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Geological Survey of Illinois, Prairies, etc. 



result of the smue causes, and form a whole in an individual system," 

 No one of these theories is sufficient to explain all the phenomena 

 noticed in making an examination of the prairies. As in most such 

 cases in theoretical geology, all of them perhaps contain some truth, 

 and may be applicable to localities more or less extended. The burn- 

 ing of the forests, in a few cases, doubtless, has changed timber into 

 prairie land, and prevented the timber from invading small tracts of 

 the prairies. But the sweeping, consuming autumnal prairie fires are 

 not sufficient to account for the origin of our wide prairies, else prairies 

 would be found scattered through all the timbered regions of the con- 

 tinent. Neither is atmospheric causes sufficient, for the observations 

 of meteorologists show the annual precipitation of moisture, in the form 

 of rains, over our northwestern prairies, quite as evenly and exten- 

 sively as in the timbered regions 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 up- 

 on the grass-bound j^rairie sod. The prairie soil is naturally adapted 

 to the growth of prairie grasses, and the prairie grasses not only resist 

 the growth of trees, but actually 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 that if all the cultivated prairies of the State 

 were 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, Rock river, and 

 other streams, much of the alluvial bottom subject to annual overflow 

 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 prairie. 



