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Stratigraphic Paleontology, continued

Molluscan Faunal Assemblages in Illinoian Deposits

The Crete and Loveland members of the Sanborn formation are the depositional representatives of Illinoian time in Kansas, and since the two members are separable only on a textural basis and are gradational with respect to each other, the molluscan fauna discussed here is a composite assemblage from Crete-Loveland deposits. The occurrence and distribution of 25 kinds of mollusks at 10 localities in the State is shown on Figure 8, and illustrations of a representative assemblage appear on Plate 16.

Figure 8--Occurrence of fossil mollusks in Illinoian deposits at 10 localities in Kansas. An Acrobat PDF version of this figure is available.

Molluscan species	Faunal localities
	SW sec. 35, T. 17 S., R. 13 W., Barton	SW sec. 33, T. 13 S., R. 5 E., Geary	NW sec. 21, T. 24 S., R. 21 W., Hodgeman	NE sec. 5, T. 2 S., R. 7 W., Jewell	NW sec. 2, T. 2 S., R. 9 W., Jewell	SE sec. 13, T. 1 S., R. 9 W., Norton	NW sec. 23, T. 2 S., R. 18 W., Phillips	NW sec. 9, T. 1 S., R. 19 W., Phillips	NW sec. 9, T. 2 S., R. 16 W., Phillips	NW sec. 7, T. 18 S., R. 7 W., Rice
Anodonta sp.
Carychium exiguum (Say)
Carychium perexiguum Baker
Deroceras laeve (Muller)
Discus cronkhitei (Newcomb)
Gastrocopta armifera (Say)
Gastrocopta holzingeri (Sterki)
Gastrocopta tappaniana (C. B. Adams)
Gyraulus similaris (Baker)
Hawaiia minuscula (Binney)
Helicodiscus parallelus (Say)
Helicodiscus singleyanus (Pilsbry)
Helisoma antrosa (Conrad)
Helisoma trivolvis (Say)
Physa anatina Lea
Pupilla blandi Morse
Pupilla muscorum (Linne)
Pupoides albilabris (C. B. Adams)
Retinella electrina (Gould)
Sphaerium solidulum (Prime)
Strobilops sparsicosta Baker
Succinea grosvenori Lea
Vallonia gracilicosta Reinhardt
Vallonia pulchella (Muller)
Vertigo tridentata Wolf

Plate 16--A representative assemblage of mollusks from Illinoian deposits in Kansas. All figures enlarged approximately 5 times natural size. An Acrobat PDF version of this plate is available that shows more detail.

Gastrocopta armifera (Say) Pupilla muscorum (Linne) Pupilla blandi Morse Vertigo tridentata Wolf Gastrocopta tappaniana (C. B. Adams) Gastrocopta holzingeri (Sterki) Vallonia gracilicosta Reinhardt Vallonia pulchella (Müller) Helicodiscus singleyanus (Pilsbry) Deroceras laeve (Müller) Pupoides albilabris (C. B. Adams) Retinella electrina (Gould) HeIicodiscus parallelus (Say) Hawaiia minuscula (Binney) Strobilops sparsicosta Baker Carychium exiguum (Say) Discus cronkhitei (Newcomb) Helisoma antrosa (Conrad) Physa anatina Lea Sphaerium solidulum Prime Gyraulus similaris Baker Helisoma trivolvis (Say) Succinea grosvenori Lea

Typically, Crete sands and gravels grade upward into fluviatile silts, which in turn grade into massive, well-sorted silts judged to be eolian in origin. Almost everywhere in the State where these sediments can be recognized, as well as in Nebraska, Iowa, Illinois, and other surrounding states, the Crete-Loveland sequence has developed in its upper part the Sangamon soil. The Sangamon soil is in fact the most reliable stratigraphic datum available for the recognition of Crete-Loveland deposits, and the fauna under present consideration has been in every case collected only where the Sangamon soil was recognizable as a stratigraphic reference.

The Illinoian assemblage of mollusks is less distinctive than that in Nebraskan, Kansan, or Wisconsinan deposits primarily because no segment of the assemblage is restricted to it. However, with care and a reasonably complete faunule, an Illinoian assemblage can be distinguished from other aggregations of Pleistocene mollusks in Kansas. In general, the Illinoian assemblage is intermediate in character between that in Kansan sediments stratigraphically below it and that in Wisconsinan deposits stratigraphically above it. But as inferred above, the age of the assemblage is based largely on its relation to the Sangamon soil.

In spite of its intermediate character, the Illinoian faunal assemblage has a number of distinctive features worthy of note.

(1) About 14 species of common occurrence in Kansan deposits do not appear in the Illinoian assemblages. None of the genera of branchiate gastropods, such as Amnicola, Pomatiopsis, and Valvata seems to have survived the Yarmouthian interglacial interval in the midcontinent region. Likewise, aquatic pulmonate snails, such as Aplexa, Ferrissia, Menetus, Planorbula, and Promenetus, most species of Gyraulus, and the larger species of Lymnaea, failed to survive the ecological changes that followed the close of deposition of Sappa silts.

(2) Four species, common in Kansan faunules, make their final appearance in the geologic column in Kansas in Illinoian sediments; these include Carychium perexiguum, Strobilops sparsicosta, Gyraulus similaris, and Helisoma antrosa. The first two species are extinct, Gyraulus similaris survives in relict populations in montane lakes in Colorado, and Helisoma antrosa, although extinct on the Great Plains, is still a commonly occurring snail in the more humid regions of central and eastern United States.

(3) A number of species, among which may be mentioned Columella alticola and Striatura milium which are relatively common in Wisconsinan loess (Tazewellian zone of the Peoria silt), are not found in Illinoian assemblages. Furthermore, the slug Deroceras aenigma, common in Nebraskan and Kansan faunas, is replaced in Illinoian molluscan assemblages by Deroceras laeve.

The small number of localities from which molluscan assemblages of Illinoian age are reported here is no indication of the extent of Illinoian sediments in the State. At most localities where Illinoian sediments can be recognized, the gravels, sands, or silts are nonfossiliferous. The reason for this is not completely understood, but a number of contributing factors are known. It is not surprising that few instances of fossiliferous Crete sand and gravel are known, because the fragile shells of mollusks cannot survive for long the abrasive action of coarse sediments in transit. In fact, it is remarkable that any examples of fossiliferous Crete materials are known, since there is not a single instance known to us of shells occurring in recognizable faunules in the coarse phases of the Holdrege or Grand Island gravels. Another contributing factor is that generally over the State, while Illinoian sediments are widespread, they exist as relatively thin strata. Not infrequently, the weathering that produced the Sangamon soil has progressed completely through the entire Illinoian sequence, which would have destroyed, of course, any shells previously present. Finally, the climate during Illinoian time may have been unfavorable to mollusks, although this seems unlikely in view of the kinds that are known to be present. The absence of molluscan remains in unleached Loveland loess at a number of localities remains unexplained.

It is difficult to escape the conclusion that a profound change in ecological conditions in the Great Plains occurred during or at the close of the Yarmouthian interglacial interval, or at the beginning of the Illinoian cycle of erosion and deposition. Wholesale extinction of great populations of branchiate and other gastropods adapted to life in permanent water, which thrived in western Kansas in late Kansan and early Yarmouthian time, is indicative of a less humid environment, or at least of a marked decline in the prevalence of permanent ponds and lakes of clear water in the Great Plains region. The assemblage of aquatic gastropods in late Kansan silt, the prevalence in them of zygospores of some Chara-like alga, and abundance at many exposures of the valves of ostracods all point toward an environment of permanent slow-flowing or ponded water, without excessive siltation, and perhaps with an average temperature somewhat below that prevalent in the same region today or in Illinoian time. By contrast, the aquatic gastropods in Illinoian deposits indicate an environment of ephemeral ponds and silt-laden streams. Anodonta, a lammellibranch pelecypod, and the pulmonate gastropods Helisoma trivolvis and Physa anatina, as well as the little clam Sphaerium solidulum, are all animals capable of living in heavily silted ponds or streams, and capable also of surviving considerable periods without open water. Gyraulus similaris probably was limited to spring-fed ponds or other cooler and clearer waters.

