0. H. Hershey — Florencia Formation. 97 



ties, of which thirty are of fresh water forms and twenty air- 

 breathing or terrestrial species. In comparing them with the 

 lists of shells from the loess at Davenport, Muscatine and Iowa 

 City, published by McGee in his memoir on "The Pleistocene 

 History of Northeastern Iowa,"* some interesting differences 

 are noticed. In the Iowa loess fauna the gasteropods are 

 mainly pulmoniferous, only a few freshwater species having 

 been discovered. In the Florencia fauna near Freeport, the 

 larger number of species are of freshwater forms, but the 

 Uniodce, which appear in the loess, are absent from this forma- 

 tion. The genus Helix, which occurs in the loess fauna of 

 Iowa and is plentiful in the Modern alluvial deposits of Illi- 

 nois, has not been identified in the collections made from the 

 Florencia formation. Furthermore, many of the terrestrial 

 species of the Iowan loess are not present in the Florencia 

 fauna as at present known. There is thus seen to be such a 

 great difference between the fossil contents of the two forma- 

 tions as to point to a great contrast in conditions. The pre- 

 ponderance of freshwater species in the Florencia fauna 

 indicates the fluvial nature of the formation just as certainly as 

 do its physical features. 



The significance of the fossils of the Florencia formation lies 

 chiefly in the evidence which they furnish of the nature of 

 the climate of that time. Undoubtedly it was neither Arctic 

 nor very cold temperate. I hereby submit the proposition 

 that these fossils demonstrate that the climate was similar to 

 the present. So far as I am aware, there is nothing about the 

 shells which indicates the proximity of a glacier or the exist- 

 ence of conditions favorable to the accumulation of land ice. 

 On the contrary, the prevailing reddish color of the soil on 

 the neighboring uplands as proved by its condition to-day 

 (buried under the loess), and the ferruginous layer at the base 

 of the loess series, points to a comparative mildness of the 

 climate of that time. This is corroborated by the large amount 

 of driftwood and the vast quantities of small shells enclosed 

 in the Florencia formation, which indicate that organic life 

 was more abundant in the valleys and streams then than it is 

 at present. This abundance of animal and vegetable life is in 

 strong contrast with preceding and succeeding epochs. The 

 Silveria formation contains a few shells of several terrestrial 

 species and a few very small pieces of lignitiferous wood ; the 

 Lake Pecatonica formation is totally unfossiliferous ; and the 

 drift nowhere presents any evidence of organic remains. 

 Throughout the Kansan epoch the climate in this region was 

 undoubtedly severe. During the formation of the Iowan loess 



* llth Annual Report of U. S. Geol. Survey, pages 460 and 411 of Part I. 



