postglacial stream­ in other places on gravel, sand, and silt. way, one may recall the four lakes of the Bedrock crops out in the valley bottom half moraine sag farther south. The ice-sheet a mile south of the disposal plant. It was served, in part, for the retention of their also encountered at several places during the waters. At the same time, the ice-front excavation of the trench and presumably rested on the Tinley moraine north of Mt. is not far below the limit of the trench else­ Forest Island as well as south of it. A where. The stream material in the floor of REGION EAST OF TINLEY MORAINE 55

Flag Creek valley is doubtless relatively LAKE BORDER MORAINIC SYSTEM thin everywhere. It also is relatively fine There are four broad, low moraines in material and so does not record a vigorous the northeastern part of the Chicago area, current. Yet it can not be a deposit of the all composed of clayey till identical in ap­ present creek because the marsh at the pearance with the Valparaiso and Tinley head of the valley is underlain by the same tills, all roughly parallel with the lake shore sort of material. The sand, silt, and fine on the east and with the Tinley moraine on gravel on the bottom of this valley hardly the West, all descending to lower elevations seems to deserve the name of valley-train, southward, and all projecting into the lake although it must have been deposited by a plain where they end. The separating glacial river. Its record is somewhat com­ sags are all occupied by southward-flowing parable with that of the outlets of the four streams and are really reciprocal projections lakes of Tinley age south of the Sag Chan­ of th� plain dovetailing with the tips of the nel. Thus one concludes that melting at morames. the Tinley morainal stage was not very These four broad low marginal moraines rapid and that the discharge here made constitute the Lake Border morainic system only an insignificant glacial river. (pl. I) . The system is recognized (though REGION EAST OF THE TINLEY MORAINE not with the same number of members) along both the east and west sides of Lake The Valparaiso and Tinley moraines ex" Michigan, just as is the older Valparaiso tend completely across the southern end of moraine. The southward termination of the Chicago area and completely along the these ridges in Chicagoland and their essen­ western side. No other topographic element tial absence around the south end of the lake of the region possesses such areal extent. is a curious thing. The ice edge certainly Between the Tinley moraine and Lake lay across the moraineless area when the Michigan are several prominent features of existing members of the system were built. varied character. Either no moraines were ever made or they The most marked and most extensive have since been obliterated-the problem land form east of the Tinley moraine is the will be discussed again when the plain itself Chicago plain. Neglecting smaller areas has been considered. which are only interruptions in it, the plain Drainage control by the Lake Border reaches from the Tinley ground-moraine to ridges is very marked. DesPlaines River the lake shore everywhere except in the enters the Chicago area from the north in north where a series of four marginal mo­ the lowland between the Tinley moraine raines with intervening sags takes its place. and the outermost member of the Lake They are, of course, younger than the Tin­ Border system, the Park Ridge moraine. It ley moraine, as is the plain itself. Inter­ continues southward along the lowest part of the Tinley ground-moraine to River rupting the plain, really protruding through Grove and Franklin Park, a distance of 22 it, are some elevations of glacial drift and miles, where, the Park Ridge moraine end­ of bedrock. Also interrupting it but really ing, the stream enters the Chicago plain. superposed on it are numerous low ridges Still flowing southward in a very shallowly of sand and gravel. These sand and gravel entrenched course across the plain it enters ridges are subparallel with the lake shore, the head of the deep valley on the north as are most linear features of the Chicago side of Mt. Forest Island, in which it flows region, but they also converge roughly fun­ southwestward across the Tinley and Val­ nel-like westward toward the two valleys paraiso moraines and out of the region. bounding Mt. Forest Island and crossing Along the northern margin of the Chi­ Tinley and Valparaiso moraines. Just as cago area, the Park Ridge moraine is fused the varied features of the Valparaiso and with the next moraine to the east, the Deer­ Tinley moraines are closely related in origin field, but about two miles south of this and easy to understand when one has the margin a slight sag appears and, increasing key, so there exists in all this complex east in depth and width farther south, separates of the Tinley moraine a simple genetic rela­ the two moraines. Run-off that gathers in tionship. Let us consider first the northern it gives rise to the south-flowing West Fork part. of North Branch of Chicago River which, 56 UNCONSOLIDA TED MA TERIALS

at the southern tip of the Deerfieldmoraine DESPLAINES VALLEY-TRAIN is joined by East Fork to make Nort Branch. Four miles south of the tip of theh For almost the full length of the Park Deerfield moraine North Branch turns Rid�e moraine, the DesPlaines valley im­ southeastward across the Chicago plain and mediately to the west contains a deposit of finally enters the lake, or did before the gravel, sand, and silt. Its width varies from flow of the river was reversed in the heart � third of a mile to 1 Yz miles. Its surface of the city. East Fork of North Branch 1s flat,except for certain low swells of gravel and for the dissection wrought by the river w i�h heads just north of the Chicago area utilizes� the depression between the Deer­'. and its tributaries. Its altitude is about 650 field and Blodgett moraines. The Blodgett feet above sea-level near the northern limits moraine is the smallest member of the of the area and thence descends uniformly. system and terminates at Northfield. East southward for 22 miles to an altitude of Fork is there joined by Skokie River, \vhich about 625 feet. The slope thus is hardly flows southward along the sag between the more than a foot to the mile. One might Blodgett and Highland Park moraines. Both therefore think the valley should be mapped Skokie River and East Fork swing away as a long finger of the Chicago plain extend­ from the lake before becoming a part of ing northward between the Valparaiso and North Branch. This is owing to a large Lake Border moraine system. But none of sand and gravel accumulation on the Chi­ the other "fingers" in the Lake Border cago plain south of the three eastern mo­ system is flooredwith gravel, nor does gravel raines of the Lake Border system. occur under the Chicago plain itself. And this gravel deposit extends northward be­ All of these stream courses are determined yond t e Ch cago area, rising gradually with by pre-existing relief features and the only mcreasmg� distance.! It is a marked feature stream-made changes here have been the just east of Libertyville and is recognizable deepening of the inherited routes. Skokie as far north as Wadsworth, 13 miles north River's relation to Skokie Marsh shows this of our area and within five miles of the strikingly. The stream water, entering the Wisconsin state line. In this distance its north end of the marsh, simply filtered surface rises 20 feet, or about 18 inches to through about two miles of marsh (before the mile. Skokie Park was made) without maintain­ ing a mappable course. The river here has Numerous pits show the material to be not even deepened its inherited valley. well stratified and generally well sorted. It s most y gravel, the size of pebbles definitely The lakeward side of the easternmost mcreasmg northward. Toward the south ridge, the Highland Park moraine is the � � the deposit is mostly sand and its gravel is wave-cut cliff already described. Be ore the composed only of small pebbles. The maxi­ cliff-making, this eastern slope descended to f mum known thickness is about 15 feet with much lower altitudes than do any of the the bottom not reached. The till f the sags among the ridges, although it probably adjacent moraine country goes beneath the was not much steeper than those elsewhere � eposit, indicating that the gravel and sand on the ridges today. ?1s younger than the glacial drift. Ten miles south of the tip of the longest Every feature of the DesPlaines valley moraine of the group, the Park Ridge mo­ gravel deposit points to one interpretation­ raine, and entirely surrounded by the plain it is a river deposit, but made by a far is the elevation known as Blue Island. It larger stream than the DesPlaines River is clearly a morainic ridge in origin. Its of today. Only when the continental ice­ marked elongation and its orientation sug­ sheet was building the Lake Border mo­ gest that it belongs to the Lake Border raine system could the valley have carried system. Perhaps it is a relict frag;ment of �o great a river. l\1eltwater then discharged a once continuous ridge from the north, the long sag between the Tinley mo­ perhaps no continuous ridge was ever built. 111rame�0 and the Lake Border system, escaping It is considered as a part of the Park Ridge southward through it to the Chicago plain. moraine. It is older than the surrounding The deposit is a valley-train, a good example plain and possesses some very interesting of the type and the only good one in our marginal features intimately associated with region. Other valley-trains lie a few miles the origin of that plain. to the west beyond the larger Valparaiso REGION EAST OF TINLEY MORAINE 57 moraine. The DuPage valley contains one, the plain, and second, the topography and so does the Fox valley, and even the Des­ composition of the higher tracts which inter­ Plaines valley below Joliet, but these valley­ rupt it. trains had all been completed and abandoned During the past 20 years there has been before that in the upper DesPlaines valley in Chicago an almost uninterrupted series of our region was made. of excavations and some knowledge of what Material of the valley-train is increasing­ lies beneath the surface has been almost ly finer toward the south until in the termi­ unavoidable for the average resident. In nal portion it is almost wholly sand. It some places the surface material is sand, grades into the Chicago plain in the vicinity perhaps with gravelly layers ; in most places of River Grove and Franklin Park. Des­ it is a dense stony clay without layers or Plaines River continues sou thward across stratification. Heavy structures built on the plain for miles but nowhere is it ac­ the plain require piling or special under­ companied by deposits of the glacial stream. pinning for their support because of the The glacial river did not flow farther south weakness of the natural foundation. than the two towns named. It did not reach The stony clay is identical with that in quite as far south as the tip of the Pa.rk the moraine ridges. It is a glacial deposit Ridge moraine. Why should the glacial but without the accompanying sag and swell river have ended where the modern stream topography. The sand and gravel can be flows continuously on? It is a simple ques­ traced back to the same transporting agent tion and has a simple answer when the plain but they have gone through some later ex­ is understood. perience, to which they owe their sorted and CHICAGO PLAIN stratified condition. The plain, therefore, although composed of glacial drift and its Next to the Valparaiso moraine, the Chi­ derivatives, was fashioned by other agents cago plain has the largest surface area of after the ice retreated. Where unmodified any geological feature in the region (pl. I). drift underlies the plain, erosion of some The plain is the "vast prairie" of many sort apparently has occurred, destroying the 7 5 visitors to the growing city years ago. characteristic relief of a glacial deposit and Lack of roads forbade adequate acquaint­ producing the plain surface. Where the ance with the prairie in which the city was subjacent material is stratified sand, glacial situated and it appeared illimitable, prob­ till generally occurs beneath it. Deposition ably because it was viewed only from the by an agent capable of sorting the drift ap­ little settlement at the river mouth. The parently has happened in such places, bury­ width of the plain (east to west) ranges ina the drift and making the plain surface from 5 to 15 miles, its length is only 40 0 by aggradation. In a general way, the higher miles. Its crescentic outline, between the parts of the plain (not its interruptions) Valparaiso moraine and Lake Michigan, has are underlain by unmodified drift and the already been noted. lower places by modified (sorted and strati­ Neglecting interruptions in it, the plain fied) drift. Though erosion and deposition nowhere is more than 60 feet above the are essentially opposite changes, we know lake, and it averages perhaps 25 feet above. that the same agent may do both, provided In a general way it slopes lakeward from the conditions vary from place to place. its western highest parts, but large tracts on it were originally marsh land, so poor Of the postglacial agents operating in was Nature's drainage. Another general Chicagoland, only one set is at all likely to feature of the plain is an irregularly longi­ have made a plain by eroding away higher tudinal elongation and distribution of most tracts and depositing on lower ones. That is of its interruptions, so that they lie roughly the group of shore agencies now working parallel to the lake shore. In this lies the along the margin of Lake Michigan. Vis­ explanation for the curious parallelism of ualize the lake surface immediately after the the plain's streams and the lake shore. ice-sheet withdrew, 60 feet higher than the Clues enough have already been given the lake at present. Put the waves and shore reader as to the geologist's explanation for currents at work on the margins of that this plain. Let us check over the evidences expanded lake. Allow sand and silt to be and establish the case inductively, consider­ carried out into the deeper places from the ing first the kinds of materials underlying sites of erosion. Then slowly lower this 58 UNCONSOLIDA TED MA TERIALS

ancient lake surface through centuries of Chicagoland's ex1stmg lake shore time, sweeping the migrating shoreline com­ marked by cliffs, sand beaches, and rows ofis pletely across the emerging plain. In this dunes. If the sand ridges of the plain are way, we believe, the plain has been made old beach ridges, they should be accom­ from a tract of gently undulatory glacial panied by cliffs and dunes. The cliffs should topography. The lake was dammed between occur in the intervals along lines of inter­ the ice-sheet on the east and the moraine rupted ridges, thus continuing the supposed on the west, and it became extended east­ shoreline across the stretches where wave ward as fast as the ice melted away. There erosion instead of deposition occurred. was no interval of exposure of the plain to These cliffs should face eastward, toward weathering and stream work.4 In the ex­ what was the open lake. The dunes, argued istence of a lake over the entire Chicago from relations to present shores, should lie plain we find the explanation for the termi­ in belts alongside the ridges or perhaps occur in place of some ridges in any one line. nation of the glacial DesPlaines River at River Grove and Franklin Park, for there Cliffs are not depicted on plate I-it it entered the lake, or a bay of the lake, shows only deposits. Several dune belts and whereas the modern river continues across groups are on the map however, one between the lake bottom that emerged after the Homewood and Thornton, one between glacial river had ceased flo:wing. The Thornton and Lansing, one through the glacial lake and river were necessarily con­ corporate limits of Calumet City, one along temporaneous. the western edge of the "Blue Island" por­ tion of Park Ridge moraine, one in the If the Chicago plain is former lake bot­ corporate limits of Wilmette, and a few tom, the margins and any former islands of others. They are not, of course, active the lake should possess old shoreline fea­ today, nor are any of them comparable in tures. Allowing for subsequent modifica­ size to the Indiana dunes. tions, they should resemble the different types of shorelines Lake Michigan now The old shorelines are best developed possesses. Plate I shows the generalized where facing broad areas of the plain­ tracts which were swept by waves travelling characteristics of the plain. Its most strik­ in from the open lake. They are faintly ing features are the sand (and gravel ) developed or even lacking in protected and ridges here and there along or very near constricted places. They wrap around the the higher western margin and much more elevations in the plain (formerly islands prominently displayed out on the plain itself. in the lake). All this is as the theory re­ Most of them are narrow and curvilinear. quires. But there is one peculiar feature Many have short, barb-like ridges project­ which the theory, as presented, does not ing from the moraine side rather than the explain. Old shore features-sand ridges, lake side. They lie the plain, hence are on cut banks, dunes-occur not only along the not glacial deposits of any kind. Each ridge contact of plain and moraine, but they also has an essentially horizontal base, a fact not occur out on the plain, miles from the shown on the map but very suggestive of "shoreline" contact. Indeed, the sand and their method of origin. Where close to­ gravel ridges on the plain are better de­ gether these ridges are usually subparallel veloped than those along the margin. They with each other or are disposed end to end are essentially horizontal, as undeformed a row. shore features should be, but they occur at m The sand ridges are clearly construction­ lower altitudes successively eastward across al. They are not the product of any agency the plain, so that those about Lake Calumet now altering the plain, yet they post-date and Wolf Lake are 50 to 55 feet lower than the highest one to the west. This change the glaciation. It is logical to see them as in elevation is not because the ridges them­ a product of the same general conditions selves are smaller and lower, for there is under which the plain itself was made. The no progressive change in ridge height in the theory that they are old shorelines should series. It is an expression of the gentle east­ therefore be tested. ward slope of the plain itself. 4This statement takes account of only the latest Obviously, the eastern beach ridges were gluciation, c1 uring whose closing stage's the plain was form eel. not formed in water 50 feet deep. Judging REGION EAST OF TINLEY MORAINE 59 from present lake shores, the ridge crests it could never reach the high former level were probably built up a little above the unless the DesPlaines valley, west of the average water-level of their time. It fol­ plain, were dammed. Obviously then, this lows, therefore, that this descending series valley probably did not exist to its present of ridges records an intermittent lowering depth when the ancient lake lapped up of the lake level, slow enough to allow a against the moraine country. The valley succession of later and lower shorelines to was, without question, the outlet of that form as the lake margin retreated eastward lake and undoubtedly was deepened by such across the sloping bottom. use. If the lake had a constant volume of The patterns of these old shores out on discharge during its existence, it was low­ the plain (pl. I) afford several interesting ered by the deepening of the outlet channel. puzzles. Why the festoon outlines near Thus the lake margin would be shifted suc­ Dyer, Thornton, and Niles Center and be­ cessively eastward, exposing the western tween Lake Calumet and Chicago River ? higher parts of the submerged area. This Why the almost complete circular outline explains the occurrence of shorelines out on in and near Thornton ? Why the elongated the plain, successively lower toward the east. loop in Alsip ? Why the short isolated ridges There are two outlet channels leading in many places ? Why the disposition at westward from the old lake, one on each right angles of several closely adjacent side of Mt. Forest Island. They join after ridges ? The explanation must harmonize crossing five or six miles of moraine country. with known variations among existing Both lengthened eastward as they were shores, else the theory becomes suspect. Con­ deepened and the lake was lowered. The sideration of these and other peculiarities southern outlet, or Sag Channel, tripled in are given in a later chapter. length, becoming at least twice as long on One more feature of the Chicago plain the plain as it was across the moraine be­ and we are through for the present. Al­ fore water ceased to use it; the northern one though the plain in general slopes eastward about doubled its length by this eastward toward the lake, some of its drainage escapes extension into the plain. westward to reach Mississippi River. With­ Since the channel heads do not reach the in the plain lies a "continental divide," how­ present shore and are at least 10 feet higher ever unlike the summit line of the Rocky than the lake today, it is obvious that mod­ Mountains it may be. The two largest ern Lake Michigan never has discharged stream-formed valleys of the region, those of through them and that events outside our Sag Channel and DesPlaines River, lead region caused the final lowering by which the Mississippi's share of the drainage west­ the channels went dry. The old lake, with ward across the Valparaiso moraine, al­ discharge across the moraine to Mississippi though the moraine crest is elsewhere 50 River, is known as Lake Chicago. feet or more above the highest part of the plain. Profilesof all but two of the railroads CONCLUSION which cross the moraine (fig. 38) show this The character and topography of the un­ strikingly. The railroads climb as much as consolidated materials record unequivocally 100 feet above the plain before leaving the the presence of glacial ice and glacial water region. But the Alton and the Santa Fe in the Chicago region. The changes wrought railroads have no climb to make. They fol­ by them were far greater than all subsequent low the DesPlaines valley and their profile changes by agents and processes now at is a continuous downgrade out of Chicago. work. The record is far different from that One may recall the Drainage Canal and the of the bedrock beneath the unconsolidated reversal of Chicago River in this connection. materials. In presenting and interpreting Both are further evidence that the plain at the evidence, we have inductively deciphered one place on its western margin is as low as the larger elements of Chicagoland's glacial its entire eastern margin. history. More careful attention to the de­ If the level of Lake Michigan should rise tails of this history follows in the historical enough to flood back on the old lake plain, section. 60 BEDROCK