With the exception of Strobilops sparsicosta, which probably lived in or near woodlands, the terrestrial fauna associated with Illinoian deposits is adapted for life in prairies, meadows, or perhaps woodland borders or in small areas of shrubs. Gastrocopta armifera, Hawaiia minuscula, and Pupoides albilabris live in the prairies of western Kansas today, and survive periods of great aridity. Pupilla muscorum, however, and Retinella electrina, Carychium perexiguum, C. exiguum, Helicodiscus singleyanus, Vallonia gracilicosta, Vertigo tridentata, and others are absent from the living molluscan fauna in the Great Plains, so it must be conceded that in Illinoian time ecological conditions were somewhat more favorable toward mollusks than those prevalent today. Certainly the contrast between ecological conditions in Illinoian time and Kansan as well as Nebraskan time was much greater than that between Illinoian and modern time, and we judge that climatic conditions in Kansas during the Illinoian Age were not significantly different than present-day conditions, except for slightly greater rainfall and greater and more widespread sedimentation. It seems, for example, that the ecological situation in Norton or Phillips County in Illinoian time might have been not unlike that in Dickinson or Marion County today.

Molluscan Faunal Assemblages in Wisconsinan Deposits

The molluscan faunal assemblage associated with Wisconsinan sediments has been previously treated by Frye and A. B. Leonard (1951), and by A. B. Leonard (1951, 1952). In the present report, the Wisconsinan molluscan fauna is divided into pre- and post-Bradyan assemblages; the occurrence and distribution of 28 kinds of mollusks from pre-Bradyan Wisconsinan silts at 137 localities is shown on Figure 9, and illustrations of a representative assemblage appear on Plate 17. The occurrence and distribution of 16 species of mollusks at 27 localities where post-Bradyan Wisconsinan deposits have been studied is shown on Figure 10, while a representative assemblage of these mollusks is illustrated on Plate 18.

Figure 9--Occurrence of fossil mollusks in pre-Bradyan Wisconsinan deposits at 137 localities in Kansas. Asterisk in location indicates collection from hand auger samples. An Acrobat PDF version of this figure is available.

Molluscan species	Faunal localities
	SW sec. 30, T. 3 S., R. 38 W., Cheyenne	SE sec. 28, T. 3 S., R. 39 W., Cheyenne	SE sec. 17, T. 1 S., R. 41 W., Cheyenne	SE sec. 16, T. 1 S., R. 42 W., Cheyenne	NW sec. 6, T. 30 S., R. 23 W., Clark	NW sec. 20, T. 33 S., R. 23 W., Clark	NE sec. 26, T. 33 S., R. 24 W., Clark	NW sec. 31, T. 5 S., R. 3 W., Cloud	NE sec. 3, T. 3 S., R. 27 W., Decatur	NE sec. 6, T. 3 S., R. 27 W., Decatur	NW sec. 35, T. 3 S., R. 27 W., Decatur	SW sec. 23, T. 4 S., R. 27 W., Decatur	SW sec. 26, T. 4 S., R. 27 W., Decatur	SW sec. 7, T. 5 S., R. 27 W., Decatur
Gastrocopta holzingeri (Sterki)
Succinea ovalis Say
Gastrocopta armifera (Say)
Hendersonia occulta (Say)
Discus shimeki (Pilsbry)
Succinea grosvenori Lea
Vertigo modesta (Say)
Discus cronkhitei (Newcomb)
Columella alticola (Ingersoll)
Striatura milium (Morse)
Retinella electrina (Gould)
Cionella lubrica (Müller)
Vertigo gouldi coloradensis (Cockerell)
Zonitoides arboreus (Say)

Molluscan species	Faunal localities
	NE sec. 1, T. 3 S., R. 28 W., Decatur	NW sec. 23, T. 5 S., R. 28 W., Decatur	NE sec. 14, T. 5 S., R. 29 W., Decatur	SE sec. 6, T. 2 S., R. 20 E., Doniphan	NE sec. 8, T. 1 S., R. 19 E., Doniphan	SW sec. 29, T. 15 S., R. 18 W., Ellis	SW sec. 18, T. 14 S., R. 19 W., Ellis	SW sec. 24, T 21 S., R. 29 W., Finney	NE sec. 34, T. 22 S., R. 30 W., Finney	SE sec. 4, T. 24 S., R. 32 W., Finney	SW sec. 9, T. 24 S., R. 32 W., Finney	NW sec. 16, T. 29 S., R. 24 W., Ford	NE sec. 2, T. 27 S., R. 22 W., Ford	NE sec. 35, T. 15 S., R. 27 W., Gove
Gastrocopta holzingeri (Sterki)
Succinea ovalis Say
Gastrocopta armifera (Say)
Hendersonia occulta (Say)
Discus shimeki (Pilsbry)
Succinea grosvenori Lea
Vertigo modesta (Say)
Discus cronkhitei (Newcomb)
Columella alticola (Ingersoll)
Striatura milium (Morse)
Retinella electrina (Gould)
Cionella lubrica (Müller)
Vertigo gouldi coloradensis (Cockerell)
Zonitoides arboreus (Say)

Molluscan species	Faunal localities
	SW sec. 36, T. 14 S., R. 29 W., Gove	SW sec. 23, T. 9 S., R. 21 W., Graham	NE sec. 28, T. 9 S., R. 22 W., Graham	SE sec. 28, T. 27 S., R. 35 W., Grant	*NE sec. 1, T. 25 S., R. 29 W., Gray	NW sec. 9, T. 16 S., R. 40 W., Greeley	*NW sec. 19, T. 21 S., R. 40 W., Hamilton	SE sec. 12, T. 25 S., R. 41 W., Hamilton	SW sec. 36, T. 25 S., R. 41 W., Hamilton	SE sec. 35, T. 35 S., R. 8 W., Harper	NW sec. 3, T. 28 S., R. 32 W., Haskell	NE sec. 22, T. 30 S., R. 34 W., Haskell	NE sec. 27, T. 23 S., R. 22 W., Hodgeman	NW sec. 26, T. 23 S., R. 25 W., Hodgeman
Gastrocopta holzingeri (Sterki)
Succinea ovalis Say
Gastrocopta armifera (Say)
Hendersonia occulta (Say)
Discus shimeki (Pilsbry)
Succinea grosvenori Lea
Vertigo modesta (Say)
Discus cronkhitei (Newcomb)
Columella alticola (Ingersoll)
Striatura milium (Morse)
Retinella electrina (Gould)
Cionella lubrica (Müller)
Vertigo gouldi coloradensis (Cockerell)
Zonitoides arboreus (Say)

