TRANSACTIONS OF HORTICUIiTURAL SOCIETY OF NORTHERN ILL. 305 



says, "that all the prairies of the Mississippi valley have been formed 

 by the slow recession of the sheets of water of various extents, first trans- 

 formed into swamps and by and by drained and dried. The high rolling 

 prairie, the prairies around the lakes, and those of the bottoms along the 

 rivers, are all the result of the same causes and form a whole in an indi- 

 vidual system." 



I have already said that no one of these theories is sufficient to explain 

 all the phenomena noticed in making an examination of the prairies. As 

 in most cases in theoretical geology, all of them contain some truth, and 

 may be applicable to localities more or less extended. The burning of 

 the forests in some cases, doubtless, has changed timber land into prai- 

 rie, and prevented timber from invading tracts of the prairies. But 

 these sweeping 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 continent. Neither are these 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 extensively as in the timbered regions of the 

 eastern and northern part of the continent. I suppose the chief cause 

 of the treelessness of the prairies is found in the soil itself It is very 

 true that trees, whose habitat even seems to be the damp, alluvial soil of 

 our river banks, will flourish and grow when planted upon the prairies; 

 but much of this adaptability comes from the artificial process of plant- 

 ing, which seems to fit the soil for their reception and growth. Even 

 vines, Indian corn, and many other kinds of vegetation, will flourish 

 when thus artificially planted, but never would grow naturally of their 

 own accord upon our grass-sodded prairie land. 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. Indian 

 corn would never grow naturally upon our prairies ; but under the hand 

 of cultivation they are the grandest corn lands in the world. 



Trees do not naturally cover the prairies, but under favoring cir- 

 cumstances, and when planted by man, they grow and flourish luxuri- 

 antly. By destroying the grasses and sod the roots of the trees strike 

 deep into the nourishing subsoil, and forests easily spring up. The prai- 

 rie soil is the sifted silt of the slow-receding waters. It has certain anti- 

 septic qualities, and is permeated by ulmic and other acids, making it at 

 first sour, compact, and pottery-like in closeness and hardness. The 

 prairie grasses first cover such a surface and naturally flourish in such a 

 soil. Having once taken possession, they more than hold their own in 

 the struggle with the trees. The trees kill many grasses with their shades; 

 but these grasses bind and smother the roots of the trees, and kill the 

 monarchs of the forest. 



These properties in the soil and these sour grasses are all unfavorable 

 to forest growths, and it is only when their deleterious influences are 

 counteracted by the sweetening influences of cultivation, or other counter- 

 acting causes, that healthy and vigorous trees replace the grasses. Culti- 

 vation does destroy this sourness in the soil ; and successive vegetable 

 21 