BEDROCK OF THE REGION INTRODUCTION and lower in the southeast. Thus the for­ mations are not exactly horizontal but slope Though bedrock is the most extensive geological feature of the Chicago region or dip gently down toward the southeast. and is almost nowhere more than a hundred This is of great significance in the drilling feet distant from any resident of the metro­ and use of deep wells, as will appear later politan area, few people in Chicago are in this section. conscious of its existence. The same might "Bedrock," a term used repeatedly in pre­ be said for most citizens of the state of ceding pages, implies consolidated rock. The Illinois or indeed those of all the Great glacial drift, the glaciofluvial deposits, the Lakes and upper Mississippi Valley states, lake sediments-all are rock but are uncon­ : so nearly complete is the thick mantle of solidated aggregates. The Niagaran lime­ glacial drift. In our region a few streams stone is as hard and as strong as concrete. have uncovered it, a few places along the Only by drilling and blasting can it be lake show it, a few hillside ledges occur. penetrated. It is not a monolithic mass, Our best sources of information about it however, for there are innumerable hori­ are quarries and deep wells. The wells are zontal planes along which it may be split, of value only if careful logs were kept at and many vertical partings. The horizontal the time they were drilled. Walls of aban­ structure is stratification, a record of the doned quarries remain satisfactory exposures deposition, layer upon layer, of lime mud of the bedrock unless the quarry fills with to make that entire thickness of 450 feet. water or is filled with rubbish.1 The consolidation to "bedrock" came later. The surface of the underlying bedrock is 2 not horizontal, nor, as we have seen, is the N rAGARAN FoRMATION surface of the overlying glacial and lake There is no greater contrast in Chicago detritus. Only where the bedrock surface geology than that between the Niagaran is relatively high and the overlying drift is limestone3 and the overlying glacial drift thin are outcrops and quarries possible. and its derivatives. The limestone appears There are at present fifteen quarry open­ almost monotonously the same in every ex­ ings in the region well suited to our purpose. posure. It possesses nearly uniform indura­ All openings, good or poor, and all the nat­ ural exposures, are in the same rock, a for­ tion, color, structure, composition. The mation known as the Niagaran dolomite or drift is uniform only in lack of induration ; limestone. The name comes from Niagara in allt other characters there are variations Falls, for the rock that holds up the lip of in every township, almost in every square the cataract is the same formation. Only mile. wells penetrate deeply enough to go com­ That the apparent monotony of the Ni­ pletely through it and into other kinds of agaran limestone means uniform conditions rock beneath. throughout the region during its deposition The well logs (records of thicknesses and should not be accepted hastily or uncrit­ kinds of material penetrated) show that for ically. The monotony is only by contrast a depth of nearly half a mile the bedrock with the extraordinary diversity of glacial of the Chicago region is stratified limestone, deposits. The N iagaran limestone carries sandstone, and shale. The N iagaran lime­ a record of changes during its deposition, a stone at the ton of the series has a maximum record of diverse conditions at different thickness of about 450 feet. With few ex­ places at any one time, and a record of vari­ ceptions each formation underlies the entire ous changes to which the rock was subjected area, so that all wells sufficiently deep, no 2The rock strata covered by the name Niagaran con� matter where they are located, penetrate stitute actually a series of at least fivegeological formations, nearly the same succession of sedimentary but for simplicity the series is discussed in this report as a single formation. rocks. Altitudes of the contact between any aThe term limestone is used in this report in the popular sense, to include the common carbonate rocks. Technically, two successive formations, however, are however, the common carbonate rocks of Illinois are classi­ higher in the northwestern part of the region fiedas limestone and dolomite. Limestone consists chiefly of calcium carbonate and dolomite is composed mostly of calcium carbonate and magnesium carbonate. Most of the iseveral deep quarries in the city have already been carbonate formations in the Chicago area fall into the filledwith refuse and doubtless all eventually will be. dolomite group. NIA GARAN FORMATION 61 after its making but before the glacial con­ of the rock shows enormous numbers of ditions arrived. fossil one-celled animals, too small to be The limestone was originally lime mud. detected by the unaided eye. The lime mud I ts thickness shows that the region was un­ of the Niagaran sea, therefore, is believed der water for a very long time. The mud to have been largely an organic sediment, was continuously added to the floor of the the product of a thriving marine fauna ancient water body. Its composition is more whose abstraction of calcium carbonate from than 90 per cent calcium and magnesium the wa ter was greater than the re-solution carbonate ; it contains comparatively little of that material after the death of the ani­ weathered detritus from older rocks. The mals. The net result, now that the Niag­ debris did not come directly from erosion aran epoch is millions of years past, is the of adjacent lands as mud does in Lake great limestone formation beneath our gla­ Michigan today. cial drift. The Niagaran sea, like the great A source for this great quantity of car­ ice-sheet, was far more extensive than the bonate mud is suggested by the shells and region we are studying. An explanation skeletal parts of marine animals, now fos­ for its existence is deferred for a few pages. silized, embedded in the rock. They are Limestone is a common sedimentary rock, mostly imperfect, broken, worn, disarticu­ widely distributed on all continents. Some lated ; obviously they were swept about by limestone is doubtless a chemical precipitate, waves and currents after the animals died. without the agency of life in its accumu­ Locally the limestone is crowded with such lation ; some is fresh-water in origin, some fossils. Furthermore, a microscopic study may be largely a product of calcareous plant secretions. The Niagaran is undoubt­ edly marine and its material probably is largely of animal origin. The material was removed from solution in the sea water of the Niagaran embayment by these animals. The sea today is the recipient of soluble substances leached from the land by rain, streams, groundwater-and so it doubtless was during Niagaran time. Thus the lime­ stone does, in spite of our denial, record wastage of the land of its time, although through the medium of solution and later precipitation.

REEFS AND KLINTAR In many quarry walls, one sees the strata at various inclinations from horizontal (figs. 44, 45 ), even dipping in opposite directions in the same wall. In the latter case the

FIG. 44.-Dipping beds of Niagaran limestone in Moulding-Brownell quarry at Thornton Above-the beds dip toward the right and diagonally away from the observer at an angle of about 30° with the hori­ zontal surface of the pool. Below-the beds dip directly toward the ob­ FIG. 45.-Dipping beds of Niagaran limestone in server. old quarry at Stony Island. 62 BEDROCK

FIG. 46.-Unstratified core of small reef, overlain by dipping stratified rock (Moulding-Brownell quarry at Thornton ). dips are like the slopes of a hill, down away pared with the fixed and semifixed forms from each other, not like valley slopes which that characterize the dome cores. approach each other downgrade. Exception­ The facts, and the reasoning from them, ally good exposures show these dome or hill lead us to one conclusion, and only one. dips to be less in the successively higher The domes are ancient reefs, coral reefs as strata and to grade up into horizontal strata they are commonly called. While the col­ over the dome top. One quarry, now filled onies thrived many kinds of corals grew on with rubbish, showed the bottom of such the wreckage of their ancestors, and their a dome, beneath which were also essentially compound skeletons gave anchorage and horizontal strata. Quarries in the Niagaran shelter to other forms. More food, more formation near Milwaukee, Wisconsin, also oxygen, less danger of burial in mud, greater show horizontal strata beneath dome struc­ variety of exposure owing to agitated water ture. created by the reef itself-all these con­ A good observer at a good exposure notes ditions favored a denser and more varied also that the dome has a core of unstratified population. When some conditions became limestone (fig. 46), that the color of the core differs a little from that of the strati­ fied rock, that the core rock is highly fos­ siliferous and is full of cavities from which ooze little driblets of asphaltum on hot summer days (fig. 4 7). Weighing these facts, one concludes that the domes are original aggregates of limey material on the ancient sea floor, formed at places where for some reason the marine population was more dense, or the calcareous detritus was more resistant to being swept about beneath the waves, or both. A representative collection of fossils from the unstratified core rock, compared with one from flat-lying strata, shows a prepon­ derance of sessile and non-swimming forms -corals occur in profusion, bivalve shells are very abundant, coiled shells are com­ mon. In the adjacent flat-lying strata there are far fewer fossils, but the free-travelling forms-floating, swimming, crawling-oc­ FIG. 47.-Asphaltum oozing from a cavity in cur in a considerably higher percentage com- core rock. REEFS AND KLIN TAR 63

FIG. 48.-Block diagram of the Thornton reef. altered and consequently upset the nice bal­ of the bedding in its walls may be seen from ance required for the growth of corals (in­ Halsted Street. creased muddiness might be adequate), the The reef rises 10 to 15 feet above the sessile branching foundational forms died, surrounding lake plain. If the glacial and the forms dependent on them also died or lake deposits were stripped away, the reef moved away, and the reef ceased growing. would be considerably more conspicuous Continued deposition of lime mud from topographically because the bedrock surface storm-stirred waters eventually covered the descends markedly out in all directions be­ reef with stratified sediment, thinner on the neath the drift. The reef apparently con­ top and thicker on the flanks, until finally stituted a preglacial hill, being more re­ it was completely buried and a smooth bot­ sistant than was the surrounding rock to the tom was again restored. ordinary processes of erosion before the Ice Age. An alternative view is that the reef Thornton reef.-Probably the largest Ni­ rock was left in relief by glacial erosion agaran reef in the Chicago region is at itself. Perhaps its present expression is due Thornton (fig. 48 ) (Harvey and Calumet to both experiences. We shall have more quadrangles),. It is approximately circular definiteopinions on this after the buried bed­ in ground plan and a little more than a mile rock topography of the entire region has in diameter. Erosion has stripped off any been examined. horizontal strata that may once have over­ Quarrying in the Thornton reef has re­ lain it and only a few feet of glacial and vealed no definite core nor horizontal strata lake deposits now cover it. The large quarry above or below. If any underlie it, quarry­ of Moulding-Brownell Company has been ing has not gone deep enough to demon­ excavated in the southeast quarter and is strate the fact. The exposed reef structure being extended northward almost entirely consists only of the beds dipping outwardly across the reef. The southeastward dip of at angles close to 30° from the central part the bedding can be seen very clearly on both of the low rock hill. In the quarry south sides of Ridge Road, just west of Thorn­ of Ridge Road, the dip may be seen to de­ crease southward and pass gradually into ton village. At the extreme' north end of the quarry, too distant to be seen from the the flat strata farther southeast, outside the road, the beds dip northeastward. The reef proper. The large Thornton reef there­ south limit of quarrying is beyond the mar­ fore fails to show a number of the features gin of the reef, in the surrounding hori­ listed as characteristic of reefs. zontal strata. Another quarry, now aban­ There exists another interpretation of doned, just west of Halsted Street, is in the these radially outward-dipping beds, an west edge of the reef. The westward dip earlier interpretation which perhaps should 64 BEDROCK be reconsidered. They may be uplifted have been perhaps 1000 feet higher than it domes due to movement of the rock since now is. Furthermore, if it was originally the formation was deposited. Without hori­ an unbroken fold, overlying beds of the zontal strata above or below, and without dipping strata would have been forced by the peculiar core rock, this hypothesis may the folding to slide upward on underlying look as satisfactory as the one of reef origin. beds. This becomes clear if we bend a pack Perhaps there may be both reef domes and of cards or a closed book to the same extent. uplift domes in the region. Without more Such sliding might be expected to leave facts we might assert or deny with all vehe­ abrasion marks between beds, scratches or mence and without limit, we might even gouges to show the adjustment that occurred take a vote on the question, but get no nearer under a heavy load during the folding. This is a good test to apply. the truth. More facts are necessary. Linear marks on the surfaces of these The southern side of the Moulding­ dipping beds do exist and they extend along Brownell quarry supplies the facts. Here the dip. But the way they fit into each is that gradation from beds standing 30° other clearly shows that each overlying bed from the horizontal to beds that are flat­ moved down the dip slope with reference the margin of the reef, we earlier called it. to the underlying bed. So far as this evi­ 25 For the past years this wall has been dence goes, the strata have settled down, almost continuously pushed southward as they have not been crowded up. This could the quarry area has been increased. During occur if the dip is original, namely if the this time there has come to light in this dome is a reef ; it surely is not a record of wall a series of little domes, from 30 to folding and uplift. perhaps 100 feet across, each with a core of dark gray dolomite, full of cavities, usu­ Yet even if figure 48 represents the cross­ ally fossiliferous, unstratified, and contain­ section of a part of a reef, the upper surface ing asphaltum. Many of them have shown of the block is erosional. It was erosional horizontally bedded rock above and some at the time the reef was growing. Detritus have shown it below the core. Most of them won by the waves from the core was carried have had a minor amount of dipping strata by the undertow radially outward to deeper on their flanks. On every count they are water. Here it was dropped and slid down true reefs, though only "baby" ones (fig. the slope to make the inclined beds. De­ 46). As the quarrying has been pushed tritus to make the outer beds travelled across southward, farther from the large struc­ the edges of beds already deposited. tures, the number of exposed baby reefs has From the various dips in the quarry, as decreased. The little reefs are certainly re­ shown in the block (fig. 48 ) , one would lated in some way to the main structure. infer that the reef core must lie north and They seem to be small colonies which grew west of the quarried areas. I ts nearly flat up like suburban villages about a metropolis. surface has been glacially eroded and bears Still, the case is not perfectly clear. striae that are oriented nearly northeast­ The Thornton tract is diagrammatically southwest. It had already suffered attack shown in figure48. The only exposed struc­ by weather and water before the ice-sheet tures, as shown in the diagram, are in the invaded from the north. To what extent quarry walls. All else is inferential. The the original structure has been reduced by east side of the block shows what relations these erosional experiences cannot be de­ must exist below the quarry floor level if termined. The pristine dome surface may the structure is a reef. Let us ignore this have been many feet higher; it may even for a moment and consider the surface of have been buried beneath later horizontal the block. If the dome is a product of push­ beds like some of the baby reefs. ing up of originally horizontal strata, then A strong suggestion that the dome is a a great deal of the structure has been "coral" reef and was considerably higher destroyed by erosion. The dome has been at the time of its maximum growth is found scalped, even beheaded. To see it as it in the west wall of the south quarry, a little would have been if formed by doming, we south of the right angle in Ridge Road. must connect the eroded edges of dipping Here are numerous masses of thin-bedded beds at comparable distances on each side of limestone with the stratification dipping the center. The dome, thus restored, would variously, neither in the same direction nor REEFS AND KLIN T 11R 65

Fie. 49.-Sketch showing dislodged fragments of reef-rock embedded in thick-bedded horizontal layers of limestone, over· which a "baby" reef was subsequently built while thin-bedded limestone was accumulating. at the same degree in any two masses. In several, the dip is actually northward, against the direction in which the strata in the adjacent dome dip. Inclinations as steep as 7 5 ° to 80 ° exist, more than twice as steep as any beds in the dome. These masses are very irregular in outline, range up to 100 feet in maximum exposed length, and are embedded in indistinctly stratified lime­ stone whose layers are thick and are nearly horizontal. Figure 49 shows the relation­ ships in one section and shows also a "baby" reef that grew later on top of the assemblage of variously oriented masses. Figure 50 shows horizontal beds overlying the nearly vertical beds of one of these masses. These masses are dislodged reef frag­ ments. Their strata could never have been deposited in their present positions. They are believed to have been broken from the main reef while it was growing and to have fallen, rolled, or slid down its sub­ marine slope to their final resting place, where they became buried in the off-reef horizontal strata. If this is correct, the reef must have been considerably higher than at present. It is impossible to explain them Fie. 50.-Displaced fragment of reef-rock stand­ by the hypothesis that the dome is the result ing nearly vertical and overlain by nearly of bending of originally horizontal beds. horizontal beds in place (Moulding-Brown­ ell quarry at Thornton). The man and dog Stony Island.-Another tract of relative­ stand at the base of the strata deposited in inclined position on the surface of the reef ly high bedrock, thinly covered or cropping fragment. out on the surface, is the elevation known 66 BEDROCK