Molluscan species	Faunal localities
	NE sec. 4, T. 1 S., R. 7 W., Jewell	SW sec. 19, T. 5 S., R. 8 W., Jewell	*NW sec. 31, T. 23 S., R. 38 W., Kearny	NW sec. 3, T. 28 S., R. 9 W., Kingman	SW sec. 18, T. 16 S., R. 28 W., Lane	NW sec. 7, T. 20 S., R. 28 W., Lane	SE sec. 29, T. 20 S., R. 28 W., Lane	SW sec. 2, T. 16 S., R. 29 W., Lane	NW sec. 3, T. 16 S., R. 29 W., Lane	NE sec. 15, T. 16 S., R. 29 W., Lane	SE sec. 15, T. 16 S., R. 30 W, Lane	*NE sec. 17, T. 17 S., R. 30 W., Lane	SE sec. 27, T. 11 S., R. 32 W., Logan	NW sec. 13, T. 12 S., R. 32 W., Logan
Gastrocopta holzingeri (Sterki)
Succinea ovalis Say
Gastrocopta armifera (Say)
Hendersonia occulta (Say)
Discus shimeki (Pilsbry)
Succinea grosvenori Lea
Vertigo modesta (Say)
Discus cronkhitei (Newcomb)
Columella alticola (Ingersoll)
Striatura milium (Morse)
Retinella electrina (Gould)
Cionella lubrica (Müller)
Vertigo gouldi coloradensis (Cockerell)
Zonitoides arboreus (Say)

Molluscan species	Faunal localities
	SE sec. 3, T. 14 S., R. 32 W., Logan	NW sec. 27, T. 15 S., R. 32 W., Logan	NE sec. 2, T. 14 S., R. 35 W., Logan	NE sec. 9, T. 15 S., R. 35 W., Logan	SE sec. 3, T. 11 S., R. 26 W., Logan	NE sec. 32, T. 12 S., R. 37 W., Logan	NE sec. 8, T. 33 S., R. 27 W., Meade	NE sec. 11, T. 30 S., R. 28 W., Meade	SW sec. 30, T. 31 S., R. 28 W., Meade	NW sec. 6, T. 30 S., R. 30 W., Meade	NW sec. 28, T. 8 S., R. 8 W., Mitchell	NW sec. 10, T. 16 S., R. 22 W., Ness	NE sec. 16, T. 16 S., R. 22 W., Ness	NE sec. 29, T. 16 S., R. 24 W., Ness
Gastrocopta holzingeri (Sterki)
Succinea ovalis Say
Gastrocopta armifera (Say)
Hendersonia occulta (Say)
Discus shimeki (Pilsbry)
Succinea grosvenori Lea
Vertigo modesta (Say)
Discus cronkhitei (Newcomb)
Columella alticola (Ingersoll)
Striatura milium (Morse)
Retinella electrina (Gould)
Cionella lubrica (Müller)
Vertigo gouldi coloradensis (Cockerell)
Zonitoides arboreus (Say)

Molluscan species	Faunal localities
	NW sec. 26, T. 2 S., R. 23 W., Norton	NW sec. 11, T. 3 S., R. 23 W., Norton	NE sec. 10, T. 4 S., R. 23 W., Norton	SE sec. 27, T. 4 S., R. 23 W., Norton	SE sec. 13, T. 1 S., R. 24 W., Norton	NE sec. 7, T. 5 S., R. 24 W., Norton	SE sec. 5, T. 2 S., R. 17 W., Phillips	NW sec. 23, T. 2 S., R. 18 W., Phillips	NE sec. 25, T. 1 S., R. 20 W., Phillips	NE sec. 2, T. 3 S., R. 31 W., Rawlins	NW sec. 8, T. 5 S., R. 31 W., Rawlins	SW sec. 2, T. 3 S., R. 33 W.,, Rawlins	NE sec. 9, T. 3 S., R. 33 W., Rawlins	NW sec. 20, T. 4 S., R. 33 W., Rawlins
Gastrocopta holzingeri (Sterki)
Succinea ovalis Say
Gastrocopta armifera (Say)
Hendersonia occulta (Say)
Discus shimeki (Pilsbry)
Succinea grosvenori Lea
Vertigo modesta (Say)
Discus cronkhitei (Newcomb)
Columella alticola (Ingersoll)
Striatura milium (Morse)
Retinella electrina (Gould)
Cionella lubrica (Müller)
Vertigo gouldi coloradensis (Cockerell)
Zonitoides arboreus (Say)

Molluscan species	Faunal localities
	NE sec. 8, T. 3 S., R. 34 W., Rawlins	NE sec. 29, T. 3 S., R. 36 W., Rawlins	NW sec. 5, T. 3 S., R. 4 W., Republic	SE sec. 7, T. 10 S., R. 16 W., Rooks	SW sec. 30, T. 9 S., R. 19 W., Rooks	SW sec. 28, T. 17 S., R. 19 W, Rush	SE sec. 17, T. 18 S., R. 31 W., Scott	SE sec. 6, T. 17 S., R. 32 W., Scott	*SW sec. 31, T. 20 S., R. 34 W., Scott	SW sec. 15, T. 6 S., R. 28 W., Sheridan	SW sec. 3, T. 7 S., R. 28 W., Sheridan	SE sec. 28, T. 7 S., R. 28 W., Sheridan	NW sec. 34, T. 8 S., R. 28 W., Sheridan	SW sec. 10, T. 9 S., R. 28 W., Sheridan
Gastrocopta holzingeri (Sterki)
Succinea ovalis Say
Gastrocopta armifera (Say)
Hendersonia occulta (Say)
Discus shimeki (Pilsbry)
Succinea grosvenori Lea
Vertigo modesta (Say)
Discus cronkhitei (Newcomb)
Columella alticola (Ingersoll)
Striatura milium (Morse)
Retinella electrina (Gould)
Cionella lubrica (Müller)
Vertigo gouldi coloradensis (Cockerell)
Zonitoides arboreus (Say)

Molluscan species	Faunal localities
	NE sec. 33, T. 10 S., R. 28 W., Sheridan	NW sec. 19, T. 8 S., R. 29 W., Sheridan	NE sec. 13, T. 6 S., R. 30 W., Sheridan	NW sec. 14, T. 6 S., R. 30 W., Sheridan	NW sec. 15, T. 6 S., R. 30 W., Sheridan	NW sec. 31, T. 8 S., R. 30 W., Sheridan	SE sec. 34, T. 10 S., R. 37 W., Sherman	SW sec. 26, T. 10 S., R. 38 W., Sherman	NW sec. 32, T. 7 S., R. 39 W., Sherman	SW sec. 36, T. 6 S., R. 39 W., Sherman	SW sec. 20, T. 7 S., R. 40 W., Sherman	SE sec. 28, T. 1 S., R. 13 W., Smith	SW sec. 11, T. 27 S., R. 39 W., Stanton	NE sec. 2, T. 29 S., R. 40 W., Stanton
Gastrocopta holzingeri (Sterki)
Succinea ovalis Say
Gastrocopta armifera (Say)
Hendersonia occulta (Say)
Discus shimeki (Pilsbry)
Succinea grosvenori Lea
Vertigo modesta (Say)
Discus cronkhitei (Newcomb)
Columella alticola (Ingersoll)
Striatura milium (Morse)
Retinella electrina (Gould)
Cionella lubrica (Müller)
Vertigo gouldi coloradensis (Cockerell)
Zonitoides arboreus (Say)

