STATE OP ILLINOIS WILLIAM G. STRATTON, Governor DEPARTMENT OP REGISTRATION AND EDUCATION VERA M. BINKS, Director DIVISION OP THE STATE GEOLOGICAL SURVEY JOHN C. PRYE. Chief URBANA REPORT OF INVESTIGATIONS 198 FARMDALE DRIFT IN NORTHWESTERN ILLINOIS BY PAUL R. SHAFFER PRINTED BY AUTHORITY OF THB STATE OF ILLINOIS URBANA, ILLINOIS 1956 STATE OF ILLINOIS WILLIAM G. STRATTON. Governor DEPARTMENT OF REGISTRATION AND EDUCATION VERA M. BINKS. Director DIVISION OF THE STATE GEOLOGICAL SURVEY JOHN C. FRYE. Chief URBANA REPORT OF INVESTIGATIONS 198 FARMDALE DRIFT IN NORTHWESTERN ILLINOIS PAUL R. SHAFFER PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA, ILLINOIS 1956 ORGANIZATION STATE OF ILLINOIS HON. WILLIAM G. STRATTON. Governor DEPARTMENT OF REGISTRATION AND EDUCATION HON. VERA M. BIXKS. Director BOARD OF NATITRAL RESOURCKS AND CONSERVATION HON. VERA M. BIXKS, Chairman W. H. NEWHOUSE. Ph.D., Geology ROGER ADAMS, Ph.D., D.Sc, Ll.D.. Chemistry ROBERT H. ANDERSON, B.S.. Engineering A. E. EMERSON, Ph.D., Biology LEWIS H. TIFFANY, Ph.D., Pd.D., Forestry W. L. EVERITT, E.E., Ph.D. Representing the President of the University of Illinois DELYTE W. MORRIS, Ph.D. President of Southern Illinois University GEOLOGICAL SURVEY DIVLSION JOHN C. FRYE, Ph.D.. D.Sc, Chief (42848—2500—9-56) CONTENTS Page Introduction 5 Location, size, and drainage of the area . 5 Acknowledgments 5 Early studies 5 Age of the drift 5 Methods of study 7 Classification of the Pleistocene series 10 Illinoian drift 10 Wisconsin drift 11 Farmdale drift 11 Thin drift in the upland areas 13 Thickness of the ice 15 Origin of the stratif.ed deposits 15 Character of the drift 16 Upper Farmdale sandy silts with rock flakes 20 Calcareous loess above calcareous Farmdale drift 20 Size analyses of Farmdale till matrix 21 Humic-glei soils 21 ShelbyviUe drift 22 Sand-silt-clay ratios of the till matrix 24 References cited 25 ILLUSTRATIONS Figure - Page 1. Map of Illinois showing area studied 6 2A, 2B. Map of area studied 8 3. Diagram showing distribution of sand-silt-clay ratios of till matrix 23 Plate 1-A, B. Exposures of Farmdale ice-contact gravels 12 2-A. Stony calcareous Farmdale till 14 2-B. Calcareous Farmdale drift 14 2-C. ShelbyviUe till 14 Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/farmdaledriftinn198shaf FARMDALE DRIFT IN NORTHWESTERN ILLINOIS PAUL R. SHAFFER ABSTRACT The Farmdale drift, consisting of till and stratified deposits is present over a wide area of northwestern Illinois. It covers the area from the Belvidere lobe on the east and the Green River lobe on the south (both regarded as Shelbyville) to the unglaciated area on the west and northwest. Both south and east of this area calcareous Farmdale drift Is overlain by calcareous lowan or pro-Shelbyville loess, in turn overlain by calcareous Shelbyville till and Peorian loess. In the main area of Farmdale drift there is no Farmdale loess, although the loess is present in the surrounding areas. The Farmdale drift is more thoroughly weathered than lowan drift at the same latitude in Iowa. The Wisconsin age of the Farmdale drift is indicated by its lack of thorough dissection, its lack of evidence of continued exposure during Sangamon interglacial time, and its stratigraphic relationships with lowan or pro-Shelbyville loess and Shelbyville till. The Farmdale till is markedly different in texture from the Shelbyville till, which occurs both as continuous deposits and as isolated discontinuous patches west and north of its previously mapped extent in Ogle, Lee, and Whiteside counties. INTRODUCTION Location, Size, and Drainage of the Area The area included in this study (fig. 1) consists of about 2,930 square miles and embraces eastern Jo Daviess, Stephenson, Winnebago, northwestern Boone, Ogle, Carroll, northern Whiteside, and northern Lee counties in northwestern Illinois. It lies essentially within the Rock River Hill Country of Leighton, Ekblaw, and Hor- berg (1948, p. 25). The major portion of the area is drained by the Rock River system — Kishwaukee River, Pecatonica River, Rock Creek, and their many tributaries. A small area in northern Carroll and eastern Jo Daviess counties is drained by relatively short trib- utaries to Mississippi River, namely, Apple River and Plum River. Acknowledgments The writer is grateful to many persons for their aid in his field and laboratory studies and in the preparation of this report. M. M. Leighton, Chief Emeritus, Illinois State Geological Survey, initiated the proj- ect. He has on several occasions examined critical exposures in the field and has aided in the preparation of the report. John C. Frye, Chief, Illinois State Geological Sur- vey, lent his support to the continuation of the study. H. B. Willman and George E. Ekblaw have contributed valuable informa- tion and suggestions throughout the study and have also reviewed the manuscript. Vincent C. Shepps, aided by the writer, made the mechanical analyses, and John B. Droste made the x-ray studies. George W. White, Head, Department of Geology, University of Illinois, has given valuable suggestions and encouragement. Herman L. Wascher, Agronomy Department, Uni- versity of Illinois, spent several days in the field with the writer and made valuable suggestions concerning the material in Boone and McHenry counties. To these persons and to all others who have contrib- uted in any way the writer is grateful. EARLY STUDIES Age of the Drift The origin, character, and age of the glacial drift in northwestern Illinois east and southeast of the unglaciated area have engaged the attention of geologists for more than a century. Although earlier observa- tions were made and recorded, the detailed [5] ILLINOIS STATE GEOLOGICAL SURFEY reports of Shaw (1873, p. 1-201) and of Chamberlin and Salisbury (1884-85, p. 199-322) focused attention on the area and its unusual geologic aspects and problems. The drift was regarded by Chamberlin and Salisbury (1884-85, p. 265, footnote) as older than th^ moraine just south and southwest of Madison, Wisconsin, now re- garded as of Gary age (Glacial Map of North America). Chamberlin and Salis- bury stated, * We do not here wish to as- sert or imply any final opinion as to whether this older sheet is the oldest of the drift sheets known to us in the interior or not. We do, however, desire to be understood as holding that this belongs to one of the two or more ancient drift sheets, as disinguished from the two or more later drift sheets whose margins are marked by the great mo- raines of the interior." Leverett (1899, p. 26) states, ''In the portion of Illinois north from the latitude of Rock Island the lowan drift occupies a large part of the interval betw^een the glacial boundary and the outer moraine of the Wisconsin series. A drift, tentative!) referred to the lUinoian, forms the surface sheet in that region in Stephenson County and parts of Winnebago, Ogle, Whiteside, Carroll, and Jo Daviess counties." The term lowan as used above, unlike its present usage to denote a substage of the Wisconsin, referred to a drift that was re- garded as post-Sangamon in age and sep- arated from the early Wisconsin drift sheets by an interval of recession or deglaciation which Leverett (1899, p. 20) designated Peorian. The glacial deposits were mapped as probable Illinoian in Stephenson, Car- roll, northeast Whiteside, northwest Ogle, and