Geological Survey of Illinois, Prairies, etc. 81 



Geological Survey of Illinois, Prairies, etc. 



The fifth volume of the geological survey of the State of Il|iuoi.?, 

 for ability displayed, excellence of engravings, and neatness and cor- 

 rectness in the execution of the work, has not been surpassed, if it 

 has even been equaled, by any other publication on the science of 

 geology in the United States. 



The first 300 pages of the volume are devoted to a general geologi- 

 cal description of a few counties. The next 300 pages contain paleon- 

 tological descriptions of invertebrates from the carboniferous rocks, 

 which are beautifully engraved on 32 lithographic plates at the end of 

 the volume. 



The following, from the preliminary chapter upon the causes which 

 led to the formation of the great prairies of that State, is quite inter- 

 esting : 



"The largest portion of this part of the State is prairie land. In 

 it all kinds of prairies may be seen, such as the high upland prairies, 

 the river bottoms or alluvial prairies, and the low, wet swamp lands. 

 There is' quite a diversity of opinion as to the origin and formation of 

 these treeless and grass-covered regions of the Northwest. One theory 

 attributes them to annual fires sweeping through the grass, and kill- 

 ing every tree germ and young tree almost before they could take root. 

 In some places the fires are supposed to have encroached, year by year, 

 upon the forests ; in other places, as for instance along the streams, in 

 the deep hollows, or in wet places, where the fires would be checked, 

 the timber would spring up and displace the prairies. Another theory 

 accounts for the treeless character of these plains from the lacrustine 

 origin and nature of the prairie soils and subsoils. Trees will not nat- 

 urally grow in this sedimentary, finely comminuted prairie soil accord- 

 ing to this theory. Others attempt to explain j)raii'ie phenomena by 

 atmospheric and climatic influences, marking out certain zones of mois- 

 ture and dryness. They bound forest and prairies by certain isotlier- 

 nial lines. Another theory, advocated with force and plausibility by 

 Professor Lesquereux, in the first volume of the geological reports of 

 this State, finds all our prairies to originate from causes similar to those 

 which form pe&t beds, and are in fact incipient peat beds, drained be- 

 fore completed. In his own clear language, he finds " that all the 

 prairies of the Mississippi valley have been formed by the slow reces- 

 sion of sheets of water of various extent, first transformed into swamps, 

 and by-and-by drained and dried. The high, rolling prairies, the prai- 

 ries around the lakes, those of the bottoms along the rivers, are all the 



