G}tc^ Su-ruo 
 
 **A 
 
 STATE OF ILLINOIS 
 
 WILLIAM G. STRATTON, Governor 
 
 DEPARTMENT OF REGISTRATION AND EDUCATION 
 
 VERA M. BINKS, Director 
 
 WISCONSINAN MOLLUSCAN 
 FAUNAS OF THE 
 ILLINOIS VALLEY REGION 
 
 A. Byron Leonard 
 John C. Frye 
 
 ILLINOIS GEOLOGICAL 
 
 SURVEY ' IBRARY 
 R 1986 
 
 DIVISION OF THE 
 
 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 JOHN C. FRYE, Chief URBANA 
 
 CIRCULAR 304 
 
 1960 
 
ILLINOIS STATE GEOLOGICAL SURVEY 
 
 3 3051 
 
 00004 1099 
 
ILL OLOGICAL 
 
 SU MBRARY 
 
 MAY 28 1986 
 
 WISCONSINAN MOLLUSCAN FAUNAS 
 OF THE ILLINOIS VALLEY REGION 
 
 A. Byron Leonard and John C. Frye 
 
 ABSTRACT 
 
 In the Illinois Valley region, the Altonian Substage (between 
 50,000 and 70,000 to 28,000 B. P.), Farmdalian Substage (28,000 to 
 22,000 B. P.), and Woodfordian Substage (22,000 to 12, 500 B. P.) of 
 the Wisconsinan Stage are represented by loess, water-laid elastics, 
 and glacial till. Molluscan faunas of these sediments are here listed 
 both geographically and stratigraphically, and 61 species are illus- 
 trated. Woodland faunas distinctive of the Roxana silt (Altonian) are 
 found at 11 localities. Two of the Farmdalian localities yielded a- 
 quatic faunas and one woodland fauna. Faunas characteristic of the 
 Woodfordian are abundant but differ in the various geographic areas. 
 The faunas of the several Woodfordian rock-stratigraphic units are 
 not distinguishable, but those of the three substages are distinctly 
 so. During Wisconsinan time the glaciers did not produce rigorous 
 climates in Illinois very far from the ice fronts. During Altonian and 
 part of Farmdalian time the southern half of Illinois was heavily for- 
 ested, but this was not so in Woodfordian time. 
 
 INTRODUCTION 
 
 Deposits of glacial till and associated outwash, loess, and alluvium of 
 Wisconsinan age are the surficial materials of a large part of Illinois and thereby 
 determine to a considerable extent the character of the soils, affect the occurrence 
 of ground-water supplies, and pose problems for engineering construction. Conse- 
 quently, in order to enable more precise recognition and better comprehension of 
 these materials and their relationships, the Illinois State Geological Survey has been 
 investigating the nature of these sediments, conducting fundamental studies of their 
 mineralogy, stratigraphy, and content of fossil mollusks. This report deals with 
 fossil mollusks and is integrated with Illinois Geological Survey studies of the stra- 
 tigraphy of the deposits and with radiocarbon determinations of their age made by 
 the United States Geological Survey. 
 
 For the most part the fossils reported on were collected from the loesses, 
 but some were taken from terrace deposits, outwash sands, and silt and sand in- 
 clusions within glacial till. The geographic distribution of the faunal localities 
 and geologic sections are shown in figure 1 . 
 
 [1] 
 
ILLINOIS STATE -GEOLOGICAL SURVEY CIRCULAR 304 
 
 Fig. 1 - Collecting localities of molluscan faunas from Wisconsinan deposits in 
 Illinois, and locations of measured geologic sections. 
 
WISCONSINAN MOLLUSCAN FAUNAS 3 
 
 George E. Ekblaw and H. B. Willman of the Illinois Geological Survey, and 
 Paul R. Shaffer of the University of Illinois assisted in the field and in making strat- 
 igraphic interpretations. All radiocarbon dates referred to were determined in the 
 Washington, D. C., laboratory of the United States Geological Survey. 
 
 STRATIGRAPHY OF FOSSILIFEROUS UNITS 
 
 The Wisconsinan Stage in the Lake Michigan glacial lobe recently has been 
 discussed and reclassified by Frye and Willman (1960), and their rock-stratigraphic 
 and time-stratigraphic terminology is used in this report. 
 
 The molluscan faunas described herein were collected from deposits included 
 within the Altonian, Farmdalian, and Woodfordian Substages of the Wisconsinan 
 glacial stage. In radiocarbon years the time span of these substages started between 
 50,000 and 70,000 years before present (B. P.) and extended to 12,500 years before 
 present. 
 
 Altonian Substage 
 
 All the loess of Altonian age is included in the Roxana silt (Frye and Will- 
 man, 1960). The Pleasant Grove School section, which occurs in the bluffs of the 
 Mississippi River valley in Madison County, Illinois, was designated as the type 
 section of the Roxana. Roxana silt is described in 7 of the 11 measured geologic 
 sections included with this report. 
 
 In the thick sections along the valley bluffs the Roxana silt contains at least 
 five distinctive stratigraphic units. At some localities the base of the Roxana is 
 colluvium, consisting of silt locally containing sand and pebbles like those in the 
 underlying deposits. The basal colluvium, where observed, is noncalcareous and 
 nonfossiliferous; it is in sharp contact with the beds below but is gradational with 
 the overlying deposits. 
 
 The second unit of the Roxana is commonly a gray, massive, noncalcareous 
 and nonfossiliferous silt. Locally this zone may contain sand (Browns Mound sec- 
 tion) or sandy silt, and in some places (Pleasant Grove section) it is marked at the 
 top by a humic streak, or an A-C soil profile. Both of the two lower units of the 
 Roxana may or may not be present in a particular exposure, they are not generally 
 loess, and they are clearly separable from the three higher units. 
 
 The third unit of the Roxana is light to dark pink, massive, coarse loess, 
 and contains fossil snails in the upper part. The carbonate content is largely dol- 
 omite, and the zone is gradational with the overlying deposits. In some exposures 
 the pink color diminishes upward and the upper part of the zone consists of inter- 
 stratified pale pink and yellow-tan loess. 
 
 The fourth unit generally is gray-tan to yellow-tan, calcareous, fossiliferous 
 loess. At many places it contains lenticular streaks of tan sand and coarse silt 
 and locally may be quite sandy. The top of this zone is commonly gradational with 
 the fifth, or uppermost, unit of the Roxana. 
 
 The fifth unit of the Roxana is pink-tan, massive loess. Commonly it is non- 
 calcareous in the upper part and dolomitic and fossiliferous in the lower part, but 
 at some places it is weakly calcareous throughout. Although the contact at the top 
 of the Roxana generally is sharp, it is not strikingly apparent in many exposures be- 
 cause of the absence of a B-zone in the leached material in the upper few feet. 
 
4 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 304 
 
 The foregoing descriptions apply to the internal stratigraphy of the Roxana 
 silt only where it is thick, near the bluffs of the Illinois, Sangamon, and Missis- 
 sippi River valleys. East of these valleys it thins rapidly (much more rapidly than 
 the overlying Peoria loess), becomes leached throughout, and its internal subdivi- 
 sions are not recognizable. 
 
 The geographic distribution of thick, fossiliferous Roxana silt is significant. 
 It occurs from the region just above the mouth of the Sangamon River southward along 
 the Illinois River valley and the Mississippi River valley below the mouth of the Il- 
 linois. It is absent farther north along the Illinois River valley, but is exposed 
 along the Sangamon River valley eastward to the mouth of Salt Creek and for a con- 
 siderable distance up Salt Creek valley. This distribution pattern suggests that out- 
 wash in the pre-Shelbyville course of the Illinois River was the source of the loess 
 that constitutes the Roxana silt. 
 
 Farmdalian Substage 
 
 The Farmdale silts are the deposits next younger than the Roxana. The orig- 
 inal type area (Leighton, 1948) is retained. The unit is well exposed in the Farm 
 Creek railroad cut section (Frye and Willman, 1960). The Farmdale generally consists 
 of noncalcareous silt, massive to laminated, pinkish brown to pale purple; it char- 
 acteristically contains humic or woody material (Banner section). In some places 
 it is very peaty and in some places is a compacted mass of twigs and limbs of trees. 
 Although locally it may be in part or entirely ("The Rocks" section) eolian loess, it 
 is thought to consist largely of silts derived by wash from the older Roxana and 
 earlier deposits. In some places (Wedron section) the Farmdale silts were deposited 
 in ponded water and are fossiliferous and somewhat calcareous. However, even in 
 such places they retain the characteristic plant material and predominant composition 
 of silt. 
 
 Woodfordian Substage 
 
 The loesses of the Woodfordian Substage that occur above the Farmdale silts 
 have been classed in three rock-stratigraphic units; the Morton loess, the Peoria 
 loess, and the Richland loess (Frye and Willman, 1960). Beyond the Shelbyville 
 moraine, which marks the outermost extent of Woodfordian glaciers, the loess of 
 this substage is not readily subdivisible on lithologic evidence and therefore is 
 all classed together as Peoria loess. Peoria loess is described in 9 of the 11 
 measured geologic sections included with this report. It consists of tan to yellow- 
 tan, massive, calcareous, fossiliferous silt. In some places along the major valley 
 bluffs (Browns Mound section) it contains lenticular masses of sand and is indis- 
 tinctly bedded, generally with the bedding inclined away from the valley bluff line 
 (Cottonwood School section; Bluffdale section). Where the Peoria loess is quite 
 thick and well exposed it commonly contains incipient soils, or humic streaks, in 
 the mid-portion and higher (Frederick South section; Cottonwood School section and 
 exposures one mile east; exposures at Peters). One of the incipient soils included 
 within the Peoria loess was described by de Heinzelin (1959, p. 271) . Although the 
 color contrast, partial leaching, and small secondary nodules of CaC03 make these 
 minor soil zones conspicuous in some exposures, a recognizable B-zone has not so 
 far been found associated with them. In a few exposures as many as half a dozen 
 humic streaks have been observed in the upper part of the Peoria loess. 
 
WISCONSINAN MOLLUSCAN FAUNAS 5 
 
 Away from its major valley source, the Peoria loess thins more gradually 
 than does the Roxana (Smith, 1942), but generally within a few miles of the valley 
 bluff it becomes leached and nonfossiliferous . Although the internal subdivisions 
 of the Roxana become indistinguishable within a relatively short distance of the 
 major valleys, differentiation of the Peoria loess from that of the Farmdale and 
 Roxana is possible far from the source valleys, even where the total loess section 
 has become thin and is completely leached. 
 
 Within the limits of the Shelbyville moraine, the Woodfordian loess that 
 occurs stratigraphically below the Shelbyville and younger tills and above the 
 Farmdale silts is called the Morton loess. The Morton is a calcareous to weakly 
 calcareous, massive, sparsely fossiliferous, gray to gray-tan, thin loess. It is 
 clearly distinguishable from the noncalcareous, dark, humic to peaty Farmdale silts 
 below and the glacial till above. No evidence of weathering has been observed at 
 its top, and the stratigraphic relations, as well as carbon-14 dates, demonstrate 
 its conformability with the overlying Woodfordian till. It is equivalent in age to, 
 and stratigraphically continuous with, the lowermost part of the Peoria loess. 
 
 Loess overlies the Woodfordian tills along the Illinois River valley from the 
 Peoria area where the Shelbyville moraine crosses the valley northeast to Grundy 
 County. The loess, which is equivalent in age to, and stratigraphically continuous 
 with, the upper part of the Peoria loess, has been named the Richland loess (Frye 
 and Willman, 1960). It is tan to gray-tan, massive silt, calcareous below the sur- 
 face soil profile, and commonly fossiliferous where it is calcareous. It rests on 
 calcareous glacial till that shows no evidence of weathering at the top, and in gen- 
 eral becomes progressively thinner up the valley as the underlying Woodfordian till 
 sheets become progressively younger. The Richland loess thins away from the valley 
 bluffs, and fossiliferous deposits are limited to relatively narrow belts adjacent to 
 the valley. 
 
