124 LIFE OF THE PLEISTOCENE 



Pleurocera subulare Vahata tricarinala 



Amnicola limosa " bicarinata 



cincinnatiensis (=sayana) Vivipara interlexta 



" emarginata( = Bythinella obhtsa) Campeloma siibsolidum 



" coar datum 

 Pulmonate species, mostly from stratum A 

 Polygyra multilineata Bifidaria penlodon 



" profunda Galba rcflexa 



" dausa " caper ata 



Vitrea kammonis " obrussa ( =desidiosa, of authors) 



" indentata " humilis modicella 



Zonitoides arborea Segmentina armigera 



" minuscula Planorbis trivolvis 



Succinea ovalis ( = obliqua) " parvus 



" avara Physa gyrina 



Bifidaria coniracta Ancylus rivularis 



The strata described by Tiffany 20 at Rock Usand evidently represent the 

 same period as the above deposits described by Shimek. "The locality is 

 situated at the western extremity of the arsenal grounds and the shells were 

 discovered in an excavation 300 feet long and 8 feet deep. Three feet from 

 the top (which is 18 feet above the highest level of the river) is a deposit of 

 shells, mostly Unios, with Campeloma subsolidum, and two species of Helix. 

 The shell bed is from 6 to 16 inches thick. Human remains were found in the 

 lower part of the shell bed, associated with antler of elk or deer and part of shin 

 boneofBison(P)." 



Shell beds referable to the same period (post- Wisconsin) as those described 

 by Shimek and Tiffany, are reported from the vicinity of Davenport, Iowa, 



Figure 3. Diagram of shell bed at head of Rock Island, o, Bed of limestone; b, shell 

 bed; c c, general surface; r, river (After Pratt, Prac. Daven. Acad. Sci., II, page 161, fig. 16). 



and Rock Island, Credit Island, Gilbert, Moline, and New Boston, Illinois. 

 These beds are from 1-1J^ to over 3 feet in thickness, and range in position 

 from just above high water mark to about 5 feet above high water. A section 

 at the head of Rock Island is diagrammatically pictured by Pratt in figure 3. 

 The shell beds lie immediately above the bed rock (limestone) and are covered 

 by deposits brought down by the river. Pratt 20a lists a number of fluviatile 

 mollusks but ascribes the shell beds to the agency of modern ice which he 

 believes has pushed them from the river bed to their present location. While 

 this agency does perform such feats with boulders and other objects, it is totally 



20 Proc. Daven. Acad. Sci., I, pp. 42-43. 



203 Proc. Davenport Acad. Sci., II, pp. 156-162. 