northwest and southwest Winnebago counties and as lowan in eastern Winne- bago, southeastern Ogle, and northwestern Lee counties and in a narrow strip in cen- tral Whiteside County north of Rock River. Leverett summarized his concept of the lowan drift of northwestern Illinois and its age relationship to the Illinoian drift at that time as follows (Leverett, 1913, p. 698): "The so-called lowan drift may stand in about as close relation to the Illinoisan as do V//.A7///y/yx\ \\ eio«,./.oooro«o I 1 1 k^ Fig. 1. — Map of Illinois: diagonal lines show the area studied. the later moraines to the earlier Wisconsin. It does not seem to be separated from the Illinoisan drift by a definite inter-glacial stage, but instead to represent a substage or stadium of the Illinoisan. It may, therefore, be advisable, pending further study, to ap- ply to it the double name Later Illinoisan or lowan." Trowbridge and Shaw (1916, p. 92) made the following statement: "The age of the drift in the Elizabeth quadrangle is not definitely known. It does not belong to the last or Wisconsin stage of glaciation, as its surface has been much more altered by streams, wind, and other agents than the surface of the Wisconsin drift north and east of our area. From the relations of this drift to drift of known age in Wisconsin and Iowa, it is usually considered to be METHODS OF STUDY 7 lllinoian, though this is by no means proved." Alden included observations in north- western Illinois along with his detailed studies of the "Quaternary Geology of Southeastern Wisconsin," which was called by T. C. Chamberlin "a first serious study after a first serious reconnaissance." Alden (1918, p. 160) made a major contribution toward unravelling the Pleistocene history of the area when he stated, "After consid- eration of all factors in reference to the pre- Wisconsin drift the writer is convinced that the conditions were, in general, the same in the tracts north and south of the state line, and he is led to the conclusion already stated (p. 152) that the uppermost drift outside the moraines of the Wisconsin stage in southern Wisconsin and northern Illinois (at least in that part of it examined by him- self — Boone County, north of Kishwaukee River ; Winnebago County ; eastern Ste- phenson County ; Ogle County ; northern Lee County; and northeastern Whiteside County) is of practically the same age throughout instead of representing two or m.ore distinct stages of glaciation separated by stages of deglaciation, and that the whole was probably deposited at the llli- noian stage of glaciation. He admits, how- ever, that there is legitimate ground for difference of opinion in regard to this matter and that the question of age is not to be considered as positively settled." Leighton (1923, p. 267) extended the Wisconsin drift considerably westward with his discovery of the Belvidere lobe and his westward extension of the Green River lobe. The drift west of the Belvi- dere lobe he regarded as lllinoian in age. Flint (1931, p. 424) also regarded the drift west of the Belvidere lobe as lllinoian in age. He stated, "Between the Driftless Area and the outer edge of the Wisconsin drift sheet east and south of Rock River, lies a broad upland developed on nearly horizontal dolomites and shales and subma- turely dissected into a dendritic system of rather shallow valleys and correspondingly low ridges controlled by a single large stream. Rock River (fig, 1). The topog- raphy of this upland merits the adjective "subdued," partly because its relief is nec- essarily slight owing to control by a high baselevel, and partly because glaciation and the accumulation of loess have delicately smoothed out some of the slight irregulari- ties in the landscape profiles caused by out- crops of the more resistant strata. . . . "The surface of the upland is covered in- completely with a thin mantle of loess, which over much of the area is imperfectly separated from the underlying bedrock sur- face by a thin and discontinuous accumula- tion of lllinoian till." It is interesting to note that the age of the bulk of the drift west of the Blooming- ton moraine and Marengo Ridge was re- garded as probably or tentatively lllinoian until Leighton's work in 1923. His west- ward extension of the Wisconsin drift em- phasized the fact that west of the Belvidere lobe and extending to the east border of the unglaciated area there was a drift that was older than the Belvidere lobe (Shelby- ville). The only possibilities for its age as- signment then were lllinoian or older be- cause the Farmdale substage of the Wiscon- sin stage was then unrecognized. However, Leighton noted that this older drift seemed less weathered than the lllinoian drift far- ther south and southwest in Illinois. Later, after he recognized the Farmdale loess as Wisconsin, his feeling that the difference in weathering might denote an age younger than lllinoian prompted the present study. METHODS OF STUDY Significant Pleistocene sections were stud- ied, measured, and recorded at 105 road- cuts, railroad cuts, and stream bank expos- ures, 14 quarries, and 21 gravel pits (fig. 2). In 42 roadcuts that were too shallow to reveal vital information and at 123 addi- tional locations, borings with a H/^-inch auger and ranging in depth from a few to 18 feet were made to obtain samples for study. Depth of leaching was determined on divides and upland areas rather than on slopes exposed to erosion. In addition to the collection of general samples, 25 samples from as many sample areas (fig. 2) were studied for sand-silt-clay ratios of the matrix. The coarse fraction ILLINOIS STATE GEOLOGICAL SURVEY Fig. 2A. — Map of area studied,. showing principal glacial boundaries and location of exposures examined and of auger borings made during the study. MAP OF AREA STUDIED R. lOE ^^^ Border of unglociated area •y^ Leverett ( 1898), Trowbridge and Show (1916), EKblaw(l942), modified by Shoffar. • • ' Leigfifons 1923 boundary of Belvidere and Green River lobes. Shelbyville boundary (discontinuous deposit"^ common in outer 3 or 4 miles) O Section discussed in fex 8 10 Miles Fig. 2B. — Map of area studied, showing principal glacial boundaries and location of expo.sures examined and of auger borings made during the study. 10 ILLINOIS STATE GEOLOGICAL SURVEY has been retained for a proposed study of the heavy minerals. CLASSIFICATION OF THE PLEISTOCENE SERIES The current classification of the glacial and correlative deposits in Illinois is given below (Leighton and Willman, 1950, p. 602; Horberg, 1953, p. 12). Siage Recent postglacial Wisconsin glacial Sangamon interglacial lUinoian glacial Yarmouth interglacial Kansan glacial Aftonian interglacial Nebraskan glacial S-ubstage Mankato Gary Tazewell lowan Farmdale r Buffalo Hart J Jacksonville 1 Payson [ Loveland (pro-Illinoian) ? (pro-Kansan) ILLINOIAN DRIFT In this study no Illinoian drift was found in northwestern Illinois north roughly from the latitude of Morrison (41° 49'), or ap- proximately 45 miles south of the Wiscon- sin state line. In a railroad cut near the village of Irene (Leverett, 1899, p. 138 and p. 575; Leigh- ton, 1923, p. 271 ; Horberg, 1953, p. 43) a succession is exposed which Horberg re- garded as Illinoian drift overlain by younger loess and drift. It constitutes the northernmost and westernmost of his ex- posures containing Illinoian drift overlain bv Wisconsin drift. No. 1.