The Lcess and its Fossils. 95 



the species, it is far from sufficient to indicate a temperature 

 such as would be necessary to retain lakes and streams within 

 shores of ice durini^ the summer, and that consequently the 

 Loess was not deposited during a glacial climate, but at a time 

 when the temperature had moderated sufficiently to enable 

 many land-shells, now restricted to or abundant in middle 

 latitudes, to flourish in considerable numbers. 



The great predominance of strictly terrestrial' species of 

 molluscs in the Lcess indicate that during its deposition large 

 areas of land-surface were exposed, at least during the greater 

 part of the summer, upon which these molluscs lived and mul- 

 tiplied under conditions which exist now in the habitats of 

 their modern representatives. 



For the belief that the fossils as now found are not far ' 

 removed from the localities in which they lived and developed, 

 a number 9f valid reasons exist the most striking of which 

 are the following: 



1. Their usually per/eel -preservation. Such delicate 

 shells as many of those under consideration could not be trans- 

 ported far by turbulent streams without being broken. 



2. Their distribution, both vertically and horizontally. In 

 many exposures of the Loess the species which to-day have the 

 habit of remaining in considerable numbers in very restricted 

 localities, as Helicina occulta., Patula strigosa coopcri, Mcso- 

 don multilineata, the I^ininceiP, etc., are likewise similarly 

 restricted in their horizontal distribution to very narrow 

 "pockets," though the same species may often be traced ver- 



I In the SketcJics of the Physical Geografhy and Geology oj Nebraska, pages 

 277-290, Prof. Aughey gives a long list of Loess fossils, in which are included 

 forty-two aquatic species, quite a number of them being fluviatile. These are 

 not taken into consideration hei-e, because, while Prof. Aughey is a close 

 observer and an able geologist, there is no doubt that many of his identifica- 

 tions of these fossils were erroneous. His method of identifying many of them 

 (/'. e. by making sections) as given on p. 2S7 will at once convince anyone fami- 

 liar with such genera as Zoitites, Helix, Snccinea, Physa, etc., of the unreliabili- 

 ty of the entirp list. It is extremely difficult to identify many of the species 

 there listed even from perfect recent specimens. 



