IOWA ACADEMY OP 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 Polygyra 
multilineata 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. Keyei— Am. Jour, of Se)., (4:),Vol. VI, p. 304. 
+At the base of the bluff in exposure K, what seemed to be a second shell-bearing 
layer was observed about seventy-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 shell 
.stratum. 