FIG. 51.-Map of Stony Island (part of Calumet Lake topographic map). as Stony Island (Calumet Lake quad­ bedding planes parallel linear markings rangle). Ninety-third Street, between Stony which somewhat resemble glacial striae in Island Avenue and Kingston Avenue, tra­ appearance, though of course not in loca­ verses its length, about 1 miles. I ts width tion. From these markings it is clear that (north-south dimension));4 is hardly more in all cases the overlying beds have moved than a quarter of a mile (fig. 51 ) . It rises down the slope. They testify that the dome 10 to 20 feet above the surrounding lake has settled and flattened a little. They are plain and, like the Thornton tract, the rock not a record of uplift. surface lies many feet below that plain, so Like the Thornton tract in another re­ that if the glacial and lake deposits were spect, the Stony Island reef has been scalped removed the "islands" would be even more and lowered by glacial erosion, with striae conspicuous. As at Thornton also, the well shown along the south and east sides stratification is not horizontal but dips radi · of the larger quarry. Glacial erosion seems ally outward in conformity with the topo­ to have lowered the elevation. What made graphic slopes. it a topographic eminence originally ? Two abandoned quarries afford the best Very questionable indeed would be the exposures. The larger one, on the west flank idea that the Stony Island and Thornton of the "island", shows the dipping beds very elevations are simply surviving elevations on well, descending at an angle of 25 to 30° ° the Niagaran sea floor. In fact there is toward the surrounding plain (fig. 45). A evdience that in the Chicago region there smaller quarry on the south side of the was marine deposition after the Niagaran "island" shows dips correspondingly south­ epoch closed, followed by long continued ward. No core is now exposed but a core is erosion which removed the overlying de­ known to exist. Trenches for sewers and posits before the glacial epoch. It is signifi­ watermains, blasted out along several streets cant that nearly all of the more marked on the summit of the "island" about 1920, rock elevations of the region, whether ex­ encountered typical core-rock, unstratified, posed or known from borings and soundings, very fossiliferous as compared with the are reef structures. The reef rock was stratified rock in the two quarries, and apparently more resistant to the preglacial possessing numerous small cavities, some of attack of weathering and running water, which contained asphaltum. and thus was left in relief. The same con­ Movement of strata has occurred on the clusion has been reached in studies of very flanks of the "island" and has produced on similar reefs in the Niagaran limestone REEFS AND KLIN TAR 67 along the upper Wabash Valley of northern Lake Shore Kli11tar.-There is imperfect Indiana, where the rock hills have reef struc­ evidence along the shore of Lake Michigan tures and the reefs constitute the hills.4 of two more rock hills, each determined by Similar hills in Sweden have long been an ancient reef. Both occur south of the known as klintar. A single hill with reef loop district. The northern one is entirely structure is a klint. Adoption of the Swed­ out in the lake and below lake level, the ish terminology is advocated by the Indiana southern one lifts reefy ledges a few feet geologists and their suggestion is followed above the lake surface on the shoreline and in this report. includes some poor outcrops a few blocks Chicago H eights.-A rock hill partially inland. buried by glacial drift so that only its north­ The northern and submerged feature may ern and eastern slopes crop out occurs in be termed the Hyde Park klint. It reaches East Chicago Heights near the intersection from Pershing Road ( 3900 block) south of Cottage Grove Avenue and Lincoln to Jackson Park ( 5900 block), a distance Highway about four miles south and one of 2Yz miles, and is marked by seven named mile east of the Thornton klint (Calumet shoals.5 Of these the outermost is more City quadrangle). It rises rather steeply than two miles from the shore, in line with from the highest level of the lake plain on 49th Street projected eastward. Rock bot­ the north and has a relief of 25 to 30 feet. tom can be seen on three of the shoals and In an old quarry along Cottage Grove more than 40 exploratory borings made Avenue there are northward-dipping reef from scows have found rock in this area beds. No core is exposed. 30 feet or less below lake level. lVl cCook.-ln the southwest part of the Fewer borings have been made on the Berwyn quadrangle, about half way be­ land bordering this tract of shoal water but tween LaGrange and Argo, there is another enough exist t.o prove that the bedrock rock hill, so low and so nearly buried in surface descends westward from these shoals drift that nothing in the topography betrays with unusual steepness approximately along its presence. A small drainage way down the made-land waterfront. Where the pres­ its northern slope has been eroded to bed­ ent surface of the lake plain descends east­ rock, and a large quarry belonging to the ward, the older surface of the limestone Consumers Company has been excavated descends landward, in exactly the opposite partly in the klint and partly in lower flat­ direction. lying limestone south of the reef. The in­ On three of the shoals, rock ledges may clined reef bedding is very well shown in be seen through the water. On Morgan the north and west walls of the quarry. shoal the rock is smoothed by glacial erosion Judging from the direction of dips (south­ and shows reef bedding which dips lake­ ward in the west wall and eastward in the ward on the outer part and landward on north wall), the unexposed core should lie the inner slope. The shoal appears to be north of the adjacent Joliet highway and a reef in structure. Each named shoal is a little west of the Consumer's quarry. probably a reef and the unusually large Another large quarry, that of Dolese and tract of relatively high bedrock is probably Shepard, lies just to the southwest of the a composite of several reefs, seven of which Consumer's quarry. It is 3,000 feet long, may now be identified on the lake bottom. 2,000 feet wide, and 70 feet in maximum If there is a dominant central reef, it must depth, larger than the Consumer's quarry lie somewhat deeper and on it as a founda­ and nearly as large as· the Moulding­ tion the smaller reefs have grown later. Brownell quarry at Thornton. Throughout Burial of earlier reefs by growth of later its entire area, except at the extreme north­ ones is well shown in two places in the east end, the limestone is horizontal and McCook quarry walls, the later reefs de­ thick bedded. Only close to the Consumers veloping without reference to the tops of quarry is there any reef structure, the beds older, lower ones. It is also shown in other here dipping southward. The McCook reef Chicago quarries and therefore seems a per- structure is probably about three-quarters 'See "Chicago Lake Front No. 2" map of the United of a mile in diameter. States War Department's "Survey of the Northern and Northwestern Lakes." Oakland shoal is off 39th Street; •Cumings, E. R. and Shrock, R. R . Geology of the Morgan, Clemson, and the Outer and Inner Hyde Park . Silurian rocks of northern Indiana: Indiana Dept. of Con­ shoals are off 47th Street; Madison Park shoal is 0>ff 52nd servation, Division of Geology, Pub. 75, 1928. Street; and South Park shoal is off 54th Street. 68 BEDROCK missible idea to use. The Hyde Park klint, by this view, is compound. The other lake shore klint, which may be termed the South Shore !dint, occupies a considerable area lying mostly south of the South Shore Country Club. It is exposed along the shore approximately from 70th Street to 79th Street, a distance of about miles, and extends out into the lake atl Vz least as far as Clark Point shoal, a bed­ rock outcrop beneath the lake about 3,000 feet offshore. I ts greatest dimension, along a nearly north-south line, is about 2Yz miles. I ts sou them end is not far from the Frc. 52.-A glacially smoothed and grooved sur­ smaller but topographically conspicuous face of Niagaran limestone in Rocky Ledge Park showing reticulated pattern due to Stony Island klint. Like the Hyde Park jointing and stratification. The beds dip klint, the South Shore klint's surface slopes lakeward, the truncated edges of the strata westward, but gently. The highest place on trending from lower left to upper right. the klint is in the vicinity of 82nd Street The course of the joints is from upper left and Exchange Avenue. to lower right. (Jackson Park quadrangle.) Some structure is shown in the outcrops later been covered through conversion of a in Rocky Ledge Park, which extends north quarry into a dump. about 1,500 feet along the shore from 79th ( 1) Sag Bridge quadrangle, central part, Street. These ledges are low and at high along Archer Avenue grade on the south lake stages most of them may be entirely slope of Sag Channel valley. submerged. They carry traces of glacial (2) Hinsdale quadrangle, southeastern smoothing and grooving (fig. 52) but striae, part, along Flag Creek south of the Joliet if ever present, have all been worn away. Road. Almost the entire periphery of a Stratification is poorly shown in general but reef is shown in shallow quarries and out­ where recognizable it dips in various direc­ crops. tions and degrees. Al though not recording ( 3) Elmhurst quadrangle, southwestern a single symmetrical reef, such variations part, western limits of Elmhurst, quarry of really are the best evidence of reef origin. Elmhurst-Chicago Stone Company. The alternative hypothesis of warping and ( 4) Berwyn quadrangle, western part, bending of once horizontal strata cannot along 47th Street. Three closely grouped be used. Folds in the rock caused by def­ quarries along the Indiana Harbor Belt ormation must have systematic relations Railway south of Brookfield show some among themselves. Downfolding cannot reef structure. exist beneath or above upfoldings except in ( 5) Berwyn quadrangle, west-central minute crumplings. By the concept of irreg­ part, along banks of DesPlaines River, at ular reef gro-wth, these variants are possible. mouth of Salt Creek, and south of the bridge Neither of these lake shore features is at about 43rd Street, east of Lyons. truly a klint today, for neither constitutes ( 6) Englewood quadrangle, western a hill. But they were hills before the glacial part, north of Stickney village, just west of and lake deposits were laid do-wn over them. Chicago City limits. The former Haw­ Their existence explains the shoals and the thorne quarry, now filled with rubbish, Rocky Ledge Park outcrops, both known exposed the only large reef in the Chicago to residents of this section of Chicago. Some area known to have horizontal beds beneath of the shoals are obvious even to one never the inclined beds. out in a small boat ; they are marked by ( 7) Englewood quadrangle, northeast­ breakers during onshore storms and by pil­ ern part, quarry of Stearns Lime and Stone ing up of floe ice on them in winter. Company on 27th Street, two blocks west of Halsted Street. Reef structure is best Minor Reef Exposures.-Portions of shown in the upper part of the east wall. other reef structures have been exposed in The quarry is more than 200 feet deep, the following places, some of which have most of it in horizontal strata.

.\ JOINTS 69

Frc. 53.-Traces of two systems of joints on bedding plane forming the floor of Con­ sumer's quarry at Hillside. The joints are unusually close. (Hinsdale quadrangle. )

( 8) Englewood quadrangle, north-cen­ tral part, quarry of Chicago Union Lime Works Company at Darnen and 18th Street. This was the deepest quarry ever excavated in the region, 380 feet below the level of the surrounding plain, 360 feet below the lake surface, and nearly two­ thirds of the way to sea-level, almost to the bottom of the Niagaran formation. Reef structure showed in the upper beds of the east wall, but because this quarry was taken over as a city dump, these exposures are obliterated. FIG. 54.-Vertical joints in the Niagaran lime­ stone. JOINTS A bo'Ve-Quarry of Elmhurst Chicago Sterne 1\-fost consolidated rock in place, what­ Company, Elmhurst. ever its character or origin, is penetrated Befoqu-Quarry of Consumer's Company, by deep closed cracks called joints. They Hillside. generally form sets of nearly vertical planes parallel with each other. Two sets of par­ making of the rock and are therefore allel joints, approximately at right angles younger than any stratification. The Niag­ with each other, are common (fig. 53). aran limestone possesses two joint systems, Joint traces appear on flat outcrops or recognizable in almost every good outcrop quarry floors but joint faces, expressing or large quarry (figs. 52, 53, and 54). The their extent in depth, appear best on cliffs reefs of the region possess the poorest joint­ and quarry walls (fig. 54). Weathering ing; thick-bedded horizontal strata show it attacks rock more vigorously along these cracks or joints, cliffed outcrops break down best. The two systems are oriented con­ rather readily along them, and they facili­ sistently throughout the region. One set tate quarrying operations. Vertical joints, runs northeast-southwest, the other north­ in combination with horizontal bedding­ west-southeast. The two systems extend be­ planes, may produce rude rectangular blocks yond the limits of the Chicago region and in the quarrying operations both of Nature shmv in outcrops and quarries in the Niag­ and of man, the size of the blocks depend­ aran dolomite at Joliet, at Kankakee, at ing on the spacing of the joints and of the l\!I ilwaukec, and even farther afield. In at­ bedding-planes. tempting to understand the origin of these Joints are due to different causes in dif­ joints, this widespread consistency of orien­ ferent cases, but all are subsequent to the tation is an important item. 70 BEDROCK

Photograph by FIG. 5 5.-Sol ution of limestone is concentrated F,. TI. S/e1'ens along joints and consequently develops an Frr.. 56.-I rregul arly weathered surface devel­ intricate system of small channels on flat oped by solution along a fissure wall. One exposed surfaces. Dolese and Shepard side of the fissure has been quarried away. quarry (Berwyn quadrangle ). Note etching of more soluble layers and rounding of edges of less soluble ones. The beds are a part of the Thornton reef struc­ FISSURES AND FISSURE FILLINGS ture. Joint cracks may have become fissures through tensional adjustments in the lime­ looked at it critically. "How did it get stone. Indeed, the original joints may be here ? Where did it come from ?" he queried. only tensional cracks formed after consol­ There was no book, no report, no person idation of the lime mud, if drying out or to answer his question. No one knew. crystallization caused later shrinkage in No one had ever really raised the question volume. Warping stresses (for the forma­ before. He found the answer in the clay tion certainly has suffered some earth move­ itself, the only place where it could b� ments) may make joints and conceivably found. The clay contained jet-black shiny may open some to become fissures. Joints teeth, the teeth of sharks (figs. 58). There afford main routes for groundwater circula­ were not only cutting teeth of the type tion, and some fissure wallsshow undeniable associated with sharks, but "pavement" solution work (figs. 55 and 56). The open­ teeth also, crushers or grinders with which ing of such may be due wholly to this their possessors cracked the shells and car.. process. apaces of their prey. No fish teeth are If joints become open cracks, they consti­ known in the Niagaran limestone itself, tute fissures, into which loose material from their occurrence being limited to the clay above may fall. The debris may remain un­ fissure fillings. consolidated, or it may become indurated From studies in other regions where and thus the "wound" may become "healed". younger sedimentary rocks occur, these But a scar will remain, recognizable on shark teeth are known to be Devonian or quarry walls. The Niagaran limestone of Mississippian in age, some few millions of our region has some open fissures and many years younger than the Silurian system to fissure fillings, most of the latter still un­ which the N iagaran limestone belongs. A great gap in time occurred between the consolidated, known to the quarrymen as making of the Niagaran limestone and of "clay seams." the fissure clay. The fissuring appears to lVI ost of the limestone fissures are filled have occurred in this interim. If weather­ with clay (fig. 57). One might lose interest ing and groundwater action opened the at once on hearing this for "clay" does not fissures along joint cracks, as one theory sound very intriguing. Some one, however, holds, then we have here a record of emerg­ moved as the scientific investigator always ence of the region after the limestone vvas must be, dug out some of this clay and deposited, the sea being drained off and the FISSURES 71

FIG. 58.--Shark teeth (black) and limestone frag­ ments (light colored ) in clay filling from a fissure in the Niagaran limestone in quarry at Elmhurst. Teeth are about half natural size.

FIG. 57.-An irregular fissure filled with brown shale in which shark teeth are fairly com­ mon (Moulding-Brownell quarry at Thorn­ ton). Niagaran limestone undergoing its first en­ counter with the processes of degradation. The fissures that formed during this time were standing open to receive the first sedi­ ments of the returning sea. Sharks that in­ habited that sea left a record of their presence. Probably the Niagaran formation was entirely covered with thick marine deposits FIG. 59.-A fragment of pisolitic (pea-like) lime­ before this episode closed. The fissure fill­ stone from fissure filling (north quarry, ings, then, are only the roots of vanished Moulding-Brownell Company, Thornton ). formations that once overlay the region and cracks much as a filling of cement mud were removed when still later erosion might joint the walls together again. Lime­ scoured the surface down to the more re­ stone fillings are difficult to detect because sistant limestone. the material is so similar to the surrounding Most of the "seams" are of gray or green­ rock. Once found, however, they present ish-gray clay, and all search for fossils in interesting problems. In some the filling this material thus far has proved fruitless. is vertically banded as though deposited in It is only in black or dark clay that the layers on the fissure walls. In others the sharks' teeth are found. Still other fissure� limestone filling is composed of pellets, the contain limestone which has healed the size of peas, all cemented together (fig. 59). 72 BEDROCK

Fro. 60.--Layers of white chert in the Niagaran limestone exposed in a quarry near Lemont (Sag Bridge quadrangle). (Illinois Geo!. Survey Educational Series No. 3, fig.32.)

Broken pellets show by concentric bands reddish, full of black silicified fossils, the hmv they grew from tiny beginnings. These original calcium carbonate replaced by features seem to record deposition from so­ quartz. These fossils are mostly new to lution rather than from suspension. They science, their age unknown except that they are something like veins in the rock. Where more nearly resemble those of the Niagaran clay seams are associated with the lime­ limestone than of any other known forma­ stone fillings the clay is definitely younger, tion. occupying only the central part of the fill. The subject of fissuring and fissure filling Other fissure fillings consist of fragment8 in the Niagaran limestone has not yet been of the wall rock which fell into the crack fully studied. From what is now known, as it was opened. Their interstices may or fissuring appears to have occurred at dif­ may not be packed with clay. Still other ferent times and under different conditions. fissures contain brightly colored tough sandy Perhaps different causes for fissures of diL clay, brown, bluish, greenish, yellowish, and ferent ages will eventually be recognized. CHERT 73

Frc. 61.-Cross-section of spheroidal chert nod­ Frc. 62.-Irregular chert nodules the ule in a limestone fragment. Most of the m Niagaran limestone. nodule is hard and white but the dark cen­ tral portion is porous and friable. where closely crowded, the "tentacles" of CHERT adjacent nodules are tangled with each other or actually join. Such branched shapes One may see in some exposures of the (fig. 62) are obviously impossible in pebbles. Niagaran limestone what looks like rows of pebbles in the rock, distributed parallel with Many of the nodules contain silicified the bedding-planes (fig. 60 ). They are fossils, originally made of calcium carbonate. rarely if ever on the actual parting itself Some large coral fossils contain nodules but occur in the midst of a stratum. Though which faithfully reproduce those parts of the they are composed of hydrated silica and coral in chert, the rest being lime carbonate. quartz and thus are unlike the limestone Thin limestone layers penetrating chert in composition, they are not "pebbles." They nodules or thin chert seams penetrating lime­ are nodules of chert, a form of quartz or stone suggest strongly that the chert is of silica which "grew" by chemical aggrega­ secondary origin, its growth necessitating tion on the sea floor while the limy sedi­ concomitant removal of calcium carbonate ments were being deposited or which grew to make room for the silica. Only ground­ in the rock at some later date. The problem water could do this, but apparently it could of their origin leads us into two fields about not occur under present conditions. Perhaps which we know very little : ( 1) the con­ at depths of hundreds of feet this might hap­ ditions at the bottom of wide, shallow, lime­ pen, and if so the chert nodules suggest the depositing seas, and (2) alterations in lime former presence of a thick cover of sedi­ mud occuring during its change to firm mentary rocks younger than the Niagaran dense limestone. Neither field can be actu­ limestone but since eroded away. ally entered and studied at first hand. We The texture of the chert nodules also as yet understand but little better what varies widely. Some are dense and flinty, goes on in these situations than we would others are porous and somewhat chalky in understand political conditions in a strange appearance. The porous ones tend to blacken country by glimpses from an aeroplane of on exposure, the dense ones remain pure processions and pyrotechnics below us. white or light gray. Some have dense cores The chert nodules of the Niagaran lime­ and porous exteriors, in others the reverse stone have exceedingly variable shapes. Most is true. Causes for these variations are as of them are elongated parallel to the strati­ yet unknown. There is still much to be fication. Some are simple egg-shapes (fig. learned about the Niagaran chert nodules 61). Some are branched in all directions and and their origin. 74 BEDROCK

BULLETIN 65 . PART I PLATE II

2

3 5

4

6 7 BRACHIOPODS

EXPLANATION OF PLATE II

FIG. 1.-Schuchertella subplana FIG. 2.-Leptaena rhomboidalis FIG. 3.-Uncinulus stricklandi FIG. +.-Pentamerus oblongus FIG. 5.-Spirifer radiatus FrG. 6.-Meristina maria FIG. 7.-Conchidium laqueatum FOSSILS 75

