PRAIRIES AND THEIR TREEIESMNESS. 267 



raphy and soil-constitution of the Illinois prairies points 

 to a different and a peculiar history. Moreover, trees oc- 

 cupy the drier knolls of the prairies in the midst of the 

 common atmospheric conditions. 



Exactly the reverse of this theory is that which attrib- 

 utes the absence of trees to an excess of moisture in the 

 soil at certain seasons. But we well know that there is no 

 soil or situation so wet and stagnant but certain trees will 

 flourish upon it — the willow, the Cottonwood, the beech, 

 the black ash, the alder, the cypress, the tupelo, the water- 

 oak, the tamarack, the American arbor-vitaa, or some other 

 tree — some of them standing joyously half the year, if need 

 be, in stagnant water. Many swales are indeed treeless ; 

 but is this in consequence of the inability of a willow to 

 take root and maintain itself, or rather in consequence of 

 the formation of the swale in times so recent that the 

 germs of trees have not yet been scattered over it ? More- 

 over, wetness can not be attributed to many portions of the 

 Illinois prairies- which are entirely treeless. Is there a dif- 

 ferent cause for treelessness here ? 



Lastly, it has been suggested within a few years, by high 

 geological authority, that the lack of trees is caused by ex- 

 'cessive fineness of the prairie soil. It can scarcely be de- 

 nied, however, that other soils, as pulverulent as that of the 

 prairies, are densely covered with forest vegetation, and 

 that in the same latitudes and under the same meteoro- 

 logical conditions. On the other hand, certain soils of a 

 coarser texture are equally treeless. But the final objec- 

 tion to this theory, and to all theories which look to the 

 physical or chemical condition of the soil, or even to cli- 

 matic peculiarities, for an explanation of the treeless char- 

 acter of the upland prairies of the Mississippi Valley, is dis- 

 covered in the fact that trees will grow on them when once 

 introduced — not water-loving trees exclusively, but ever- 