Molluscan species	Faunal localities
	NW sec. 12, T. 28 S., R. 41 W., Stanton	SE sec. 25, T. 29 S., R. 41 W., Stanton	SE sec. 21, T. 7 S., R. 31 W., Thomas	NE sec. 27, T. 7 S., R. 31 W., Thomas	NW sec. 10, T. 8 S., R. 32 W., Thomas	NE sec. 17, T. 8 S., R. 32 W., Thomas	NW sec. 31, T. 7 S., R. 33 W., Thomas	NW sec. 18, T. 9 S., R. 33 W., Thomas	SE sec. 27, T. 10 S., R. 33 W., Thomas	NW sec. 8, T. 8 S., R. 35 W., Thomas	SW sec. 8, T. 8 S., R. 35 W., Thomas	SW sec. 32, T. 7 S., R. 36 W., Thomas	SW sec. 7, T. 8 S., R. 36 W., Thomas	SW sec. 19, T. 8 S., R. 36 W., Thomas
Gastrocopta holzingeri (Sterki)
Succinea ovalis Say
Gastrocopta armifera (Say)
Hendersonia occulta (Say)
Discus shimeki (Pilsbry)
Succinea grosvenori Lea
Vertigo modesta (Say)
Discus cronkhitei (Newcomb)
Columella alticola (Ingersoll)
Striatura milium (Morse)
Retinella electrina (Gould)
Cionella lubrica (Müller)
Vertigo gouldi coloradensis (Cockerell)
Zonitoides arboreus (Say)

Molluscan species	Faunal localities
	NW sec. 3, T. 11 S., R. 23 W., Trego	SW sec. 5, T. 12 S., R. 24 W., Trego	NW sec. 26, T. 15 S., R. 38 W., Wallace	SW sec. 35, T. 11 S., R. 40 W., Wallace	SW sec. 23, T. 12 S., R. 40 W., Wallace	NW sec. 1, T. 15 S., R. 40 W., Wallace	*SE sec. 35, T. 20 S., R. 35 W., Wichita	SW sec. 12, T. 17 S., R. 37 W., Wichita	SE sec. 1, T. 19 S., R. 37 W., Wichita	NE sec. 12, T. 19 S., R. 37 W., Wichita	SE sec. 32, T. 16 S., R. 38 W., Wichita
Gastrocopta holzingeri (Sterki)
Succinea ovalis Say
Gastrocopta armifera (Say)
Hendersonia occulta (Say)
Discus shimeki (Pilsbry)
Succinea grosvenori Lea
Vertigo modesta (Say)
Discus cronkhitei (Newcomb)
Columella alticola (Ingersoll)
Striatura milium (Morse)
Retinella electrina (Gould)
Cionella lubrica (Müller)
Vertigo gouldi coloradensis (Cockerell)
Zonitoides arboreus (Say)

Molluscan species	Faunal localities
	SW sec. 30, T. 3 S., R. 38 W., Cheyenne	SE sec. 28, T. 3 S., R. 39 W., Cheyenne	SE sec. 17, T. 1 S., R. 41 W., Cheyenne	SE sec. 16, T. 1 S., R. 42 W., Cheyenne	NW sec. 6, T. 30 S., R. 23 W., Clark	NW sec. 20, T. 33 S., R. 23 W., Clark	NE sec. 26, T. 33 S., R. 24 W., Clark	NW sec. 31, T. 5 S., R. 3 W., Cloud	NE sec. 3, T. 3 S., R. 27 W., Decatur	NE sec. 6, T. 3 S., R. 27 W., Decatur	NW sec. 35, T. 3 S., R. 27 W., Decatur	SW sec. 23, T. 4 S., R. 27 W., Decatur	SW sec. 26, T. 4 S., R. 27 W., Decatur	SW sec. 7, T. 5 S., R. 27 W., Decatur
Vertigo milium (Gould)
Vertigo tridentata Wolf
Carychium exiguum (Say)
Deroceras laeve (Müller)
Helicodiscus singleyanus (Pilsbry)
Vertigo gouldi paradoxa Sterki
Helicodiscus parallelus (Say)
Euconulus fulvus (Müller)
Hawaiia minuscula (Binney)
Pupilla muscorum (Linne)
Pupilla blandi Morse
Vallonia gracilicosta Reinhardt
Succinea avara Say
Lymnaea parva Lea

Molluscan species	Faunal localities
	NE sec. 1, T. 3 S., R. 28 W., Decatur	NW sec. 23, T. 5 S., R. 28 W., Decatur	NE sec. 14, T. 5 S., R. 29 W., Decatur	SE sec. 6, T. 2 S., R. 20 E., Doniphan	NE sec. 8, T. 1 S., R. 19 E., Doniphan	SW sec. 29, T. 15 S., R. 18 W., Ellis	SW sec. 18, T. 14 S., R. 19 W., Ellis	SW sec. 24, T 21 S., R. 29 W., Finney	NE sec. 34, T. 22 S., R. 30 W., Finney	SE sec. 4, T. 24 S., R. 32 W., Finney	SW sec. 9, T. 24 S., R. 32 W., Finney	NW sec. 16, T. 29 S., R. 24 W., Ford	NE sec. 2, T. 27 S., R. 22 W., Ford	NE sec. 35, T. 15 S., R. 27 W., Gove
Vertigo milium (Gould)
Vertigo tridentata Wolf
Carychium exiguum (Say)
Deroceras laeve (Müller)
Helicodiscus singleyanus (Pilsbry)
Vertigo gouldi paradoxa Sterki
Helicodiscus parallelus (Say)
Euconulus fulvus (Müller)
Hawaiia minuscula (Binney)
Pupilla muscorum (Linne)
Pupilla blandi Morse
Vallonia gracilicosta Reinhardt
Succinea avara Say
Lymnaea parva Lea

Molluscan species	Faunal localities
	SW sec. 36, T. 14 S., R. 29 W., Gove	SW sec. 23, T. 9 S., R. 21 W., Graham	NE sec. 28, T. 9 S., R. 22 W., Graham	SE sec. 28, T. 27 S., R. 35 W., Grant	*NE sec. 1, T. 25 S., R. 29 W., Gray	NW sec. 9, T. 16 S., R. 40 W., Greeley	*NW sec. 19, T. 21 S., R. 40 W., Hamilton	SE sec. 12, T. 25 S., R. 41 W., Hamilton	SW sec. 36, T. 25 S., R. 41 W., Hamilton	SE sec. 35, T. 35 S., R. 8 W., Harper	NW sec. 3, T. 28 S., R. 32 W., Haskell	NE sec. 22, T. 30 S., R. 34 W., Haskell	NE sec. 27, T. 23 S., R. 22 W., Hodgeman	NW sec. 26, T. 23 S., R. 25 W., Hodgeman
Vertigo milium (Gould)
Vertigo tridentata Wolf
Carychium exiguum (Say)
Deroceras laeve (Müller)
Helicodiscus singleyanus (Pilsbry)
Vertigo gouldi paradoxa Sterki
Helicodiscus parallelus (Say)
Euconulus fulvus (Müller)
Hawaiia minuscula (Binney)
Pupilla muscorum (Linne)
Pupilla blandi Morse
Vallonia gracilicosta Reinhardt
Succinea avara Say
Lymnaea parva Lea

Molluscan species	Faunal localities
	NE sec. 4, T. 1 S., R. 7 W., Jewell	SW sec. 19, T. 5 S., R. 8 W., Jewell	*NW sec. 31, T. 23 S., R. 38 W., Kearny	NW sec. 3, T. 28 S., R. 9 W., Kingman	SW sec. 18, T. 16 S., R. 28 W., Lane	NW sec. 7, T. 20 S., R. 28 W., Lane	SE sec. 29, T. 20 S., R. 28 W., Lane	SW sec. 2, T. 16 S., R. 29 W., Lane	NW sec. 3, T. 16 S., R. 29 W., Lane	NE sec. 15, T. 16 S., R. 29 W., Lane	SE sec. 15, T. 16 S., R. 30 W, Lane	*NE sec. 17, T. 17 S., R. 30 W., Lane	SE sec. 27, T. 11 S., R. 32 W., Logan	NW sec. 13, T. 12 S., R. 32 W., Logan
Vertigo milium (Gould)
Vertigo tridentata Wolf
Carychium exiguum (Say)
Deroceras laeve (Müller)
Helicodiscus singleyanus (Pilsbry)
Vertigo gouldi paradoxa Sterki
Helicodiscus parallelus (Say)
Euconulus fulvus (Müller)
Hawaiia minuscula (Binney)
Pupilla muscorum (Linne)
Pupilla blandi Morse
Vallonia gracilicosta Reinhardt
Succinea avara Say
Lymnaea parva Lea

