THE ILLINOIAN ICE INVASION 297 



Stratified clay (Yarmouth) 6 feet 



Tough blue clay (Kansan) 20 " 



In Pike County a similar division of the loess occurs and Worthen reports 

 the mammoth and Castoroides from marl-like deposits, associated with land and 

 fresh water shells. 62 These are probably referable to the post-Illinoian interval. 



It is not always an easy matter to discriminate between these two loesses 

 in the matter of fossils when the author has failed to indicate the character 

 of the loess from which they came. Udden 63 lists nine species from Moline, 

 Rock Island County, which are probably referable to the Illinoian loess. These 

 are: 



Succinea avara Pyramidula cronkhitei anthonyi 



" luteola'* Sphyradium edentulum alticola 



" ovalls( = obliqua) Pupilla muscorum 



Helicina occulta Bifidaria pentodon 



Vallonia pidchella( = gracilicosta?) 



From Virginia, Cass County, 13 species are listed. 65 



Helicina orbicidata or occulta Polygyra clausa 



Succinea obliqua( = ovalis) " monodon 



Pyramidula cronkhitei anthonyi{ = striatella) " multilineata 



" alter nata " pennsylvanica 



Oreohelix iowensis (cited as Helix strigosa) Galba humilis modicella 

 Circinaria cancova 



Arionta exarata ( = Epiphragmophora) and Bui inns dealbatus are also cited, 

 but these species belong to a totally different part of the United States, and 

 are doubtless examples of erroneous identifications. Bulimus dealbatus may 

 be an erroneous name for Bulinus or Aplexa hypnorum, a species sometimes 

 occurring in the loess. 



Loess deposits as well as ancient soils occur in Vermilion County. The 

 old soils are believed to represent the Sangamon interval. 66 A pre-Wisconsin 

 loess also occurs near Danville beneath 15 feet of Wisconsin till. 67 It has been 

 disturbed by the Wisconsin ice and in many places has been incorporated with 

 the upper till. Before the advent of the later ice sheet, the deposit probably 

 included both post-Illinoian and post-Iowan loess, but these have been badly 

 mixed in most exposures and are now indistinguishable. Five small gastro- 

 pods, typical of the loess, were collected; wood identified as white cedar {Thuja 



12 Geol. Pike County, Geol. 111., IV, p. 36. 



83 Leverett, op. cit., pp. 170-171. 



M Succinea luteola is a distinctly southern species which has never been authentically 

 reported from the loess or from any deposits so far north. It might be Succinea grosvenori 

 which is a characteristic loess fossil. 



85 Leverett, Illinois Glacial Lobe, p. 171. 



" Leverett and Campbell, Danville Folio, pp. 4-5. 



" Wegemann, Univ. 111. Studies, III, no. 2. 