 Several molluscan faunas are listed from silts interbedded with glacial till 
 (Lake Bloomington Spillway section), from included masses of sands and silts with- 
 in glacial till, and from terrace deposits. However, it is not our purpose here to 
 redescribe the stratigraphy of the many Wisconsinan glacial pulses. In such cases 
 stratigraphic terminology is that in accepted use by the Illinois State Geological 
 Survey and documented in many Survey publications. 
 
 RADIOCARBON DATES OF FAUNAS 
 
 All of the Wisconsinan faunas described here are correlated with a time 
 scale based on carbon-14 dates determined in the Washington, D. C, laboratory 
 of the United States Geological Survey (Frye and Willman, 1960) . Thus the bio- 
 stratigraphic zones defined by the faunal assemblages also may be referred to in 
 terms of isotopically determined years. Dates ranging from 37,000 ± 1500 (W-869) 
 to 17,100 ± 300 (W-730) were determined directly on shells collected from these 
 faunal zones, but a much larger number of dates have been determined on wood from 
 the beds that contain the shells and from beds above and below the fossil zones. 
 
 Snail shells from the Roxana silt have been dated at 37,000 ± 1500 (W-869) 
 at the Gale section and at 35,200 ± 1000 (W-729) at the Pleasant Grove section. 
 As the fossil zone within the Roxana is restricted approximately to its midportion, 
 these two dates are judged to give a satisfactory indication of its age. On the 
 basis of these dates, it seems reasonable that a range of radiocarbon years of 
 32,000 to 40,000 B. P. would include all of the elements of this fauna in Illinois. 
 
6 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 304 
 
 The Farmdale silt is the most extensively dated stratigraphic unit in the 
 Pleistocene of Illinois, but at only two localities has an adequate molluscan fauna 
 been obtained. At the Wedron Quarry section a date of 26, 800 ± 700 (W-871) was 
 determined on flecks of wood associated with the shells, and earlier a date of 
 24, 000 ± 700 (W-79) had been determined on a sample of wood from the immediately 
 overlying bed. At "The Rocks" section, southeast of the Shawneetown bridge across 
 the Ohio River, a date of 22, 200 ± 450 (W-867) was obtained on the shells. The 
 time span of the Farmdalian is judged to extend from 28,000 to 22,000 B. P. 
 
 Dates related to the age of the fauna from the Morton loess have been re- 
 ported from the vicinity of the Farm Creek section where wood dates of 20, 340 ± 
 750 (W-349) and 20,700 ± 650 (W-399) have been obtained. Although in general 
 not directly associated with faunal localities, there are a large number of dates 
 from the Farmdale silts below the Morton loess and a few dates from the Shelbyville 
 till above it. The available dates indicate a range in radiocarbon years of 20, 000 
 to 22,000 for this faunal zone. 
 
 Beyond the limits of the Shelbyville moraine, the Peoria loess includes de- 
 posits and faunas that are equivalent in age to the Morton loess, the overlying 
 Woodfordian till, and the Richland loess. Two radiocarbon dates have been deter- 
 mined from the snail shells of this fauna; they are 20,300 ± 400 (W-870) from the 
 Enion area (Fulton County), and 17, 100 ± 300 (W-730) from the Burdick Branch ex- 
 posures north of the Pleasant Grove section. In addition, several dates determined 
 on wood have direct relation to the age of the fauna of the Peoria loess. Wood from 
 immediately below the fossiliferous loess in the Enion area has been dated 23, 500 ± 
 400 (W-745), and this agrees well with the date of 20, 300 determined on shells 
 from the upper part of the overlying loess. No radiocarbon dates have been ob- 
 tained directly from the Richland loess, but wood from fossiliferous terrace deposits 
 in Fulton County has been dated 15,600 ± 600 (W-381). From these data it appears 
 that the age of the molluscan fauna of the Peoria loess, and its stratigraphic equiv- 
 alents, ranges from approximately 22,000 to approximately 15,000 radiocarbon years 
 before the present. 
 
 Several anomalous dates do not properly fit the patterns developed by the 
 majority of the dates. It will be noted that in the Lake Bloomington Spillway section 
 an upper date is listed as greater than 34, 000 (W-67), whereas a date from wood 
 lower in the section is reported as 31,000 or older (W-186). This anomaly is as yet 
 unexplained. A date determined on shells from the Peters exposures, north of the 
 Pleasant Grove section, is reported at 27,500 ± 900 (W-868), which is 5,000 to 
 10,000 years younger than would be anticipated for Roxana faunas in the area. The 
 sample of shell material that was dated from this exposure was collected by several 
 persons on several visits, and it is judged that a small quantity of shell material 
 from the overlying Peoria loess (dated 17, 100 ± 300 [W-730] at the Burdick Branch 
 exposures a third of a mile to the south) was intermixed in the sample, which could 
 easily account for the discrepancy. 
 
 FOSSIL MOLLUSCAN FAUNAS 
 
 Recent revision of the classification of the late Pleistocene deposits in Il- 
 linois has produced the framework necessary for a systematic study of fossil mol- 
 luscan faunas associated with the stratigraphic units currently assigned to the Wis- 
 consinan Stage. Knowledge of the relative ages of many units, derived from radio- 
 carbon dates, stratigraphic position, and relationship of moraines to the fossil- 
 
WISCONSINAN MOLLUSCAN FAUNAS 7 
 
 bearing deposits, has enabled us to elaborate criteria for the recognition of faunas 
 characteristic of the several Wisconsinan substages. Assignment of assemblages 
 to specific substages makes it possible to recognize within reasonable limits the 
 variations and discrepancies produced by local ecological conditions, geographic 
 differences, and hazards of random sampling. It allows a greater degree of assur- 
 ance in correlating the fauna contained in sediments at localities where the relative 
 age has not been determined by any other method. Bulk samples were processed 
 from most of the approximately 60 localities shown in figure 1 . Experience has 
 shown, however, that repeated bulk sampling is required in order to approach full 
 recovery of an assemblage. In one instance, pooling of two bulk samples taken at 
 the same locality at different times resulted in a 30 percent increase in the total 
 number of species recovered, although each sample contained more than 200 identi- 
 fiable specimens. Therefore, claim can not be made for more than reasonable com- 
 pleteness of the snail collections discussed here. 
 
 Before focusing attention on the fossil mollusks discussed in this paper, it 
 seems appropriate to review the complex factors that influence the composition of 
 local faunal populations. Aside from the distortions induced by random and inade- 
 quate sampling and by the vagaries of preservation, assemblages of fossil organisms 
 reflect the combined and interacting effects of a wide variety of forces upon the 
 formerly living populations. Among these, perhaps the most obvious, if not always 
 the most important, are changing climates, local ecological conditions, including 
 details of sedimentation, and the relative genetic stability of the organisms involved. 
 
 Climatic changes occur constantly (if sometimes slowly) under the influence 
 of numerous complex factors, and such changes keep the living organism in a per- 
 petual state of nonequilibrium with its environment. The frequency and distribution 
 of precipitation, the total annual precipitation, and the evaporation rate are of para- 
 mount importance to any animal or plant. Average temperatures and diurnal and 
 seasonal temperature extremes impose stresses upon the organism and make neces- 
 sary continual adjustments. Regional long-range climatic changes related to orogeny, 
 changes in mean sea level, fluctuations in the prevailing patterns of air-mass move- 
 ments, or other changes are additional hazards to survival. Climatic differences re- 
 lated to latitude or altitude and cyclic climatic changes coincident with repeated 
 continental glaciation constitute environmental stresses to which the organism must 
 adapt or succumb, or from which it must escape by migration. 
 
 Local ecological conditions are notedly variable. Soils, important elements 
 of local environment, vary with parent materials, maturity, vegetative cover, and 
 relative position in the microtopography . Availability of appropriate food and cover, 
 inter- and intra-specific competition, and selective predation produce profound 
 effects upon animal populations. Moreover, small and sedentary animals, such as 
 gastropods, utilize microhabitats that may be considerably at variance with the 
 general environmental pattern of a region, making analysis of their precise ecological 
 requirements extremely difficult. 
 
 Faunal change is not necessarily related to the physical separation of two 
 stratigraphic levels, but rather to the time that elapsed during their deposition and 
 to the concomitant ecological changes involved. These are the factors that provide 
 opportunities for the mutations, genetic drift, extinctions, or mass migrations of 
 organisms that serve to alter the composition of populations. Populations at dif- 
 ferent stratigraphic levels do not necessarily differ greatly, especially when the 
 amount of time involved is relatively small, provided that the ecological conditions 
 are reasonably similar. 
 
8 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 304 
 
 Finally, the composition of successive populations is profoundly influenced 
 by the relative genetic stability of the organisms under consideration. The Mollusca 
 seem to have long since passed the peak of their adaptive radiation and, when com- 
 pared with many other kinds of animals, to have reached a high degree of genetic 
 stability. Although there is ample evidence that terrestrial and fresh-water mollusks 
 are still making evolutionary progress, their genetic conservatism and the brief 
 interval of time involved suggest that faunal changes within the Wisconsinan result 
 from migrations in response to fluctuating ecological conditions. 
 
 These considerations lead to the conclusion that assemblages of fossil mol- 
 lusks at any stratigraphic level may have distinctive character over a considerable 
 area if the ecological conditions are similar and relatively stable. The species- 
 composition of a fauna may comprise well known taxa, found perhaps in younger 
 and in older rocks. Distinctive qualities of a specific assemblage need not include 
 extinctions, the presence of newly evolved taxa, or even so-called "index- fossils"; 
 as we have pointed out, nearly identical assemblages may reappear from time to 
 time in the stratigraphic column without nullifying their significance and usefulness 
 at any specific stratigraphic level. All molluscan fossils considered in this report 
 are housed in the paleontological collections of the Illinois State Geological Survey. 
 
 Altonian Faunas 
 
 Altonian molluscan faunal assemblages are shown in figure 2, in which lo- 
 calities of occurrence are arranged geographically, and a summary of Altonian oc- 
 currences appears on figure 3, in which relationships between Altonian and other 
 Wisconsinan faunal assemblages are shown. 
 
 Inasmuch as Altonian faunas have been recovered only from the Roxana silt, 
 it is not surprising that the northernmost locality of occurrence should be in extreme 
 southeastern Schuyler County (locality 29). Ten additional localities are distributed 
 southward to Alexander County (locality 58b). As the Roxana silt generally thickens 
 southward, there is a corresponding increase in the variety of species as well as in 
 density of the local populations in the southern localities. This effect can be attri- 
 buted to at least two factors: improved preservation of shells in the thicker deposits 
 and probably more favorable ecological conditions in the south, where the forests 
 were denser and more stable. 
 
 A total of 28 species of mollusks are known to occur in the Roxana silt, al- 
 though the average local fauna comprises no more than half this number. Among 
 these, six species, Angulsplra alternnta, Haplotrema concavum , Rendersonia occulta, 
 Stenotrema fraternum, S. hlrsutum, and Succinea ovalis, are found in all three of the 
 Wisconsinan substages — Altonian, Farmdalian, and Woodfordian. Eighteen species, 
 including Clone lla lubrica, Discus cronkhitei, D. maccllntorkl , Gastrocopta arml- 
 fera, G. contractu , Hawaiia mlnuscula. , Hellcodlscus pornllelus, Mesodon thyroldus , 
 Pomatiopsis scalarls, Punctum mlnutlsslmum, Retlnella electrlna, Strobllops laby- 
 rlnthlca, Succinea gelida, S. grosvenori, Vallonla graclllcosta, V. parvula, Vertigo 
 hubrlchtl (not shown on fig. 2), and Zonitoldes arboreus occur in Altonian and Wood- 
 fordian deposits but have not been found in sediments of Farmdalian age. Two spe- 
 cies, Allogona profunda and Aniulsplra kochi, range from Altonian into Farmdalian 
 deposits, but have not been recovered from Woodfordian sediments. Only two spe- 
 cies, Trlodopsis hubrlchtl and T. altonensls, seem clearly restricted to the Altonian. 
 Allogona profunda also is restricted to the Altonian except for its occurrence in the 
 Farmdalian at the Shawneetown locality (57b) . 
 