FOSSILS unlike their Silurian relatives, are soft­ There is perhaps nothing in the Niagaran bodied and without an external shell. The limestone more interesting to the average squid and octopus are examples. Cephalo­ observer than its fossils. They are unequally pods of Silurian time lived in shells which distributed so that large exposures may yield are always recognizable, whatever their no recognizable forms whereas other layers shape or size, by the presence of numerous may be crowded with them. The reef struc­ partitions across the shell length dividing tures in particular afford good fossil hunt­ the structure into separate compartments. ing. The collector must not expect to find As the animal grew, it built successive floors the petrified shells themselves however. behind it and thus successively abandoned its What he collects will almost invariably be old living quarters for new and larger ones. casts of the interiors of the shells and hard Abandoned chambers, sealed offby the parti­ coverings or moulds of the exteriors, made tions, were gas-filled, buoying up the shell in the lime mud in which the organisms be­ so that the animal was free-swimming. One came buried. The actual hard parts have surviving shelled cephalopod with this habit been removed by groundwater during the is known-the pearly or chambered Nautilus formation's long subsequent experiences. In­ of the Indian Ocean. Modern cephalopods teresting "squeezes" may be made from the are tentacled and predaceous. Early forms moulds by forcing soft wax into them. This, doubtless were also, though the fossil re­ on removal, is a replica of the animal's ex­ mains, not recording the soft parts, cannot terior. be expected to prove this. Early cephalopod There are seven large groups of animals shells were straight. Later came the habit well represented by various species in the of coiling as snails have always done, but Niagaran fauna. One unfamiliar with mostly in a plane, whereas most snails are marine animals must learn a few new names coiled in a spire. The initial stages of coil­ and forms, but paleontology is a science in ing are shown in some of the Niagaran itself and no adequate presentation of its forms. elements can be attempted here. Plate V shows specimens of trilobites. Plates II-VII are photographs of speci­ Trilobites are very interesting fossils. The mens of Niagaran fossils from the Chicago group has been extinc.;t for many geological region and illustrate some of the more com­ periods, probably for two hundred million mon representatives of all the seven groups. years, but some of their relatives are living Plate II shows brachiopod shells. The today. These are the aquatic crustaceans brachiopods are bivalve-shelled forms, some­ like the crab, the crayfish, the lobster, and what resembling clams in general appear­ the shrimp. They are not, however, direct ance. The two valves of the clam shell, descendants of the trilobites. however, are mirror images of each other Crustaceans have a jointed or articulated whereas the two brachiopod valves are in­ shell or exo-skeleton, like a suit of armor, variably unlike each other. There are living which allows a much more complex and de­ brachiopods in the sea today, although they tailed body structure than does a shell, even are not to be found in collections made along a hinged two-piece shell. Complete trilobite the beach. They were far more abundant in fossils show a head, a series of body seg­ earlier periods of the earth's history such as ments, and a tail. Decomposition and shift­ the Silurian, when the Niagaran limestone ing about by the currents often separated was deposited. Almost all bivalve fossils these articulated portions before burial so found in this limestone are brachiopods. that lone heads or tails are more common Plate III shows gastropod and pelecypod than complete forms. An individual trilobite (clam) shells. Gastropods are snails and may have left several fossils. This follows about as common today as during Niagaran from their habit, possessed also by modern time. Most of them are closely coiled shells, crustaceans, of moulting or shedding the en­ with the coil more or less extended into a tire armour as the animal increased in size. spire. Each shell constituted a continuous Discarded exo-skeletons made as good fossils chamber in which the animal lived. as did the suit in which the creature died. Plate IV shows members of the cephalo­ Some of the fossil trilobites of the Niagaran pod group. Most cephalopods today, quite formation are found rolled up. 76 BEDROCK

Corals (pl. VI) include both single and called sea-lilies or stone-lilies, because of compound forms, the compound ones resem­ their limited resemblance in form and bling in a general ·way modern reef-building position when alive. But the crinoid is anm forms that live in tropical and subtropical animal and the calyx is like a lily only in seas. Simple or single corals are commonly shape, the crinoid stem is merely a support called cup corals or horn corals from their for the calyx and crinoid "roots" are simply shapes. Two common compound corals of holdfasts for the stem. Fragments of jointed the Niagaran fauna are the honeycomb and crinoid stems, known as "Indian beads," chain corals, each named from fancied re­ are fairly common fossils. The calyx is less semblances in their cross-sections. frequently found. Cystoids are related to the crinoids (fig. Bryozoa (pl. VI) still exist although only 63 and pl. VII). They both belong to a as encrusting forms, none as upright struc­ larger group whose best known modern tures standing by themselves. Bryozoa have representatives are starfish and sea-urchins. the compound or colonial habit exclusively Cystoids are extinct, crinoids still survive and their Silurian fossils somewhat resemble although they are not shore forms and there­ those of compound corals. The individual fore do not appear in collections made dur­ bryozoan lived in a tiny compartment, with ing a stroll along the sea beach. All mem­ one window, in the composite structure. bers of this larger group have calcareous Other groups such as foraminifera, sponges, exo-skeletons or body walls made up of and pelecypods, are more rarely or less con­ plates which fit together in various mosaic spicuously present. patterns. Commonly a fivefold symmetry is Most of the Niagaran fossils have living observable in members of the larger group. relatives in modern oceans. Few have living It is shown in the arrangement of plates and fresh-water relatives and only gastropods pores on the sea-urchin calyx and in the five have living land-dwelling relatives. In this arms of the starfish. Crinoids show this, we find further support for the idea of cystoids do not. Living crinoids have been marine origin of the Niagaran limestone. FOSSILS 77

BULLETIN 65 . PART I PLATE III

2

PELECY PODS

GAST ROPODS

EXPLANATION OF PLATE Ill PELECYPODS FIG. 1.-Mytilarca denticostia FIG. 2.-Matheria recta GASTROPODS Frc. 3.-Phanerotrema occidens Frc. 4.-Lophospira rotunda Frc. 5.-Tremanotus alpheus 78 BEDROCK

BULLETIN 65 . PART I PLATE IV

3

4

CEPHALOPODS

EXPLANATION OF PLATE IV

FIG. 1.-Kionoceras cancellatum FIG. 2.-Cyrtoryzoceras fosteri FIG. 3.-Dawsonoceras bridgeportensis FrG. 4.-Discoceras marshi FOSSILS 79

BULLETIN 65 . PART I PLATE v

2

4

5

TRILOBITES

EXPLANATION OF PLATE V FIGS. 1, 2.-Bumastus insignis FIGS. 3, 4. -Dalmanella platycordata FIG. 5.-Calymene ce lebra FIG. 6.-Arctinurus chicagoensis 80 BEDROCK

BULLETIN 65 . PART I PLATE VI

SPONGE BRYOZOAN

4 CORALS

EXPLANATION OF PLATE VI SPONGE FIG. 1.-Calathium sp. BRYOZOAN FrG. 2.-Fenestella sp. CORALS FrG. 3.-Lindstromia sp. FIG. 4.-Pycnostylus sp. FrG. 5.-Favosites niagarensis FOSSILS 81

PLATE BULLETIN 65 . PART I VII

CYSTOI DS 2

4

6 CRINOIDS

EXPLANATION OF PLATE VII

CYSTOIDS FIG. 1.-Holocystites sp. FIG. 2.-Caryocrinites sp. CRINOIDS FIG. 3.-Periechocrinus infelix FIG. 4.-Eucalyptocrinus crassus FIG. 5.-Syphonocrinus nobilis FIG. 6.-Crotalocrinus cora 82 BEDROCK

Fro. 63.-Restoration of a fossil crinoid, commonly called sea-lily. (Illinois Geo!. Survey Bull. 51, fig. 12, 1925.) DISTRIB UTION AND STRUCTURE 83

MINERALS GENERAL DISTRIBUTION AND STRUCTURE A number of minerals may be found in OF THE FORMATION the Niagaran formation. The principal ones There is or once was, a complete con­ are calcite, dolomite, quartz, pyrite, and tinuity of t e Niagaran formation from Chi­ sphalerite. The Niagaran formation is very cago to Niagarah Falls ; both places were largely composed of calcium-magnesium car­ under the same shallow sea at the time this bonate but it is only microscopically crystal­ lime mud was laid down. So with every line. It therefore yields but few specimens other place where the Niagaran limestone is of either calcite ( CaC03) or dolomite identified. A geological formation is a body (Ca Mg ( Co3) 2) for the mineral collector. of rock made at a particular time, it is the Of the two, calcite may be expected. It is record of its time, a page of the book of a transparent or translucent crystal, only earth history in which the events of that slightly harder than the finger nail, and time are inscribed. The extent of the forma­ possesses marked cleavage in three direc­ tion expresses the extent of the Niagaran tions so that broken pieces of calcite are sea. usua iy rhombohedrons, their angles being At Chicago, deep wells penetrate four aboutl 75° and 105°. Calcite crystals are differentlimestones. At Milwaukee several likely to occur in cavities in the limestone, limestones are similarly known to underlie deposited there by groundwater. Dolomite the city completely, and the uppermost one is similar to calcite but is commonly pinkish is also the Niagaran. At Grand Rapids and or brownish in color and has the unusual Muskegon, wells penetrate different lime­ feature of curved crystal faces. Its hardness stones also but the Niagaran is there identi­ is about that of calcite. fied far down in the series instead of at the Quartz (Si02, silica) occurs as crystal­ top. So at Detroit and at Cleveland. How line growths in cavities. The crystals are does the geologist identify any one limestone, small and crowded but some of them show or other sedimentary formation ? the typical six-sided prism capped by a six­ The most important evidence for identi­ sided pyramid. It is generally colorless and fication isthe fossil content. You may collect transparent or translucent and is a ground­ the same species from the uppermost forma­ water deposit. It is readily distinguished tion in the river gorge below Niagara Falls from calcite by its superior hardness, as a that you find in the Chicago quarries. Your knife blade will not scratch it, and it shat­ friends at Milwaukee or in the upper Wa­ ters or breaks irregularly. Chert or flint bash Valley of Indiana will find the same (hydrous silica), a cryptocrystalline variety species in their local limestone. The collec­ of quartz, occurs as the nodules described. tor working the Mississippi River bluffs Pyrite (FeS2, iron sulfide, "fool's gold") between Clinton and Davenport will find a is not uncommon, occurring in thin seams formation yielding the same suite of fossils. or as separate crystals on the walls of cracks. But he is more fortunately situated because It has a bright brassy or golden color when he will find other formations cropping out fresh a metallic lustre, and crystallizes in in the bluffs below and above the Niagaran cube or modifications of cubes. Pyrite is and yielding different species of fossils, each readily; attacked by the air and oxidizes to form rusty stains in the rock. Incipient formation having its own suite. He must oxidation produces beautiful peacock colors conclude that each formation is identifiable on the surface of the crystal. by its fossil fauna. Sphalerite is rare. It is a sulphide of zinc Each formation possesses essentially the ( ZnS) of the color and lustre of rosin. It is same fossils in all its exposures. Significant not likely to show crystal form. It has a differences exist between the fossil assem­ tendency to break along cleavage planes at blages in different formations. The order angles of 60° and 120°. of age is indicated by the order of super­ Other minerals are known in the N iag­ position, the lowest being the oldest, the aran limestone but are very rare. Some are highest the youngest. In these three con­ brought to light only by dissolving a lime­ clusions lie the principles of identification stone sample with acid and studying the and correlation. But "significantdifferences" insoluble residue under a compound micro­ does not mean "complete dissimilarity" in scope. fossil fauna. 84 BEDROCK

FIG. 64.-0utcrop belt of the Niagaran formation in the Great Lakes region.

Now the Mississippi Valley student, older, it follows that if they were all per­ knowing the order of superposition and the fectly flat-lying, the Michigan peninsula character of the fauna of each formation in inside the curve would be higher than sur­ his section, moves to Chicago or Milwaukee rounding land. It would stand above its or Detroit where only the uppermost of the surroundings as high as the younger rocks bedrock series of each place is exposed. He are thick, which in central Michigan is collects fossils from it and thus identifies it about 4500 feet. But central Michigan is as the formation which yields the same fos­ not higher than Ontario or Wisconsin or sils in the Mississippi River bluffs. Using Illinois. There is only one other explanation Niagara as a type locality we thus identify -the Niagaran and overlying formations the outcropping bedrock at Chicago as the are depressed so that they dip radially in­ Niagaran limestone. ward toward the center of the rude circle of The Niagaran formation of the Great the Niagaran outcrop. This conclusion is Lakes region is exposed in enough places to supported by well logs, the Niagaran occur­ allow the mapping of its outcrop areas. ring deeper and deeper toward the center Figure 64 is such a map, drawn as though (fig. 65) . Lower Michigan is a basin struc­ there were no glacial drift. The outcrop ture. The Niagaran formation in the Great belt swings northward along the west side Lakes region is shaped like a saucer and the of Lake Michigan from Chicago, then east saucer is full of younger rocks, each unit of through the eastern end of Michigan's upper them being a smaller saucer and all nested peninsula and a row of islands in northern perfectly together. In the same manner, Lake Huron, then south across the peninsula the older formations that crop out or under­ that pinches Georgian Bay off the main area lie the glacial drift outside the Niagaran of Lake Huron, and across Ontario to cross belt extend beneath the Niagaran forma­ back turning eastward into the United tion in the Lower Michigan basin. As the States between lakes Erie and Ontario where basin was depressed, the formations in its Niagara River takes its spectacular tumble. elevated rim were weathered and eroded Thence the outcrop belt continues eastward away so that except for the youngest and into New York State. smallest saucer in the stack only their rims The rocks immediately below the drift on may show at the surface or occur immedi­ the outside of this great curved course are ately beneath the glacial drift. As the for­ older, on the inside they are younger. Since mations immediately overlying and under­ younger rocks in a section must overlie lying the Niagaran limestone are less WELL LOGS 85

"' c: " c: -"' > ·a_ e u c: ro ro 0 0 :r: er: :::> "' :r: "' :!: +- -0 +-· c E c: '- '- 0 "' o ro :s: ...... Cl... (/) :r: LAKE ONTARIO

FIG. 65.-Geological cross-section of lower Michigan and southern Ontario. Vertical scale is exaggerated. resistant to erosion, they were worn down (fig. 65 ) . It was gone long before the ice­ more and along their outcrop belts are the sheet arrived to cover the area with its drift. depressions occupied by Green Bay and Using this method of reconstructing the Georgian Bay (on older rocks) and by lakes Niagaran sea, outcrops of the same forma­ Michigan and Huron (on younger rocks), tion near Lake Winnipeg and about James whereas the more resistant Niagaran lime­ Bay and Hudson Bay in Canada, on the stone, holding up better than the weaker archipelago north of the continent, and even rocks adjacent, constitutes the peninsulas in northern Greenland, less than 9° from and islands, and borders the outer coasts of the Pole, are tied together to show the ex­ the two lakes. tent of this great continental marine flood­ If the outcrop belt of the gigantic Niag­ ing. Other regions, known in the same way aran saucer is itself an eroded edge, it can to have been submerged, make the amazing not be the original shore line of the Niagaran total of 40 per cent of present North Amer­ sea. The limestone must have been more ica then under shallow sea water (fig. 66). extensive to the west of the Chicago region, Collections of marine animals today from to the north towards Canada, and to the the coast of Florida, of Maryland, of New east of Lake Huron. In the southeastern England, of Labrador, and of Greenland part of the Chicago region, where the show very great differences, for which the Niagaran limestone emerges from beneath decreasing temperature toward the north younger rocks, it is almost 500 feet thick. It pole is most largely responsible. One of the thins gradually westward across the outcrop most surprising things about the Niagaran belt until at the western edge, near Joliet, formation is that its fossil fauna in the Chi­ it disappears and its place beneath the drift cago region is essentially duplicated in is taken by the next older formation. This northern Greenland. Its reefs are known thinning is wholly a matter of erosion and from northern Indiana to Hudson Bay. so is its absence farther west in Illinois. It There could not then have existed a tem­ once was present-it has been entirely re­ moved. The Niagaran limestone along perature range in latitude such as we have Mississippi River, 200 miles farther west, today. Mild and equable temperatures seem is an isolated portion of this ancient sea­ to have prevailed-subtropical as we now bottom lime mud deposit. The Niagaran rank them. The Silurian earth did not have marine faunas are alike in both places and climatic zones. must have migrated freely across the gap. v\7ELL LOGS AND THEIR INTERPRETATIONS There must have been a continuous sea from eastern Iowa to western New York, The deepest well in the Chicago region is even though there is not today a continuous located at South Chicago Heights (Steger Niagaran formation between these points. quadrangle). It was drilled in 1893 as an Downwarping of the Michigan basin (the oil and gas test well and is reported to have basin of saucers, not the lake basin) pro­ penetrated to a depth of 27 56 feet, more tected the Niagaran in that region from than half a mile.6 Other reports place the erosion, while upwarping in Illinois exposed depth of the well as 2500 or 2700 feet.7 the Niagaran there to inevitable destruction Later the well was purchased by the village 86 BEDROCK

FIG. 66.-The Niagaran interior sea of North America, shown stippled ; white areas were land. and used asthe source of its municipal water limestone was 350 feet thick below the supply. The water apparently comes from glacial drift. Below it, the well entered formations in the upper part of the well. shale, passing into more limestone 180 feet The altitude of the surface of the ground deeper. The second limestone proved to be is 712 feet above sea-level and the bottom of 300 feet thick, sandstone being encountered the well is therefore a little more than 2,000 beneath it. At this depth the well was feet below sea-level. The drift is 56 feet already 174 feet below sea-level. This sand­ thick8 at the well site and penetration into stone was 200 feet thick and below it the bedrock is thus 2,700 feet. The Niagaran drill entered still another limestone forma­ "Habermeyer, G. C Public ground water supplies in tion, 350 feet thick. Another sandstone 250 .• Illinois: Illinois State Water Survey Bull . 21, p. 607, 1925. feet thick was found beneath this third 7Alden, W. C., U. S. Geo!. Survey Geo!. Atlas, Chicago folio (no. 81), p. 2, fig. 2, 1902. limestone, with a fourth limestone 190 feet Anderson, Carl B., The artesian waters of northeastern Tllinois: Illinois Geo!. Survey Bull. 34, pp. 107-108, 292, thick below it. Under the fourth limestone 1919. there was a third sandstone into which the SThe thicknesses of the formations as given here are derived from Alden's record in the Chicago folio, cited drilling was carried 880 feet without pass­ above. They are not exactly accordant with the thickness­ es revealed by more recently drilled wells in the vicinity. ing through it. WELL LOGS 87

SOUTH CHICAGO HEIGHTS c6�WILSON����· s WELL , s ITTU . m o;�·);;. / o.....-: '\•"-0 · ��"). .. \./." •.-"o\0 � &5A' ) N · ORIFT· . v-..· ,· . . . ' . , \ '•,j ':..-: o OC LAC IAL .. ·" 1' 592 ·,'yt·/: G I I I "'5°£1� -?:/.\ ..... �/.o · ... ·' 0• • ' \ ·--:J' ."t. ' ../ I I I I I I l I \ I I I I I I N I A G A R A N I I I I I I I L I I I I I I 312 I 306 ------�

��------SEA-LEVEL------L-� FIG. 67.-Relations of Niagaran formation in two wells in the Chicago area.

