GEOLOGICAL REPORT. O 



GEOLOGY. 



It is not deemed expedient, in this report, to enter into a de- 

 failed description of the rocks in the region under considera 

 tion, as that has been done in the Second Annual Report of our 

 Survey, where any one desiring it can find a full exposition of 

 these rocks, their classification, and catalogues of the fossils 

 upon which that classification was based. In this connection, 

 therefore, we shall merely mention the extent of each forma 

 tion, its economical relations, and whatever may appear pecu 

 liar in the localities observed. 



QUATERNARY SYSTEM. 



All of the deposits of sand, clay, marl and humus in the 

 bottoms of the streams, together with the clays and marls 

 spread over the consolidated strata on the high lands, belong to 

 the Quaternary period. These deposits cover the entire region. 

 and are particularly important, as they furnish a large part of 

 all the mineral ingredients that enter into the composition of 

 the soils which rest upon them. 



The Alluvial Formation, in the bottoms, is made up of clays, 

 sands, marls and humus, more or less commingled. The char 

 acter of these materials explains the wonderful fertility of the 

 soils resting upon them. 



The Bluff Formation consists of impure clays and marls, and 

 is best developed on the eastern end of the line, particularly in 

 St. Louis county, where it covers the high country and forms 

 the basis of the soils. On the central and western portions, the 

 superficial deposits are more argillaceous and sparingly devel 

 oped, often leaving the underlying rocks to exert their due in 

 fluence upon the soil. The Quaternary is represented on the 

 map by the carmine color. 



CARBONIFEROUS SYSTEM. 



The Coal Measures underlie about 160 square miles in St. 

 Louis county, a portion of St. Charles, and some small patches 

 in Crawford, Phelps and Newton. It is represented by the 

 purple color in the accompanying geological map. This forma 

 tion in St. Louis countv contains three beds of coal ; one of 



