32 IOWA ACADEMY OF SCIENCES. 



IS THE LOESS OF AQUEOUS ORIGIN? 



BY B. SHIMEK. 



Organic remains furnish the best criterion for the measure 

 of conditions which prevailed during any given age of the 

 earth's geological history, provided, of course, that their rela- 

 tion to the deposit can be clearly shown. 



To such an extent is this true of the older rock formations, 

 that the modern geologist has generally accepted without 

 question the conclusions long ago reached by the paleontolo- 

 gist, and has turned his attention to the physical, rather than 

 the biological, phenomena presented by the various horizons. 



In every case the paleontologist reached these conclusions 

 in the main by comparisons with modern forms of life. The 

 more remote the age, the greater the gap between its fauna and 

 the fauna of the present day. Ordinal, family, and at best 

 generic characters and relationships alone furnish a clue to the 

 then existing conditions. Yet these have been considered 

 sufficient. How much easier then is the task, and how much 

 more satisfactory the deductions, if in the investigation of a 

 much more modern horizon, we find the similarity of faunas 

 extending to the species, and if for purposes of study we may 

 place by the side of its fossils representatives of the same 

 species which exist abundantly to-day under conditions which 

 may easily be studied. 



This is the advantage presented by the fauna of the loess. 

 This fauna is in the main moUuscan. A few remains of the 

 vertebrates have been found, but the characteristic, most 

 abundant and most widely distributed species are molluscs, and 

 to these we must turn for the chief paleontological explanation 

 of loess conditions. 



The majority of the geologists who have given attention to 



