IOWA ACADEMY OF SCIENCES. 107 



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, espe- 

 cially 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 r<>ly{/!/ra 

 inultilineata 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 regions. Surely no 

 conditions of excessive moisture prevail in that region to-day. 

 Yet a recent writer,* 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 

 optimum 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 eighty 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 curva- 

 ture. (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 eighty feet in a block.) Its limits 

 are not sharply defined above or below, and it varies in thick- 

 ness from about six to at least twenty feet. Overlying it 

 is a deposit of more or less laminated loess-clay, which is 

 usually non-fossiliferous, and which varies from a few to more 

 than thirty feet in thickness. When fossils occur in this upper 

 stratum, they are few in number and widely scattered, f 



*C. R. Keye<— Am. Jour, of Sci., (4), Vol. VI, p. 304. 



+At the base of the bluff in exposure K, what seemed to be a second sheU-bearing' 

 layer was observed about sfventy-five feet below the main fossiliferous band. The 

 section, however, was more or less obscured, and the mass may have slipped from the 

 bluff above. The fossils in column K. in the table, are from this stratum. It will be 

 observed that they are ordinary forms which are abundant in the main she'l 

 stratum. 



