166 THE ILLINOIS GLACIAL LOBE. 



niollusks have been reported from the loess, but closer investigation tends 

 to render doubtful their occurrence in unmodified loess. In other cases, 

 notably in the deposits near Freeport, from which collections have been 

 made by Hershev, the relation to the loess is not clearly determined and 

 the deposits may prove to be entirely independent of the loess deposition. 



Concerning the mammalian remains reported from the loess, it is neces- 

 sary to state that their relation to the loess deposition is, in most if not in 

 all cases, very vaguely determined. The remains of a mammoth, found 

 near Davenport, and reported by W. H. Pratt, 1 were apparently from near 

 the base of the loess and just above the Sangamon soil, which is there rep- 

 resented by a bed of peat and soil 3 feet in thickness. Possibly the remains 

 were derived from the Sangamon soil horizon and redeposited in the basal 

 portion of the loess. The remains of a deer are reported by Witter 2 to 

 have been found in the loess near Muscatine. A fine fragment of the jaw 

 of a mastodon is reported by Worthen 3 to have been found just above the 

 city of Alton, Illinois, beneath 30 feet of loess, and separated from the 

 underlying limestone by 2 or 3 feet of local drift. Worthen also reports 4 

 the occurrence of the remains of extinct mammalia in brown clays overly- 

 ing the limestones, as well as in the crevices of the limestone in the driftless 

 region of northwestern Illinois. Whether these are beneath or within the 

 loess deposit which covers that region has not been ascertained. 



As yet the molluscan fossils have been collected and specifically 

 identified in but a few localities within the region under discussion. Since 

 there is some variation from place to place, the identifications of each 

 locality are represented. Those in List 1, from Savanna, Illinois, repre- 

 sent the fauna in the southern portion of the Driftless Area. In addition 

 to these, Helicodiscus Uneatus Anth. has been found near Galena and Lim- 

 nophysa Jvwmilis Say has been-found on the heights east of Prairie du Chien. 

 These are thought by Salisbury to be in unmodified loess, and are separated 

 from a list of fossils found in the terraces of streams traversing the Driftless 

 Area. 5 



'Proe. Davenport Acad. Sci., Vol. I, 1876, pp. 96-99. Also Geol. of Iowa, by C. A. White, Vol. 

 I, 1870, p. 119. 



; Proc. Iowa Acad. Sci., Vol. I, 1880, p. 16. Also Eleventh Ami. Eept. U. S. Geol. Survey, 

 1890, p. 471. 



3 Geol. of Illinois, Vol. I, 1866, pp. 38 and 315. 



^Ibid., p. 39. 



5 Sixth Ann. Rept. U. S. Geol. Survey, pp. 285 and 286. 