— Railroad cut, NW % sec. 29, T. 43 N., R. 3 E. (Flora Twp.), Boone Co.; description by M. M. Leighton, correlation by Horberg. Thickness Ft. In. Pleistocene series Wisconsin drift Tazewell drift Soil, dark, loessial, sparse pebbles 2 6 Thickness Ft. In. Leached till, dark buff, clayey, hard .... 1 6 Calcareous till, yellow when dry, gray-yellow with pink tint when damp, limestone pebbles 7 Fine sand, no pebbles, yel- low, highly calcareous . 2 6 Calcareous till, banded, yellow and grayish lime- stone pebbles, compact . 1 6 Blue gummy clay, near- ly gritless in some places and pebbles up to 1 inch in others, highly calcar- eous 4-8 lowan loess Fossiliferous loess, gray- yellow, rusty streaks near base, calcareous throughout, sand streaks, cross-bedded, southward dip ... 5 Sangamon sand Stratified yellow sand and gray silt with few peb- bles, few fossils, discoi- dal, calcareous ... 1 6 Illinoian drift (Farmdale per Shaffer) Light blue silt, pebbly, some limestone pebbles, highly calcareous, may be till 1 Sandy to gravelly till, yel- low to rusty, limestone pebbles, matrix calcar- eous 2 Probable till, gray with pink tint, calcareous. . 7 In his discussion of the section above, Leighton stated, "Here two glacial tills are separated by fossiliferous loess and fos- siliferous silts and sands with some sugges- tion of old vegetation, but neither the fossil content nor the vegetation excludes the pos- sibility of a retreat and readvance of the same ice sheet." The section was not examined during the current study, but because of its similarity to other geologic sections that were studied (especially nos. 4-8) it is believed that the material correlated by Horberg as Illinoian drift is actually Farmdale and that there are no Sangamon materials present. In the area studied, till older than the Farmdale and regarded as Illinoian in age was found at the following two locations. FARMDALE DRIFT 11 No. 2. — Exposure in east bank of Deer Creek, at east side of sec. 19, T. 21 N., R. 6 E., about 500 feet north of U. S. Highway 30; elevation at top 680 ± feet. Thickness Ft. In. Wisconsin drift Peorian, loess, buff-yellow, be- coming gray and calcareous in bottom 3 inches. ... 8 Farmdale, loess, more clayey than above, becomes siltier downward, calcareous in spots only, chocolate-brown, rusty brown at base ... 2 Illinoian Silt, leached, chocolate- brown, with gray mottling. 1 Till, clayey, with a few peb- bles; compact, fairly hard, yellow, top foot leached, secondary carbonate in spots in bottom foot . . 2 Till, clayey, pebbly; com-^ pact, yellow-gray, "ghosts" of limestone pebbles; sec- ondary carbonate in spots . 6 No. 3. — Roadcut and auger boring, SW 34 NW }/i sec. 7, T. 21 N., 705 feet. Wisconsin R. 7 E.; elevation top of section. Thickness Ft. In. Peorian Loess, leached, yellow-buff Loess, calcareous, yellow- buff Farmdale, loess, more clayey than above, brown, with flakes of carbonaceous ma- terial Illinoian drift Clay, leached, waxy, tough, gritty; becomes more grit- ty downward and small pebbles appear, gray where fresh with orange oxida- tion streaks Till, pebbly, gritty, leached, yellow, with a badly weath- ered pebble of pink granite . At the same latitude and within the same township other auger borings encountered no Illinoian drift but only Farmdale loess above the Maquoketa shale with or without a soil profile on the shale. Also at this same latitude near the town of Elburn in Kane County there is reported an occur- rence of Illinoian drift (Horberg, 1953, p. 43). Thus there is no established evidence, from exposures, of Illinoian till in northern Illinois within 45 miles of Wisconsin. The distribution of known Illinoian till indicates that the Illinoian glacier Invaded Illinois from the east, across the Lake Mich- igan basin, as Ossian Guthrie stated long ago (1895, p. 305). He suggested four ma- jor Ice invasions In Illinois with two ice sheets that moved directly south from Lake Superior and remained west of Illinois River and two ice sheets from Lake Huron. Of the latter, one moved Into the Lake Erie basin and Ohio, while the other "left Lake Huron at Saginaw Bay, passed diag- onally across the State of Michigan, entered Kankakee valley near South Bend, and fol- lowed thence along that valley to the Illi- nois, which valley it followed to the Mis- sissippi River, scattering the red jasper or Huron conglomerates, all of Canadian ori- gin, all along its tortuous pathway." Although on the basis of present knowl- edge the details of movement of this ice sheet are questionable, the general direction from which it came seems borne out by the evidence In northern Illinois. No attempt was made to show an Illi- noian boundary on the map (fig. 2), as none can be drawn accurately until more de- tailed subsurface studies are made. WISCONSIN DRIFT Farmdale Drift Leigh ton In 1920 observed a loess be- neath the Peorian and above the Sangamon weathered zone in Illinois. In 1926 he re- garded it as "late Sangamon loess" (1926, p. 170) but later called it "Farmdale." Leighton and Willman (1950, p. 603) noted that the Farmdale loess "has definite valley relationships to the Illinois River Valley (ancestral Mississippi), the present Mississippi Valley below the mouth of the Illinois River, and the Wabash and lower Ohio valleys. Such a relationship suggests a valley-train source. This In turn implies an extension of an Ice sheet during the Farmdale substage Into the drainage basin 12 ILLINOIS STATE GEOLOGICAL SURVEY ,-9»» ^ Plate 1. — Exposures of Farmdale ice-contact gravels in pit in NW34 sec. 24, T. 24 N., R. 4 E., about two miles southwest of Mt. Carroll. A — Gravel over lens of pink till near base. B — Contorted gravel over- lain by Farmdale silt and Peorian loess. Photographs by H. B. Willman. FARMDALE DRIFT 13 of the ancestral Mississippi prior to the lowan substag;e but not yet recognized in the series of drift sheets because it fell short of the subsequent ice lobes." The Farmdale loess has been tentatively identified (White, 1953, p. 362) at Cleve- land, Ohio, on the east, and has been rec- ognized in Indiana, Illinois, Iowa, and westward into the Great Plains of Kansas (Frye and Leonard, 1951, p. 298) and Leonard (1951, p. 323). Sand and gravel deposits regarded as age equivalents of the Farmdale loess are recognized in central and western Nebraska (Condra et al., 1950, p. 12) also. Although loess, stream silts, and pond and swamp deposits of Farmdale age were known, Shafifer (1954b, p. 693) announced the first discovery of deposits of Farmdale drift (till and glacio-aqueous deposits) in northwestern Illinois, coextensive with an area which had come to be regarded as con- taining a single drift of Illinoian age. His later studies confirmed that the Farmdale drift (fig. 2) is the only drift in this area. Younger Wisconsin drift overlaps the Farm- dale drift east and south of this area. On the west the border of the Farmdale drift adjoins the unglaciated area and is marked by large deposits of ice-contact materials in the valleys and scattered pebbles, cobbles, and boulders on the uplands. (PL 1.) The invasion of northwestern Illinois by the Farmdale glacier resulted in the diver- sion of Apple River and the formation of its very youthful-appearing canyon. Thin drift in the upland areas. — A re- markable feature of the upland areas