WISCONSINAN MOLLUSCAN FAUNAS 9 
 
 Despite the small number of species restricted to the Altonian, the assem- 
 blage is distinctive and easily recognizable even in the field, inasmuch as the most 
 characteristic species are of large size and most of them occur consistently at most 
 localities. Triodopsis altonensis and Alloiona profunda, both easily recognized, 
 occur most consistently at all of the eleven Altonian localities studied. Although 
 apparently restricted to the Altonian, Triodopsis hubrichti does not occur frequently 
 enough to make it of significant value in faunal characterization. Aniuispira alter- 
 nate also is a conspicuous member of the Altonian assemblage although it ranges 
 throughout the Wisconsinan in the area under consideration. Like Alloiona pro- 
 funda, it occurs at each of the eleven localities studied. 
 
 Ecological Considerations 
 
 The characteristic Altonian molluscan fauna is typical of those occurring in 
 well established hardwood forests, an observation confirmed by the abundance of 
 Aniuispira kochi at some localities. Of A. kochi Goodrich (1932, p. 35) says: 
 " . . .one of the typical mollusks of old forests, and seldom found even in thick 
 second-growth timber. It hides during the hours of bright days under rotting logs 
 and decaying leaves." Of the habits of Triodopsis altonensis nothing is known, 
 but because of its close genetic relationship with T. multilineata it may be inferred 
 that it lived in especially humid portions of forests or forest borders. T. multilineata 
 has been observed living in heavily forested Missouri River bluff situations in north- 
 eastern Kansas, where contact springs along beds of shale keep fallen leaves and 
 leaf-mold constantly wet. Alloiona profunda also is a species of the deep forest, 
 and at many stations occurs with T. altonensis, Succinea ovalis, and Haplotrema 
 concavum along wooded bluff lines. The relation of Aniuispira alternata to wood- 
 lands also is well known, but this species often inhabits forest borders under rela- 
 tively small shrubs. 
 
 The association of Aniuispira alternata, A. kochi, Alloiona profunda, Steno- 
 trema fraternum, S. hirsutum , Succinea ovalis , Triodopsis hubrichti, and T. altonen- 
 sis presents a paleoecological picture of a well watered, heavily forested bluff-line 
 habitat, which in Altonian time was receiving heavy deposits of loess. None of the 
 remaining species in the total Altonian assemblage serves to alter this picture, al- 
 though some species, such as Hendersonia occulta and Pomatiopsis scalaris, oc- 
 curred along stream banks and on low floodplain habitats, and many species, such 
 as Gastrocopta armifera, Hawaiia minuscula , and Helicodiscus parallelus may occur 
 in open prairie situations as well as in woodlands. 
 
 The extremely rare occurrence of some typically woodland species, including 
 Cionella lubrica, Strobilops labyrinthica ,and Zonitoides arboreus is unexplained. 
 
 Taxonomic Considerations 
 
 Inasmuch as the shells known asTriodopsis fosteri hubrichti Baker and T. 
 multilineata altonensis Baker are distinctive enough to be readily recognized, and 
 as each is, so far as known, separated from its typical species by a time, rather 
 than a geographical interval, each is here treated as a full species, and they are 
 called T. hubrichti and T. altonensis. In a later section, the gastropod described 
 by Baker as Vertiio iouldi hubrichti, for the same reasons, is called Vertiio hubrichti 
 The same is true of Triodopsis multilineata alionquinensis Nason, herein called 
 Triodopsis alionquinensis . 
 
10 
 
 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 304 
 
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WISCONSINAN MOLLUSCAN FAUNAS 
 
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12 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 304 
 
 Succinen grosvenori gelida of Baker, although it occurs at many places with 
 Succinea grosvenori Lea, has nowhere been observed to intergrade with the kind of 
 shell here treated as acceptable grosvenori , and is likewise treated as a full species 
 and called Succinea ielida. It should be remarked that the names Succinea gelida 
 and S. grosvenori are here used in the sense of "form" species, inasmuch as it is 
 virtually impossible to distinguish many species of Succineidae from the shells 
 alone. It is therefore difficult to assess the value and significance of the variations 
 seen. Wayne's (1959, p. 11) remark, "Only .. .Succinea ielida is known at this time 
 to have stratigraphic application in Indiana, " probably reflects the difficulties en- 
 tailed in distinguishing among different species of the smaller kinds of Succinea 
 and related genera . 
 
 Farmdalian Faunas 
 
 Farmdalian molluscan faunas in the area under consideration are not yet well 
 characterized. Only three localities (8, 24, 57b) are known, and each of these is 
 atypical in some manner or other. Locality 8 (the Wedron section) exposes, among 
 other sediments, 25 feet of dark gray silt with some clay and sand streaks from which 
 an abundant molluscan fauna was recovered. A radiocarbon date in the upper third 
 of this unit clearly places the deposit well within the Farmdalian, but the fauna, 
 composed exclusively of aquatic species, does not present a complete picture of the 
 total assemblage living in the area at the time. 
 
 The collections from the Lake Bloomington Spillway section (locality 24) have 
 been referred to the Farmdalian fauna because of their general resemblance to those 
 at the Wedron Quarry section and in spite of two contradictory radiocarbon dates. 
 
 The third locality (57b, "The Rocks" section), judged by lithological rela- 
 tions and radiocarbon years (22,200 ± 450; W-867), is transitional between the 
 Farmdalian and Woodfordian substages, but the mollusks contained in bed 4 of the 
 geologic section are so unlike those in the overlying Peoria loess that they are as- 
 signed to the Farmdalian assemblage. The fauna here bears a strong resemblance 
 to that of the Altonian, but differs in the presence ofTriodopsis foster i rather than 
 T. hubrichti, and in the predominance of Anguispira kochi , which is relatively rare 
 in Altonian deposits. For reasons not readily apparent, almost all the species here 
 are represented by individuals that are larger than usual, each approaching or oc- 
 casionally exceeding the upper limits of the ordinary range in size. This observa- 
 tion is especially true of A I logona profunda , Anguispira alternata, and A. kochi. 
 
 With these reservations, the Farmdalian molluscan fauna as now known from 
 these localities consists of 24 species. Six of these, Anguisvira alternata, Haplo- 
 irema concavum f Hendersonia occulta, Stenotrema fraternum , S. hirsutum , and 
 Succinea ovalis range from Altonian through the Woodfordian Substages; in fact 
 they are generally more abundant in Woodfordian deposits than they are now known 
 to be in the Farmdalian. A second group of species, including Gyraulus altissimus , 
 Lymnaea dalli , L. obrussa dec amp i , L. parva , Helisoma antrosa , Pisidium compres- 
 sum , P. caseratanum , Triodopsis fosteri, andValvata tricarinata are known to occur 
 in Woodfordian and Farmdalian assemblages. Two species, Allogona profunda and 
 Anguispira kochi, occur in the Altonian as well as the Farmdalian but have not been 
 seen in Woodfordian collections in the area under consideration. 
 
 Finally, a group of species, conspicuous among which is Amnicola leightoni, 
 A. lustrica Gyraulus cristus, Lymnaea palustris , Sphaerium striatinum, and Valvata 
 sincera found only in Farmdalian faunas. 
 
WISCONSINAN MOLLUSCAN FAUNAS 13 
 
 Ecological Considerations 
 
 Although the limited number and erratic geographical distribution of avail- 
 able Farmdalian fossiliferous localities restrict generalizations about ecological 
 conditions during Farmdalian time, a few observations seem pertinent. "The Rocks" 
 section (locality 57b) reveals a woodland fauna of the type found in well established 
 hardwood forests. It would appear that the heavy forests of Altonian time persisted 
 through the Farmdalian Substage until the beginning of, or perhaps slightly into, 
 earliest Woodfordian time, at least in southern Illinois. There is no evidence of 
 heavy forest cover in northern Illinois at any time during the Wisconsinan Stage. 
 
 The abundance of Aniuispira kochi and the robust individuals of Allogona 
 profunda, Aniuispira alternata, and Succinea ovalis confirm the concept of deep 
 forests at the southern locality at the time the shells were buried in the loess. It 
 is evident that the terrain was well watered, but there is little to indicate that the 
 climate was anything more than slightly cooler than at present. 
 
 The absence of terrestrial species in the two northern localities (8, 24) does 
 not permit speculation concerning vegetational cover of the uplands of this part of 
 Illinois in Farmdalian time. There is reason, however, to doubt the occurrence 
 there of forest cover, because it seems likely that the large shells of forest species 
 would almost certainly have found their way into pond deposits. All that can be 
 conjectured is the presence of permanent, clear, ponded water at the sites from 
 which the collections came. There is nothing to indicate that these waters were 
 more than slightly cooler than lakes and ponds existing in the area today. Pending 
 the discovery of fossiliferous upland Farmdalian silt, the terrestrial molluscan 
 fauna (and a more complete paleoecological picture) of the Farmdalian Substage 
 in the northern parts of Illinois must remain unknown. 
 
 Woodfordian Faunas 
 
 Woodfordian molluscan assemblages comprising an aggregate of 55 species 
 have been recovered from a total of 50 localities; at some of them, Altonian or 
 Farmdalian faunas occur in their proper stratigraphic positions. Of the total assem- 
 blage, 22 species were restricted to the Woodfordian. These include: Aplexa 
 hypnorum , Carychium exile canadense , Columella alttcola, Euconulus fulvus , 
 Gastrocopta holzingeri, G. procera, G. pent odor. , Gyraulus parvus, Helisoma 
 trivolvls Mesodon clausus , Pisidium nitidum, P. uariabile, Planorbula armiiera, 
 Pupilla muscorum , Pupoides albilabris, Stenotrema leai, Triodopsis alionquinensis , 
 T. multilineata, Vertigo alpestris oughtoni, V. milium, and V. modesta . 
 
 Woodfordian faunas are divided into several categories, based on whether 
 they were recovered from Peoria loess, Morton loess, Richland loess, terrace de- 
 posits, or moraines (fig. 2). 
 
 Faunal Assemblages from the Peoria Loess 
 
 The Peoria loess, which includes all post-Farmdalian loessial deposits 
 outside the borders of the Shelbyville moraine, comprises silts ranging in age 
 throughout the Woodfordian Substage. This gray to gray-tan or grayish yellow silt 
 is almost everywhere fossiliferous except where it has been leached. Fossil 
 mollusks from the Peoria loess at 37 localities are here reported (fig. 2); the 
 number could be increased almost indefinitely by additional collections. 
 
PLATE 1 
 
 LARGE TERRESTRIAL GASTROPODS FROM WOODLAND ASSEMBLAGES 
 
 All figures approximately natural size 
 
 Figs. A, B, C. - Mesodon clausus (Say); spiral, apertural, and umbilical views, 
 
 respectively. Peoria loess, North Enion section, SE{ SE\ SW| sec. 28, 
 
 T. 4N., R. 3E., Fulton County. 
 Figs. D, E, F. - Triodopsis fosteri (Baker); spiral, apertural, and umbilical views, 
 
 respectively. Peoria loess, Gale section, center sec. 33, T. 14 S., R. 3 
 
 W., Alexander County . 
 Figs. G, H, I. -Triodopsis hubrichti Baker; umbilical, apertural, and spiral views, 
 
 respectively. Roxana silt, Gale section, center sec. 33, T. 14 S., R. 3 
 
 W., Alexander County . 
 Figs. J, K, L. -Aniuispira alternata (Say); umbilical, apertural, and spiral views, 
 
 respectively. Roxana silt, Gale section, center sec. 33, T. 14 S., R. 3 
 
 W., Alexander County. 
 Figs. M, N, O. - Mesodon thyroidus (Say); spiral, apertural, and umbilical views, 
 
 respectively. Roxana silt, Peters section, SW{ NW{ sec. 4, T. 3 N., R. 
 