Molluscan species	Faunal localities
	SE sec. 3, T. 14 S., R. 32 W., Logan	NW sec. 27, T. 15 S., R. 32 W., Logan	NE sec. 2, T. 14 S., R. 35 W., Logan	NE sec. 9, T. 15 S., R. 35 W., Logan	SE sec. 3, T. 11 S., R. 26 W., Logan	NE sec. 32, T. 12 S., R. 37 W., Logan	NE sec. 8, T. 33 S., R. 27 W., Meade	NE sec. 11, T. 30 S., R. 28 W., Meade	SW sec. 30, T. 31 S., R. 28 W., Meade	NW sec. 6, T. 30 S., R. 30 W., Meade	NW sec. 28, T. 8 S., R. 8 W., Mitchell	NW sec. 10, T. 16 S., R. 22 W., Ness	NE sec. 16, T. 16 S., R. 22 W., Ness	NE sec. 29, T. 16 S., R. 24 W., Ness
Vertigo milium (Gould)
Vertigo tridentata Wolf
Carychium exiguum (Say)
Deroceras laeve (Müller)
Helicodiscus singleyanus (Pilsbry)
Vertigo gouldi paradoxa Sterki
Helicodiscus parallelus (Say)
Euconulus fulvus (Müller)
Hawaiia minuscula (Binney)
Pupilla muscorum (Linne)
Pupilla blandi Morse
Vallonia gracilicosta Reinhardt
Succinea avara Say
Lymnaea parva Lea

Molluscan species	Faunal localities
	NW sec. 26, T. 2 S., R. 23 W., Norton	NW sec. 11, T. 3 S., R. 23 W., Norton	NE sec. 10, T. 4 S., R. 23 W., Norton	SE sec. 27, T. 4 S., R. 23 W., Norton	SE sec. 13, T. 1 S., R. 24 W., Norton	NE sec. 7, T. 5 S., R. 24 W., Norton	SE sec. 5, T. 2 S., R. 17 W., Phillips	NW sec. 23, T. 2 S., R. 18 W., Phillips	NE sec. 25, T. 1 S., R. 20 W., Phillips	NE sec. 2, T. 3 S., R. 31 W., Rawlins	NW sec. 8, T. 5 S., R. 31 W., Rawlins	SW sec. 2, T. 3 S., R. 33 W.,, Rawlins	NE sec. 9, T. 3 S., R. 33 W., Rawlins	NW sec. 20, T. 4 S., R. 33 W., Rawlins
Vertigo milium (Gould)
Vertigo tridentata Wolf
Carychium exiguum (Say)
Deroceras laeve (Müller)
Helicodiscus singleyanus (Pilsbry)
Vertigo gouldi paradoxa Sterki
Helicodiscus parallelus (Say)
Euconulus fulvus (Müller)
Hawaiia minuscula (Binney)
Pupilla muscorum (Linne)
Pupilla blandi Morse
Vallonia gracilicosta Reinhardt
Succinea avara Say
Lymnaea parva Lea

Molluscan species	Faunal localities
	NE sec. 8, T. 3 S., R. 34 W., Rawlins	NE sec. 29, T. 3 S., R. 36 W., Rawlins	NW sec. 5, T. 3 S., R. 4 W., Republic	SE sec. 7, T. 10 S., R. 16 W., Rooks	SW sec. 30, T. 9 S., R. 19 W., Rooks	SW sec. 28, T. 17 S., R. 19 W, Rush	SE sec. 17, T. 18 S., R. 31 W., Scott	SE sec. 6, T. 17 S., R. 32 W., Scott	*SW sec. 31, T. 20 S., R. 34 W., Scott	SW sec. 15, T. 6 S., R. 28 W., Sheridan	SW sec. 3, T. 7 S., R. 28 W., Sheridan	SE sec. 28, T. 7 S., R. 28 W., Sheridan	NW sec. 34, T. 8 S., R. 28 W., Sheridan	SW sec. 10, T. 9 S., R. 28 W., Sheridan
Vertigo milium (Gould)
Vertigo tridentata Wolf
Carychium exiguum (Say)
Deroceras laeve (Müller)
Helicodiscus singleyanus (Pilsbry)
Vertigo gouldi paradoxa Sterki
Helicodiscus parallelus (Say)
Euconulus fulvus (Müller)
Hawaiia minuscula (Binney)
Pupilla muscorum (Linne)
Pupilla blandi Morse
Vallonia gracilicosta Reinhardt
Succinea avara Say
Lymnaea parva Lea

Molluscan species	Faunal localities
	NE sec. 33, T. 10 S., R. 28 W., Sheridan	NW sec. 19, T. 8 S., R. 29 W., Sheridan	NE sec. 13, T. 6 S., R. 30 W., Sheridan	NW sec. 14, T. 6 S., R. 30 W., Sheridan	NW sec. 15, T. 6 S., R. 30 W., Sheridan	NW sec. 31, T. 8 S., R. 30 W., Sheridan	SE sec. 34, T. 10 S., R. 37 W., Sherman	SW sec. 26, T. 10 S., R. 38 W., Sherman	NW sec. 32, T. 7 S., R. 39 W., Sherman	SW sec. 36, T. 6 S., R. 39 W., Sherman	SW sec. 20, T. 7 S., R. 40 W., Sherman	SE sec. 28, T. 1 S., R. 13 W., Smith	SW sec. 11, T. 27 S., R. 39 W., Stanton	NE sec. 2, T. 29 S., R. 40 W., Stanton
Vertigo milium (Gould)
Vertigo tridentata Wolf
Carychium exiguum (Say)
Deroceras laeve (Müller)
Helicodiscus singleyanus (Pilsbry)
Vertigo gouldi paradoxa Sterki
Helicodiscus parallelus (Say)
Euconulus fulvus (Müller)
Hawaiia minuscula (Binney)
Pupilla muscorum (Linne)
Pupilla blandi Morse
Vallonia gracilicosta Reinhardt
Succinea avara Say
Lymnaea parva Lea

Molluscan species	Faunal localities
	NW sec. 12, T. 28 S., R. 41 W., Stanton	SE sec. 25, T. 29 S., R. 41 W., Stanton	SE sec. 21, T. 7 S., R. 31 W., Thomas	NE sec. 27, T. 7 S., R. 31 W., Thomas	NW sec. 10, T. 8 S., R. 32 W., Thomas	NE sec. 17, T. 8 S., R. 32 W., Thomas	NW sec. 31, T. 7 S., R. 33 W., Thomas	NW sec. 18, T. 9 S., R. 33 W., Thomas	SE sec. 27, T. 10 S., R. 33 W., Thomas	NW sec. 8, T. 8 S., R. 35 W., Thomas	SW sec. 8, T. 8 S., R. 35 W., Thomas	SW sec. 32, T. 7 S., R. 36 W., Thomas	SW sec. 7, T. 8 S., R. 36 W., Thomas	SW sec. 19, T. 8 S., R. 36 W., Thomas
Vertigo milium (Gould)
Vertigo tridentata Wolf
Carychium exiguum (Say)
Deroceras laeve (Müller)
Helicodiscus singleyanus (Pilsbry)
Vertigo gouldi paradoxa Sterki
Helicodiscus parallelus (Say)
Euconulus fulvus (Müller)
Hawaiia minuscula (Binney)
Pupilla muscorum (Linne)
Pupilla blandi Morse
Vallonia gracilicosta Reinhardt
Succinea avara Say
Lymnaea parva Lea