in Winnebago County north of the Pecatonica River, in Stephenson County, and in the small glaciated portion of Jo Daviess Coun- ty, is the extreme thinness of the Farmdale drift. The roadcuts generally expose bed- rock with an overlying succession of : 1 ) a foot or two of heavy brown or red-brown residual clay "geest" with many chert frag- ments; 2) scattered pebbles, cobbles, and boulders of ice-laid origin; and 3) a few inches to 5 feet of leached loess. In some areas only four or five erratics can be found in an extensive hilltop roadcut although in an adjacent cut the erratics may be numerous and included in several inches of till. Pebbles and cobbles of coarse- and fine-grained granites, diorites, gabbros, quartzites, and basalts are remarkably fresh and usually show but a small amount of etching. When broken the erratics show no evidence of a weathering rind. Shaw (1873, p. 63) in his discussion of the Quaternary deposits in Stephenson County remarked, "That part lying west of the Illinois Central Railroad and south of Yellow Creek — being mostly, low, level prairie, underlain mostly by the Cincinnati shales, and also that low, rich, level part between Waddam's Mound and the range of mounds running from the neighborhood of Warren towards the southwest, and un- derlain by the Galena limestone — may al- most be denominated a driftless region. Few boulders are seen over it, and few or no real gravel deposits can be found." The passage from glaciated to the un- glaciated region occurs almost impercepti- bly on the uplands although in the valleys the ice-contact deposits indicate the approxi- mate extent of the ice sheet. Chamberlin and Salisbury (1884-85, p. 265) describe the transition as follows, "Even a keen observer fails to note the point of passage from the drift-bearing to the driftless region, unless his attention is studiously directed to the subject. Even then he will be able to determine the exact limit only by a vigilant outlook for erratics. In general, the drift terminates in this way: approaching the edge from the drift side, the till becomes gradually thinner and dis- continuous, until, at length, it disappears in an irregular and patchy border." On page 268 these authors clearly de- scribe the thinning of the drift toward the unglaciated area: "A part of the attenuation of the old drift border is doubtless due to erosion subsequent to the time of its for- mation, but we have been unable to find any evidence that the border ever consisted of any special aggregation of drift to which we would apply the name terminal moraine. On the contrary, the drift mantle seems to us to have originally thinned out gradually to an attenuated edge." 14 ILLINOIS STATE GEOLOGICAL SURVEY Plate 2-A. Stony calcareous Farmdale till in roadcut in SWM SW3^ sec. 9, T. 27 N., R. 10 E., about two and a half miles north of Pecatonica, with upper 1^ feet weathered brown, overlain by 13^ feet of Peorian loess. Plate 2-B. Calcareous sandy Farmdale drift in sec. 18, T. 25 N., R. 11 E., three miles north of Byron, with upper part weathered brown beneath a thin sandy topsoil. Plate 2-C. Shelby ville till in roadcut in NWM sec. 12, T. 21 N., R. 4 E., with upper V^ feet leached and overlain by 3 feet of leached brown Peorian loess. I'ARMDALE DRIFT 15 In the valleys the maximum extent of the ice is marked in some places by masses of ice-contact gravels. In the area just east of Waddam's Grove in Stephenson County, in sees. 5, 6, 7, 8, 16, and 22, T. 28 N., R. 6 E., the constructional topography of the deposits of till and stratified drift has the appearance of an end moraine although Farmdale drift is known to extend farther west. Thickness of the ice. — Another remark- able aspect of the upland areas in Winne- bago, Stephenson, and glaciated Jo Daviess counties is the widespread presence of bed- rock residuum beneath the scattered errat- ics. The fact that this preglacial surficial material remained on the hilltops and hill- sides despite their glaciation indicates that the Farmdale glacier was thick enough to create ice-flow, as otherwise the residual material would have been readily removed. Throughout most of the upland area there is about 300 feet of relief, and another 200 feet of ice would probably be necessary for flow to occur. On this basis the Farm- dale ice sheet had a minimum thickness of 500 feet and probably thickened consider- ably back from its margin. The thinness of the Farmdale drift and its relationships with the overlying lowan or pro-Shelbyville loess and Shelbyville till indicate that : 1 ) after the Farmdale ice sheet invaded the area it melted down and back fairly rapidly; 2) loess was deposited; and 3) then the Shelbyville glacier ad- vanced over a portion of the area without a long weathering interval between. Some staining of sand in the upper part of the Farmdale drift is present at some places and an accumulation of Farmdale peat is known at several others, but at no place is there ..evidence of a significant period of weather- ing between the deposition of the Farmdale till and the deposition of the overlying lowan or pro-Shelbyville loess or between the deposition of the loess and the deposi- tion of the overlying Shelbyville till. Origin of the stratified deposits. — The Farmdale drift consists not only of till but also of huge stratified deposits in the form of kames, kame terraces, crevasse fillings, and water-laid silts and clays with peat de- posits. Shaw (1873, p. 109), in speaking of de- posits in Ogle County, remarked, "If the phenomena in this interesting locality indi- cate glacial action, and we think they most unmistakably do, it was probably combined with aqueous forces, and the two causes contributed to the results observed." The vast accumulations of stratified drift were described by Flint (1931, p. 422- 440), and regarding their mode of forma- tion he stated (p. 431), "When the evi- dence yielded by the stratified deposits is reviewed, the results are interesting. The evidence of composition indicated deposi- tion in lakes with highly variable currents, in certain cases fluviatile deposition, and in all cases deposition in direct contact w^ith ice. The evidence of form indicates that the masses of deposits are not erosion remnants, but original forms of accumula- tion built in contact with ice. The evidence of distribution indicates deposition in ponded water controlled by pre-existing to- pography. "This evidence presents no conflicting elements. It points consistently to a single definite reconstruction of the conditions un- der which the stratified deposits had their origin. The terraces at several accordant levels require for their development the for- mer presence of several extensive lakes. Their ice-contact form and stratification re- quire that ice shall have been present in the valleys throughout their accumulation. Since each level is represented throughout nearly the whole region, each lake, to- gether with ice, must have existed in nearly every valley. These requirements are satis- fied only by the melting-away of an ice sheet in situ, not inward from a lateral margin but from the top down. Under such con- ditions, and only under such conditions, can the simultaneous presence of ice and lakes in all the valleys be explained. Since the form and structure of the stratified de- posits yield no evidence whatever of bodily