 8 W., Madison County. 
 Figs. P, Q, R. - Triodopsis alionquinensis Nason; spiral, apertural, and umbilical 
 
 views, respectively. Peoria loess, SW| NE{ SW{ sec. 4, T. 8 N., R. 13 
 
 W., Jersey County. 
 Figs. S, T, U. - Alloiona profunda (Say); umbilical, spiral, and apertural views, 
 
 respectively. Roxana silt, Gale section, center sec. 33, T. 14 S., R. 3 W., 
 
 Alexander County. 
 Figs. V, W, X. -Triodopsis altonensis Baker; spiral, apertural, and umbilical 
 
 views, respectively. Roxana silt, Pleasant Grove section, center SE{ sec. 
 
 20, T. 3 N., R. 8 W., Madison County. 
 Figs. AA, BB, CC. - Aniuispira kochi (Pfeiffer); spiral, apertural, and umbilical 
 
 views, respectively. Roxana silt, Gale section, center sec. 33, T. 14 S., 
 
 R. 3 W., Alexander County. 
 Fig. Y. - Succinea ovalis Say; apertural views. Peoria loess, SW| NE{ SW| sec. 
 
 4, T. 8 N., R. 13 W., Jersey County. 
 
 
 '14" 
 
Illinois State Geological Survey 
 
 Circular 304 — Plate 1 
 
 Leonard and Frye — Wisconsinian Molluscan Faunas of the Illinois Valley Region. 
 
Illinois State Geological Survey 
 
 Circular 304 — Plate 2 
 
 Leonard and Frye — Wisconsinian Molluscan Faunas of the Illinois Valley Region. 
 
PLATE 2 
 AQUATIC GASTROPODS AND SPHAERIID FRESH-WATER MUSSELS 
 Various magnifications 
 
 Figs. A, B, C. - Gyraulus parvus (Say); spiral, apertural, and umbilical views, 
 respectively. Basal zone of Peoria loess, SE| SW| sec. 26, T. 4 N., R. 
 3 E., Fulton County. Enlarged approximately 5X. 
 
 Figs. D, E, F. - Valvata trlcarinata{Say); spiral, apertural, and umbilical views, 
 respectively. Farmdalian water-laid silts, Wedron Quarry section, SE| 
 SE| SW{ sec. 9, T. 34 N., R. 4 E., La Salle County. Enlarged approxi- 
 mately 3^X. 
 
 Figs. G, H, I. - Gyraulus altissimus Baker; spiral, apertural, and umbilical views, 
 respectively. Farmdalian water-laid silts, Wedron Quarry section, SE| SE{ 
 SW{ sec. 9, T. 34 N., R. 4 E., La Salle County. Enlarged approximately 
 5X. 
 
 Figs. J, K, L. - Valvata slncera Say; spiral, apertural, and umbilical views, re- 
 spectively. Farmdalian water-laid silts. Lake Bloomington Spillway sec- 
 tion, SW{ NE{ sec. 1, T. 25 N., R. 2 E., McLean County. Enlarged ap- 
 proximately 4X. 
 
 Figs. M, N, O. - Planorbula armigera (Say); spiral, apertural, and umbilical views, 
 respectively. Basal zone Peoria loess, SE^ SW{ sec. 26, T. 4 N., R. 3 E., 
 Fulton County. Enlarged approximately 4X. 
 
 Fig. P. - Amnicola leightoni Baker; apertural view. Farmdalian water-laid silts, 
 Wedron Quarry section, SE| SE| SW} sec. 9, T. 34 N., R. 4 E., La Salle 
 County. Enlarged approximately 4X. 
 
 Fig. Q. -Amnicola lustrlcn (Say); apertural view. Farmdalian water-laid silts, 
 Wedron Quarry section, SE{ SE| SW{ sec. 9, T. 34 N., R. 4 E., La Salle 
 County. Enlarged approximately 4X. 
 
 Fig. R. - Aplexa hypnorum (Linne); apertural view of incomplete specimen. Basal 
 zone Peoria loess, SE{ SW{ sec. 26, T. 4 N., R. 3 E., Fulton County. 
 Enlarged approximately 2 1/3X. 
 
 Fig. S. - Lymnaea parva (Say); apertural view. Sandy silt inclusion in Metamora 
 moraine, center NE{ sec. 25, T. 27 N., R. 4W., Woodford County. En- 
 larged approximately 3|X. 
 
 Fig. T. - Lymnaea dalll Baker; apertural view. Basal zone Peoria loess, Enion 
 North section, SE| SE| SW| sec. 28, T. 4 N., R. 3 E., Fulton County. 
 Enlarged approximately 4X. 
 
 Figs. U, V. - Pisidium nitidum (Mighels); internal and exterior views of right valve, 
 respectively. Farmdalian water-laid silts, Wedron Quarry section, SE| SE| 
 SWi sec. 9, T. 34 N., R. 4 E., La Salle County. Enlarged approximately 
 6X. 
 
 Figs. W, X. - Pisidium obtusale Prime; interior and exterior views of right valve, 
 respectively. Farmdalian water-laid silts, Lake Bloomington Spillway 
 section, SW^- NE} sec. 1, T . 25 N . , R. 2 E . , McLean County. Enlarged 
 approximately 6X. 
 
 Figs. Y, Z. - Pisidium compressum Prime; exterior and interior views of right valve, 
 respectively. Farmdalian water-laid silts, Wedron Quarry section, SE| 
 SE{ SW{ sec. 9, T. 34 N., R. 4 E., La Salle County. Enlarged approxi- 
 mately 7X. 
 
 15: 
 
PLATE 2 - continued 
 
 Figs. AA, BB. - Pisidium varlnb He Prime; interior and exterior views of right valve, 
 respectively. Farmdalian water-laid silts, Wedron Quarry section, SEj SE^ 
 SW{ sec. 9, T. 34 N., R. 4 E., La Salle County. Enlarged approximately 
 6X. 
 
 Fig. CC. - Lymnaea palustris (Miiller); apertural view. Farmdalian water-laid silts, 
 Lake Bloomington Spillway section, SW^ NE{ sec. 1, T.25N., R. 2E., 
 McLean County. Enlarged approximately 2X. 
 
 Figs. DD, EE. - Sphaerlum occidentale Prime; interior and exterior views of right 
 valve, respectively. Basal zone Peoria loess, SE^ SW| sec. 26, T. 4 N., 
 R. 3 E., Fulton County. Enlarged approximately 3|X. 
 
 Figs. FF, GG . - Pisidium caseratanum (Polis); interior and exterior views of right 
 valve, respectively. Farmdalian water-laid silts, Wedron Quarry section, 
 SE| SE| SW{ sec. 9, T. 34 N., R. 4 E., La Salle County. Enlarged approx- 
 imately 3jX. 
 
 Figs. HH, II, LL. - Helisoma trivolvis (Say); umbilical, spiral, and apertural 
 
 views, respectively. Basal zone Peoria loess, SE| SW| sec. 26, T. 4 N., 
 R. 3 E., Fulton County. Enlarged approximately 2 1/3X. 
 
 Figs. JJ, KK. - Sphaerium striatinum (Lamarck); interior and exterior views of right 
 valve, respectively. Basal zone Peoria loess, SE{ SW| sec. 26, T. 4 N., 
 R. 3 E., Fulton County. Enlarged approximately 2X. 
 
 Figs. MM, NN, OO. - Helisoma antrosa (Conrad); umbilical, apertural, and 
 
 spiral views, respectively. Farmdalian water-laid silts, Wedron Quarry 
 section, SE} SE} SW{ sec. 9, T. 34 N., R. 4 E., La Salle County. En- 
 larged approximately 2^X. 
 
 "161 
 
WISCONSINAN MOLLUSCAN FAUNAS 
 
 17 
 
 SPECIES 
 
 WISCONSINAN SUBSTAGES 
 
 ALTONI AIM 
 
 FARMDALIAN 
 
 WOOOFORDIAN 
 
 APLEXA HYPNORUM 
 CARYCHIUM EXILE CANADENSE 
 COLUMELLA ALT I COLA 
 EUCONULUS FULVUS 
 GASTROCOPTA HOLZINGERI 
 GA S T ROC OP TA PEN TODON 
 G YRA ULUS PARVUS 
 HE LI SOMA TRIVOLVIS 
 ME SO DON CLAUSUS 
 PLANORBULA ARMIGERA 
 PUPILLA MUSCORUM 
 PUPOIDES ALBILABRIS 
 STENOTREMA LEA I 
 TRIODOPSIS ALGONQUINENSIS 
 TRIODOPSIS MULTILINEATA 
 VERTIGO ALPESTRIS OUGHTONI 
 VERTIGO MILIUM 
 VERTIGO MODE ST A 
 ANGUISPIRA ALTERNATA 
 HAPLOTREMA CONCAVUM 
 HENDERSON/A OCCULTA 
 STENOTREMA FRATERNUM 
 STENOTREMA HIRSUTUM 
 SUC CINE A OVAL IS 
 C ION ELLA LUBRICA 
 DISCUS CRONKHITEI 
 DISCUS MACCLINTOCKI 
 GA S T ROC OP TA A RMIFERA 
 GASTROCOPTA CONTRACT A 
 HAWAII A MINUSCULA 
 HELICODISCUS PARALLELUS 
 MESODON THYROIDUS 
 POMATIOPSIS SCALAR IS 
 PUNCTUM MINUTISSIMUM 
 RETINELLA ELECTRINA 
 STROBILOPS LABYRINTHICA 
 SUCCINEA GEL IDA 
 SUCCINEA GROSVENORI 
 VALLONIA GRACILICOSTA 
 VALL ONI A PA R VUL A 
 VERTIGO HUBRICHTI 
 ZONITOIDES AR BORE US 
 GYRAULUS ALTISSIMUS 
 HE LI SOMA ANT ROSA 
 LYMNAEA DALLI 
 LYMNAEA OBRUSSA DEC AM PI 
 LYMNAEA PARVA 
 TRIODOPSIS FOSTER! 
 VA L VA TA TRI CARINA TA 
 AMNIO OLA LEIGH TON I 
 AM NICOLA LUST RICA 
 GYRAULUS CRISTUS 
 LYMNAEA PALUSTRIS 
 VALVATA SINCERA 
 ALLOGONA PROFUNDA 
 ANGUISPIRA KOCH I 
 TRIODOPSIS HUBRICHTI 
 TRIODOPSIS ALTONENSIS 
 
 RARE 
 
 COMMON 
 
 ABUNDANTI 
 
 Fig. 3 - Time-stratigraphic distribution of Wisconsinan snail faunas. Gastrocopta 
 procera also should be included in the Woodfordian. 
 
PLATE 3 
 
 MISCELLANEOUS TERRESTRIAL GASTROPODS OF 
 WOODLAND BORDERS AND PRAIRIES 
 
 Various magnifications 
 
 Figs. A, B, C. - Euconulus fulvus (Muller); umbilical, apertural, and spiral views, 
 respectively. Peoria loess, NW| NE{ sec. 33, T. 9 N., R. 13 W., Greene 
 County. Enlarged approximately 6X. 
 
