132 B. SHIMEK 



The modern fauna of the more or less exposed hills at Coun- 

 cil Bluffs is much poorer in species and in specimens than the 

 fossil fauna of the underlying loess, but every species thus far 

 discovered in the loess of Council Bluffs occurs more or less 

 abundantly (certainly as abundantly in some places as in any 

 part of that loess) living along the Missouri River, especially on 

 the western, more heavily timbered bluffs. All the species 

 above mentioned as not found in the surface collections have 

 been collected, by the writer, on the banks and hills along the 

 Missouri between Omaha, Neb., and Hamburg, Iowa, usually 

 not in very damp places, but living under the conditions which 

 prevail along those bluffs. Even Polygyra multiline ata is there 

 often found on high grounds, and then appears as a stunted 

 form like that which is common in the loess. 



The loess fauna of Council Bluffs is thus not only wholly 

 terrestrial, but, with the exceptions noted, is almost identical 

 with the modern upland fauna of the same region — and surely 

 no conditions of excessive moisture prevail in that region today. 

 Yet a recent writer, 1 referring to the loess of the Missouri region, 

 says: "In the Bluff loess more than nine tenths of the total 

 number of individuals belong to species that are found only in 

 unusually damp situations The species having an opti- 

 mum habitat that is not excessively moist have not been 

 observed to occur abundantly in the Bluff loess." 



Another interesting fact noticeable in the exposures of loess 

 at Council Bluffs is the occurrence of the great majority of the 

 fossils in a more or less distinct stratum which varies (so far as 

 observed) in altitude from about 80 to at least 200 feet above 

 the river valley, and which follows in general the contours of 

 the present surface, but with a less convex curvature. In 

 exposure N it seems to be a continuation of the shell-bearing 

 layer in E, yet it is at least 100 feet higher. In exposure M it 

 drops about 80 feet in a blocks Its limits are not sharply 

 defined above or below, and it varies in thickness from about 

 6 to at least 20 feet. Overlying it is a deposit of more or less 



1 C. R. Keyes, Am. Jour, of Science, Vol. VI, p. 304. 