movement of the ice in contact with them, and since movement inevitably would have swept away those deposits built in exposed positions, it follows that by the time the 16 ILLINOIS STATE GEOLOGICAL SURVEY lakes came into existence, all such motion had ceased. We have to deal, then, with an ice sheet that lost its motion, passed into a stagnant condition, and melted away in place, from the top down, disappearing first from over the interfluves and remaining longest in the valleys." Character of the drift. — The Farmdale till is frequently light pink to salmon in color (7.5 YR 8/4 dry) and sandy tex- tured. It is considerably different textur- ally from the overlying Shelbyville till (fig. 2). A characteristic feature of the upper 3 or 4 feet of both ice-laid and water-laid Farm- dale deposits is the widespread presence of a conspicuous red-brown to rusty brown leached zone (pi. 2, A and B) developed by weathering. The material is clay-bound pebbly sand or clay-bound sand which con- tains pebbles, cobbles, and occasional boul- ders of coarse- and fine-grained granite, diorite, gabbro, and basalt. Etching of the granites is common and the coarse-grained basic materials are generally altered, but the weathering and etching phenomena, upon close examination, do not indicate or suggest exposure throughout both Sanga- mon and subsequent time, as would have to be the case if the materials were of Illi- noian age. The thickness of the red-brown zone of leaching and staining is highly irregular, depending upon the thickness of the loess over it and the texture of the till or strati- fied drift in which it occurs. Where strati- fied drift is very sandy the leaching and staining may be as much as IIV2 ^^^^ thick, but in the same gravel pit a few yards away the red-brown zone may be only 3 feet thick with calcareous sands and gravels be- low. Excellent examples of the variation in thickness of this zone are present in the ex- posures of stratified drift near Forreston (No. 10) and in the Hazelhurst gravel pit (No. 9). The following geologic sections show some of the characteristics of the Farmdale drift. The first five (Nos. 4-8) contain Farmdale drift overlain by younger Wis- consin till and the later ones (Nos. 9-21) contain Farmdale drift overlain by Peorian loess. No. 4. — Railroad cut at village of Stratford, sec. 8, T. 23 N., R. 9 E. Thickness Ft. In. Wisconsin Peorian Clay, silty, leached, dark gray 8 Loess, leached, brown to light yellow-brown .... 3 4 Shelbyville Till, clayey, pebbly, top 6 inches silty, leached, yel- low-brown 1 6 Till, clayey, pebbly, leached, yellow-gray 6 Till, clayey, pebbly, calcar- eous, yellow-gray ... 1 6 lowan or pro-Shelby ville, loess, calcareous, gray, limonite stains and streaks, espec- ially in top few inches . , 1 Farmdale Sand, with a little clay binder, calcareous, brown and yellow 3 Sand, with an occasional silty mass or streak, calcareous, brown and yellow ... 1 3 The contact between the Farmdale and the overlying loess in this railroad cut was determined by digging or boring in a num- ber of places. At many places there was a slight concentration of clay in the upper few inches of the Farmdale drift and usu- ally there was a concentration of iron oxide, but it was always calcareous and at no place was a soil developed or a significant weathering interval recorded. In some auger borings on the south side of the rail- road pinkish-red calcareous sandy Farmdale till is present beneath the lower loess. No. 5.— Roadcut in NW i^ SW M sec. 31, T. 23 N., R. 11 E., about 17 miles east-by-southeast of No. 4. Thickness Ft. In. Wisconsin Peorian, topsoil and brown loess, leached; lower 9 inches contains scattered pebbles 1 6 Shelbyville Till, clayey, pebbly, leached, yellow-gray 9 Till, clayey, pebbly, calcar- eous, yellow-gray 2 3 FARMDALE DRIFT 17 Thickness Ft. In. lowan or pro-Shelbyville, loess, calcareous, gray and yel- low-gray Farmdale, sand with pebbles, some cobbles, and some gravel; calcareous, yellow, occasionally stained light rusty brown in upper few inches The thickness of the lower loess ranges from 3 inches to as much as 3 feet over a distance of several hundred yards in this cut. No. 6. — Roadcut and auger boring on east side of road on hilltop in NW M SE M sec. 1, T. 23 N., R. 9E. Thickness Ft. In. Wisconsin Peorian, topsoil and loess, leached, bufF-brown. . . 3 Shelbyville Till, clayey, pebbly, stony, leached, light yellow to yellow-gray 1 Till, clayey, pebbly, stony, calcareous, light yellow to yellow-gray, top 6 inches brown 1 6 lowan or pro-Shelbyville, loess, calcareous, pink and rusty brown 3 Farmdale Till, pebbly, sandy, with clay binder, calcareous, red- brown to rusty brown . . 9 Till, sandy, pebbly, with a little clay binder, calcar- eous, red-brown to light yellow 5 No. 7. — Roadcut and auger boring on east side of road in sec. 1, T. 23 N., R. 9 E., about 150 yards north of C. B. and Q. R.R. Thickness Ft. In. Wisconsin Peorian, loess, leached brown . 1 Shelbyville Till, clayey, pebbly, leached, yellow-gray 6 Sand and pebbles, calcareous 3 Till, clayey, pebbly, with cobbles and boulders, cal- careous, yellow-gray . . 2 Sand, pebbles, cobbles, and boulders, calcareous, yellow 9 Till, clayey, pebbly, calcar- eous, yellow-gray ... 9 lowan or pro-Shelbyville Loess, calcareous, yellow and gray 1 Loess, calcareous, yellow and gray, fossiliferous Farmdale, till, sandy, calcar- Thickness Ft. In. 1 6 eous, bouldery at top, pink . 6 In roadcuts at the railroad crossing just south of the above geologic section the pink Farmdale till is well exposed interbedded with sand, pink silts, and gravel. No. 8.— Auger boring in S j^ NW \i sec. 15, T 24N., R. 11 E. Thickness Ft. In. Wisconsin Peorian, topsoil, powdery, gray, and loess, leached, yellow- buff with gray mottling from 2 to 3 feet .... 4 Shelbyville Till, silty, pebbly, leached, fairly soft, light yellow and gray 3 Till, clayey, silty, pebbly, cal- careous, light yellow and gray ....... 7 9 lowan or pro-Shelbyville, loess, calcareous, gray with rusty yellow streaks, bottom 3 inches rusty brown ... 9 Farmdale, till, clay-bound, sandy, pebbly, calcareous, yellow to yellow-gray . . 6 Boulder or bedrock at base sec. 22, T. 23 N., R. 7 E Thickness Ft. In. Wisconsin Peorian, topsoil and loess, leached 1 Farmdale Sand and gravel, clay-bound, leached, red-brown. . . 2 Sand and gravel, leached, slightly iron-stained . . 2 Sand and gravel, calcareous, gray 2 The red zone is variable in thickness in this pit depending on the texture of the un- derlying material. No. 10. — Gravel pit near Forreston, in NW 3^ NE M sec. 20, T. 25 N., R. 8 E.; elevation at top 940-f feet. Thickness Ft. In. Wisconsin Peorian, topsoil and loess, leached, yellow- brown . . 3 18 ILLINOIS STATE GEOLOGICAL SURVEY Farmdale Silt and sand, pebbly, clay- bound, light brown . Sand, pebbly, clay-bound, leached, red-brown to rusty brown, granites common. Sand, clay-bound, leached, rusty brown to red-brown . Sand and gravel, calcareous, yellow, and gray; lime- stone and dolomite peb- bles a little powdery on top; iron staining near top and in some beds below . Thickness Ft. In. 70 No. 11.— Gravel pit in NE ^ NVV H sec. 22, T 25 N., R. 8 E.; elevation 900+ feet. Thickness Fi. In. Wisconsin Peorian, loess, leached, yellow to brown 2 Farmdale Gravel; clay-bound, leached, red-brown to rusty brown; granites and other igneous pebbles common ... 