 Figs. D, E, F. - Helicodiscus parallelus (Say); umbilical, spiral, and apertural 
 views, respectively. Peoria loess, SW^ NE^ SW^ sec. 4, T. 8 N., R. 13 
 W., Jersey County. Enlarged approximately 6X. 
 
 Figs. G, H, I. - Retinella e lee tr inn (Gould); umbilical, apertural, and spiral views, 
 respectively. Peoria loess, SW{ NE| SW| sec. 4, T. 8 N., R. 13 W., Jer- 
 sey County. Enlarged approximately 6X. 
 
 Figs. J, K. -Vallonia Uracil icostaReinhardt; umbilical and spiral views, respec- 
 tively. Peoria loess, "The Rocks" section, 1 mile SE of bridge on Ohio 
 River, Shawneetown, Illinois, in Union County, Kentucky. Enlarged approx- 
 imately 6X. 
 
 Figs. L, M, N. - Hendersonia occulta (Say); umbilical, apertural, and spiral views, 
 respectively. Peoria loess, "The Rocks" section, 1 mile SE of bridge on 
 Ohio River at Shawneetown, Illinois, in Union County, Kentucky. Enlarged 
 approximately 3|X. 
 
 Figs. O, P. - Discus cronkhitei (Newcomb); umbilical and spiral views, respec- 
 tively. Peoria loess, "The Rocks" section, 1 mile SE of bridge on Ohio 
 River at Shawneetown, Illinois, in Union County, Kentucky. Enlarged ap- 
 proximately 3X. 
 
 Figs. Q, R. -' Discus macclintocki Baker; umbilical and spiral views, respectively. 
 Peoria loess, SW{ NE} SW{ sec. 4, T. 8 N., R. 13 W., Jersey County. 
 Enlarged approximately 2 2/3X. 
 
 Figs. S, T, U. - Haplotrema concavum (Say); umbilical, apertural, and spiral views, 
 respectively. Peoria loess, NW corner SE| SE{ sec. 29, T. 4 N., R. 8 W., 
 Madison County. Enlarged approximately 1 2/3X. 
 
 Figs. V, W, X. - Stenotrema leal (Binney); umbilical, apertural, and spiral views, 
 respectively. Peoria loess, SE corner SW| NW| sec. 17, T. 18 N., R. 10 
 W., Cass County. Enlarged approximately 2 2/3X. 
 
 Fig. Y. - Cionella lubrica (Muller); apertural view. Peoria loess, NE corner SW| 
 SW{ sec. 17, T. 18 N., R. 10 W., Cass County. Enlarged approximately 
 7X. 
 
 Figs. AA, BB, CC. - Stenotrema hirsutum (Say); umbilical, apertural, and spiral 
 
 views, respectively. Roxana silt, Pleasant Grove section, center SE^- sec. 
 20, T. 3 N., R. 8 W., Madison County. Enlarged approximately 4X. 
 
 Fig. Z. - Succinea grosvenori Lea; apertural view. Peoria loess, "The Rocks" sec- 
 tion, 1 mile SE of bridge on Ohio River at Shawneetown, Illinois, in Union 
 County, Kentucky. Enlarged approximately 3|X. 
 
 Fig. DD. - Succinea ielida Baker; apertural view. Peoria loess, SW} NE| SW;| 
 sec. 4, T. 8N., R. 13W., Jersey County. Enlarged approximately 3{X. 
 
 Figs. EE, FF, GG . - Stenotrema fraternum (Say); umbilical, apertural, and spiral 
 views, respectively. Peoria loess, SW^ NE^ SW± sec. 4, T. 8 N., R. 13 
 W., Jersey County. Enlarged approximately 3^X. 
 
 [18] 
 
Illinois State Geological Survey 
 
 Circular 304 — Plate 3 
 
 £% 
 
 ) 
 
 Leonard and Fhste — Wisconsinian Molluscan Faunas of the Illinois Valley Region. 
 
Illinois State Geological Survey 
 
 Circular 304 — Plate 4 
 
 <Ci 
 
 4, 
 
 B 
 
 D 
 
 • 
 
 Leonard and Frye — Wisconsinian Molluscan Faunas of the Illinois Valley Region. 
 
PLATE 4 
 PUPILLID AND OTHER MINUTE GASTROPODS 
 Most figures enlarged 12 times 
 
 Figs. A, B, C. - Punctum minutissimum (Lea); umbilical, apertural, and spiral 
 
 views, respectively. Peoria loess, "The Rocks" section, 1 mile SE of 
 
 bridge on Ohio River at Shawneetown, Illinois, in Union County, Kentucky. 
 
 Enlarged approximately 12X. 
 Fig. D. - Carychium exile canndense Clapp; apertural view. Basal zone Peoria 
 
 loess, SE} SW} sec. 26, T. 4 N., R. 3 E., Fulton County. Enlarged approx- 
 imately 12X. 
 Fig. E. - Vertiio milium Gould; apertural view. Basal zone Peoria loess, SE} SW} 
 
 sec. 26, T. 4 N., R. 3E., Fulton County. Enlarged approximately 12X. 
 Fig. F. -Vertiio hubrichti Baker; apertural view. Peoria loess, NE corner SW} SW{ 
 
 sec. 17, T. 18 N., R. 10 W., Cass County. Enlarged approximately 12X. 
 Fig. G. - Gastrocopta holzinieri (Sterki); apertural view. Peoria loess, NE corner 
 
 SWi SW{ sec. 17, T. 18 N., R. 10 W., Cass County. Enlarged approxi- 
 mately 12X. 
 Fig. H. - Gastrocopta pentodon (Say); apertural view. Peoria loess, SE} SW} sec. 
 
 26, T. 4 N., R. 3 E., Fulton County. Enlarged approximately 12X. 
 Fig. I. -Vertigo alpestris ouihtoni Pilsbry; apertural view. Morton loess, SW} NE} 
 
 NE} sec. 16, T. 30 N., R. 1 W., Marshall County. Enlarged approximately 
 
 12X. 
 Fig. J. - Gastrocopta procera (Gould); apertural view. Peoria loess, NE corner SW} 
 
 SW} sec. 17, T. 18 N., R. 10 W., Cass County. Enlarged approximately 12X. 
 Fig. K. - Vertigo modesta (Say); apertural view. Peoria loess, SE corner SW} NW{ 
 
 sec. 17, T. 18 N., R. 10 W., Cass County. Enlarged approximately 12X. 
 Fig. L. - Gastrocopta contracta (Say); apertural view. Peoria loess, SE corner SW} 
 
 NW} sec. 17, T. 18 N., R. 10W., Cass County. Enlarged approximately 12X. 
 Figs. M, N, O. - Hawaiia minuscula (Binney); spiral, apertural, and umbilical views, 
 
 respectively. Peoria loess, SE corner SW} NW| sec. 17, T. 18 N., R. 10 W., 
 
 Cass County. Enlarged approximately 12X. 
 Fig. P. - Columella alticola (Ingersoll); apertural view. Peoria loess, NE corner SW} 
 
 SW} sec. 17, T. 18 N., R. 10 W., Cass County. Enlarged approximately 12X. 
 Fig. Q, R, S. -Strobilops labyrinthica (Say); umbilical, apertural, and spiral views, 
 
 respectively. Roxana silt, Gale section, center sec. 33, T. 14 S . , R. 3 W., 
 
 Alexander County. Enlarged approximately 12X. 
 Fig. T. - Gastrocopta armifera (Say); apertural view. Woodfordian terrace silts, SW 
 
 corner NW| sec. 23, T. 7 S., R. 4 W., Pike County. Enlarged approximately 
 
 10X. 
 Fig. U. - Pupoides albilabris (Adams); apertural view. Peoria loess, Irish Grove 
 
 section, center NE} sec. 25, T.19N., R. 5W., Menard County. Enlarged 
 
 approximately 12X. 
 Fig. V. -Pomatiopsis scalar is Baker; apertural view. Peoria loess, Enion section, 
 
 SE corner NW} sec. 33, T. 4 N., R. 3 E., Fulton County. Enlarged approx- 
 imately 7|X. 
 Fig. W. - Pupilla muscorum (Linne); apertural view. Peoria loess, Banner section, 
 
 NW} NE} sec. 10, T. 6 N., R. 5 E., Fulton County. Enlarged approximately 
 
 12X. 
 
 ■191 
 
20 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 304 
 
 Total numbers of molluscan species in any single Peoria fauna range from 
 as many as 26 (locality 57a) to as few as three (locality 25); a typical assemblage 
 comprises approximately 12 species. 
 
 The Peoria fauna is distinctive and readily recognizable, even in the field. 
 The predominant species are small mollusks; the only relatively large shells that 
 occur are Aniuispira alternate!, Triodopsis alionquinensis , and occasionally T. 
 multilineata. The last two, as far as present information goes, are restricted to the 
 Woodfordian. Succinea ielida, Etenotrema hirsutum , S. leal, Hendersonia occulta, 
 and either Discus cronkhitei or D. macclintocki , although of only moderate size, 
 frequently are conspicuous in a local fauna. Among the minute species Columella 
 alticola^ Euconulus fulvus , and Vertiio modesta are most commonly recovered in 
 the Peoria loess. 
 
 The Peoria fauna shows significant variation from north to south in the Illinois 
 Valley region. Among the species of reasonably frequent occurrence, Carychium 
 exile canadense , Columella alticola, Discus cronkhitei , and Pupilla muscorum are 
 either restricted to the northernmost part of the region, or reach their greatest popu- 
 lation density there, while Discus macclintocki, Hawaiia winuscula , Haplotrema 
 concavum, Vertiio hubrichti, and Aniuispira alternata occur most frequently in the 
 southern localities. 
 
 Ecological Considerations 
 
 A complete picture of the paleoecological conditions prevailing in Illinois 
 during the time of deposition of the Peoria loess cannot be fully reconstructed. The 
 thick, highly fossiliferous loess exposures are near the major valleys, and the loess 
 thins rapidly away from them. Because relief is relatively less pronounced away from 
 the valleys, suitable exposures are less frequent and those available generally are 
 so deeply leached that all snail shells have been destroyed. It is obvious from the 
 species composition of Peoria assemblages that the great deciduous forests of Al- 
 tonian time (at least as they appeared in the southern half of Illinois) did not occur 
 in Woodfordian in northern Illinois. This is not to say that the vegetative cover was 
 reduced to a prairie situation; the presence of Aniuispira alternata, Mesodon clausus, 
 and the several species of Stenotrema in the Peoria loess attests to the presence of 
 stands of trees. The general vegetational cover must have consisted of stands of 
 trees along stream courses, and perhaps elsewhere, interspersed with large areas 
 of open prairie. Correspondingly, the climate was likely less stable and perhaps 
 less humid than that existing in Altonian (and perhaps Farmdalian) time, although 
 the occurrence of Carychium exile canadense , Lymnaea parua , Pomatiopsis scalaris, 
 Triodopsis alionquinensis , and T. multilineata clearly show that the climate could 
 not have been deficient in rainfall. Carychium exile canadense , Euconulus fulvus, 
 Pupilla muscorum t and Vertiio alpestris ouihtoni support the thesis that the Wood- 
 fordian climate was somewhat cooler than today, even in northern Illinois,for these 
 species are today characteristic of molluscan faunas in the Canadian Life Zone. 
 
 Faunal Assemblages from Morton Loess 
 
 The post-Farmdale — pre-Shelbyville Morton loess (formerly classified as 
 the Iowan loess) in our studies is represented by two fossiliferous localities (10 
 and 23, fig. 2). From these a total of 12 species is known; Columella alticola. 
 Discus cronkhitei, Haplotrema concavum , Hendersonia occulta, Lymnaea dalli , 
 
WISCONSINAN MOLLUSCAN FAUNAS 21 
 
 Pupilla muscorum, Retinella electrina s Stenotrema leai , Succinea gelida, Triodopsis 
 algonquinensis , Vertigo alpestris ought on i, and V. modesta . This assemblage is 
 not unlike those typical of northern localities of the Peoria loess. It lacks Discus 
 macclintocki , which does not occur anywhere inside the Shelbyville morainal front. 
 Columella alticola, Hendersonia occulta, and Pupilla muscorum are abundant, and 
 along with Succinea gelida are the most conspicuous faunal elements of the Morton 
 loess. From the scant evidence available, it is not now possible to distinguish 
 the fauna of the Morton loess from that of Peoria loess in northern Illinois. 
 