A well at 42nd Street and Ashland Av­ region, serving municipalities, industrial enue, drilled for the Wilson Packing Com­ plants, and railroad yards. All findthe same pany, is typical of many in Chicago itself. sequence and comparable thicknesses of rocks The log is more detailed than that at South (formations) as far as they go. Virtually Chicago Heights, recording two limestones all have been continued .to the Galesville and two sandstones in place of the third sandstone ; none penetrates through it. limestone formation. The complete log, with The identification of the various forma­ formational names, is given below. tions below the Niagaran limestone could It may be noted that the Niagaran lime­ not be made if we were limited to the well stone is only 215 feet thick, 135 less than at data alone. But the first formation beneath South Chicago Heights. The top of the the Niagaran crops out immediately to the well is about 120 feet lower than that of west of the Niagaran belt, the second ap­ the South Chicago Heights well and the pears in order next west of that, and so on drift 9 feet thicker, hence the upper surface (figs. 68, 69). Due to erosion on the gentle of the Niagaran formation is 129 feet lower, upwarp west of the Michigan basin, all these which is almost the same as the difference in buried formations appear in sequence, show­ thickness. These differences are the result ing here and there through the glacial drift. of preglacial erosion which beveled the upper From studies in the outcrop areas they have part of the formation. The bottom of the been named and classified as indicated in the formation is only 6 feet higher at the Wilson log of the Wilson Packing Company well Packing Company well, so the formation is and (fig. 69). essentially horizontal throughout the 22 Two systems older than the Silurian are miles that separates the wells (fig. 67) . thus represented, the Ordovician system be­ There are numerous wells of somewhat ing essentially complete. The six lowest comparable depths scattered throughout the sandstones are upper Cambrian, the Niag-

Loe OF WnsoN PACKING COMPANY WELL, 42ND STREET AND AsHLAND AVENUE, CHICAGO, ILLINOIS

Thickness Depth SYSTEM FORMATION CHARACTER Feet Feet

Pleistocene ...... Glacial ...... Drift...... 65 65 Silurian...... Niagaran ...... Limestone ...... 215 280 . Ordovician ...... Maquoketa...... Shale ...... 245 525 Galena...... 1n1estone ...... 345 870 Platteville ...... }i . St. Peter ...... Sandstone ...... 130 1000 . Oneota...... Limestone ...... 70 1070 Cambrian...... Jordan ...... Sandstone ...... 50 1120 Trempealeau .....Limestone ...... 150 1270 Franconia ...... Limy sandstone .·...... 130 1400 Galesville ...... Sandstone ...... 180 1580 Eau Claire...... Shale, limestone, and sandstone .. 120 1700 00 00

LEGEND c::J PENNSYLVANIAN � NIAGARAN � MAQUOKETA � b;j D ST. PETER t>::i t::;j � a

�

o 0 o 0 o o o o o o o Cl 0 0 0 0 l 0 0 0 0 I SCALE 0 5 10 20 30 40 MILES

FIG. 68.-Map of northern Illinois showing the general distribution of the various rock formations under the glacial drift. Limited outcrops of Devonian formations in the vicinity of Rock Island are included with the Niagaran, and outcrops of formations older than St. Peter sandstone are included with that formation in the vicinities of La Salle, Dixon, and Oregon. WELL LOGS 89

"' 0: � � "' "' o.:< ' "' a:� z ..J . 0 a: a: < ..J a: 00 0 ..J,__ "' :::> IL "' ..J ,__ .. "" <�

,,, ' '..!�h�' ESTIMATED POSITION OF GRANIT

FrG. 69.-Geological cross-section of northern Illinois P-Pleistocene SP-St. Peter I-Jordan G-Galesville Si-Silurian S-Shakopee T-Trempealeau EC-Eau Claire M-Maquoketa N-New Richmond F-Franconia MS-Mt. Simon G-P-Galena-Platteville 0-0neota aran limestone is middle Silurian. All the At the date of writing, only three wells in formations listed, except the St. Peter sand­ Illinois have ever been drilled through the stone, are known from their fossils to be Cambrian. They enter granite, a wholly marine. The St. Peter usually is nonfos­ different rock whose origin was quite unlike siliferous and is composed of remarkably that of the marine sedimentaries or of the clean quartz sand. I ts grains are very well glacial drift. rounded and locally there is considerable If we travel northward or northwestward cross-bedding in the formation. These facts across Wisconsin, we cross the outcropping have led some geologists to infer that the edges of all the sub-Niagaran formations St. Peter formation may be a great wind­ and find outcrops of granite and other pre­ blown sand deposit, made perhaps along the Cambrian rocks less than half way up the low sandy shores of the Ordovician interior length of the state. In the northern half of sea, and later submerged by a spreading of vVisconsin, there is only pre-Cambrian rock the sea so that marine deposits covered it, beneath the glacial drift over many counties. but most geologists now believe that most The marine sediments of southern Wiscon­ if not all of it was actually deposited in the sin and the Chicago region, if ever covering sea although it may have been wind-worked these northern counties, have been wholly before its final deposition.0 The Platteville removed by erosion. Yet this is higher coun­ try in general than Illinois. and Galena formations are much alike and In going "uphill" into Wisconsin, we to the average well-driller pass for one for­ cross the edges of formations which are mation. Their outcrops, however, yield suf­ hundreds of feet beneath us at Chicago (fig. ficiently different fossil faunas to show that 70). This can be only if the formations rise they deserve separate formational names. in that direction and rise more than does the The Galesville sandstone is so deeply land surface. They are but gently inclined, buried that it has no outcrops in the state. it is true, and the dip (amounting to only HLamar, ] . E., Geology and economic resources of the a few feet to the mile) cannot be detected in St. Peter sandstone of Illinois: Illinois Geo!. Survey Bull. an outcrop. It is an exceedingly important 53. p. 26. 1928. Dake. C. L., The problem of the St. Peter sandstone: factor, however, in the water supply from Univ. of Missouri School of Mines and Metallurgy Bull., technical series, vol. 6, No. 1, p. 224, August, 1921. bedrock wells at Chicago. 90 BEDROCK

_; "' .,; .':i > 0 "' <1> � 3: .Ji "< c ..c :' "' c" <1> " "" .�<1> !,' .� ..c � L.."' <1> _§ ""O :r u � "' "' "iii c cO :::;;; _J � � , tifi� i�li��l�lfx� ��i�i{�i�fi1 �;r�£;i,rt�e: / .. I. PRE - CAM BRIAN GRANITE PLATTEVILLE GALENA CAMBRIAN SANDS TONES 5. LIMESTONES.!. 2 TREMPEALEAU LIMESTONE MAQUOKETA SHALE ::.-.....�I 3. ST. PETER SANDSTONE 6. NIAGARAN LIMESTONE 4. 7.

FIG. 70.-Geological cross-section of southeastern vV isconsin and northeastern Illinois.

ARTESIAN WELLS the normal rate of flowthrough them, which In 1864, a well drilled at the corner of caused the wells to cease flowing. It is Chi­ Chicago and Western Avenues encountered cago's present and probable future use of water at a depth of 711 feet, water which the wells now being pumped, which banishes rose to the surface and flowed from the any hope that they will ever flow again. mouth of the well. It is reported to have Artesian water, like many other natural risen 80 feet above the ground but probably resources, is not inexhaustible. Earlier wells this was when confined in a pipe, not as a obtained their flow from the St. Peter sand­ fountain jet. Within a few decades Chicago stone. When this ceased to supply the de­ had many flowing wells, supplying many mand, which it did in the 1880's, the old thousands of gallons of water a day. Today wells were deepened and new ones were it has none, and never again under present drilled past the St. Peter to the Galesville conditions will water flow from its wells. sandstone about 400 feet below. Although Water in a pipe will rise no higher than the Galesville is a thicker sandstone and the surface of its reservoir. Lake Michigan has a larger outcrop area in Wisconsin, it therefore, which lies below the mouths of also gradually failed to supply the increas­ the wells in Chicago, has no relation to their ing number of flowing wells. Pumps have flow. The reservoir must be sought in coun­ been installed and this has further lowered try higher than Chicagoland. That country the "head" until today in the Stockyards dis­ lies to the northwest, in central and south­ trict, where the heaviest draft is made on the central Wisconsin. The reservoir, however, subterranean supply, the lift is more than does not consist of a lake or lakes on the 250 feet, a lift which Nature provided gratis surface-the reservoir is underground. It a few decades ago. does not consist of a cave or of caves with Serious conditions in the artesian basin of subterranean lakes. It is the sum total of northeastern Illinois are limited to the dis­ many millions of tiny interstices among the tricts where there are numerous wells and millions of sand grains in the two sandstones heavy demands. Some suburban towns and which crop out in this higher land (fig. 71) railroad yards right at the city limits still and descend southeastward beneath im­ had, as late as 1919, an artesian lift from the pervious limestone and shale formations to Galesville sandstone to within 10 or 20 feet altitudes below sea-level at Chicago. Rain­ of the surface. fall in Wisconsin enters the sandstones and Although the water from Chicago's deep moves slowly down-dip, to supply Chicago's wells is sup?lied by Wisconsin rainfall, the deep wells. It is Chicago's relatively low long slow Journey underground (its esti­ altitude as compared to Wisconsin which mated rate of flow is half a mile a year) made possible the flow from these wells 40 gives ample opportunity for the water to to 70 years ago. It was Chicago's enormous acquire soluble substances from the rock it demands on these two reservoirs, exceeding so minutely seeps through. By the time it TOPOGRAPHY OF BEDROCK 91

) I

Milwaukee

IOWA

Frc. 71.-Map showing outcrop of Cambrian (diagonal lines) and St. Peter (horizontal lines) formations in vV isconsin and Illinois. (Illinois State Geo!. Survey Bull. 43, fig. 76, 1923.) reaches Chicago it is so "hard" that it must TOPOGRAPHY OF THE BEDROCK SURFACE be treated for some uses. Differenthorizons The Lake Michigan basin, as a closed in the Cambrian sandstones yield differently basin, is a product of glaciation. It was mineralized water, the least desirable being occupied by a great lobe of ice during the deepest, so drillers are careful to stop their last glacial episode, ice erosion having wells as soon as the supply is adequate. scoured out the bottom, and deposits by the However, the Chicago area is still an ice having mounded up the margins during artesian basin, for water still rises in the this and earlier episodes. But the basin was different wells varying distances above the a lowland before glaciation occurred. There tapped water-bearing horizon. Any well in is plenty of evidence that streams had al­ which the water rises when the impervious ready excavated a large portion of its pres­ overlying rock is penetrated is an artesian ent depth and width. Part of this evidence well. If the pressure is such that it rises to is found in the buried topography of the the surface and there escapes, it is a flowing Niagaran limestone beneath Chicagoland. well, the most desirable kind of artesian Referring again to the cross-sections (fig. well. 65 ) one notes that the lake lies on the eroded 92 BEDROCK edges of the soft Devonian shales, and that and belonging to another system. The out­ harder rocks bound it on the east and on the crop belt of the Niagaran formation in Chi­ west. The soft shales, being most easily cago's latitude is nearly twice the width of eroded, determined the location of the larg­ our mapped region, so that we can hope for est preglacial valley. The harder rocks con­ but little evidence from our bedrock map. stituted uplands and possessed only small Geological studies of the Herscher, Wil­ tributary valleys leading down toward the mington, Joliet, Wheaton, Barrington, and main valley, the precursor of the lake basin. Elgin quadrangles supply the information. Laborious search for all existing data on There are such buried valleys in the bed­ . depths to bedrock in the Chicago region has rock and they deepen, widen, and converge yielded literally thousands of records of westward as the theory requires. They were wells, tunnels, trenches, caissons, test-bor­ apparently tributaries to the preglacial ings, etc. These, carefully located on th Mississippi system just as those of our own maps and adjusted to altitudes above sea­ region were tributaries to the preglacial St. level, will make possible the construction of Lawrence. The preglacial regional divide a contour map of the buried surface. stood almost where the present Mississippi­ There are two different elements in the St. Lawrence divide now stands. The Val­ topography of the bedrock surface. One is paraiso moraine here was built on the old the kl int type of elevation ( p. 66), a mound Niagaran upland, and postglacial streams or hill standing alone, its relief due to obey its control as preglacial streams were superior resistance of its rock. The other is controlled by the limestone belt. a linear trench or trough prevailingly ori­ On this identification of the troughs or ented nearly at right angles to the present trenches in the buried Niagaran as stream lake shore and increasing in depth toward valleys depend several other conclusions. the lake. The positive form, the klint, has One is that the lake basin is not wholly a been explained but the share that the two product of glacial erosion, with minor up­ unlike erosional attacks, preglacial and gla­ building of the rim by moraine construction. cial, played in producing it, has not been Even though no one has yet located the settled. The explanation of the second, the continuation of the major preglacial valley negative or valley form, should have a bear­ toward the St. Lawrence (the strait of ing on the problem of the first. Mackinac is too shallow and too narrow) we must accept the conclusion. Similarly, These troughs in bedrock are true val­ the location of the preglacial regional divide leys, without doubt. They lead toward the is based on the concept of stream origin of lake basin. For their erosion, an agent is the buried valleys. The inadequacy of gla­ required whose attack is concentrated along cial erosion to bevel off all the older rock­ a linear course. This clearly points to run­ carved topography is likewise concluded water-streams tributary to the larger ning from them. Thus the klintar must be a valley in softer rock which now holds the product largely of preglacial erosion. lake. If these valleys were by any chance gigantic grooves cut by glacial ice, they In spite of the coincidence of the pregla­ should be oriented parallel with the striae cial and postglacial divide, the older stream and smaller grooves which the ice produced. pattern of the Chicago region differs If they were weathered out of belts of markedly from that of today. The former streams flowed almost directly eastward and weaker rocks, they should parallel the edges down the slope beneath the present lake. of the formations, and correspond roughly Some of today's streams wander for miles to the lake basin. Neither of these two con­ parallel to the lake, trying to find escape ditions is true. It seems safe to conclude from the obstructing moraines and beach that in them Chicagoland has a record of ridges. Lakes and marshes exist along their minor preglacial streams descending the dip courses. They have not yet wrested control slope of the outcrop belt of Niagaran. of their routes from the still-living mastery Since softer rock underlies, as well as of the vanished ice-sheet. They are young overlies, the Niagaran, the outcrop belt of in their own cycle of erosion. The earlier the Niagaran should have been a preglacial streams had established direct routes to the divide and the western portion should have major valley, they had developed with that similar buried minor stream valleys draining valley, they were much older in terms of westward down the far slope of the divide the growth of a simple drainage pattern. GEOLOGICAL HISTORY 93

GEOLOGICAL HISTORY OF CHICAGOLAND Adventure by land and sea, in the tropics back and telling stranger stories than any­ and in the Arctic-these have all come to thing in our own geological archives. With­ Chicagoland while that region has stayed at out doubt, such rocks are here also ; we home. "In the beginning ...." but we can­ simply have not yet gone deep enough to not use that phrase for earth history does find them. not carry back to a beginning. "The earliest Above the Mt. Simon sandstone lie layer record ..." this is correct ...the earliest upon layer of sedimentary rock, each with record of our region is at the bottom of the an interesting contribution to the geological deepest well. That record is the Mt. Simon history of the region. Geologists have found sandstone. A shallow sea was here, land to that rock formations may be logically the north was discharging muddy rivers into grouped into major and minor divisions it, waves and tides were sweeping its floor, which record equivalent divisions of time sandy waste from the northern land was in geologic history. To each of the divisions being carried far and wide over the great has been applied a distinctive name, sig­ midcontinental marine embayment. The nificant either of the type of life existing at time was Cambrian, the first geological the time or of the localities in which the period to leave us an adequate record of life. rocks are well developed or were first Beneath the Mt. Simon sandstone in studied. The world-wide geological time­ Wisconsin lie granite and gneiss and schist table, almost universally accepted, is as fol­ and quartzite-rocks dating much farther lows, the youngest being at the top :

------�------

Cenozoic era The glacial record, and geological Pleistocene period processes now at work Pliocene period } Miocene period Oligocene period Eocene period Mesozoic era Cretaceous period No rock making in the Chicago region Jurassic period Triassic period Paleozoic era Permian period Rock making perhaps, but if so the Pennsylvanian period deposits have all been eroded } away Mississippian period Devonian period Silurian period The Chicagoland bedrock records Ordovician period made Cambrian period Proterozoic era All rocks beneath the Cambrian in the Keweenawan period Great Lakes region date from H uronian period these eras. The accessible geo­ logical record at Chicago begins Archeozoic era with the Cambrian. Laurentian period Kewatin period 94 GEOLOGICAL HISTORY

FIG. 72.-Cross-bedding in Cambrian sandstone, Dells of Wisconsin River.

