8 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 486 



directly dated, and the fauna occurring below the Jules Soil is stratigraphically 

 framed by the date of the Jules Soil (about 16, 000 B.P.) and the older dates 

 (about 17,000 B.P.) obtained at the Burdick Branch and Collinsville Sections, 

 previously referred to. 



The molluscan faunas compiled on figure 3 comprise 17 genera and a 

 total of 22 species. All are typical terrestrial gastropods, except Lymnaea dalli 

 and L, parva, which belong to a family of aquatic pulmonates; however, these 

 two species tend to live out of the water on mud flats and dead vegetation, at 

 the water's edge, in contrast to the other members of the family Lymnaeidae, 

 which are typically aquatic in habit. Sucoinea (Catinella) sp., a member of a 

 family of terrestrial habitat preference, also prefers to live among or on vege- 

 tation in very wet situations. Derooeras laeve, a small slug, likewise prefers 

 wet environments, although it can tolerate habitats far from open water as long 

 as it can find some moisture. Basically, D. laeve is a species inhabiting wet 

 woodlands and low terraces along streams. 



At least seven of the species collected are no longer found living, at 

 least in Illinois: these include Columella altioola, now restricted to montane 

 habitats above 7,000 feet in altitude; Eendersonia oooulta, once widespread in 

 Illinois, but now restricted to relatively few localities along brushy creeks; 

 Pupilla musoorwn, like C. altioola, now restricted to higher elevations and/or 

 latitudes and cooler climates; Suocinea gelida, known only as a fossil; Sucoinea 

 pleistooenica , known only from late Wisconsinan loess; Vertigo alpestris 

 oughtoni, once common in Illinois, but now restricted to high latitudes; and 

 Vertigo hannai, known only as a Pleistocene fossil. The remaining species still 

 live in Illinois; in fact, the majority may be found in appropriate habitats within 

 the areas of this report. Anguispira altemata, Retinella eleetrina, Stenotrema 

 leaii, and Triodopsis multilineata are essentially woodland species; the others 

 frequent woodland borders or even prairie habitats. 



Cottonwood School South Faunal Assemblages. Although differences do 

 exist among the three faunal assemblages known from the loess at this locality, 

 they seem to reflect no more than minor fluctuations in the local environment 

 and/or limitations in the methods of collection. None of the variations among 

 the three faunal assemblages seems clearly related to their respective strati- 

 graphic position or relative age. Six of the species occur in all three of the 

 faunal assemblages, while five species occur in two faunal assemblages. 

 Three species occur in only one. 



It seems reasonable to interpret the local habitat as a well-watered up- 

 land savanna, varying between woodland and prairie with the passage of time 

 and fluctuations in climatic conditions. Indications are that the climate through 

 the interval 17,000-13,000 B.P. was generally cooler than the present one. 

 A fauna at approximately the same stratigraphic position and of equivalent age, 

 that indicates a comparable habitat, has been described (Leonard and Frye, 

 1960, locality no. 23) from Richland Loess above Tiskilwa Till along the east 

 side of the Illinois Valley in Tazewell County. 



Bunkum South Faunal Assemblages. The uppermost 2 1/2 feet of Peoria 

 Loess is leached and is in the modern solum. From the base of the solum down- 

 ward to 8 feet below the top, only a few fossil shells occur; and the upper 

 fauna described here was collected from a zone 8 to 12 feet below the top. The 

 lower fauna was collected from a somewhat more fossiliferous zone 14 to 22 feet 

 below the top. The upper sample yielded four molluscan species from a relatively 