 Faunal Assemblages from Richland Loess 
 
 The Richland loess, situated stratigraphically above the earliest Woodfordian 
 moraines, is represented at localities 2, 14, and 22 (fig. 2). The combined assem- 
 blage from these collecting stations totals 12 species: Columella alticola, Discus 
 cronkhitei, Euconulus fulvus , Gyraulus altissimus , Lymnaea dalli , L. obrussa 
 decampi , Pisidium compressum, P. caseratanum, Pupilla muscorum, Succinea gelida, 
 Vallonia gracilicosta, and Vertigo modesta. 
 
 The character of the assemblage is not significantly different from that of 
 those found in the Morton loess or in the Peoria loess of northern Illinois. At 
 locality 22 the loess evidently accumulated on a poorly drained surface, as attested 
 by the presence of three genera (Gyraulus , Lymnaea , and Pisidium) of aquatic mol- 
 lusks. We believe this reflects nothing more than an anomalous local ecological 
 condition. 
 
 Faunal Assemblages from Normal and Metamora Moraines 
 
 At two localities fossil shells were obtained from silt inclusions in glacial 
 till, one in the Normal ground moraine (locality 9) and one in the Metamora ground 
 moraine (locality 13). From the first deposit only a meager series was obtained: 
 Discus cronkhitei , Helicodiscus parallelus , and Succinea grosvenori . The second 
 collecting station yielded eight species, including Columella alticola, Discus 
 cronkhitei , Euconulus fulvus, Pupilla muscorum, Succinea gelida, Vallonia gracili- 
 costa f Vertigo hubrichti, and V. modesta . 
 
 The first of these collections obviously has little significance aside from 
 its unusual occurrence within a till mass; the second closely resembles that from 
 the Morton and Richland loess, or, for that matter, the Peoria loess of northern 
 Illinois. 
 
 The ecological significance of these molluscan assemblages from silt-in- 
 till inclusions is considerable, especially as the shells at locality 13 are abundant 
 and had suffered no discernible damage before our collections were made. Several 
 hundred shells were obtained from a bulk sample of approximately 100 pounds of 
 silt. Inasmuch as the fauna is similar to that found in loesses of the region, in- 
 cluding those outside the Wisconsinan glacial boundary, it is evident that continen- 
 tal glaciation at the latitude of northern Illinois did not have a profound effect upon 
 local climate at any considerable distance from the ice front. As the nearly perfect 
 state of preservation of the shells argues against long transportation from other de- 
 posits, we can safely assume that the gastropods found in the silts lived at one 
 time within a stone's throw of the glacial front. Although well preserved shells 
 were collected from sand and silt streaks in till in northeastern Kansas (Frye and 
 Leonard, 1952), to our knowledge the Illinois localities are the most northerly yet 
 reported to yield from a till mass shells in sufficient numbers to make it evident that 
 the animals were living near the ice front. 
 
22 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 304 
 
 Faunal Assemblages from Woodfordian Terrace Deposits 
 
 The emphasis in this report is on faunal assemblages from loess deposits, 
 but during our field work we made six collections (fig. 2) from deposits that may be 
 referred to as Woodfordian terraces. The snails from locality 2 were collected from 
 terrace sand and silt; those from locality 6 were recovered from a 6-inch zone of 
 coarse gray silt below Bloomington till; those from locality 7 occurred in sand and 
 silt in deltaic deposits in front of the Arlington (Cropsey) moraine; shells at locality 
 35 were collected from a silty band in a 15-foot roadcut exposure of sand and silt 
 below loess. Only the assemblages from localities 41 and 42 came from typical 
 terrace deposits. An organized study of molluscan faunal assemblages in Pleistocene 
 terraces in Illinois remains to be made. 
 
 The total assemblage from these six collecting stations ranges from six 
 species (localities 6, 7) to 11 species (locality 35). Except for the occurrence of 
 Valvata tricarinata atlocality 41, each of the local faunas has little to distinguish 
 it from Woodfordian assemblages from loess in the near vicinity. In view of the 
 paucity of data from the terraces, no generalities concerning them can, or should, 
 be made at this time. 
 
 SUMMARY 
 
 The recent revision of the classification of the Wisconsinan Stage of the 
 Pleistocene in Illinois (Frye and Willman, 1960) has made possible a systematic 
 evaluation of late Pleistocene molluscan faunas within a firmly established strati- 
 graphic framework. Although Pleistocene mollusks have been known for many years 
 (Baker, 1920), this paper presents for the first time the results of an organized study 
 of fossil mollusks within a discrete segment of Pleistocene time over a significant 
 geographical region of Illinois. 
 
 The molluscan faunal assemblages treated here are grouped under the Altonian, 
 Farmdalian, and Woodfordian Substages of the Wisconsinan Stage; fossiliferous 
 sediments of Twocreekan and Valderan Substages have not yet been recognized in 
 the Illinois Valley region. 
 
 The Altonian Substage is represented by the Roxana silt from the approximate 
 latitude of the mouth of the Sangamon River to Alexander County . The Roxana silt, 
 although not fossiliferous throughout, yields a molluscan fauna of distinctive qual- 
 ities, characteristic of those found in climactic deciduous forests. Only two species, 
 Trlodopsis altonensis and T. hubrlchti, seem to be definitely restricted to Altonian 
 faunas, but the typical assemblage embraces also Alloiona profunda (which occurs 
 outside the Altonian at only one Farmdalian locality), Aniuisplra alternnta, and 
 occasionally A. kochi , Hendersonia occulta, Stenotrema fraternum , Stenotrema 
 hlrsutum , Succinea oualis, and other less frequently occuring species. A total of 
 28 species are known from the Roxana silt at 11 localities. 
 
 Collections from three exposures of Farmdale silts yielded a total of 24 
 species, but because of the widely separated geographic distribution of the localities 
 and the unusual qualities of each, the Farmdalian faunal assemblage is not yet well 
 characterized. In the water-laid deposits in LaSalle and McLean Counties the pre- 
 dominant species are Valvata tricarinata, V. sincera, Amnicola leiihtoni , A. lustrica, 
 and shells of several species of Pisidium . Predominant species in the single southern 
 locality, at the latitude of Gallatin County, are Aniuisplra alternatn, A. kochi, Allo- 
 iona profunda, and Succinea ovalis. This southern fauna, like that from the Altonian 
 of the same region, is characteristic of deep forests. 
 
WISCONSINAN MOLLUSCAN FAUNAS 23 
 
 Molluscan faunas were recovered from loess, moraines, outwash, inclusions 
 of sand and silt within till, and from terrace deposits of Woodfordian age. Collect- 
 ing stations include 37 localities in the Peoria loess, two in the Morton loess, and 
 three in the Richland loess; two collections were made from silt-in-till inclusions 
 in the Normal and Metamora moraines, and six from Woodfordian terrace silts. 
 
 The total Woodfordian faunal assemblage comprises 55 species, of which 
 22 species were not found at other stratigraphic levels. Predominant species in 
 the well defined assemblage include Columella alticola, Euconulus fulvus , Steno- 
 trema leal, Trlodopsis algonquinensls, and Vertigo modest a , all seemingly restricted 
 to the Woodfordian, and Angulspira alternata } Hendersonla occulta, Stenotrema 
 hirsutuw , Succinea ovalis, S. ielida , S. grosvenorl , Discus cronkhitei , and D. 
 macclintocki , each of which also occurs in other Wisconsinan assemblages. 
 
 Woodfordian faunas display distinctive geographical differences from north 
 to south, but on the basis of present evidence it is not possible to make strati- 
 graphic distinctions within the substage. 
 
 Interpretations of paleoecology may be generalized as follows: At least in 
 the region south of Sangamon River, Illinois was heavily forested in Altonian time; 
 these dense forests, existing in a climate more humid than the present one, con- 
 tinued through Farmdalian time and perhaps, in southern Illinois, into earliest Wood- 
 fordian. After Farmdalian time the vegetative cover was of a much more open type, 
 perhaps essentially a mixed prairie, with trees and shrubs restricted to borders of 
 stream courses and other favorable situations. 
 
 There is no evidence of extremely rigid climates during Woodfordian time, 
 even in areas adjacent to ice fronts, although northern Illinois is judged to have 
 had a climate approximating that of the present Canadian Life Zone. 
 
 REFERENCES 
 
 Baker, F. C, 1920, The life of the Pleistocene or glacial period: Univ. Illinois 
 Bull. 17. 
 
 Frye, J. C, and Leonard, A. B., 1952, Pleistocene geology of Kansas: Kansas 
 Geol. Survey Bull. 99, 230 p. 
 
 Frye, J. C, and Willman, H. B., 1960, Classification of the Wisconsinan Stage 
 in the Lake Michigan glacial lobe: Illinois Geol. Survey Circ . 285, 16 p. 
 
 Goodrich, Calvin, 1932, The Mollusca of Michigan: Univ. Michigan Michigan 
 handbook ser. mus. zool . no. 5, p. 1 - 120, figs. 1-7. 
 
 de Heinzelin, J., 1959, Problemes du Pleistocene dans le Middle West (U . S. A.): 
 Soc. beige ge'ologie Bull., tome LXVII, p. 265 - 290. 
 
 Leighton, M. M., 1948, Footnote on p. 390, in Washer, H. L., et al., Loess in 
 the southern Mississippi Valley — Identification and distribution of loess 
 sheets: Soil Sci. Soc. Amer. Proc . 1947, v. 12, p. 389 - 399. 
 
 Smith, G. D., 1942, Illinois loess — variations in its properties and distribution: 
 a paleologic interpretation: Univ. Illinois Agr. Exp. Sta . Bull. 490, p. 
 139 - 184. 
 
 Wayne, W. J., 1959, Stratigraphic distribution of Pleistocene land snails: Sterkiana, 
 no. 1, p. 9 - 18. 
 
24 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 304 
 
 GEOLOGIC SECTIONS 
 
 The locations of the 11 measured geologic sections presented here and of 
 four similar sections published in Circular 285 are shown on the map in figure 1. 
 The numbers enclosed in parentheses, for example (P-762), refer to samples collec- 
 ted for mineralogical study and will be described in a subsequent report. The 
 sections are arranged alphabetically by name. 
 
