14 <;i-X)LO(iY OF ILLINOIS. 



slowly drained off, either by the breaking away of southern 

 water barriers, or the slow upheaval of this whole region, 

 parts of the bottom were undoubtedly left as broad marshes, 

 swales, and bogs, which assumed in due course of time a 

 peaty character; but other parts must have been left com- 

 paratively dry, and covered with the line, impalpable sedi- 

 ment, constituting the basis of our present prairie soils. 

 The swamp and peat lands of Lee, Whiteside and Carroll 

 counties, afford fine examples of the former condition of 

 things ; the rolling, dryer, sandier prairies of Stephenson, 

 Winnebago, and parts of Carroll and Ogle counties, afford 

 just as fine illustrations of the latter condition of things, 

 while Boone county exhibits very plainly, both. 



The treeless nature of the marshes is very satisfactorily 

 accounted for upon Professor LESQUERErx's theory of the 

 origin of the prairies. The treeless character of the high 

 prairies must be accounted for by the nature of the soil 

 itself; the natural tendency of an herbaceous, rather than 

 of an arboreal vegetation, to gain and keep possession of 

 the prairie soil, aided perhaps by tires and other local 

 causes. 



These views of mine may contain erroneous suggestions. 

 I have had no special means to examine soils, or compare 

 wide extents of prairie regions with each other. I arrive 

 at my conclusions from simple observations of the prairies 

 in this part of the State. I am satisfied that no one theory 

 yet advanced, as to the origin and formation of the prairies, 

 will account for all their phenomena, even in this limited 

 portion of the State. Combined causes, operating with 

 different degrees of force in different parts of the great 

 prairie regions of the country sometimes one cause pre- 

 dominating, sometimes another, and sometimes all together 

 are more in harmony, it seems to me, with the effects left 

 for our observation. 



Geological Formations. Leaving the surface geology and 

 turning our attention to the rocky strata beneath, we find 