CAMBRIAN PERIOD tinental interior apparently was filled about The Cambrian strata beneath Chicago­ as rapidly as its waters rose, so that its bot­ land are late Cambrian in age. Earlier sedi­ tom most of the time was swept by the ments of the period are known in the Ap­ currents. palachian Mountains, about the Adirondack But the rising sea-level meant a shifting Mountains, in New England, and in Que­ of the Cambrian coastline farther and far­ bec. Our region during the early Cambrian ther away from Chicagoland. Limey sand was probably a land of granite and gneiss. and limestone appeared in Franconia and Slow, inexorable spreading of that shallow Trempealeau times, and again in the Jor­ Cambrian sea in the east finally reached us, dan. In the Franconia and Trempealeau we went under and became buried in sand formations are good fossil records of the brought from surviving portions of the con­ late Cambrian marine life. tinent. ORDOVICIAN PERIOD The Mt. Simon sandstone is thick­ Because of increasing distance to the re­ several times as thick as any other formation treating shore, the supply of sand eventually in our wells. The sea, however, never was entirely ceased coming into Wisconsin and as deep as the thickness might suggest. Most Illinois. Lime mud was deposited on the exposures of the formation show current­ Jordan sand ; the Oneota formation was be­ bedding, splendidly displayed in sandstone gun. Approximately coincident with this, cliffs of the Wisconsin Dells (fig. 72). Cur­ the sea in the eastern part of the continent rents in the sea are superficial affairs. At was largely withdrawn, mountains were ,considerable depth the sea is still. The late raised in New England by earth movements Cambrian marine embayment of the con- there, and the Cambrian period came to an ORDO//ICIAN PERIOD 95

ST. PETER

FIG. 73.-Diagrammatic cross-section of the LaSalle anticline along the north bluff of Illinois River. Definitely known positions of formations are drawn with full lines, inferred positions of formations below the present surface are shown by dashed lines, and their former positions across the eroded portion of the anticline are shown by dashed lines and dotted names. The Pennsylvanian (coal-bearing) rocks on the west were deposited horizontally across . the anticline after an early erosion period, were themselves deformed by a second arching of the anticline, and were in turn eroded off the crest. end. The second period of the Paleozoic era 500 feet of these formations was removed began, the Ordovician. in the Chicago region. Supporting this view During the Ordovician period seven dif­ is the occurrence of Shakopee and Oneota ferent major formations were deposited in chert nodules as pebbles in the base of the the interior sea : the Oneota limestone, the St. Peter sandstone. Weathering of these New Richmond sandstone, the Shakopee limestones during the interval of exposure limestone, the St. Peter sandstone, the had left the insoluble nodules while remov­ Platteville and Galena limestones, and the ing the lime of the formations. The nodules Maquoketa (or Richmond) shale. Geo­ were rehandled and incorporated in the first graphical changes in land and sea are surely of the St. Peter sand to be laid down. In on record in these changes from lime mud our region part of the Oneota still remained. to sand and back to lime mud twice over, The St. Peter sandstone lies on the old and then finally to a land-derived mud, the land surface exposed when the sea withdrew Maquoketa shale. Perhaps climatic changes after Shakopee times. The sand to make the are also involved. It is difficult to make a St. Peter formation must have come from precise analysis of the causes-changes in distant lands of granite and of Cambrian depth of water, in distance from the land, formations, as it could not have been derived in direction to the land, in character of the by weathering of the local Oneota and land, in climate-all of these may have Shakopee limestones. Probably northern played a part. rivers, lengthening as the sea withdrew, car­ At least once during the Ordovician ried this sand southward to low coastal period the sea was entirely withdrawn fr.om lands where it accumulated as deltas and the upper Mississippi Valley and Great broad sandy beach flats. Here the waves Lakes states. It happened between Shakopee and wind reworked it to that remarkable and St. Peter times. The record is found in purity and evenness of grain which charac­ wells in northern Illinois but is better shown terizes the St. Peter sandstone. With the in the Wisconsin outcrop areas. It consists return of the sea, this coastal belt of deposi­ of an irregular thickness or even complete tion shifted northward over the eroded land absence of the Shakopee and older forma­ surface, and the former sand belt was in­ tions as far down as the Franconia (fig. 69) . undated and buried beneath the Platteville This irregularity is the expression of an limestone. eroded land surface identical in origin with Another notable feature of Ordovician that of the bedrock surface buried beneath history lies in the great extent of limestone the glacial drift. From 200 to as much as of Galena and equivalent age. It was de- 96 GEOLOGICAL HISTORY

FIG. 74.-Starved rock, composed of St. Peter sandstone. posited over a greater area in North Amer­ Utica and Split Rock. Nearby, Deer Park ica than any other marine formation of all Canyon and Vermilion River valley show time, originally covering 60 per cent of the Platteville limestone overlying St. Peter present continent. It therefore records the sandstone. most widesprea\i known floodingof the con­ Shrinkage of the great marine sea of tinent by the sea, the nearest approach to Middle Ordovician time was accompanied victory of those forces which destroy the by other changes. The interior sea became lands and extend the kingdom of the sea. muddy with the wash from the adjacent, Yet this mid-Ordovician sea was shallow­ newly emerged lands. The resulting sedi­ it is not to be compared with the true oceans. ment constitutes the Maquoketa shale, most Good exposures of the Ordovician forma­ of it composed of clayey detritus but cal­ tions are found in the gently upwarped por­ careous where the sea was clearer and tion of northern Illinois. One particularly organisms could give character to the de­ sharp upfold, the LaSalle anticline (fig. posit. The Maquoketa shale, named from 73), brought up the Ordovician formations outcrops in Iowa, is more limited in extent as high as younger rocks on either side, and than any other formation of the Ordovician subsequent erosion has exposed them, espe­ system. The sea was withdrawing and the cially where Illinois and Rock rivers cross close of the period is marked by the largest the anticline near LaSalle and Dixon respec­ area of land in North America since the tively. Starved Rock and its associated early part of the Cambrian period, millions canyons (figs. 7 4, 7 5) are carved from the of years before. In southern New England, St. Peter sandstone, and the glass-making in New York, and in Pennsylvania, strong industry at Ottawa obtains its sand from the lateral compression at this time folded up a same formation. The Shakopee formation mountain range parallel with the Atlantic forms cliffs along Illino;s River between coast. ORDOVICIAN PERIOD 97

FIG. 7 5.-Amphitheater in the St. Peter sandstone at the head of the gorge in French Canyon, Starved Rock State Park. 98 GEOLOGICAL HISTORY

SILURIAN PERIOD in north Greenland were folbirches. These in turn were de­ sylvanian period and perhaps the gentle stroyed as the ice entered into its climacteric upwarping of northern Illinois and the stage. All but the southern tip of Illinois downwarping of the Michigan basin date became buried under glacial ice ; Chicago­ from this time. Mountain-making occurred land became part of another Antarctica or in other continents. Great withdrawal of Greenland. the shallow seas over much of the world, In the ice and beneath it, dragged by the great climatic stress (aridity and glaciation), enormous power of the thick spreading gla­ great changes in plants and animals came cier, was borne the debris from Canada, with or in immediate consequence of this northern Michigan, and Wisconsin. The mountain-making revolution. With these preglacial soils were wiped off, thepreglacial events, the Paleozoic era closed and a new valleys were buried in the debris, except era opened. The Mesozoic era began. where oriented in the direction of ice move­ During the Mesozoic era startling forms ment. The hard Niagaran limestone was of grotesque reptiles moved across the land­ scoured and grooved by detritus in the basal scape ; their lowly contemporaries, the early ice ; in fact the limestone itself yielded much mammals, appeared briefly now and then ; debris to travel far down the state and to seed-bearing land plants developed, interior be left as burial clods over the Pennsylvanian seas came and went in the present Rocky coal beds. Mountain region ; and finally, to climax the The glacial epoch was long and it was Mesozoic era, the Rocky Mountains and varied. Three times the ice-sheet was melted other mountain ranges from Alaska to Cape back, each time only to gather strength and Horn were upheaved. advance again from Canadian territory. The None of these ·events find record in our fourth defeat of the Arctic invader brought region. Nor do we learn anything of the the geological present. The events of the great volcanic activity of the next era, the enemy's last rout are learned from the Cenozoic, nor of additional mountain-mak­ battlefield. Moraines are entrenched posi­ ing, nor of the wonderful rise and spread of tions where for long the conflict became a the mammals over the world, supplanting stalemate. The glaciofluvial deposits are the reptilian dynasties which went out with the stains of the glacier's prodigious bleed­ the birth of the Rocky Mountains. All these ing. Weapons abandoned in its retreat lie events occurred during the great gap in our everywhere--the battered striated weapons record-the hiatus between the Niagaran that scarred the country rock. The rein­ limestone and the glacial clrift. forcements poured into the Illinois sector 100 GEOLOGICAL HISTORY

H u r o n P I a n below the escarpment

Toronto LAKE ONTARIO

FrG. 76.-The Niagaran escarpment between Lakes Erie and Ontario. along the valley now containing Lake Michi­ sheet failed to obliterate the cliff,but it filled gan still held the front after most of Wis­ the valleys completely with detritus. When consin, lllinois, and lower Michigan had the retreating ice finally abandoned the dis­ been surrendered. The great pool of Lake trict, the glacial Great Lakes to the west Chicago was formed as this valley became poured their discharge across it, but the impossible to hold. It lengthened north­ escaping waters found no valley to follow. ward, it received discharge from a similar Flowing across the open country, they came great pool in the Erie basin, and then from to the edge of the cliff at Queenston and another in the Huron basin. All this water plunged directly into Lake Iroquois, the ex­ went to the Gulf of Mexico. Finally, the panded glacial Lake Ontario. From Lake ice retreated so far that a lower outlet was Iroquois they flowed through Mohawk opened to the east, the Great Lakes dis­ River to Hudson River. charged to the Atlantic Ocean, Niagara Beneath the Niagaran limestone in the Falls was born, and shortly the Sag and cliff is the softer Clinton formation. This, DesPlaines outlets to the Gulf of Mexico more rapidly eroded away by the cataract, went dry. left the edge of the limestone unsupported. NIAGARA FALLS AS A GEOLOGICAL CLOCK It broke off from time to time and the When Niagara Falls began, a geological waterfall thus became recessed or notched clock started running. It has run continu­ back in the· cliff (fig. 77). Recession, con­ ously ever since and its present reading tells tinued ever since, has lengthened the notch how many years ago it started. The clock into a gorge seven miles long-a gorge consists of the falls and gorge of Niagara. which still is lengthening as the cataract Preglacial erosion in western New York recedes. The present average rate of retreat had etched out the softer rocks, leaving a of the falls is about four and a half feet a north-facing cliff of Niagaran limestone year. The gorge is about 36,000 feet long. (fig. 7 6) 200 feet high. Capacious stream If the clock has run at the present rate since valleys drained from the upland south of the it was started, the falls have existed 8,000 cliff to the lowland on the north. The ice- years. NIA GARA FALLS 101

ing rim was reached by their rising waters and a spill over into a new outlet occurred. This was at the southern end of the Huron basin and for a time the three-fold lake (Michigan-Huron-Superior) had two out­ lets, the new one through St. Clair and Detroit rivers to Lake Erie and to Niagara Falls. Continued rising finally brought the floor of the northeastern outlet above the surface of the new St. Clair outlet, Niagara River again secured the whole discharge, and the geological clock resumed its forme1 rate. Frc. 77.-Diagram illustrating the conditions at We have passed hastily through this com­ Niagara Falls (After Gilbert) . plicated lake history, noting briefly only the leading items which bear on Niagara Falls. But the story of the glacial Great Lakes The original rate of cataract recession was has been more complicated than this brief approximately re-established. How long a sketch indicates. When the falls were born, time is recorded in the making of the the edge of the continental ice-sheet was gorge ? Like most clocks, our geological still in sight. But its continued northward clock was an imperfect timekeeper. This retreat in Ontario eventually uncovered a became obvious when the outlets across On­ still lower outlet for the Superior, Michi­ tario were discovered. Various geologists gan, and Huron basins, an outlet from well acquainted with the glacial Great Georgian Bay through Trent River valley Lakes history have made estimates of the directly to the Ontario basin. Niagara thus time this stage endured. They find the lost all but the discharge from Lake Erie. stage recorded in the gorge itself, as a nota­ The clock then ran much more slowly-at ble narrowing of the part made by Erie dis­ what rate can only be estimated. charge alone. Their figureshave been recast In the meantime a curious thing was as new details have come to light. Most of happening. The weight of the great ice­ the significant evidence seems now to have sheet appears actually to have depressed this been collected and present estimates prob­ part of the continent. After the melting ably will not be greatly changed in the back was well under way, the region of the future. We say now that Niagara Falls Great Lakes and north of them began to has existed between 25,000 and 30,000 rise, very slowly and very slightly but in years.1 Chicago outlet has been abandoned increasing amount with increasing distance for almost that length of time, and Lake northward, enough to tilt the abandoned Chicago's lowest stage dates almost that shorelines of the earlier glacial lakes. North far back. of Sheboygan, Wisconsin, and of Saginaw This is not a measure of the time since and Port Huron, Michigan, they became the last ice-sheet stood at its maximum. The progressively higher northward. The oldest ice reached 600 miles south of Niagara, and highest ones were tilted most, the latest down into southern Ohio, at that maximum. and lowest ones least. The movement thus The entire history of the last glacier in Illi­ was in progress as the lake stages came and nois was written before Niagara Falls were went. born. Perhaps 15,000 years were consumed This movement raised the Trent River in the slow wastage which finally bared the country, across which the eastward discharge region of Niagara Falls, so that the total was occurring. It thereby raised the level in time from the last glacial maximum to the the upper three lakes, which had been lower­ present may well have been 50,000 years. ing during the earlier lake stages. The time 'Kindle, E. M. and Taylor, F. B., U. S. Geo!. Survey came when the lowest notch in the surround- Geo!. Atlas Niagara Folio (no. 190), 1913. 102 GEOLOGICAL HISTORY

Glenwood LAKE CHICAGO (Gl [llWOOD STAG[) ) CHICAGO '"'"l HEIGHTS BAY

I Lincoln Highway / SCALE

Frc. 78.-Sketch map of Glenwood Island and associated features of the Glenwood stage of Lake Chicago. HISTORY OF LAKE CHICAGO they are not markers for the contact of gla­ In any account of the history of Chicago­ cial and lacustrine topography. land, the history of Lake Chicago, the In some places the Glenwood waves broke glac al ancestor of Lake Michigan, should against fairly abrupt moraine slopes. There receive! more attention than almost any other they eroded sea-cliffs, just as Lake Michigan event, for the records lie under our feet waves are doing today in the North Shore wherever we may be on the Chicago plain. district. In other places the ground-moraine There were three marked lake stages, was so low and featureless that no cliffs about 20, 35, and 55 feet above the present could be formed. But where sufficiently ex­ lake level. The Sag and DesPlaines chan­ posed to large waves from the open lake (in nels (the Chicago Outlet) served as outlets open water waves grow larger, the farther for all of them. Their sequence is generally they travel), sweeping of the shallow bottom accepted as in the order of altitude, the brought sand and gravel shoreward, to be highest being oldest, the lowest youngest. deposited as beach ridges along the lake The lake surface is generally thought of as margin or perhaps across the mouths of ex­ having been lowered rather rapidly from ceptionally shallow lagoons or small bays. one stage to the next. The cause of the Where littoral currents existed, sand and lowering is commonly considered to have gravel were swept along the shore and built been down-cutting of the outlet channel, into spits at places where the current crossed although geologists are not all agreed on it. the mouths of re-entrants in the original Glenwood stage.-The highest and earli­ shoreline. A shoreline with a littoral cur­ est shoreline of the extinct glacial lake is rent is a transportation line, at the collecting called the Glenwood shore, the highest lake­ end of which is usually a cliff. A spit, re­ level was the Glenwood stage. Only the ceiving the wastage from the cliff, is the Glenwood shore has moraine topography on delivery end of the line. one side and lake bottom on the other. The Let us make a rapid traverse of the Glen­ lower shores were made on what had been wood shore to see where some of these fea­ lake bottom during earlier stages, and thus tures occur. The shoreline is named from JA KE CHICA GO 103 the village of Glenwood, 1 )/z miles south of Thornton (Calumet City quadrangle), through which it runs. East of Glenwood, along the Glenwood-Dyer road, a small "island" of ground-moraine is shown (fig. 78 and pl. I). The north side of the island is steep and straight, a Glenwood sea-cliff, its base 630 feet above sea-level. The broad lake-plain stretches off to the north, higher and gently rolling country lies to the south. At the inception of the Glenwood stage, no cliff existed and the "island" extended some­ what farther north. On the north side waves from the open lake attacked the island while in the shallows between the island and the mainland no effective waves were possible. Some of the detritus removed by cliff-making may underlie the flatto the north, but much of it travelled along the shore, both south­ eastward toward Dyer and northwestward toward Glenwood. It came to rest where the storm waves broke in the shallowing water. A fine spit grew out toward Dyer, four successive "fingers" of it curving back into what we may call Chicago Heights Bay. The northwest spit was built under some­ 0<===="'3Y4===::5� - what differentconditions and failed to curve MILE \;-WAVE cuf CLIFF back toward the south or to develop fingers. SCALE As it grew across its part of the bay, it en­ FIG. 79.-Sketch map of La Grange spit, Glen­ countered competition in the form of another wood stage of Lake Chicago. spit growing southeast from Homewood, the debris for which was coming from a Glen­ The Thornton klint was an offshore wood cliff north of that village. Apparently shoal during the Glenwood stage, and be­ the Homewood and Glenwood spits never fore the stage closed, a shallowly submerged joined to close this opening into Chicago bar had grown back of it, connecting the Heights Bay. Thorn Creek's use of the shoal with the Homewood spit. Its altitude unclosed space seems to indicate a passage is 630 feet. Indeed, much of the Glenwood there for the earliest drainage after the shore deposits are below 635 feet, the speci­ Glenwood stage closed. fied height of the lake-level. The tips of The 635-foot contour is approximately the spit fingers are 625 to 630 feet where they terminated in the deeper water of the the initial shoreline of the Glenwood stage. bay. Even the base of the cliffs may be a Here the cliff and sand ridges associated little lower than the actual water surface with the Glenwood islands stand as the final if no beach was formed in front of them. product of this stage. Note the striking All told, these shoreline changes from Dyer simplifications accomplished (fig. 78). Had to Homewood exemplify early maturity of this stage endured long enough, all the shal­ the shore cycle. The initial irregularities low waters south of the island and its de­ had been largely removed by reduction of pending sand ridges would have been filled headlands and closing off of bays, a new in, a further simplification of the kind in­ coast line far simpler had been outlined, evitable on initial shores of this type. The only the filling in of the shallow bays re­ Glenwood stage offeredmuch greater oppor­ mained to be done. No changes on such a tunity for such changes than did either of scale mark the later shores of the glacial the later stages. Its waters lapped back on lake, chiefly because they never were initial­ the irregular ground-moraine; the later ly so irregular. levels made contact only with the smooth Triangular Mt. Forest Island had the bottom-plain of higher lake levels. Glenwood lake on the east and outlet rivers 104 GEOLOGICAL HISTORY

Nortl1 Ave.

ONorth Park

Roosevelt Road .,,}�''''":� ''• �"�� I FIG. 80.-Sketch map of Oak Park spit, Glenwood�� stage of Lake Chicago. on the northwest and on the south sides, the two rivers uniting six miles from the lake at the west end of the island. Wave work is recorded of course only at the east end and largely in cliffs. Most of the re­ sulting debris carried along this shore was swept off down the outlet channels.