 ALTON QUARRY SECTION 
 
 SE-f SW?- NE-f sec. 10, T. 5 N., R. 10 W. , Madison County, Illinois; measured in 
 Mississippi Lime Company quarry, 1958. (Type locality of Altonian Substage). 
 Measured by John C. Frye and H. B. Willman 
 
 Pleistocene Series Thickness 
 
 Wisconsinan Stage (feet) 
 
 Woodfordian Substage 
 Peoria loess 
 
 9. Loess, coarse, massive, yellow-tan, weakly calcareous 
 
 (P-20). 12.0 
 
 Altonian Substage 
 Roxana silt 
 
 8. Loess, coarse, massive, pinkish tan (P-21 ), gradational 
 
 with yellow-tan above;weakly calcareous; fossil snails 
 
 sparse (locality 54). 14.0 
 
 7. Loess, massive, noncalcareous, non fossilif erous, medium 
 gray to gray-tan (P-22); sharply truncated at top and 
 a darker zone gradational at base. 5.0 
 
 Illinoian Stage 
 
 6. Silt, sand, and clay, massive, noncalcareous, reddish brown, 
 general appearance of colluvium (P-23). This zone is 
 entirely within the A- and B-horizons of a soil profile 
 7 feet thick that extends into the underlying unit. 2.0 
 
 5. Till, massive, highly calcareous except the uppermost 5 feet 
 which is leached (P-24, 2 feet below top), relatively 
 fine-textured, blue-gray to dark gray (P-26, 10 feet below 
 top). A one-foot sand zone (P-25) occurs 8 feet below 
 the top; lowermost 10 feet contains distorted masses and 
 bands of gray silt, fragments of wood, and scattered 
 snail shells. 35.0 
 
 4. Silt, massive, light gray at bottom grading upward to 
 dark gray, calcareous, fossilif erous, gradational at 
 base, stems and wood fragments in upper part, and at 
 top a thin clay slickenside zone suggesting glacial 
 override. 1.0 
 
 3. Silt, loess or loess-like, massive, calcareous, yellow- 
 buff, limonite banding in upper part (P-27); contains 
 abundant fossil snails. 4.0 
 
 2. Silt, loess or loess-like, massive, weakly calcareous, 
 
 tan to yellowish buff, limonitic banding. 6.0 
 
 1. Silt, very fine sand, and clay, thinly laminated, non- 
 calcareous, rusty brown to chocolate (P-28); rests on 
 Mississippian St. Louis Limestone at a low point on 
 the unconformable surface. 3.5 
 
 Total Pleistocene 82.5 
 
WISCONSINAN MOLLUSCAN FAUNAS 25 
 
 BANNER SECTION 
 
 NWf NE5- sec. 10, T. 6 N. , R. 5 E. , Fulton County, Illinois 
 Measured in new cuts along Highway 9, 1958 
 
 Pleistocene Series Thickness 
 
 Wisconsinan Stage (feet) 
 
 Woodfordian Substage 
 Peoria loess 
 
 4. Loess, massive with local platyness, medium, yellow-tan- 
 gray, calcareous (P-118); upper 8 feet leached in 
 
 surface soil; contains fossil snails (locality 15). 18.0 
 
 Farmdalian Substage 
 Farmdale silt 
 
 3. Silt, massive to platy, purple-brown to purple-gray, 
 
 noncalcareous; charcoal flakes in upper part (P-117 
 
 upper; P-116 lower). 5.0 
 
 2. Sand, silt, and a few pebbles, massive, yellow-tan at 
 
 bottom grading upward to gray-brown; locally weakly 
 calcareous; colluvium (P-115). 2.0 
 
 Illinoian Stage 
 
 1. Till, compact, pebbly, gray and tan, calcareous (P-113); 
 
 contains included blocks of gray silt with a few 
 
 fragmentary snail shells; upper 2 feet leached (P-114), 
 
 appears to be truncated soil. 20.0 
 
 Total Pleistocene 45.0 
 
 BLUFFDALE SECTION 
 NW? NWi sec. 3, T. 10 N. , R. 13 W. , Greene County, Illinois, 1953, 
 overburden of abandoned quarry 
 
 Pleistocene Series Thickness 
 
 Wisconsinan Stage (feet) 
 
 Woodfordian Substage 
 Peoria loess 
 
 4. Loess, massive to indistinctly bedded, gray-tan, weakly 
 
 calcareous, sparsely fossiliferous; gradational at base; 
 basal contact and indistinct bedding dip away from 
 valley. 15.0 
 
 Altonian Substage 
 Roxana silt 
 
 3. Loess, massive, pink, weakly calcareous to noncalcareous; 
 
 basal contact forms arch in truncated spur; contains 
 several pods of Celt is occi'lentalis seeds and fossil 
 snails (locality 46). 20.0 
 
 2. Silt, massive, gray and gray-tan mottled, scattered 
 
 angular chert fragments. 3.0 
 
 1. Rubble of angular chert fragments with random orientation 
 
 in a clay matrix, covered at the base. 4.0 
 
 Total Pleistocene measured 42.0 
 
 BROWNS MOUND SECTION 
 
 NEi SEi sec. 27, T. 14 N. , R. 13 W. , Scott County, Illinois, 1958-9, (i mile 
 southwest of deep cuts along Hwy. U. S. 36, studied and collected in 1953 and 
 1955). Section as exposed in August 1958 and May 1959. 
 
 Measured by John C. Frye, A. Byron Leonard, and H. B. Willman 
 
26 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 304 
 
 Pleistocene Series Thickness 
 
 Wisconsinan Stage (feet) 
 
 Woodfordian Substage 
 Peoria loess 
 
 9. Loess, with lenticular inclusions of sand; loess massive, 
 gray to yellow-tan, coarse, calcareous except in soil 
 profile at top, fossiliferous; sand medium to fine and 
 coarse, cross-bedded, light tan to gray, locally mottled 
 with soft limonite, sand lentils occur throughout and 
 locally truncate bed below. Fossil snails were collected 
 both here and from the upper and presumed equivalent unit 
 in the nearby roadcut (locality 43). (P-282, P-283 loess; 
 P-286 cross-bedded sand.) Maximum thickness. 25.0 
 
 8. Silt and fine to medium sand, thin-bedded, horizontal, gray- 
 tan, gray and yellow-tan, contains sparse Succinea cf. 
 irosvenori; occurs only as lenticular body on east side of 
 quarry, basal contact truncates pink loess below and top 
 is truncated by the cross-bedded sands of unit 8 (P-285). 6.0 
 Altonian Substage 
 Roxana silt 
 
 7. Loess, medium to coarse, massive, pink to pinkish tan, 
 
 weakly calcareous to noncalcareous, lenticular bodies of 
 
 sand (P-280) occur at west side of quarry, gradational at 
 
 top with overlying loess where lenticular bodies of sand 
 
 and interbedded sand and silt are not present (P-281 from 
 
 pink loess above sand body). [Re-examination of the quarry 
 
 in September 1959 and May 1960, after the overburden face 
 
 was significantly farther back from the buff-line and past 
 
 the limit of the sand lentils, showed bed 9 resting on 
 
 pink loess, above gray-tan loess that rested directly and 
 
 conformably on bed 7. The top of the Roxana is at the 
 
 top of the upper pink loess.] (Fauna locality 45). 17.0 
 
 6. Silt, gray, massive, noncalcareous, gradational at top but 
 resting with sharp contact on top of soil below. (The 
 face as exposed in May 1960 showed this unit thicker and 
 with 2 feet of sand locally at base.) 4.0 
 
 Pre-Wisconsinan Stages 
 
 5. Silt, sandy, massive, gray, noncalcareous except locally at 
 base where it is weakly calcareous, in east side of quarry 
 has soil at top with well developed red-brown B-horizon 
 and some structure and manganese staining; westward across 
 quarry face, soil is truncated, and at west end the over- 
 lying loess rests directly on the leached till below. 
 Locally contains a sparse snail fauna. (P-278 gray loess; 
 P-279 B-horizon of soil.) 6.0 
 
 4. Till, massive, compact, blue-gray, calcareous in lower part; 
 at west side of quarry a truncated soil was observed in 
 1958 in upper part of till; in middle part of quarry till 
 pinched out over bedrock high (P-277). 8.0 
 
 3. Silt, massive, tan, noncalcareous, occurs in local lenses 
 
 between till and underlying sand (P-276). 2.0 
 
 2. Sand, with a few pebbles, massive to bedded, gray to tan, 
 noncalcareous, loose; lenticular, ranges from a few 
 inches to 6 feet in thickness (P-275). 6.0 
 
WISCONSINAN MOLLUSCAN FAUNAS 
 
 27 
 
 Silt) indistinctly bedded to massive, compact, red-tan 
 to gray-tan, with a few streaks of sand; maximum 
 thickness in west side of quarry, pinching out to 
 the east (P-274). 
 
 Pleistocene depo-sits rest on Mississippian limestone. 
 
 Maximum total thickness 
 
 Thickness 
 (feet) 
 
 5.0 
 
 79.0 
 
 ickness 
 (feet) 
 
 25.0 
 
 15.0 
 
 COTTONWOOD SCHOOL SECTION 
 
 Center E. line, sec. 11, T. 18 N. , R. 11 W. , Cass County, Illinois 
 Measured along road cuts, 1958, 1959, by John C. Frye, 
 A. Byron Leonard, and H. B. Willman. 
 
 Pleistocene Series Th 
 
 Wisconsinan Stage 
 
 Woodfordian Substage 
 Peoria loess 
 
 9. Loess, coarse, gray-tan to pale yellow, massive to 
 indistinctly thin-bedded and laminated, sparsely 
 fossilif erous, calcareous (P-110). 
 
 8. Loess, coarse to medium, massive, gray-tan, a fine- 
 textured zone gradational at top (P-109), indistinct 
 streaks of pale pink throughout, calcareous (P-107 
 and P-108); contains fossil snails (locality 32). 
 Altonian Substage 
 Roxana silt 
 
 7. Loess, coarse, massive, dark pink in lower part (P-104) 
 grading upward (P-105) to pinkish gray in upper part 
 (P-106); noncalcareous to weakly calcareous, very 
 sparsely fossiliferous throughout. 15.0 
 
 6. Loess, medium, massive, neutral gray, limonite tubules, 
 weakly calcareous; sharp contact at top (P-102, lower; 
 P-103 upper). 10.0 
 
 5. Loess, medium, massive, pinkish-tan, gradational upward 
 with gray loess and sharp contact at base; limonite 
 tubules and small calcium carbonate concretions through- 
 out, weakly calcareous but nonfossilif erous (P-100, 
 lower; P-101 upper). 8.0 
 
 4. Silt, massive, light gray to medium gray with some mottling 
 with tan, noncalcareous; small angular fragments of chert 
 and small pebbles sparsely throughout; colluvium (P-99). 5.0 
 Illinoian Stage 
 
 3. Till, compact, pebbly and cobbly; in lower half gray, 
 
 calcareous, tough (P-97); upper half in soil profile, 
 
 leached, red-brown, sandy, clayey, friable (P-98). 8.0 
 
 2. Silt, compact, blocky, calcareous, banded gray and tan, 
 
 contains some sand and pebbles (P-96). 3.0 
 
 1. Till, compact, massive, pebbly, calcareous, gray to gray- 
 brown (P-95); rests on Pennsylvanian shale and siltstone. 5.0 
 
 Total Pleistocene 
 
 94.0 
 
28 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 304 
 
 FREDERICK SOUTH SECTION 
 
 SEi NEi NEi sec. 18, T. 1 N. , R. 1 E. , Schuyler County, Illinois. 
 
 in borrow pit, 1959. 
 Measured by John C. Frye, A. Byron Leonard, and H. B. Willman. 
 
