12 GEOLOGY OF ILLINOIS. 



gin of our wide prairies, else prairies would be found scat- 

 tered through all the timbered regions of the continent. 

 Neither is atmospheric causes sufficient, for the observa- 

 tions of meteorologists show the annual precipitation of 

 moisture in the form of rains, over our North-western prai- 

 ries, quite as evenly and extensively as in the timbered re- 

 gions of the eastern and northern parts of the continent. 

 The chief causes of the treeless character of our prairies 

 are undoubtedly found in the soil itself. 



It is very true that trees, even those whose native habitats 

 seem to be the damp alluvial soils of our river banks, will 

 flourish and grow when planted upon the prairies ; but the 

 artificial process of planting, seems to fit the soil for their 

 reception. Even vines, Indian corn, and many other sorts 

 of vegetation, will flourish when thus artificially planted, 

 but never would grow naturally and of their own accord 

 upon the grass-bound prairie sod. The prairie soil is na- 

 turally adapted to the growth of prairie grasses ; and the 

 prairie grasses not only resist the growth of trees, but act- 

 ually kill them out. By destroying the grasses and sods 

 and cultivating the trees, they will grow vigorously. The 

 prairie soil has certain antiseptic properties, and ulmic and 

 other acids, which give it a sourness. The prairie grasses 

 naturally flourish in such a soil. These properties in the 

 soil, and these grasses, are all unfavorable to the growth of 

 trees ; and it is only when their influences are counteracted 

 by cultivation or other local causes, that trees will grow in 

 health and vigor. Cultivation does destroy this sourness 

 in the soil ; and I believe if all the cultivated prairies of 

 the State w T ere suffered to relapse into uncultivated wastes, 

 instead of going back to their prairie condition, they would 

 become eventually covered with brambles, thickets and 

 growths of timber. 



In this part of the State, along the Mississippi, Bock 

 river, and other streams, much of the alluvial bottom sub- 

 ject to annual overflow, is covered with timber. There are, 