Molluscan species	Faunal localities
	NW sec. 3, T. 11 S., R. 23 W., Trego	SW sec. 5, T. 12 S., R. 24 W., Trego	NW sec. 26, T. 15 S., R. 38 W., Wallace	SW sec. 35, T. 11 S., R. 40 W., Wallace	SW sec. 23, T. 12 S., R. 40 W., Wallace	NW sec. 1, T. 15 S., R. 40 W., Wallace	*SE sec. 35, T. 20 S., R. 35 W., Wichita	SW sec. 12, T. 17 S., R. 37 W., Wichita	SE sec. 1, T. 19 S., R. 37 W., Wichita	NE sec. 12, T. 19 S., R. 37 W., Wichita	SE sec. 32, T. 16 S., R. 38 W., Wichita
Vertigo milium (Gould)
Vertigo tridentata Wolf
Carychium exiguum (Say)
Deroceras laeve (Müller)
Helicodiscus singleyanus (Pilsbry)
Vertigo gouldi paradoxa Sterki
Helicodiscus parallelus (Say)
Euconulus fulvus (Müller)
Hawaiia minuscula (Binney)
Pupilla muscorum (Linne)
Pupilla blandi Morse
Vallonia gracilicosta Reinhardt
Succinea avara Say
Lymnaea parva Lea

Plate 17--A representative assemblage of mollusks from pre-Bradyan Wisconsinan deposits in Kansas. All figures enlarged approximately 5 times natural size. An Acrobat PDF version of this plate is available that shows more detail.

Species represented by figures b, c, l, m, o, t, u, and z characterize the faunal assemblage of the Iowan faunal zone. All but those represented by figures u and z may also appear in the Tazewellian faunal zone, but species indicated by figures a, d, e, g, h, i, j, s, w, y, aa, and bb do not occur below the transitional zone between the Iowan and Tazewellian faunal zones, and may be thought of as characterizing the Tazewellian faunal assemblage.

a--Gastrocopta armifera (Say) b--Pupilla muscorum (Linne) c--Pupilla blandi Morse d--Columella alticola (Ingersoll) e--Vertigo gouldi paradoxa Sterki f--Vertigo tridentata Wolf g--Vertigo modesta (Say) h--Vertigo gouldi coloradensis (Cockerell) i--Vertigo milium (Gould) j--Gastrocopta holzingeri (Sterki) k--Euconulus fulvus (Müller) l--Helicodiscus parallelus (Say) m--Hawaiia minuscula (Binney) n--Helicodiscus singleyanus (Pilsbry) o--Vallonia gracilicosta Reinhardt p--Discus shimeki (Pilsbry) q--Discus cronkhitei (Newcomb) r--Carychium exiguum (Say) s--Striatura milium (Morse) t--Deroceras laeve (Müller) u--Succinea avara Say v--Zonitoides arboreus (Say) w--Cionella lubrica (Müller) x--Retinella electrina (Gould) y--Succinea grosvenori Lea z--Lymnaea parva Lea aa--Hendersonia occulta (Say) bb--Succinea ovalis Say

The great majority of the 137 pre-Bradyan Wisconsinan faunal localities discussed here are situated in deposits of loess which in Kansas classification is included in the Peoria silt member of the Sanborn formation. The faunas from terraces of equivalent age have not been studied until recently, and although these studies are incomplete, the molluscan assemblages from terraces have provided a means of determining age and correlation of sediments in local areas where other stratigraphic criteria are lacking or unsatisfactory. For example, in Harper County (SE sec. 35, T. 35 S., R. 8 W.) the principal terrace along a branch of Plum Creek is determined to be pre-Bradyan Wisconsinan in age from the characteristics of the contained molluscan assemblage, which includes Pupilla muscorum, P. blandi, Vallonia gracilicosta, Euconulus fulvus, and Succinea avara. The first three of these species are extinct in the State, and Euconulus fulvus is now limited in its range in this region to extreme eastern Kansas. By contrast, a post-Bradyan terrace, channeled into these pre-Bradyan sediments, contains Vallonia parvula, Hawaiia minuscula, Physa anatina, and Succinea avara, all of which are living near the exposure. These data make it possible to date, trace, and correlate terraces throughout the drainage system in this area, and incidentally to date the pediment slope cut in Permian shales which is graded to this terrace complex. Exposures in Clark County (NE sec. 26, T. 33 S., R. 24 W.), Barber County (SW sec. 20, T. 33 S., R. 11 W.), and elsewhere have yielded molluscan faunas which are equally useful for purposes of stratigraphic correlation. The stratigraphic position of the Peoria silt is discussed elsewhere in this report; it has been previously reviewed and discussed at length by Frye and A. B. Leonard (1951) and by A. B. Leonard (1951), and its early Wisconsinan age firmly established.

The 28 species of fossil mollusks which comprise the assemblage associated with pre-Bradyan Wisconsinan deposits are almost without exception gastropods of terrestrial habit. Detailed studies of the early Wisconsinan faunal assemblage have made it possible to divide the massive Peoria silt into three well-characterized zones, which are equivalent to recognized stratigraphic units in the glaciated part of the Mississippi Valley. These faunal zones are here referred to as (1) the basal or Farmdale zone, (2) the lower or Iowan zone, and (3) the upper or Tazewellian faunal zone.

The basal or Farmdale faunal zone--The Farmdale faunal zone of the Peoria ranges from a few inches to more than 6 feet in thickness, and it consists of loess which has been oxidized to a greater or lesser degree and from which the greater part of the free carbonates have been leached. The greatest degree of leaching occurs near the base of the zone, directly above the A horizon of the Sangamon soil, upon which the Peoria normally rests. Usually no effervescence can be elicited from the silts here by the use of dilute acid, and the color, due to various degrees of oxidation of iron salts, is some shade of pink or red, darkened somewhat with humic stains. All these effects disappear by imperceptible degrees upward into calcareous, unoxidized, and fossiliferous loess. The basal part of this zone is typically devoid of fossil shells, but etched fragments may appear in the upper part of the Farmdale zone. It may be inferred, since vertebrate fossils occur in this material (Condra, Reed, and Gordon, 1947) that gastropods also lived during the interval when this silt was being deposited, and that the shells were subsequently destroyed by weathering processes. The molluscan fauna may have been sparse, however, since the fauna in the lower part of the Iowan zone above it is not a rich one.

In some places along the bluffs of Platte and Missouri Rivers in Nebraska and Iowa, the Farmdale zone silts are thicker than they are anywhere in Kansas, and it is obvious that they were there deposited more rapidly, for at several such places the loess is calcareous and fossiliferous below an incipient soil. Wherever a molluscan fauna has been observed in the Farmdale zone, it has been found to be essentially similar to the molluscan assemblage in the Iowan zone.

