Geological Survey of Itlinois, Prairies, etc. 83 



The swamp lands of Whiteside, Lee, and Carroll counties afford a 

 fine illustration of Professor Lesquereux's theory of the gradual trans- 

 formation of swampy , boggy ponds, marshes and swales, into the black, 

 spongy moulds of our richest prairies. Aquatic vegetation, the grad- 

 ual encroachment of the land into ponds, the slow drying of our wet 

 lands, and the gradual filling up of the ponds by successive growths and 

 decays of aquatic vegetation, is building up rapidly sour-soiled, treeless 

 prairies. The processes are similar to those forming the peat beds. 

 The results of the processes are curtailed and modified, and a peaty- 

 soiled prairie is formed instead of a bog or bed of peat. 



But the high rolling prairies of Carroll, Stephenson, Winnebago, and 

 parts of Ogle and Whiteside counties, with, in many instances, but 

 thin soils covering the coarser drift materials below, do not show 

 so plainly the same sort of originating causes. They are interspersed 

 with numerous small groves of timber. These grow along the alluvial 

 mixed soil of the streams, and upon the ridges and patches thrown up 

 and beat together by the waves and currents of the broad, lake-like 

 expanse of water, which covered this part of the State immediately 

 subsequent to the glacial ice period. A few of these drift ridges, as in 

 northwestern Ogle county, are treeless, owing perhaps to fires, or 

 other local causes. 



Excessive humidity of these high rolling, somewhat sandy prairies 

 does not exist, and can not satisfactorily account for their treeless 

 character. Neither do they bear in their soils and subsoils the evi- 

 dence of having once been swampy, marshy plains. 



When the waters of the broad, shallow, fresh water sea, once extend- 

 ing south and west of Lake Michigan, were 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 comparatively dry, and 

 covered, with the fine impalpable sediment, constituting the basis of 

 our present prairie soils. The swamp and peat lands of Lee, Whiteside, 

 and Carroll counties afibrd fine examples of the former condition of 

 things ; the rolling, drier, 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 Lesquereux'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, 



