THE NAUTILUS. 61 



ANIMAL LIFE IN LOESS DEPOSITS NEAR ALTON, ILLINOIS, WITH 



DESCRIPTIONS OF TWO NEW VARIETIES OF LAND SHELLS 



FROM THE SAME DEPOSITS.* 



BY FRANK COLLINS BAKER. 



Many years ago Worthen (Geol. 111., Vol. I, p. 315, 1866) 

 reported the remains of a mastodon from near the City of Alton, 

 from a deposit near the bottom of the loess, about thirty feet 

 beneath the surface, where it was separated from the limestone 

 by two to three feet of local drift. It was also stated by Worthen 

 that the loess above the drift contained land and fresh-water 

 shells. The only other reference to this deposit or its animal 

 life, as far as known to the writer, is by Wm. McAdams (Proc. 

 A. A. A. S., Vol. XXXII, p. 268, 1883). Recently Dr. M. M. 

 Leighton, of the Department of Geology, University of Illinois, 

 and also connected with the State Geological Survey, visited 

 Alton and vicinity, and made a careful study of the Quaternary 

 deposits, to determine the stratographic horizon of the concre- 

 tions with which the mammalian remains are associated. Dur- 

 ing his study of the loess deposits he collected from them at 

 different specified levels the remains of molluscan life, and has 

 given me the following statement concerning the character and 

 age of these deposits. 



"The bluffs just northwest of Alton have a height of from 

 125 to 175 feet above the Mississippi River. Several quarries 

 are located along the bluffs, which offer fine sections of the Mis- 

 sissippian limestone, some 50 to 100 feet thick, overlain by thin 

 drift and thick loess deposits. 



"The loess is separable into two deposits, a lower pink loess 

 and an upper buff loess. The pink loess lies unconformably 

 on the glacial till below, the till showing strong evidence of a 

 long interval of weathering before the deposition of the pink 

 loess. The till may well be as old as the Kansan, in which 

 case the pink loess is probably Sangamon; if the till is Illinoian 

 the pink loess cannot be older than late Sangamon, and may be 



* Contribution from the Museum of Natural History, University of Illinois, 

 No. 14. 



