THE L(ESS AND ITS FOSSILS.' 



B. SHIMEK. 



In the determination of the physical conditions under which 

 the formation of various strata of the earth took place, the 

 fossils have always furnished one of the most satisfactory, 

 and consequently most important considerations. Organic 

 forms, being dependent for their very existence upon these 

 conditions, and usually readily responding to any modification 

 of them, would certainly reflect their character most clearly. 

 This importance of organic remains being manifest, it is pur- 

 posed here to view the extensive Lcess deposits which overlie 

 the drift over large areas of the Mississippi and Missouri 

 River drainage in the light of their fossils. The fauna of the 

 Loess is essentially molluscan. While remains of Vertebrates, 

 and perhaps representatives of other branches, are occasion- 

 ally found, certainly the Mollusks furnish the most abundant 

 and the clearly characteristic fossils. 



Consequently such conclusions as we draw from the charac- 

 ter of the life of the Loess must be based primarily upon 

 the molluscan remains. 



I As the writer contemplates publishing very soon a detailed description 

 and comparison of the Loess MoUusca, proper credit will then be given for 

 material kindly furnished by a number of persons. The observations here 

 recorded were made upon many thousands of fossil specimens from Dubuque, 

 Bremer, Scott, Muscatine, Johnson, Iowa, Polk, and Pottawattamie counties in 

 Iowa; and Douglas, Saunders, Lancaster, and Cuming counties in Nebraska. 

 These were compared with recent specimens from all portions of this continent 

 north of Mexico, as noted in connection with each species. The comparisons 

 were made by placing large series of the recent and fossil shells side by side, 

 and, where necessary, by making careful measurements. The partial results 

 here noted represent a more or less continuour study of the Loess and its 

 fossils during the past eight years. 