1 9 Gravel, sandy, clay-bound, leached, rusty brown to dark brown 3 Sand and gravel, calcareous, cross-bedded, iron staining common, limestone and do- lomite pebbles, powdery in top 2 feet 36 The rusty brown to red layer is variable in thickness in the gravel pit. No. 12.— Roadcut in NW ^ NW i^ sec. 17, 25 N., R. 9 E.; elevation 828 feet. Thick) Wisconsin Peorian, topsoil and loess, leached, brown . . . . Farmdale Till, silty-textured, leached . Till, clay-bound, sandy, leached, yellow-brown to brown Till, clay-bound, sandy, peb- bly, bouldery, leached, light yellow-gray Till, sandy, pebbly, calcar- eous, light yellow-gray . Ft. In. 6 9 No. 13. — Roadcut and auger boring in NW 34 sec. 4, T. 25 N., R. 9 E. Thickness Ft. In. Wisconsin Peorian, topsoil and loess leached, brown . T,'.ickness Ft. In. Farmdale Till, pebbly, leached, yellow- bufF 3 Till, clay-bound, sandy, peb- bly, leached, red-brown to rusty brown 1 6 Till, sandy, pebbly, calcar- eous except for top 6 inches, with enough clay to bind it loosely, soft, yel- low-bufF 3 6 No. 14. — Auger boring on top of Bunker Hill, NE li NE M sec. 19, T. 26 N., R. 9 E.; elevation 965 feet. Thickness Ft. In. Wisconsin Peorian Topsoil and silt, leached, light brown 2 Loess, leached, brown, with a clayey layer from 2 to 3 feet 1 9 Farmdale Till, clay-bound, pebbly, leached, brown to brown- ish-yellow 9 Till, sandy, pebbly, calcar- eous, light yellow, soft on auger 7 No. 15.— Roadcut in SE 3^ SW ^ sec. 34, T. 28 N., R. 9 E., elevation 805± feet. Thickness Ft. In. Wisconsin Peorian, topsoil and loess, leached, brown .... 2 6 Farmdale Till, clay-bound, sandy, peb- bly, leached, brown. . . 1 Till, sandy, pebbly, calcar- eous, yellow-gray, sandy above, more compact below 2 6 Cobbles and boulders are common in this section, indicating much water action dur- ing deposition of the till. No. 16. — Roadcut and auger boring in SW 34 SW }4 sec. 9, T. 27 N., R. 10 E.; elevation 835 feet. Thickness Ft. Wisconsin Peorian, topsoil, gray; and loess, leached, brown . . 1 Farmdale Till, clay-bound, pebbly, leached, chocolate-brown to dark brown .... 1 Till, clayey, sandy, pebbly, leached, rusty brown and dark brown Till, sandy, pebbly, calcar- eous, yellow-gray with a pink cast In. FARMDALE DRIFT 19 No. 17.— Roadcut in SW M SW M sec. 6, T. 23 N., R. 11 E. T/iickness Ft. In. Wisconsin Peorian (?), topsoil, sandy, leached, dark .... 9 Farmdale Sand, clay-bound, leached, rusty brown with scattered large boulders .... 1 Sand, pebbly, clay-bound, leached, red-brown ... 9 Sand, a little clay binder, a few pebbles and cobbles, leached, red-brown, rusty brown, and yellow-brown . 2 Sand and gravel, calcareous . 4 6 No. 18. — Roadcut and auger boring in NW 3^ SW M sec. 6, T. 43 N., R. 1 E.; elevation 812 feet. Thickness Ft. In. Wisconsin Peorian, topsoil, light gray; and loess, leached, brown . . 1 3 Farmdale Till, clay-bound, sandy, peb- bly, leached, rusty brown . 2 Till, sandy, pebbly, leached, light brown, with a few masses of dark clay . . . 1 Till, sandy, pebbly, calcar- eous, light gray, yellow- gray, and pink .... 3 No. 19. — Roadcut and auger boring in SW J^ sec. 6, T. 45 N., R. 1 E. Thickness Ft. In. Wisconsin Peorian, topsoil, dark gray; and loess, leached, brown . . 1 6 Farmdale Sand, leached, brown ... 1 Sand, clay-bound, leached, with scattered pebbles, rusty brown 1 6 Till, sandy, pebbly, calcar- eous, light yellow-buff . . 1 No. 20.— Roadcut in SE M sec. 12, T. 45 N., R. 3 E.; elevation 940 feet. Thickness Ft. In. Wisconsin Peorian, topsoil and loess, leached, yellow-brown . . 3 Farmdale Till, clay-bound, sandy, peb- bly, leached, yellow-brown to red-brown 2 Till, sandy, pebbly, calcar- eous, yellow-gray to pink . 1 No. 21.— Roadcut in NW ^ sec. 32, T. 46 N. R. 3 E.; elevation 930 feet. Thickness Ft. In. Wisconsin Peorian, topsoil and loess, leach- ed, brown Farmdale Till, clay-bound, sandy, peb- bly, leached, rusty brown . Till, sandy, pebbly, cobbly, bouldery, calcareous, yel- low-gray and pink . Alden (1918, p. 157) described the al- teration of the drift west of Rock River as follows : "Generally throughout this tract the up- per part of the drift shows the effects of alteration by exposure to the weather dur- ing the long time since its deposition. The amount of this alteration is one of the most important reasons for referring its deposi- tion to the Illinoian stage of glaciation. Where the drift is very thin it is little more than a layer of gravel composed of pebbles of less readily soluble rocks such as dense fine-grained crystallines, quartzites, quartz, and chert. Where thicknesses of 2 or 3 feet remain the drift is brown or reddish brown, sandy, and gravelly, with perhaps some non- calcareous clayey matrix but with few lime- stone pebbles (and those with surfaces roughly etched by solution). Where thick- nesses of more than 5 to 6 feet remain, the drift below this depth is usually unaltered, highly calcareous, fresh till. The top of the unaltered clayey till is generally marked by an abrupt change in color from bluish, gray, pink, or buff to dark brown or red ; the matrix becomes more gritty and less clayey, is largely or quite leached of its lime carbonate, and the limestone pebbles are few and rotted or have roughly etched surfaces. A few inches above or within about a foot, the limestone pebbles disap- pear entirely and only sand and pebbles of the less easily soluble rocks are found, com- pactly bound together by a little sticky, non- calcareous clay. In this part, which in many places is 2 to 4 feet thick, there is sometimes an indefinite banding as though due to set- tling or pressure." 20 ILLINOIS STATE GEOLOGICAL SURVEY The above is not a description of glacial drift of Illinoian age subjected to the long- continued weathering and leaching during and since Sangamon time. It is descriptive of materials of much more recent age which have suffered much less weathering. This is one of the important reasons for referring its deposition to the Wisconsin stage of glaciation. Upper Farmdale sandy silts with rock flakes. — Another feature found at some places in the upper part of the Farmdale drift is a bed of sandy silt with numerous small rock flakes. The bed is present east of Freeport, east of the village of Dakota, north of Mt. Carroll, and in several large gravel pits just south and west of Mt. Car- roll. It is in the following geologic sec- tions and is indicated by an asterisk. No. 22. — Roadcut and auger boring in SW ^ NE )i sec. 30, T. 27 N., R. 9 E. Thickness Ft. In. Wisconsin Peorian Loess, leached, bufF-brown . 3 Loess, calcareous, buff-brown 5 Farmdale *Silt, calcareous, brown to chocolate-brown, with fine sand, medium sand, small rock flakes, and small peb- bles, igneous pebbles at base; conformable above and below 2 Along the road down slope to the east there is calcareous sandy Farmdale till with some rusty brown staining in the upper por- tion. No. 23.^ — Roadcut and auger boring near center of south line sec. 33, T. 28 N.,^R. 9 E. ^ Thickness Ft. In. Wisconsin Peorian, topsoil and loess, leach- ed, brown 7 Farmdale *Silt, and fine sandy silt, very slightly calcareous, brown to chocolate-brown, with some rock flakes. ... 2 Pebbly and gritty gradation to geest No. 24.— Gravel pit in NE H NW M sec. 24, T. 24 N., R. 4 E. Thickness Ft. In. Wisconsin Peorian Topsoil and loess, leached, buff 7 8 Loess, calcareous, buff . . 