3o6 ILLINOIS STATE HORTICULTURAL SOCIETY. 



growths, living and decaying with the seasons, make our black, fat, 

 prairie mould. If all the cultivated prairies of the State were suffered to 

 relapse into uncultivated wastes, I believe the grasses would not again 

 take possession ; but that brambles and hard-wood trees would eventually 

 cover the land with thickets and a forest growth of hard woods. 



In this part of the State much of the alluvial bottoms subject to over- 

 flow, and constituting the flood-plain of the rivers, is covered with timber. 

 There are, however, alluvial prairies along these streams, timberless and 

 for the most part sandy and coarse-grained, and entirely different in 

 composition and texture from the usual Illinois upland prairies. 



The swamp lands, swales and boggy lands scattered through these 

 counties aff"ord a fine illustration of Professor Lesquereaux's theory of the 

 gradual transformation of swampy, boggy ponds, marshes, swales and 

 shallow margins of rivers and lakes into the black, spongy moulds of our 

 richest prairies. Aquatic vegetation, the gradual encroachment of the 

 land into ponds and lakes and swamps, the slow drying of flat, wet 

 prairies and sloughs, and the gradual filling up of water-logged and 

 water-soaked basins by successive growths and decays of aquatic vegeta- 

 tion, is building up rapidly sour-soiled, treeless prairies. 



The processes are similar to those forming the peat-beds. The proc- 

 esses are modified by varying conditions of dryness, and a peaty-soiled 

 prairie is formed, instead of a bog or bed of peat. Around the Winne- 

 bago Swamp or Lake Koshkonong we may actually see the formation of 

 the prairies taking place in the historic period. Here it is a contest 

 between the land and the water. 



But the high, rolling prairies, with, in many instances, thin soils 

 covering the coarse 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 soils of the 

 streams, and upon the ridges and patches thrown up and beaten 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 and gravely-subsoiled elevations are 

 treeless, owing perhaps to fires or other local causes. 



Excessive humidity of these high, rolling, somewhat sandy prairies 

 does not exist, and cannot satisfactorily account for their treelessness. 

 Neither do they bear in their soils and subsoils the evidence of having 

 once been swampy, marshy plains. 



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

 ing south and west from 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, 

 shallow 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 a fine, impalpable sediment, constituting the basis of 

 our present prairie soils. 



Such must have been the primeval condition of much of the Grand 

 Prairie of Central Illinois. 