The lower or Iowan faunal zone--The lower molluscan faunal assemblage consists of 14 species of small size and terrestrial habit, two of which are restricted to this zone, while the remainder also appear in the upper or Tazewellian zone. The presence of these restricted species, however, and the universal absence of at least 14 species known to occur only in the Tazewellian zone make the Iowan faunal zone distinctive enough for practical purposes and readily discernible on outcrops of the loess.

Among the Iowan zone species, Vallonia gracilicosta, Pupilla muscorum, P. blandi, and Vertigo gouldi paradoxa are presently absent from Kansas; the remainder are restricted to favorable situations in the eastern part of the State, except Succinea avara, Hawaiia minuscula, and Deroceras laeve, which are widely distributed over the State, even on the semi-arid High Plains. Strangely, Pupoides albilabris, which today lives on the western prairies, has not been found in the Peoria loess.

The most widespread species in the Iowan faunal zone are Vallonia gracilicosta, Succinea avara, Pupilla muscorum, P. blandi, and Hawaiia minuscula, which occur at almost every locality studied, including those in southwestern Kansas, where conditions then as now, seem to have been unfavorable for terrestrial gastropods. Since all of these but Hawaiia minuscula and Succinea avara, are extinct in the State, the Iowan faunal zone is readily recognizable in southwestern Kansas where the loess is thin and the molluscan fauna sparse.

Above the Farmdale zone, the Iowan zone assemblage increases progressively upward, both in numbers of species and in individuals. For example, in an exposure in Decatur County (NE sec. 1, T. 3 S., R. 28 W.) the lower 5 feet of a 25-foot exposure of Peoria loess contains no shells (Farmdale zone); 7 feet above the base, 139 shells grouped in four species were recovered from a cubic foot of loess, while 13 feet above the base, a cubic foot of loess yielded 753 shells belonging to six species (Iowan zone). At this same locality, the transitional area between the Iowan and Tazewellian zones contained 5,079 shells per cubic foot, belonging to 11 species; the Tazewellian zone fauna was comprised of 14 species, numbering 1,578 shells per cubic foot of loess.

There is in the Peoria loess no definite faunal unconformity between the Iowan and Tazewellian faunal zones, but the two are associated through a transitional faunal zone where the molluscan fauna gradually changes in character. Discus cronkhitei, followed by D. shimeki are the first of the Tazewellian zone species to appear in the transitional zone, usually in association with Succinea avara, which is otherwise restricted to the Iowan zone. Succinea grosvenori and S. ovalis appear higher in the transitional zone, usually after the disappearance of Succinea avara, but this is not invariable. The order of appearance of other Tazewellian zone species seems to follow no definite pattern, and perhaps reflects local conditions more than anything else.

The upper or Tazewellian faunal zone--The upper or Tazewellian faunal zone assemblage comprises 26 species, of which 14 do not occur in the Iowan zone. Four species, Columella alticola, Striatura milium, Vertigo gouldi coloradensis, and Discus shimeki, which are restricted to this zone, do not now live in the Great Plains region. Such species as Discus cronkhitei, Pupilla muscorum, P. blandi, Hendersonia occulta, Vallonia gracilicosta, and Vertigo modesta are likewise extinct in the State, but they are known from earlier Pleistocene horizons in Kansas. In all, 11 of the 26 species in the Tazewellian faunal assemblage are absent from the living molluscan fauna of the State, making the Tazewellian zone assemblage easily recognizable in the field. The remaining species are not generally present over the State in the living fauna, but are more or less limited to local favorable habitats.

It is clear that ecological conditions in the State in pre-Bradyan times were more favorable to mollusks than at present. Even the Iowan zone assemblage, sparse in the lower part of the Peoria loess, is more varied than Recent faunas in the same area. It is likely that population density was also greater than now, judging from samples of loess which yield as many as 5,000 shells per cubic foot, but since the rate of deposition is not known, this figure may be somewhat misleading.

A reasonable amount of rainfall, at least more than present average amounts, and a floral cover somewhat denser than that on the Great Plains today may be inferred from the molluscan faunas in pre-Bradyan sediments. The climate may also have been somewhat cooler than that which characterizes the Great Plains today. Two kinds of faunal evidence support these views: (1) the pre-Bradyan species now extinct in Kansas presently live at higher altitudes or latitudes (A. B. Leonard, 1952, figs. 7-15), and (2) Bulimulus dealbatus, a southern gastropod adapted to survive long periods of drouth which has reached the northern border of Kansas in Recent time, is absent in the Wisconsinan faunal assemblages.

The Iowan faunal zone has been traced from northeastern Kansas through central, western, and southwestern Kansas. The same faunal assemblage is known to occur in northwestern Oklahoma in Dewey County, in northern Texas in Sherman County, and in Frontier and Lincoln counties, Nebraska.

The Tazewellian faunal zone is much more restricted in its distribution in Kansas but is known from southern and central Nebraska, western Iowa, and central Illinois. This assemblage can be traced across the northern border of Kansas except for Cheyenne County in the extreme northwestern part of the State, and southward to Rush, Lane, Gove, and Logan counties. It might be concluded from this faunal evidence that these places mark the approximate southern extent of the influence of Tazewellian ice upon loess deposition in Kansas. However, since the loess of southwestern Kansas is thin, nearly half of its thickness being involved in the weathering of the soil profile in its top, it is possible that loess blown from valley trains produced by the melting of Tazewellian ice was carried even farther south, faunal evidence of it having been lost by the weathering of the shells. Further evidence of this possibility is seen in deposits in a dissected sink (NE sec. 8, T. 33 S., R. 27 W., Meade County), where the molluscan faunule is known to include Discus cronkhitei, Succinea grosvenori, and other elements of the Tazewellian assemblage.

Post-Bradyan molluscan assemblages--Sixteen species comprise the post-Bradyan Wisconsinan molluscan assemblage, but nearly half of these are limited to Bignell loess in the northeastern part of the State in Doniphan County (Fig. 10). The greater part of the 27 reported faunal localities consists of Bignell loess of local occurrence in many western counties, and work has only begun on the molluscan faunules in terraces of equivalent age. Except at the Iowa Point section described by Frye and A. B. Leonard (1949) the molluscan fauna in most post-Bradyan sediment is sparse, both in species and in individuals. No more than four or five species are typical at any one locality, and frequently a collection at any one exposure may not contain more than a dozen shells, and often less.

Figure 10--Occurrence of fossil mollusks in post-Bradyan Wisconsinan deposits at 27 localities in Kansas. An Acrobat PDF version of this figure is available.

Molluscan species	Faunal localities
	SW sec. 20, T. 33 S., R. 11 W., Barber	SW sec. 30, T. 3 S., R. 38 W., Cheyenne	NW sec. 30, T. 33 S., R. 21 W., Clark	NW sec. 6, T. 30 S., R. 23 W., Clark	NE sec. 26, T. 33 S., R. 24 W., Clark	NE sec, 28, T. 4 S., R. 26 W., Decatur	SW sec. 23, T. 4 S., R, 27 W., Decatur	NE sec. 26, T. 4 S., R. 27 W., Decatur	NE sec. 8, T. 1 S., R. 19 E., Doniphan	SE sec. 6, T. 2 S,, R, 20 E., Doniphan	SE sec. 17, T. 2 S., R. 20 E., Doniphan	NE sec. 2, T. 27 S., R. 22 W., Ford	NW sec. 9, T. 16 S., R. 40 W., Greeley	SE sec. 35, T. 35 S., R. 8 W., Harper
Anguispira alternata (Say)
Gastrocopta armifera (Say)
Hendersonia occulta (Say)
Stenotrema Ieai aliceai (Pilsbry)
Succinea grosvenori Lea
Succinea ovalis Say
Triodopsis multilineata (Say)
Vallonia parvula Sterki
Hawaiia minuscula (Binney)
Helicodiscus parallelus (Say)
Physa anatina Lea
Succinea avara Say
Helisoma trivolvis (Say)
Lymnaea sp.
Pisidium sp.