4 Farmdale *Silt, calcareous, chocolate- brown, with a few small pebbles 1 *Silt, calcareous, chocolate- brown, with gray spots and mottling; contains rock flakes and small pebbles . 1 Gravel, clay-bound, sandy, pebbly, calcareous, red- brown to orange, contains some partially decayed limestone pebbles and some slightly etched gran- ite pebbles 2 Clay, silty, calcareous, gray- brown, lens 6 Gravel, calcareous, stained yellow and brown, lime- stone pebbles are yellow and powdery 1 6 Coarse ice-contact gravels with inter- bedded lenses and layers of pink, sandy till (pi. 1, A and B) are exposed at places in this pit. These last three geologic sections are rep- resentative of the silt that sometimes oc- curs in the upper part of the Farmdale drift. In the first two sections the silt ap- pears to have been stirred up on the sur- face of the drift, possibly by wind action. Near Mt. Carroll it appears to be water- laid above the ice-contact gravels. In any event, it does not appear to have traveled very far from its source. The important fact is its conformable relationship with the loess above and the drift below. Where the loess above is calcareous, this upper Farm- dale silt is also calcareous, as is the contin- uation of the drift below. Where the loess above is thin and leached, the silt below is also partially or wholly leached. Calcareous loess above calcareous Farm- dale drift. — At two places the Farmdale drift was overlain by loess, extending to the surface, that was not completely leached of its carbonates. FARMDALE DRIFT 21 No. 25. — Auger boring near village of Hunter, in SE ^ SW M sec. 26, T. 46 N., R. 3 E. Thickness Ft. In. Wisconsin Peorian Topsoil, leached, powdery, dark gray becoming brown at base Loess, leached, clayey from IM to 2^ feet, yellow . Loess, calcareous, yellow . Farmdale, till, sandy, pebbly, with a little clay binder, calcareous, yellow-brown, rusty brown top few inches . No. 26. — Auger boring just north of Stockton, in SW M SW M sec. 1, T. 27 N., R. 4 E. Thickness Ft. In. 'isconsin Peorian Topsoil, leached, dark, be- coming brown at base . 1 Loess, leached, buff to brown 3 6 Loess, calcareous, buff to brown 6 Farmdale, till, silty, pebbly, calcareous, pink to salmon- colored 7 6 The above sections are further evidence of the young character of the Farmdale drift. Size analyses of Farmdale till matrix. — The percentages of sand, silt, and clay in ten samples of calcareous Farmdale till col- lected from roadcuts and auger borings in a zone about 20 miles wide (north-south) extending from four miles northwest of the village of Caledonia, westward 24 miles to Pecatonica, except for one sample from a roadcut 35 miles south of the northernmost sample locality, were determined according to the procedure employed by Shepps ( 1953, p. 34) in his studies of tills from northeast- ern Ohio. The procedure includes the pip- ette method of Krumbein and Pettijohn (1938, p. 166-172). The material studied was essentially the till matrix inasmuch as pebbles larger than 10 mm. were excluded. The results of the analyses (fig. 3) con- firm that the Farmdale till, which seems easily distinguishable from the younger Shelbyville till in the field, is strikingly dif- ferent texturally, and according to the classification of Shepard (1954, p. 157) is silty sand. Humic-glei soils. — Another noteworthy feature of the Farmdale drift region is the local development of some unusual soils at places near the boundary between the Farm- dale drift and Shelbyville till and at sev- eral places within the Farmdale drift area well beyond the Shelbyville border (geo- logic sections nos. 27-29). The soils, once called Wiesenboden (meadow soils) and Half Bog soils (Year- book of Agriculture 1938, p. 1110), are now generally described under the general term humic-glei soils. In the area studied they occur in low flat areas or in flat areas on slopes. The soils are generally dark be- cause they contain large quantities of or- ganic material, but may be gray near the surface and hlue-gray or greenish gray at depth. Where seen in the area the soils are not very productive, drain slowly, and ap- parently accumulated in undrained areas. No. 27.— Roadcut in NW M NW M sec. 36, T. 27 N., R. 6 E. Thickness Ft. In. Wisconsin Topsoil and loess, buff-brown . 3 Clay and silty clay, leached, olive-gray, with blue-gray streaks; scattered pebbles in upper part, more numerous below; forms lens less than 100 feet long 2 Topsoil is absent over the olive-gray clay which grades downward into bedrock re- siduum that contains many chert fragments. The pebbles in the clay are mainly siliceous, but granite, diorite, gabbro, and diabase pebbles, cobbles, and small boulders are present. No. 28. — Ditch excavation 13 feet deep and about 200 feet long, in NE M SW i^ sec. 17, T. 44 N., R. 2E. Thickness Ft. In. Wisconsin Loess or silt, mostly leached, slightly calcareous in lower 6 inches, yellow-brown . . 5 Silt, leached, gray with organic stain along joints, limonite stained, bedded .... 2 22 ILLINOIS STATE GEOLOGICAL SURVEY Thickness Ft. In. Silt, with scattered pebbles, top 6 inches very silty, remainder more clayey, slightly calcar- eous, crumbly, dark gray to black 2 3 Clay, sandy, pebbly, some lay- ers very clayey, some very sandy, slightly calcareous in places to highly calcareous in places, pink, red, gray, rusty brown and yellow .... 3 9 No. 29. — Roadcut and auger boring in NE 3^ NE % sec. 2, T. 23 N., R, 9 E.; interpretation from sample study. Thickness Ft. In. Wisconsin Loess or silt, leached, brown . 6 Clay, silty, leached, scattered pebbles, mostly siliceous, but weathered surface also con- tains granites and other igneous pebbles, gray to dark gray with dark organic ma- terial near the top and in spots below 2 3 Clay, silty, visibly calcareous from S]/2 to 83^ feet, scatter- ed pebbles and rock flakes common, greenish gray, oxi- dation stains and organic ma- terial common 5 9 Silt, calcareous, gray-green, with some oxidation to yel- low-brown 1 3 Clay, silty, with scattered peb- bles, calcareous, yellow . . 1 6 Silt, pebbly, calcareous, yellow- brown, powdery .... 6 Clay, silty, pebbly, some streaks of fine sand, calcar- eous, greenish gray, some yel- low-brown oxidation ... 2 6 Till (?), or silt with pebbles, calcareous, yellow-gray, pink cast when wet 1 6 Till (?), sandy, pebbly, calcar- eous, yellow-brown and pink 9 Bedrock or boulder Samples from both roadcut and the auger boring part of the above section were pre- pared for study by x-ray spectrometer. The spectrometer traces were interpreted by J. B. Droste as follows: Depth 0-6" good quartz peak, feldspar. G"-\' good quartz peak (possible kaolinite and feldspar). \'-\'6" good quartz peak (possible feldspar). l'6"-2' good quartz peak, feldspar, hint of car- bonate. 2'6"-3' good quartz peak, feldspar, two kinds of carbonate. Depth 3'4"-3'8" good quartz peak, feldspar, two kinds of carbonate. 4'6"-4'9" good quartz peak, feldspar, two kinds of carbonate. 4'9"-5' good quartz peak, feldspar, two kinds of carbonate. 5'-5'3" good quartz peak, feldspar, carbonate. 