North of the DesPlaines outlet, the Glen­ FIG. 81.-Sketch map of Wilmette spit, Glen­ wood shore is a cut bank as far north as wood stage of Lake Chicago. LaGrange Park. Here an embayment in the ground-moraine, now used by Salt taking its name from the former (fig. 80). Creek, furnished opportunity for the growth A low but definitecliff is recognizable north of a spit. Current-swept sand and fine of the spit for several miles along the east gravel from the cliff farther south travelled side of the Park Ridge moraine. The nearly a mile out across the mouth of the erosion of this cliff supplied much of the small bay. The spit today determines a debris of which the Oak Park spit is made. marked angle in the course of Salt Creek. Riis Park includes a portion of this cliff. Mannheim (or LaGrange) Road traverses The region between Morton Grove and most of the length of the spit (fig. 79). Winnetka has marked Glenwood features, North of Salt Creek embayment are the better developed here than anywhere else long narrow bays interfingering with the in the Chicago region. A sea-cliff 20 to 30 Lake Border moraines. Only faint traces of feet high is a very definite feature in Win­ the Glenwood shore occur in them. The netka, extending from the present lakeshore westernmost bay was· largely filled by the near the city waterworks southward along terminal portion of the DesPlaines valley­ the east margin of the Highland Park mo­ train during the Glenwood stage. It also raine for miles to Indian Hill Club. became partially closed off from the open Here both lthe };2 moraine and the sea-cliff end, lake by the Oak Park spit which grew but a large mounded deposit of sand and southwestward from the tip of the Park gravel, the Wilmette spit, on the lake-plain Ridge moraine. That spit reaches almost continues this old shoreline for at least six from Division Street to Roosevelt Road, miles farther to the southwest (fig. 81). measuring nearly three miles along its The east side of the spit is a simple flowing rather sinuous length. It lies within the curve but the west side is remarkably digi­ city limits of Oak Park and Forest Park, tate, ridges of sand projecting westward LAKE CHICA GO 105

FIG. 82.-Sketch map of Blue Island and associated features, various stages of Lake Chicago. out on the plain, the intervening linear tion of debris shoaled the water most at depressions being reciprocal dove-tailing the beginning of the curve and thus repeat­ fingers of the plain. edly these growing spit fingers were aban­ We need not analyze the situation in doned and new ones were built farther detail, it is so similar to others already de­ south. The Glenwood stage came to an end scribed. Waves from the open lake during while the southernmost, the Niles Center, the Glenwood stage undercut the east face finger was growing. There are at least a of the Highland Park moraine. A south­ dozen well marked fingers on the Wilmette ward-flowing littoral current swept the spit. Had some of them grown a mile coarser debris along the cliff to the moraine longer, both Skokie Bay and Chicago Bay tip. Here it was deposited, shoaling the would have been completely cut off from water and extending the Highland Park the main lake. peninsula southward. This made more A tract of dunes three quarters of a mile shoreline on which the current could carry long occurs on the Wilmette spit, near the debris farther and farther southward as the junction of Illinois Road, Wilmette Ave­ low growing tip of the peninsula advanced. nue, and Glenview Road. Westmoreland Storm waves tended to swing the end of Golf Club is located on their western part. the spit back into Skokie Bay, but the addi- The dune sand has a maximum known 106 GEOLOGICAL HISTORY

FIG. FIG. 83.-vVave-cut cliff of the Glenwood stage 84.-Dune on the west slope of Blue Island. of Lake Chicago, near 87th Street and West­ Built during the Glenwood stage of Lake ern Avenue, north end of Blue Island. Chicago, the dune migrated from right (west) to left (east) up on the moraine thickness of 12)/z feet and rests on gravel above the shoreline of the lake. or gravelly sand of the spit. The dunes of Blue Island is a continuation of the Park were formed after that part of the spit had Ridge moraine, the southwestern part is been built. ground-moraine belonging to the Tinley There are complications of the story as stage. outlined above, for a sand ridge continues farther south than the spit group is mapped. The east side of Blue Island (fig. 83 ) It is about 15 feet lower than the ridge is a splendid wave-cut cliff, 40 feet high in tops of the spit. It runs along the base of Morgan Park and 35 feet high in the Forest the east or lakeward side of the ridge group Preserve at the north end. A maze of and is a product of a later and lower lake anastomosing beach ridges, probably spit stage, the Calumet. A map showing the fingers in large part, lies at the foot of this area during Glenwood times should not cliff and from the north end a single sand include it. spit swings westward into the lake-plain In the northern part of Winnetka the for 1 Yz miles. A gravel spit, small and Glenwood cliff comes to the present lake blunt, swings in the opposite direction at margin, and thence northward almost to the opposite end, in the east part of the city Waukegan the present cliff summits are of Blue Island. higher than the Glenwood level so that no The west side of the island carries next old shorelines exist. These cliffs are reced­ to the largest belt of Chicago dunes in the ing today. They originally stood farther mapped area. They extend the full length out in the lake. Each of the three Lake of the island, 5 Yz miles. Though they are Chicago levels doubtless had cliffs here also. unquestionably a marker for the Glenwood All have been destroyed in the present shore shore here, they lap up on the island above cycle, lake waters encroaching on the land that level, having migrated inland from the instead of withdrawing from it as elsewhere water's edge. Some individual dunes are in Chicagoland. 30 feet high above their base. Many show We have one more district to examine the gentle windward (western) slope and for Glenwood features, the only island of steeper leeward (eastern ) slope so common this stage on the Chicago plain (fig. 82). among the present lake shore dunes (fig. It is a morainic elevation whose margins 84). are decorated with almost every type of The cliffed eastern shore and the dune­ shore feature left by old Lake Chicago. It covered western shore of Blue Island arr is known as Blue Island. Two high-class in strong contrast and record markedly dif­ Chicago residential districts, Beverly Hills ferent conditions during Glenwood time. and :Morgan Park, are built on its eastern The east side faced the open lake. On the slopes, three golf clubs and three cemeteries west, it was only five or six miles to the mark its western margin. Western Avenue land and waves here could not grow to from 85th Street to the Sag Canal traverses great size. This seems an adequate reason its entire length. The northeastern part for cliffing only on the east. For the dune LAKE CHICAGO 107 growth, we need beach sand swept by dry­ from the island. Its material came from the weather on-shore winds. Dunes attain shallow lake bottom. With essentially no marked development only on west-facing break, this Calumet shore ridge is easily and north-facing coasts of Lake Michigan traceable for nearly 15 miles, extending today, for reasons already outlined. The northwestward about 10 miles across the west side of Blue Island was a west-facing flat lake-plain to terminate at Summit in a coast in Glenwood time. Figure 85 shows spit-like form at the head of the DesPlaines Lake Chicago in our region during the outlet channel of that time and southeast­ Glenwood stage. ward to Stewart Ridge, just north of Calu­ Calumet ta e met River. Thence it swings around the g .-Much more bulky shore deposits marks the Calumet stage of Lake south end of Blue Island and continues Chicago and much more largely were they northwestward toward Oak Forest on the derived by on-shore wave-drag over the south side of the low flat land which then shallow bottom than is true of Glenwood joined Mt. Forest and Blue Islands (fig. shores. The drop of 20 feet in the level 86). Southeastward from Stewart Ridge, of Lake Chicago drained all the bays of through · Riverdale and Dolton toward Glenwood time. Large areas of Glenwood Hammond, there is a sand ridge that ap­ bottom emerged, new land, miles in width pears to be a continuation of the Calumet in places, separated the new shores from the beach, but it is 20 feet lower and is a prod­ abandoned ones. Mt. Forest Island and uct of the third or Toleston stage of Lake Blue Island became joined by a low flatthat Chicago. stood just above the new lake level. A new Worth Island has a curious hairpin­ island appeared at the head of the Sag Out­ shaped beach ridge of Calumet age, show­ let, named from the village of Worth at ing how long and narrow the island was the intersection of 111th Street, Harlem at this first stage of its history and also Avenue, and Southwest Highway. The out­ showing that the outlet river did not head let heads were extended eastward into the this far east during the Calumet stage. plain. In Evanston and the north part of Chi­ A wide beach was developed where the cago are two very marked beach deposits, Illinois-Indiana state-line now crosses the the western one of Calumet age. It is a mile Calumet shore. Some of its sand was drift­ wide at Howard Street, the boundary be­ ed into dunes, some of it was carried west­ tween the two cities. South from Howard ward along the shore to make a spit with a Street it extends 3Vz miles into Chicago, terminus near Thornton and with several bluntly terminating near the intersection small fingers curving back into North Creek of Lincoln and \Vestern Avenues. North­ Bay, nearly shutting it off from the rest of ward through Evanston, where it is fol­ the lake. lowed by Ridge Boulevard, it narrows to The Thornton klint became so nearly about two blocks in width at the junction emerged at the Calumet stage that waves of the boulevard and Sheridan Road. Six breaking on its margin built a small beach blocks farther north, it terminates in a low ridge almost completely around it, making cliff on the lakeshore just south of Wilmette the curious circular pattern shown on Plate Harbor. This deposit, named the Rose Hill I. A group of dunes grew op. the beach bar, is a spit similar to the Wilmette spit along the west side of the klint, overlying in its growth from North Shore feeding both Glenwood and Calumet beach de­ grounds. It differs in being separated from posits. 2 the cliff-line to which it was appended when The Calumet beach east of Blue Island formed, whereas about two miles of the Wilmette spit's cliff remain. lies close to the group of Glenwood shores. But whereas the Glenwood ridges were Another interesting feature is that there built largely of detritus from the local cliff­ are two Calumet shores here. One is the cutting on Blue Island, the associated Calu­ Rose Hill spit, the other is a faint sand met ridge nowhere was supplied by wastage ridge along the eastern foot of \V ilmette spit. The latter extends southward and . 2Excavation by the Illinois Central Railroad has re­ moved most of the Homewood spit and its dunes on both southwestward across Chicago, with one sides· of Ridge Road immediately west of Halsted. The interruption, to Cicero, then southwestward surface in places here is now 30 feet lower than when the earlier topographic map of the region was made. through Berwyn and Riverside into Brook- 108 GEOLOGICAL HISTORY

FIG. FIG. 85.-Sketch map of the Chicago region 86.-Sketch map of Chicago region during during the Glenwood stage of Lake Chicago. the Calumet stage of Lake Chicago. field, nearly to the north side of the Des­ Calumet stage ended the lengthening spit Plaines outlet channel. In Riverside it has had shut off about 10 miles of the earlier some of the characteristics of a spit. Calumet shore from the open lake, making The two shores lie nearly parallel, a Wilmette Bay. The bay did not become featureless plain two to three miles wide land, however, until the lake lowered to its separating them. The explanation is simple third level, the Toleston. if the growth of spit shores is understood. Toleston stage.-Before Gary, Indiana, The Wilmette spit had grown out into existed, the village of Toleston stood on a water more than 20 feet deep, so that when sandy ridge at the intersection of the Michi­ the lake lowered to the Calumet level, its gan Central and Pennsylvania railroads. It waves still reached the eastern margin of disappeared with the growth of the indus­ the deposit, and there, in early Calumet trial city of Gary. Through the built-up time, built the beach extending from Wil­ parts of the city the ridge has likewise dis­ mette to Brookfield. The Rose Hill spit appeared, but westward across the prairies was begun at the same time, gradually grow­ it is readily traceable into Illinois as the ing southward from some point now out in third shoreline of the glacial lake. The the lake north of Wilmette, and before the shoreline was named from the village of LAKE CHICA GO 109

now vanished cliffs on the east side of the Highland Park moraine. Again dunes were piled up where drying winds found newly deposited sand along the shore. Most of the present stream courses of the Chicago plain were established, and before the stage closed an abundant molluscan fauna appeared in the lake, and driftwood was buried in the lake sediments. In the southeastern part of our region, about Hammond and as far northwest as Dolton and Riverdale, there was very ex­ tensive shoreline aggradation during the Toleston stage. A series of parallel ridges constituting one broad sandy area marks the Toleston level here. The largest belt of dunes on any of the old shorelines was developed here. An alongshore current made weak spit "fingers" in South Holland Bay at Dolton. The last "finger" built was not recurved but points directly north­ westward, across the head of the Sag out­ let, toward the Stewart Ridge spit of Calu­ met age, and in so doing gives a misleading idea of the further course of the Toleston shoreline. The Michigan Avenue business district in Roseland and Kensington ( lOOth to I 15th Streets) stands on the edge of a terrace. Immediately east of the avenue is a "drop-off" of 10 to 15 feet to the level on which Pullman is built. This low bluff is the continuation of the shoreline in Dol­ ton and Riverdale. It is the only sea-cliff of Toleston age in the Chicago region and hardly deserves the name of cliff. There FIG. 87.-Sketch map of the Chicago region dur­ ing Toleston stage of Lake Chicago. is no beach at its foot, hence it cannot be located on plate I. North of 95th Street, Toleston before Gary was more than however, the Toleston shore is again a beach dreamed of. Though the village has van­ ridge, traceable with some difficulty north­ ished, its name will remain on geological westward to Garfield Boulevard, almost to maps as that of the third stage of Lake Kedzie Avenue. The ridge was faint orig­ Chicago. inally and city growth has almost obliter­ The relatively abrupt drop to the Toles­ ated it. ton stage brought the level of Lake Chicago North of Chicago River the Toleston to within about 20 feet of the present lake shore cannot be definitelylocated over many surface (fig. 87). Again large areas of miles. One reason for its very weak de­ shallow water became low, flat, poorly velopment or total absence lies in the exist­ drained land. Again the two outlet streams ence of another great bar or spit extending were lengthened eastward, the Sag Channel southward, like the Wilmette and Rose Hill to Riverdale and the DesPlaines channel to spits, from cliffs in the North Shore district. Stickney. Again new shorelines were built, The Graceland spit enclosed a bay too small nearer the present lake than any earlier and too shallow for wave action to make a ones. Again spits grew southward from good beach in the time available. 110 GEOLOGICAL HISTORY

The Graceland spit extends from the region involves two different factors. Above north part of Evanston almost to Chicago the Glenwood level, moraine ridges are the Avenue, a total distance of about 12 miles. cause. Below that level, shorelines effected I ts width, measured along such east-west the same result. Running water has not yet streets as Fullerton, Diversey, Belmont, put its mark of possession on the topog­ Irving Park, and Montrose, is about 1 Yz raphy; the constructional forms of the gla­ miles. Its top is flat and only the gravel and cial episode still control. Calumet River's sand in excavations and its marginal slopes endeavor to reach the lake did not end on indicate its existence to one crossing the securing the Sag channel head ; more diffi­ district. Like the Rose Hill spit, it is named culties lay ahead in later stages. for a large cemetery on it. Neither the Rose Worth Island in the Toleston stage was Hill nor the Graceland spits have the finger­ a river island, the Sag channel dividing like ridges so prominently developed on the around it. The lake shore was five miles back side of the Wilmette spit. to the east and the bluffs encircling the As the shoreline receded during the low­ island below its hairpin-shaped Calumet ering of Lake Chicago, streams from the beach were cut by the river. bordering moraine country lengthened across A new island appeared in the Toleston the emerging plain, but they could rarely lake. The Stony Island klint emerged or flow directly to the lake because the aban­ so nearly emerged that waves were able to doned sand and gravel ridges commonly built a beach ridge around it. Both Stony blocked their way. Thus Skokie River, Island and Worth Island are remarkable whose mouth would logically be at Kenil­ for the number and size of boulders lying worth or Wilmette, was forced to flow on them, boulders from the glacial drift, westward around Wilmette spit and to join "erratics" unlike the underlying bedrock. the North Branch of Chicago River, itself These islands were shoals in the lake stage also deflected by Wilmette spit and still just preceding their emergence and so were further detoured by Rose Hill and Grace­ vigorously swept by waves. The finer ma­ land spits for a total of nearly 10 miles terial of the glacial drift was removed, at south from its own shortest course to the least in the upper part of the deposit, but lake. Calumet River, heading about nine the boulders were too large for the waves miles south of Michigan City, flows west­ to handle and were left behind. Numerous ward into the Chicago area almost to Blue boulders strewn over the lake-plain at the Island where it is even farther from the foot of old sea-cliffs tell much the same lake than at its head. It rises in Glenwood tale-removal of the finer constituents of lake-bottom in Porter County, Indiana. the drift, accumulation of the boulders. Several streams flowing down the back Without doubt some boulders were dropped slope of the Valparaiso moraine join it, their from icebergs floating in the lake but where combined waters cross to the north side of they are grouped so significantly as above the Calumet shore near Wiclift and Ogden noted, this explanation is not adequate. Dunes. Getting but little nearer the lake by this maneuver, the stream wanders on Later lake stages.-Seeking to make a westward in search of a break in the Toles­ complicated story simple, we have omitted ton barrier. It finds none and is forced or only barely mentioned a number of actually three times as far away from the changes outside the Chicago region. In lake as it was at Wicliff. Only the Sag order to understand what happened after Outlet channel of the Toleston stage, west the Toleston stage, some of these must re­ ceive a little attention. of Riverdale, provided escape from the 3 labyrinth. Calumet River never entered The Lake Michigan basin was given its Lake Chicago. Only after the Toleston finishing touches during the retreat of the stage was closed did it finally join the St. last ice-sheet. When completed, the lowest place in the basin rim was the Strait of Lawrence drainage, and then only by util­ Mackinac at the north and the next lowest izing, in reverse direction, the break in the was the Chicago Outlet at the southwest. Toleston shore afforded by the head of the Sag channel at Riverdale. 'For a complete account of the glacial Great Lakes. from which there since have been but few departures in That remarkable parallelism of stream interpretation, see "The Pleistocene of Indiana and Michi­ gan and the History of the Great Lakes."': U. S. Geo!. ways with the lake shore in the Chicago Survey, Mon. 53, 1915. LAKE CHICAGO 111

... � ···---�····-·;

ICE SHEET

Moltawk

FIG. 88.-The Great Lakes region during the Toleston stage of Lake Chicago and the first stage in the development of the gorge below Niagara Falls. (Partly after Leverett and Taylor, U. S. Geological Survey, Mon. LIII, Pl. XIX.)