 Pleistocene Series Thickness 
 
 Wisconsinan Stage (feet) 
 
 Woodfordian Substage 
 Peoria loess 
 
 12. Loess, tan to yellow-tan, massive, strongly calcareous 
 below a 4-foot surface soil (P-599 calcareous loess; 
 P-600 B-horizon of surface soil). Yielded fossil snails 
 (locality 29). 10.0 
 
 11. Loess (weakly developed soil profile), medium tan-brown 
 with carbonaceous flecks and small spots of secondary 
 calcium carbonate, matrix weakly calcareous, non- 
 fossiliferous (P-598). 1.0 
 
 10. Loess, gray-tan, massive, coarse, strongly calcareous 
 
 (P-596 2 feet above base; P-597 9 feet above base). 15.0 
 Altonian Substage 
 Roxana silt 
 
 9. Silt, coarse, pink with transition to tan in upper 2 feet, 
 weakly calcareous becoming strongly so in transition 
 zone at top, fossilif erous (P-594 middle; P-595 top). 7.5 
 8. Silt, coarse, and very fine sand, sandier in base, tan in 
 base becoming light tan-brown in top, massive, weakly 
 calcareous, sparse snail fauna (P-592 lower; P-593 upper). 8.0 
 7. Sand, fine to very fine, grading upward to silt, medium-tan 
 in base grading upward to light tan-brown, weakly 
 calcareous; sparse snail fauna (P-590 base; P-591 upper). 2.5 
 6. Silt, coarse, and very fine sand, pink, massive, compact, 
 
 calcareous (P-589); contains fossil snails (locality 29). 3.5 
 5. Sand, fine, and coarse silt, medium gray-tan, calcareous, 
 massive, gradational top and bottom, nonfossiliferous 
 (P-588). ' 4.0 
 
 4. Colluvium of silt with some sand, scattered coarse sand 
 grains and pebbles, tan to tan-brown, noncalcareous 
 (P-587). 2.0 
 
 Pre-Wisconsinan Stages 
 
 3. Soil, with 3-foot profile, red-brown B-horizon (P-586), 
 developed in silty sand, tan, noncalcareous, grading 
 downward through tan, noncalcareous sand and silty 
 sand (P-584 lower; P-585 upper), to 2 feet of calcareous 
 tan sand in base (P-583). 15.0 
 
 2. Covered in lower part; coarse colluvium composed of sand, 
 silt, blocks of tan sandstone, metamorphic and igneous 
 rock pebbles; strongly calcareous and cemented in 
 discontinuous zones. 5.0 
 
 1. Till, gray, calcareous, sandy and pebbly, abundant nodules 
 of CaC03 in lower 3 feet (P-581), strongly oxidized in 
 upper one foot (P-582); rests on Pennsylvanian sandstone, 4.0 
 
 Total Pleistocene 77.5 
 
WISCONSINAN MOLLUSCAN FAUNAS 29 
 
 LAKE BLOOM INGTON SPILLWAY SECTION 
 
 SWi NEi sec. 1, T. 25 N., R. 2 E., McLean County, Illinois, 1957, 1958, and 1959. 
 Adapted from earlier section by George E. Ekblaw 
 
 Pleistocene Series Thickness 
 
 Wisconsinan Stage (feet) 
 
 Woodfordian Substage 
 Richland loess 
 
 10. Loess, oxidized, leached, massive, buff. 3.0 
 
 Normal till 
 
 9. Till, clayey, massive, gray-tan, leached in uppermost 
 
 part (P-148). 3.0 
 
 8. Sand and gravel, calcareous, tan (P-147). 2.0 
 
 Normal or Bloomington till 
 
 7. Till, massive, pebbly, calcareous, pink-tan (P-146). 3.0 
 
 Interstadial silt 
 
 6. Silt with some sand, massive, weakly calcareous, streaked 
 
 gray-tan and brown. 1.5 
 
 Bloomington, Leroy, or Shelbyville till 
 
 5. Till, massive, pebbly, calcareous, gray to blue-gray (P-145). 8.0 
 Farmdalian or Altonian Substage 
 
 4. Silt, massive, compact, greenish gray to pink-gray with 
 some color banding (P-144); contains peaty zones and 
 streaks; lenticular; yielded C^ 4 date (W-67) greater 
 than 34,000 years (note conflicting date from bed l). 
 Yielded fossil snails (locality 24). 2.5 
 
 Altonian Substage, or older 
 
 3. Till, cobbly and gravelly, relatively loose locally in 
 lower part, in upper part more compact, calcareous, 
 oxidized at top (P-143). 3.0 
 
 2. Till, compact, massive, pebbly, calcareous, gray (P-142). 5.0 
 1. Till, compact, massive, jointed, calcareous, pebbly, 
 
 purplish-gray, upper 8 inches slightly less calcareous 
 than remainder of till (P-141); top marked by a pave- 
 ment of pebbles, cobbles, and boulders, all faceted, 
 polished, and striated along a planeate surface. Sample 
 of wood from till gave a C^ date of 31,000 or older 
 (W-186); to level of water in spillway channel. 8.0 
 
 Total Pleistocene measured 39.0 
 
 MASON COUNTY SECTION 
 
 SEi NEi NWi sec. 36, T. 20 N., R. 7 W. , Mason County, Illinois; 
 
 along north valley wall of Sangamon River Valley, 1959. 
 
 Measured by John C. Frye, A. Byron Leonard, and H. B. Willman 
 
 Pleistocene Series Thickness 
 
 Wisconsinan Stage (feet) 
 
 Woodfordian Substage 
 Peoria Loess 
 
 5. Loess, gray and yellow-tan in indistinct zones, massive, 
 calcareous, medium coarse (P-577 base); fossil snails 
 in upper one-third below the soil profile (locality 28). 40.0 
 Altonian Substage 
 Roxana silt 
 
 4. Loess, pink, massive, weakly calcareous, compact, non- 
 
 fossilif erous (P-576). 4.0 
 
30 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 304 
 
 Thickness 
 (feet) 
 
 3. Loessj gray-tan, massive, calcareous, nonfossiliferous, 
 
 gradational contacts (P-575). 1.5 
 
 2. Silt, contains pebbles in lower part becoming sparse 
 
 upward (colluvium), pink (P-574). 4.0 
 
 Pre-Wisconsinan Stages 
 
 1. Sand and gravel with well developed soil B-horizon, red- 
 
 brown, clayey, at top truncated by colluvial contact; 
 
 grades downward into calcareous sand, gravel, and silt, 
 
 well bedded to poorly bedded (outwash), partly covered 
 
 in lower part to level of road. 50.0 
 
 Total 99.5 
 
 "THE ROCKS" SECTION, KENTUCKY 
 
 One mile southeast of bridge across Ohio River at Shawneetown, Illinois. 
 Measured July 1959 by John C. Frye, A. Bryon Leonard, and H. B. Willman. 
 
 Pleistocene Series Thickness 
 
 Wisconsinan Stage (feet) 
 
 Woodfordian Substage 
 Peoria loess 
 
 5. Loess, gray, massive, calcareous below the surface soil; 
 fossil snails from lower two-thirds of this zone 
 
 (locality 57A). (P-480 lower.) 20.0 
 
 Farmdalian Substage (latest transitional) 
 
 4. Loess, gray, massive, coarse, contains CaC03 nodules; 
 
 fossil snails (locality 57B). (P-479). Radio- 
 carbon date on snail shells 22,200 450 (W-867). 5.0 
 Altonian Substage 
 Roxana silt 
 
 3. Loess, dark gray to light brown, pink in basal part, 
 
 massive, noncalcareous to weakly calcareous, non- 
 fossiliferous. This and underlying beds are trun- 
 cated at a low angle by erosional unconformity at top 
 so that bed 4 rests on bed 1 at side of cut (P-478, 
 top; P-477, middle; P-476, base.) 6.0 
 
 Illinoian Stage 
 
 2. Sangamon soil; red to red-brown clay and silt, scattered 
 
 Mn-Fe pellets, clay skins, gradational at base. 
 
 (P-475, upper. ) 4.0 
 
 1. Silt, massive, mottled yellow, tan and red-brown in upper 
 part grading downward to yellow-tan, noncalcareous, 
 nonfossiliferous; rests on Pennsylvanian sandstone 
 (P-474, upper.) 6.0 
 
 Total Pleistocene 41.0 
 
 SAVANNA SECTION 
 
 Adjacent to Highway 80, southwest cor. NW?- sec. 11, T. 24 N., R. 3 E. , 
 
 Carroll County, Illinois (July 1959). 
 
 Measured by John C. Frye, A. Byron Leonard, and H. B. Willman 
 
WISCONSINAN MOLLUSCAN FAUNAS 
 
 31 
 
 Pleistocene Series Thickness 
 
 Wisconsinan Stage (feet) 
 
 Woodfordian Substage 
 Peoria loess 
 
 8. Loess, leached, tan, well developed soil profile in 
 
 upper part. 5.0 
 
 7. Loess, calcareous, gray, grading upward into yellow-tan, 
 massive; lower 5 feet contains abundant snail fauna 
 (locality 3). (P-526, lower; P-527, upper). 20.0 
 
 Altonian Substage, or older 
 
 6. Sand, very fine, and coarse silt, pale chocolate-brown 
 
 to medium gray-pink, noncalcareous, massive; gradational 
 
 at base with A-horizon below and erosional unconformity 
 
 at top (P-525). 3.0 
 
 5. Silt, massive, dark gray-brown, grading upward into dark 
 
 gray A-horizon of A-C soil profile at top (P-523 lower; 
 P-524 upper). 5.0 
 
 Pre-Wisconsinan Stages 
 
 4. Soil, A-horizon; silt with some clay, dark gray-brown, 
 
 crumb-structure, gradational at base (P-522). 1.0 
 
 3. Soil, B-horizon; silt and clay, red-brown, tough, columnar 
 
 structure, gradational (P-521). 3.0 
 
 2. Silt, massive, noncalcareous, locally some fine sand, 
 
 yellow-tan; locally a few scattered pebbles of chert 
 (P-520). 4.0 
 
 1. Sand and silt, irregularly bedded, tan to brown, non- 
 calcareous (P-519); rests on weathered Maquoketa Shale. 2.0 
 
 Total Pleistocene 43.0 
 
 WEDRON SECTION 
 
 Southwest end of quarry of Wedron Silica Company, as exposed on July 27, 1959, in 
 vertical face; SE^ SE^ SWi sec. 9, T. 34 N., R. 4 E. , La Salle County, Illinois. 
 Measured by John C. Frye, A. Byron Leonard, and H. B. Willman 
 
 Pleistocene Series Thickness 
 
 Wisconsinan Stage (feet) 
 
 Woodfordian Substage 
 
 Richland loess, Farm Ridge till, etc. 
 
 7. Loess, till, and gravel, weathered and partly obscured 
 
 by spoil pile. 6.0 
 
 Cropsey till 
 
 6. Till, oxidized, tan, poorly exposed. 5.0 
 Bloomington till 
 
 5. Till, pink, bouldery, massive, calcareous, tough; 
 
 indistinct boulder pavement in middle part. 15.0 
 
 Shelbyville till 
 
 4. Till, gray and tan, calcareous, bouldery, compact, sharp 
 
 contact at top with an indistinct boulder pavement in top. 3.0 
 Pro-Shelbyville outwash 
 
 3. Sand and gravel, loose, tan, calcareous, locally cross- 
 
 bedded and generally well bedded, irregular erosional 
 
 contact at base. 10.0 to 20.0 
 
 lamoss geological 
 
 SURVEY « IBRARY 
 M jtf 28 1986 
 
32 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 304 
 
 Farmdalian Substage Thickness 
 
 Farmdale silt (feet) 
 
 2. Silt, clayey, pink to red and red-brown, calcareous, 
 
 massive to indistinctly bedded but locally thin-bedded 
 and blocky, no fossils observed; locally contains small 
 lenses of fine sand, tan, calcareous; upper contact 
 irregular but lower contact conformable on unit below. 
 From the upper part of this unit in a former working 
 face, wood yielded a C 14 date of 24,000 ±700 (W-79). 10.0 to 20.0 
 1. Silt with some clay and fine sand and locally sandy 
 
 streaks near the top, gray-blue to dark gray or black 
 
 with some tan zones, massive, compact, calcareous; 
 
 contains fauna of aquatic mollusks (locality 8); humus 
 
 staining distributed throughout, numerous twigs and 
 
 wood fragments in upper one-third yielded a C^ 4 date 
 
 of 26,800 ±700 (W-871); rests on St. Peter Sandstone. 25.0 
 
 Total Pleistocene measured 94.0 
 
 Illinois State Geological Survey Circular 304 
 32 p., 3 figs., 4 plates, 11 geol. sections, 1960 
 
nnmni 
 
 CIRCULAR 304 
 
 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 URBAN A ^fff^ 166