Faunal localities													Molluscan species
NE sec. 27, T. 23 S., R. 22 W,, Hodgeman	SW sec. 1, T. 15 S., R. 32 W., Logan	NE sec. 32, T. 12 S., R. 37 W,, Logon	SE sec. 9, T. 21 S., R. 5 W., McPherson	NE sec. 29, T. 16 S., R. 24 W., Ness	SW sec. 23, T. 2 S., R. 23 W., Norton	NW sec, 26, T, 2 S., R. 23 W., Norton	SE sec. 27, T. 4 S., R. 23 W., Norton	SW sec, 2, T. 3 S,, R. 33 W., Rawlins	SE sec. 6, T. 17 S., R. 32 W., Scott	NW sec. 30, T. 4 S., R. 14 W., Smith	NE sec. 7, T. 8 S., R. 35 W,, Thomas	NW sec. 7, T. 8 S., R. 35 W., Thomas
													Anguispira alternata (Say)
													Gastrocopta armifera (Say)
													Hendersonia occulta (Say)
													Stenotrema Ieai aliceai (Pilsbry)
													Succinea grosvenori Lea
													Succinea ovalis Say
													Triodopsis multilineata (Say)
													Vallonia parvula Sterki
													Hawaiia minuscula (Binney)
													Helicodiscus parallelus (Say)
													Physa anatina Lea
													Succinea avara Say
													Helisoma trivolvis (Say)
													Lymnaea sp.
													Pisidium sp.

Plate 18--A representative assemblage of mollusks from post-Bradyan Wisconsinan deposits in Kansas. All figures enlarged approximately 5 times natural size. An Acrobat PDF version of this plate is available that shows more detail.

Species represented by figures c, f, g, i, and l are found in Kansas only in extreme northeastern Kansas in Bignell loess near the Missouri River. Those represented by figures a, b, d, e, and h comprise the characteristic sparse fauna found in post-Bradyan deposits in the Great Plains region.
Gastrocopta armifera (Say) Hawaiia minuscula (Binney) Vallonia gracilicosta Reinhardt Vallonia parvula Sterki Helicodiscus parallelus (Say) Hendersonia occulta (Say) Stenotrema leai aliciae Pilsbry Succinea avara Say Anguispira alternata (Say) Physa anatina Lea Helisoma trivolvis lentum (Say) Tridopsis multilineata (Say)

The great majority of the post-Bradyan mollusks are terrestrial species known to be capable of surviving long periods of aridity. Unlike the pre-Bradyan Wisconsinan faunal assemblage, most post-Bradyan species are now found living in the State, and often near the outcrop from which fossil shells are taken. Everywhere it has been studied, the post-Bradyan fauna bears a close resemblance to the local modern molluscan fauna. Thus, in the timbered loess hills in northeastern Kansas near Missouri River, the fauna is predominantly characteristic of the assemblage of species found today in the local forested areas, while on the Great Plains, the fauna of post-Bradyan loess and terraces of equivalent age is identical with the sparse fauna of minute gastropods which occurs there at the present time. The only exception to this observation is the occurrence of Hendersonia occulta in Bignell loess in extreme northeastern Kansas; this gastropod is no longer living in the State.

The paucity of the post-Bradyan fauna except at the Iowa Point exposures does not permit the faunal zonation of the Bignell loess or terraces of equivalent age. All that can be said of the age of the faunal assemblage is that it includes some segment, whether large or small is not known, of Caryan-Mankatoan time.

The final stage in the progressive dessication of the Great Plains which seems to have begun after Yarmouthian time and to have culminated in the semi-arid climate of modern time, took place during or after the Bradyan interglacial interval. The great populations of Discus, Pupilla, Vertigo, and Vallonia gracilicosta, together with less widespread populations of Hendersonia occulta, Columella alticola, Striatura milium, Euconulus fulvus, and several other species, completely vanished from the Great Plains at the close of Tazewellian or during Bradyan time. As we interpret conditions from the molluscan faunal assemblages the vegetative cover became reduced at this time or shortly thereafter, the climate became somewhat warmer, and it is probable that a biologically severe climate, characterized by extremes of aridity and high temperatures in summer, followed by cold, dry winters, began after Bradyan time. Only a few species of gastropods can endure the rigors of the existing Great Plains environment, and because molluscan assemblages in post-Bradyan sediments are nearly everywhere identical with the local modern fauna, the conclusion is inevitable that the environment at the time of deposition of post-Bradyan sediments was not unlike that at the present time.

Figure 11--Check list of fossil mollusks arranged according to their stratigraphic occurrence in the Pleistocene deposits of Kansas.

Molluscan species	Blanco	Sappa	Crete- Loveland	Peoria, lower	Peoria, upper	Bignell
Anguispira alternata
Stenotrema leai aliciae
Triodopsis albolabris
Vallonia pulchella
Gastrocopta armifera
Hendersonia occulta
Succinea grosvenori
Succinea ovalis
Hawaiia minuscula
Helicodiscus parallelus
Gastrocopta holzingeri
Columella alticola
Striatura milium
Vertigo gouldi coloradensis
Vertigo modesta
Carychium exiguum
Cionella lubrica
Pupilla blandi
Discus cronkhitei
Discus shimeki
Vertigo tridentata
Euconulus fulvus
Helicodiscus singleyanus
Vertigo gouldi paradoxa
Vertigo milium
Deroceras laeve
Pupilla muscorum
Retinella electrina
Zonitoides arboreus
Vallonia gracilicosta
Succinea avara
Lymnaea parva
Helisoma trivolvis
Physa anatina
Pupoides albilabris
Strobilops labyrinthica
Carychium perexiguum
Gastrocopta cristata
Gyraulus similaris
Helisoma antrosa
Sphaerium solidulum
Gastrocopta tappaniana
Strobilops sparsicosta
Vertigo ovata
Ferrissia parallela
Gastrocopta contracta
Gastrocopta falcis
Gastrocopta proarmifera
Gastrocopta procera
Amnicola limosa parva
Gastrocopta tridentata
Gyraulus labiatus
Gyraulus pattersoni
Helisoma wisconsinensis
Lymnaea bulimoides
Lymnaea caperata
Lymnaea palustris
Lymnaea reflexa
Polygyra texasiana
Menetus pearlettei
Oxyloma navarrei
Physa elliptica
Pisidium compressum
Planorbula nebraskensis
Planorbula vulcanata vulcanata
Planorbula vulcanata occidentalis
Pomatiopsis cincinnatiensis
Promenetus umbilicatellus
Pupilla muscorum sinistra
Stenotrema leai leai
Aplexa hypnorum
Valvata lewisi
Valvata tricarinata
Deroceras aenigma
Amnicola crybetes
Ferrissia rivularis
Gastrocopta paracristata
Gastrocopta rexroadensis
Gyraulus enaulus
Lymnaea diminuta
Lymnaea humilis modicella
Lymnaea macella
Lymnaea perexilis
Lymnaea turritella
Menetus kansasensis
Polygyra mooreana
Promenetus blancoensis
Vertigo hibbardi

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Kansas Geological Survey, Pleistocene Geology
Comments to webadmin@kgs.ku.edu
Web version August 2005. Original publication date Nov. 1952.
URL=http://www.kgs.ku.edu/Publications/Bulletins/99/06_paleo2.html