346 LIFE OF THE PLEISTOCENE 



penetrated in wells or otherwise located occur beneath considerable thicknesses 

 of this drift and probably represent an earlier stage of deglaciation. " 



It seems evident that the drift deposits outside the Wisconsin sheet in 

 Illinois should all be referred to the Illinoian invasion and hence most of the 

 vegetal and other remains below the Wisconsin till should probably be re- 

 ferred tp the Sangamon interval and are to be correlated with the old soils 

 overlying the Illinoian drift in central and Southern Illinois. The name Peor- 

 ian may be retained for soils overlying the Iowan drift in Iowa and for loess 

 overlying the Kansan loess in Iowa and Illinoian loess in Illinois and Indiana. 



III. The Iowan Loess 



It has been shown by Shimek and other Iowan geologists, that the loess is 

 divisible into several horizons, each horizon representing an interglacial inter- 

 val. 9 In Iowa, the lower, light bluish or post-Kansan loess is covered by a 

 yellowish loess which is thot to be post-Iowan in age. The yellowish loess is 

 likewise divisible, in certain parts of Iowa, into two deposits, representing the 

 Peorian and Sangamon intervals. These loesses are highly fossiliferous and, 

 according to Shimek, contain about the same species of mollusks. The post- 

 Iowan loess is widely distributed in Iowa. Theoretically there should be three 

 loesses overlying the Kansan drift, viz., 1, the post-Kansan (Yarmouth); 2, 

 the post-Illinoian (Sangamon); and 3, the post-Iowan (Peorian), each with 

 fossils. The post-Kansan in many places probably includes both the Yar- 

 mouth and Sangamon intervals, the Illinoian ice not being near enough, appar- 

 ently, to cause a break in the loess deposits. The same is true of the Sangamon 

 and Peorian loesses outside the influence of the Iowan ice sheet. A typical 

 western section of these deposits is exhibited near Carroll, Carroll County, in 

 the cut along the Chicago Great Western Railway northeast of the city. 10 



6. Wisconsin drift 1-5 feet 



5. Yellow loess (post-Iowan?) about 10 feet 



4. Interval marking presence of Iowan ice 



4. Bluish gray loess (post-Kansan) 5-6 feet 



3. Black, mucky, soil-like band (Yarmouth soil) 1 foot 



2. Heavy, reddish joint-clay (Loveland) • 1 foot 



1. Kansan drift x feet 



Both loesses are fossiliferous but the majority of lists of fossils do not dis- 

 criminate between the two deposits. 



Alden and Leighton, 10a after a recent exhaustive study of the Iowan loess, 

 reach the following conclusion: "The statement, therefore, seems sound, that 

 the main sheet of loess under consideration was deposited immediately follow- 



8 Shimek, Bull. Lab. Nat. Hist., Univ. Iowa, V, pp. 338-339; 364-368. 



10 Shimek, Iowa Geol. surv., XX, p. 390. 



!na An. Rep. Iowa Geol. Surv., XXVI, pp. 49-212. 