The south end of the basin became ice-free Huron basins being widely submerged. This long before the north end. This held Lake lake was Lake Algonquin (fig. 89), the Chicago, lengthening but lowering during largest continuous sheet of glacially ponded its existence. Had there been no rock floor water in the Great Lakes region. At Chi­ in the Chicago Outlet channel, or had Lake cago it was very little below the Toleston Chicago endured for a longer time, it is level and its shorelines cannot be positively conceivable that Lake Michigan would to­ separated from the last ones made by Lake day have a natural discharge to the Missis­ Chicago. sippi. But the Strait of Mackinac, and with During the life of Lake Algonquin, the it an opportunity for continuous eastward ice continued to retreat toward the north­ flow to the Atlantic, was opened before this east, and the northern region continued to happened, and Chicago Outlet ran dry. rise. Since the Trent outlet lay north of Niagara Falls had already been born, had the so-called "hinge-line" (south of which had its first great discharge, and had dwin­ the shore lines remained horizontal) its dled to a fifth of its early volume because uplift produced a rise in Lake Algonquin's the lower Trent River valley route in surface. This made no change in shorelines Ontario had been uncovered. The Toleston adjacent to the outlet, but in the south and stage was probably contemporaneous with southwest the lake surface rose on the land the early stage of Niagara Falls (fig. 88), as the northward uptilting progressed. This the immediately post-Toleston events with rise of water south of the hinge-line is what discharge through the Trent River outlet caused the spill-over at Port Huron, re­ and with the shrinkage of Niagara. turning to Niagara approximately the form­ Shorelines adjusted to the Trent River er large volume of discharge. It seems outlet from Georgian Bay show that one probable that for a short time the Toleston great lake now occupied the three upper shores were re-occupied in their entirety lake basins, the Strait of Mackinac between and that a part of Lake Algonquin dis­ the Michigan and Huron basins and St. charged through the Chicago Outlet. If Marys River between the Superior and so, it was but a shallow stream and soon 112 GEOLOGICAL HISTORY

ICE SHEET

---

:/:·:·:·.::::::::::::::::::

· ...... :::: --- -- ktlliffii · - . .. · -- . ··· · ---.I -- ·· -/ , rChica;o I #; i i i' i'

FIG. 89.-Lake Algonquin with three outlets. (After Leverett and Taylor, U. S. Geo!. Survey Mon. LIII, Pl. XXL) went dry, as the Port Huron outlet channel, history came to an end, and the first of the which is in glacial drift, was rapidly deep­ postglacial lake stages Nipissing began. ened. Both the Sag and DesPlaines channels Lake Nipissing, or the Nipissing Great already had been scoured to bedrock during Lakes, had one level throughout the three the life of Lake Chicago, and this minor upper lake basins but the connections had discharge did nothing further to them. Lake become so narrow and the levels had lo-w­ Algonquin thus may have had three different ered so much that a map of it (fig. 90) outlets functioning simultaneously for a looks very much like a map of the present time (fig. 89) -the waning Trent River lakes. The Nipissing level at Chicago was outlet, the rock-floored shallow Chicago not high enough to send water westward Outlet, and the deepening Port Huron to Mississippi River, and it is represented drift-floored outlet. by a complex group of low sand ridges be­ Lake Algonquin was an ice-dammed lake, tween the Toleston beach and the present the continued retreat of the ice gradually lake shore. They are well shown in un­ exposing most of the basin of Lake Huron developed areas about Gary and Hammond and Georgian Bay. The last area aban­ (fig. 91) but have almost entirely disap­ doned was the northeast part of Georgian peared in the built-up portions of Chicago. Bay and beneath the ice here was, in spite The geologic maps (Calumet Lake, Jack­ of the preceding northern uplift, still the son Park and Chicago Loop quadrangles) lowest place in the rim. When this was show these beaches as they were surveyed finally exposed, a new discharge route in 1902, the dotted boundaries indicating opened via the Mattawa and Ottawa rivers that they are but ghost outlines. One still to the Ontario basin, Port Huron and Chi­ recognizable member crosses the northwest cago outlets went dry, Lake Algonquin's corner of Washington Park, swings south- LAKE CHICAGO 113

------1---- 1 I

iI I '

Fie. 90.-Nipissing Great Lakes. (After Leverett and Taylor, U. S. Geological Survey, Mon. LIII, Pl. XXVII.) ward across to the west side of State Street, gonquin beaches, opening of the l\1attawa­ and terminates at 87th Street, near the foot Ottawa outlet having lowered the water of the Toleston beach. It is lower than the level in the northeastern part of the three­ Toleston and its orientation departs about fold basin (Superior, Michigan, Huron) 45° from that of the Toleston here. It that much. But the Nipissing shore in has, or had, a series of barb-like projections Chicagoland is only 5 to 10 feet below on the landward side, indicating its origin the Toleston-Algonquin shores, although as a spit from the north. Indeed, the whole the surfaces of both Lake Algonquin and group of sand ridges in the Englewood and Lake Nipissing must have been level. The South Shore districts as mapped in the Chi­ explanation lies again in that northern up­ cago Folio (1902) is a compound spit. rising which, continuing through the Nipis­ There could hardly have been a discharge sing stage, raised the outlet floor. As the down the DesPlaines channel at this time, Chicago region underwent no uplift, the for an uninterrupted alongshore current water level here was forced to rise to keep from the north for some distance would pace with the rising outlet. Thus the earli­ have been necessary to supply this sand. est Nipissing shorelines at Chicago must Furthermore, these shores are too low to have been destroyed by the rising waters, have belonged to a stage of the lake that and the existing beaches of this stage are had westward discharge. late Nipissing. The continued tilting final­ Fragments of beach ridges and spit "fin­ ly repeated at Port Huron outlet what had gers" in front of the Sag channel farther happened in Algonquin time. A spill-over south and lower than its floor indicated the occurred to Lake St. Clair and thence to same thing for this outlet. The plexus of Lake Erie ; the discharge soon became the sand ridges here is in part responsible for main outlet and finally the only outlet, and the enclosure of the basins of Lake Calumet with this, the Nipissing Great Lakes came and Wolf Lake, both very shallow pans on to an end and the modern lake-levels and the lake-bottom of the Nipissing stage. outlines were determined. The Nipissing beach in Georgian Bay is Niagara Falls must be mentioned again­ at least 40 feet below the lowest of the Al- its history as thus far outlined is too briefly 114 GEOLOGICAL HISTORY

Courtesy of the Chicago Daily Illustrated Times

Frc. 91.-Beachlets of post-Toleston lake stages between Hammond and Gary, Indiana. There are 68 separate beach ridges recognizable in the photograph. The Toleston beach, overgrown with dunes, lies between the two Calumet rivers and is the cause of the great detour. Michigan City Road follows the crest of the Toleston beach. Ridge Road is on the Calumet beach. LAKE CHICA GO 115

told for accuracy. The cataract was born and Blue Island and provided, with the full grown when Lake Chicago was still accompanying reversal of Chicago River discharging to Mississippi River, melting of . . also, two converging westward artificial out­ the closely adjacent ice front contnbutmg lets for Lake Michigan. But only the gla­ � a large v lume of water. When. the Trent cial river channels, on either side of Mt. River outlet of Lake Algonqum opened, Forest Island, have made possible these Niagara River shrank to about a fif.th of works of man. the maximum volume. The falls agam re­ Low-water stages.-Another item of Lake ceived maximum volume when tilting had Chicago history should be noted before our lifted the Trent outlet above the low place account is fairly balanced. It will be stated in the rim at Port Huron. But it lost all very briefly. There is evidence that when this gain and operated a second time on the Lake Chicago fell from the Glenwood level, discharge from Lake Erie alone when the it went much lower than the Calumet level Mattawa-Ottawa outlet of the Nipissing and that later when it rose to make the Great Lakes was exposed. Finally it re­ Calumet shoreline it re-submerged part of gained the discharge from lakes Su�eri.or, the Glenwood bottom that had been exposed :Michigan, and Huron when the contmumg during the low-water stage. There is evi­ uplift reestablished the Port Huron outlet dence that similar low-water stages, lower and the modern lakes were born. In the than each succeeding shoreline stage and gorge below Niagara Falls there ar.e three perhaps lower than the present lake-level, wide stretches and two narrow portions, to may have occurred between all of the shore­ be correlated with these outlet shiftings. line stages of the glacial lake. The evidence There is still more to Niagara's history but for the low-water stages alternating with it is not intimately bound up with events the high-level stages consists of swamp de­ in Chicagoland and is not reviewed here. posits under portions of the various beaches Calumet River, escaping from behind the and of stream channels completely buried Toleston beaches near Riverdale, encoun­ under the sand in the lake-plain. These tered more trouble during the Algonquin could have been formed only if the lake and Nipissing stages. The rate of growth water had been withdrawn. of beach ridges and spits from the nort was more than the rive.r with its low gradi­� Such low-water stages during Lake Chi­ ent could cope with. Like. Chicago River cago's history could occur only if the mar­ before dredging and harbor in provements gin of the ice-sheet had withdrawn in each ; case so far north that lower outlets toward ( p. 40 ), the mouth of the slugg�sh Calumet was forced southward by the spits constant­ the east were afforded. Re-advance of the · ice-front made the next high-level stage by ly growing from the nor�h. The �iver flowed into Lake Algonqum near River­ closing the eastward discharge routes, but dale, but by the end of Nipissing time, its the re-advance also obliterated the evidence for the temporary outlets. mouth had been shifted south and east at least as far as Gary, and by the time of Such oscillatory behavior of the ice-front is known from other evidence as well. The exploration and early settlement of Chica�o­ land its mouth was three quarters of a mile successive moraines of the northern states east f Millers, 14 miles east of the Indiana ( 32 are known between Ohio River at Cin­ cinnati and the Canadian boundary near state line. Thus about 20 miles were added � Plattsburg, New York) show in many to the river's length after it discharged at places that they probably were each formed Riverdale. Had not the shore current inter­ by a re-advance of the ice after a retreat fered, there would have been needed no from the preceding moraine several times as more than six miles of added length to reach great as the distance between the moraines. the lake today. By 1870, beach and dune Even our minor Tinley moraine ridge re­ sand had closed the mouth at Millers and cords a slight re-advance after a retreat, be­ the river was again in serious difficulty. cause in one place the drift overlies the east­ Man, for his own purposes, then provided ern part of the laminated clay and silt of a dredged route to the lake between lakes Lake Tinley. We must remember, in using Wolf and Calumet. Still later, by digging this concept, that the terms "retreat" and the Calumet-Sag canal, he reversed the flow "re-advance" refer only to the position of of that portion of the river between Millers the ice-front, and that the ice-mass itself 116 GEOLOGICAL HISTORY never moved back-it was moving forward summer high level of Lake Michigan, ac­ even when the ice-front was retreating. cording to the Sanitary District of Chicago was 579.7 feet. RECENT CHANGES OF LEVEL IN Precise causes of the longer, irregular LAKE MICHIGAN variations of lake level are difficult to de­ All the Great Lakes are known to under­ termine and no predictions of their occur­ go seasonal changes in level. Since measure­ rence or alterations are yet feasible. But ments were inaugurated in 1860, their sur­ the general causes certainly are variations faces have averaged about a foot higher in in weather. The lakes extend through 7° summer than in winter. In addition to these of latitude and 16° of longitude, an area regular changes of the year, there have also large enough to have noteworthy variations been larger variations of level, enduring for in storm tracks across it and variations irregular but longer periods. Furthermore, therefore in rainfall and snowfall and in these larger and longer fluctuations arc amount of evaporation from both land and somewhat unlike in the different lakes, water during fair weather interludes. Com­ Huron and Michigan being considered as binations of these as yet incompletely meas­ a single water body. Lake Michigan (and ured variables caused the long-term fluctu­ Lake Huron) was unusually high in the ations in levels of the different Great Lakes. summers of 1917 and 1918, reaching 582 It is to be expected that cycles of decreased feet above sea-level. Then for nearly a run-off and increased evaporation will recur decade its summer high level fell lower and in the future. The three per cent of dis­ lower, eventually failing by four feet to charge volume, recently going to Missis­ reach the mark of 1918. The steamer route sippi River through the canal and now re­ south from Lake Huron and many harbors turned to Niagara, will make only a few in both lakes became dangerously shallow. inches difference in the lake level. In 1900 the Sanitary District of Chicago LIFE OF THE GLACIAL LAKE STAGES completed a 28-mile canal extending from Chicago River across the St. Lawrence­ If swamp deposits occur immediately be­ Mississippi divide and down glacial L\lke neath the sand and gravel of the glacial Chicago's outlet as far as Lockport where lake shores, then plants must have migrated a drop of 34 feet was utilized for power. back into the region, from which the ice­ Upon completion of this canal Chicago sheet had earlier erased them, before the River and its south branch were reversed, glacial barrier had vanished from the lake and for the first time in about 25,000 years basins. In the wave of life returning to the water again flowed from the Lake Michi­ devastated country, animals should have ac­ gan basin into Mississippi River. companied the plants, or followed very During the 920's much blame for the shortly after. Pioneers of the more hardy low level was lplaced on the diversion of species would be expected to arrive first, 10,000 cubic feet per second through the then increasing numbers of them, followed Chicago Drainage Canal. Legal proceedings and replaced later by types requiring milder were instituted against the Sanitary District climates until finally the present flora and of Chicago, and eventually a reduction to fauna of northern Illinois became estab­ 4,167 cubic feet per second was ordered lished. Insofar as the sediments and beaches by the Federal Court and confirmed by the of Lake Chicago contain or cover fossil U. S. Supreme Court in 1930. While the plants and animals, they afford a consecutive Supreme court was weighing the evidence, record of the return of living forms up to during which period 10,000 cubic feet per the time of Lake Algonquin. second were still being taken for the canal, There is very little evidence in the Glen­ the lake level started rising and in little wood records that organisms had already more than a year, it had nearly touched reached the region by that time. A water­ 582 feet above sea-level again. In 1929, worn fragment of a mammoth tooth, found storm waves of the continued high level did many years ago in a gravel pit in the Oak damage estimated at many millions on the Park spit, seems to tell of these subarctic shores, particularly of Lakes Michigan and animals in Chicagoland at that early stage, Erie. In 1938, just preceding the reduction and therefore of adequate pasturage for the in volume to 4,167 cubic feet per second, great beasts. But an oyster shell also found LIFE OF GLACIAL LAKE STAGES 117 in this deposit surely does not record post­ snails. The assemblage is not like what glacial marine water here any more than Baker found in definitely dated Toleston do the Floridan and West Indian subtrop­ sediments and may be Calumet in age. The ical mollusc shells and coral once unearthed driftwood, found higher up in the alluvium, in the somewhat later Calumet beach. Man has not been identified, but its abundance has introduced these shells. The water-worn and the large size of the tree trunks tell of mammoth tooth is far better evidence. The a complete forest cover on the adjacent only other record known of Glenwood life moraine slopes. A mammoth tooth and is that of ten species of minute molluscan numerous fragments of deer antlers com­ shells found in stratified silts of Skokie plete the picture of an established biota by Bay.1 All but one are freshwater shells. Calumet time or a little later. The exception is a land snail, probably Authorities disagree on the question of a washed out into the bay from the land. low-water stage between Calumet and To­ Here, without doubt, is an aquatic fauna leston times. A peat deposit has long been of the earliest stage of Lake Chicago, a known to exist under a ridge that crosses fauna living in ice cold water even in the Northwestern University campus in Evans­ summer. ton. It is clearly older than that rid.ge. In the deeper parts of Wilmette Bay is By some, the ridge has been called a Cafu­ a wide-spread silt and peat deposit, from met offshore bar, others consider it a Toles­ 10 to 18 inches thick and nowhere more ton beach ridge. If the former, it never was than 10 feet above present lake level. It built up to the Calumet level of Lake Chi­ has yielded remains of oak, poplar, spruce,2 cago. If the latter, its crest grew by storm cedar, balsam, tamarack, and sedges and of wave action to stand a few feet higher than nearly forty molluscan species characteristic the Toleston level. The problem is further of quiet shallow ponds. This is the best, complicated by the recent discovery that this though not the only, record of life in the ridge contains two peaty horizons, separated region during the Bowmanville low-water by about six feet of sand. The upper one stage that preceded the rise to Calumet has never been reported by previous workers. levels. The flora recorded is north-temper­ Apparently there are two highwater stages ate and boreal. At the Bowmanville low­ of the lake history recorded here, the ridge water stage, Chicagoland was the extreme shape dating from the second. The finai northern limit of these trees. They had interpretation of this Evanston record has just arrived in the first forest wave re­ yet to be made. possessing the glaciated region. For Toleston and subsequent time, the Another deposit containing peat, frag­ region contains a wealth of records. Fresh­ ments of wood, and numeruos molluscan water mussels became as abundant as they shells, referred to the same interval of time, are today. In the Toleston bays were de­ is exposed in the low lake-cliffs of today, a posited layers of shell marl, containing myri­ little north of Evanston. The peat is sev­ ads of tiny gastropods. Mammoths, masto­ eral feet thick a few blocks back from the dons, and deer lived on the land, driftwood shore and is nowhere more than fifteen feet from the forest collected along the shore above Lake Michigan. and in favorable places became buried along There are no authentic records of organ­ with shells of the shore-living forms. A isms of Calumet age. The beach sand and detailed example of the Toleston (or Al­ gravel has proved to be barren and no one gonquin) record is worth recording. Exca­ has yet succeeded in dating any fossil-bear­ vation in a clay pit in the northern part of ing open-water sediments as Calumet. The Dolton in 1930 exposed 4 to 7 feet of clean alluvium of Plum Creek, south of Dyer, sand overlying glacial till, the contact oc­ has been accumulating ever since that part curring at an altitude of about 590 feet, in of the Calumet shore (the Lansing Beach) the lower edge of what is mapped as the was built. The shells from its lower part Toleston beach ridge. Here a log of oak, have been identified by F. C. Baker as lake a foot in diameter, lay in contact with the till and the thin layer of clean wave-washed •Ball. R. R. and Powers, W. E., Evidences of aquatic life from the Glenwood stage of Lake Chicago : Science, gravel that surfaces the till. The roots were N. S., Vol. LXX, 284-285. 1929. pp. mere stubs, having been worn off as the log 'Baker, F. C., 69-73 in Life of the Pleistocene or Glacial Period; Univ.pp. of Ill. Bull., Vol. XVII, 1920. rolled in the waves on the glacial lake beach. ] ] 8 GEOLOGICAL HISTORY

In a broad shallow cavity beneath the log or the Aleutian Island chain. Some would was a mat of stems, seeds, bits of wood, and have him migrate southward along the Pa­ a few beetle wing-covers, lying on a bed of cific coast, others see him go south along tiny pebbles just as they were left by the the Great Plains east of the Rockies and last waves that forced water through the actually between the waning continental hollow beneath the log. The wood was ice-sheets on the east and the glacier-clad soft and weak, and it cracked badly on Rockies on the west. Some believe that early exposure to the air. But, after drying, it Man in North America was contemporane­ burned. In the wall of this same pit was ous with the mammoth and the wasting gla­ a buried ravine, about 40 feet wide and 16 ciers, others insist that our meager evidence feet deep, eroded in the glacial till and does not justify this �arly date for Man's filled with beach sand and gravel, a record arrival. The acceptable solution of the of postglacial, pre-Toleston stream erosion problem of Man's appearance in our conti­ a low-water stage of Lake Chicago. m nent awaits the careful collection of much more evidence than we now possess. THE COMING OF MAN Many plant and molluscan species of CONCLUSION these glacial lake stages now live wholly History records and interprets the events north of our region, having followed the of the past. The significance of history be­ cooler climate to which they are best adapt­ comes apparent when one recognizes that ed. The mammoth and mastodon have van­ every "present" contains its own past. Had ished from the earth. Some of the molluscs that past been different, the present would are extinct. Chiefly because of that north­ be unlike what it is. The law of cause and ward migration, the myriad forms of our effect is implicit in this. Chicagoland did fauna and flora have changed considerably not fall ready-made out of the sky, it did in the past 25,000 years. A member of the not take origin at the wave of a wand. It fauna, a creature much like ourselves, came in some thousands of years ago. He had is the inescapable consequence, the cumu­ not lived here before ; indeed, he may not lative consequence, of things that happened have existed anywhere on the earth before thousands, millions, even hundreds of mil­ the glacial period. His home continent, it lions of years ago. The geological story is is generally agreed, was Asia. By what complex and involved. Much yet remains route and at what time did Man enter to be deciphered and understood. We have North America, thence to spread to every endeavored, in this account, to transcribe part of its vast area before Leif Erickson the high points alone in what has thus far or Christopher Columbus arrived ? been decoded and interpreted. To the mind Except for one item, this is debatable attuned, this endeavor to understand our ground. Man entered the continent, all present from the record of its past is an authorities concede, by way of Bering Strait intellectual adventure of absorbing interest.