82 TRANSACTIONS OF THE ILLINOIS 



of frost in the disintegration of rocks has always played an important part 

 in modifying the surface of the earth ; and the wearing down of the hills 

 and mountains, and the elevation of the valleys, through the joint action 

 of frost and water, is one of the eternal processes of nature that must con- 

 tinue so long as the earth itself shall endure. The atmosphere contains 

 carbonic acid, and the rain in passing through the air takes this up; and 

 this acid has the power of dissolving the carbonate of lime, which enters 

 into the composition of a large proportion of what are termed the strat- 

 ified rocks, such as the various kinds of limestone, calcareous shales, etc.; 

 and the rain water containing this gas is continually eating into the sub- 

 stance of these calcareous rocks, dissolving the carbonate of lime, which 

 is thus carried away by the water, leaving only a residuum of the more 

 refractory elements upon the surface ; and hence the small amount of 

 carbonate of lime that remains in a soil derived directly from our lime- ^ 

 stones and other calcareous formations. These highly charged waters 

 find their way either into the ocean, where their mineral contents are 

 precipitated to form new limestones, or descend into the depths of the 

 earth, to reappear as mineral springs or form the highly charged mineral 

 waters of our artesian wells. 



So, you perceive, the production of the soil is through a very simple 

 process; and if we go still farther, and inquire into the production of the 

 rocks themselves, we should find them the result of processes equally as 

 simple. Sand, lime and clay, either in chemical solution or mechanical 

 disintegration, is constantly carried into the ocean by river floods and 

 other causes, where they are deposited as sediments, and finally again 

 hardened into rock. So sang the poet : 



" Lofty mountains, whose tops appear to shroud 

 Their granite peaks deep in the vapory cloud, 

 Worn by the tempest, wasted by the rains, 

 Sink slowly down to fill wide ocean's plains." 



Having now considered the origin of those soils derived immediately 

 from the rocks upon which they rest, we pass to the consideration of tlie 

 character and origin of the prairie soil, to which a very large proportion 

 of the soils of this State belong. If we should sink a shaft or well down 

 to the bed rock, anywhere about the city of GalesbTarg, or in almost any 

 other prairie region in the State, we should find a variable thickness of 

 thirty to seventy feet or more of loose material, consisting of clay, sand 

 and gravel, containing boulders or rounded masses of rock, many of 

 which, consisting of granite, syenite, porphyry, greenstone, etc., do not 

 belong to any beds that are to be found in this State ; but associated with 

 this foreign material we should, perhaps, find similar boulders composed of 

 the Silurian limestones of Northern Illinois, indicating that this mass of 

 transported material had come from a northerly direction. 



Nuggets of native copper are also found in this transported mass ; 

 and by comparing many of the boulders with the rocks occurring about 

 Lake Superior, we should probably find that a large part of this drift 

 material had come from a high northern latitude. This transported 

 material covers the bed rock so deeply that atmospheric influences cannot 