6'-6'4" good quartz peak, feldspar, two kinds of carbonate. The presence of feldspar throughout the upper portion of the material eliminates the possibility that the material is the result of long-continued weathering of till accom- panied by decomposition of the silicates. The two different kinds of carbonates pres- ent from 21/2 ^^^t downward indicate that at least some of the carbonate may be pri- mary, which further supports the idea that the soils are accumulations in place rather than the result of weathering of till. Shelbyville Drift Leverett (1899, p. 192) states, "The oldest moraine of the Wisconsin drift, so far as recognized, is one exposed to view in central and eastern Illinois and western In- diana, but which is overridden by later mo- raines in districts farther north and east. This has for some years been known as the Shelbyville moraine, the name being de- rived from a city in central Illinois which is situated on the extreme southwest point of the morainic loop." In present classification of glacial deposits in the Upper Mississippian Valley the Shel- byville drift is regarded as the oldest drift of the Tazewell substage of the Wisconsin stage of glaciation. Leverett (1899, map opposite page 130) mapped lowan drift in a large part of northern Lee and southeastern Ogle coun- ties, north and west of the cities of Ster- ling and Dixon, sli^htlv north of the village of Stratford, with the western boundary ex- tending northeastward to include the cities of Oregon, Byron, and Rockford. The drift that Leverett called lowan, in Lee and Ogle counties at least, is now regarded as Shelbyville drift but mav turn out to be lowan drift (Shaffer. 1954a. n. 455), even though what is now called lowan is con- siderably different from Leverett's lowan drift. SHELBYVILLE DRIFT 23 100% CLAY Less than .0039 millimeters Clay 100% SAND 10 to .062 millimeters 50% 100% SILT .062 to .0039 millimeters Fig. 3. — Diagram showing distribution of sand-silt-clay ratios of till matrix (after Shepard). Numbers 1 to 12 inclusive are Shelby ville till, numbers 13 to 23 inclusive are Farmdale till. Leighton (1923, p. 270) named and de- scribed the Belvidere lobe of Wisconsin gla- ciation and the drift deposited from it. The discovery of the Belvidere drift, now re- garded as a correlative of the Shelbyville, represented a considerable westward exten- sion of Wisconsin glacial deposits beyond the Marengo Ridge and the Bloomington moraine in southern Boone, northern De- Kalb, eastern Ogle, and southeastern Win- nebago counties. In the same paper Leighton (1923, p. 269) described and mapped another west- ward extension of Shelbyville drift, the Green River lobe, approximately to Rock Island County. The question marks which he employed to show the western margin of the lobe, where it is covered bv thick loess and outwash deposits, indicated that he thought the drift might extend farther west. Subsequent work bv Leighton and Shafifer (1949, p. 1904) and by Shaffer (1954a, p. 446) indicated that the Shelbyville glacier did extend across Mississippi River in a narrow lobe between Clinton and Prince- ton, Iowa, as far west as the Goose Lake channel. Knappen (1926, p. 72 and map in pocket) mapped early Wisconsin or lowan ( ?) drift in the southernmost part of the Dixon quadrangle, in an east-west belt from one to three miles wide, south of the village of Eldena. The area north of the belt, in- cluding the exposures in Dixon which Lev- erett (1899, p. 138) reported, and the esker that caused the loop in Rock River at the 24 ILLINOIS STATE GEOLOGICAL SURVEY village of Grand Detour, he regarded as lUinoian. The drift that he called early Wisconsin or lowan (?) is now regarded as Shelbyville. Templeton (1939, unpublished thesis, University of Illinois), who did detailed work in the Sterling area, described the Shelbyville till in the following manner: "When fresh and unweathered, the Shelby- ville till has a distinct greenish-hue, or a color intermediate between blue-gray and green-gray . . . and weathers to a pale yel- low-brown." In the current study it has been deter- mined that the Shelbyville drift, which con- sists of materials like that described in the two following sections and illustrated on plate 2-C, extends considerably west and north of its former mapped limits. It oc- curs not as a continuous blanket of drift but as patches capping small hills or in broad flat areas surrounded by Farmdale drift. Discontinuities of this type were pointed out by White (1952, p. 1312) in the plateau re- gion of northeastern Ohio. The boundary as shown (fig. 2) follows the northernmost and westernmost deposits of Shelbyville drift that were found. Other isolated patches may be found beyond this boundary. The esker or crevasse filling of glacio- fluvial material that accumulated in the val- ley of Rock River near the village of Grand Detour and caused the big loop in the river is regarded as Shelbyville in age rather than Illinoian. No. 30.— Auger borinc; in NVV }4 NW }4 sec. 24, T. 22 N., R. 4 E. T/iickness Ft. In. Wisconsin Peorian, clay, silty, leached, gray-brown and brownish- yellow 3 3 Shelbyville Till, clay-bound, sandy, peb- bly, leached, brownish-yel- low 1 3 Till, clay-bound, pebbly, cal- careous, brownish-yellow . 3 lowan or pro-Shelbyville (?), silt, with loess texture, cal- Thickness Ft. In. careous, yellow, several scattered pebbles Farmdale (?), till, clayey, silty, pebbly, calcareous, yellow- brown Bedrock or boulder It is possible that in the above section all material below the Peorian loess may be Shelbyville drift, consisting of two till lay- ers with an intervening silty layer. How- ever, other exposures in the general area support the interpretation shown. No. 31.— Auger boring in SVV ^ NE M sec. 11, T. 23 N., R. 8 E. Thickness Ft. In. Wisconsin Peorian Topsoil, clayey, leached, black 1 6 Clay, leached, mottled, gray- brown 2 Loess, silty, leached, yellow and gray, soft .... 1 6 Loess, silty, calcareous, yel- low and gray, soft ... 1 Shelbyville Till, silty, clayey, calcareous, yellow 1 Till, clayey, pebbly, yellow to yellow-gray, some thin beds of gray to whitish- gray pebbly clay till, espe- cially between 8 and 11 feet. 7 Sand-silt-clay ratios of the till matrix. — Sand-silt-clay ratios of the matrix of eleven samples of calcareous Shelbyville till were determined by the method already men- tioned. The samples were collected from roadcuts and auger borings in an area ex- tending from just north of Morrison to seven miles southeast of Oregon, a distance of about 40 miles in a northeast-southwest direction. Some of the samples were col- lected close to the outer margin of the Shel- byville drift and some from localities at least ten miles inside the boundary. The results (fig. 3) indicate that the Shelbyville till is considerably different from the Farm- dale till and, with the exception of one sam- ple, would be classified after Shepard (1954, p. 157) in the sand-silt-clay area as clayey sandv silt. REFERENCES 25 REFERENCES CITED Alden, \V. C, 1918, The Quaternary geology of southeastern Wisconsin: U. S. Geol. Survey Prof. Paper 106, 356 p. Chamberlin, T, C, and Salisbury, R. D., 1884- 85, Driftless Area of the Upper Mississippi Valley: U. S. Geol. Survey Sixth Ann. Report, p. 199-322. CoNDRA, G. E., Reed, E. C, and Gordon, E. D., 1950, Correlation of the Pleistocene deposits of Nebraska: Nebraska Geol. Survey Bull. 15 A, 74 p. Ekblaw, George E., 1942, Distribution of the glacial deposits of Wisconsin age in Illinois (Map): Illinois State Geol. Survey. Flint, R. 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