A, Winchell on the Prairies of the Mississippi Valley. 343 
1. The old and popular belief that the treelessness of the prai- 
ries was caused by the annual burning of the grasses by the 
Indians,” is now generally admitted to be inadequate. 
west may have originated in extreme aridity of the atmosphere ™ 
—as others have from the highly saline character of the soil— 
but all our discussions have had reference to the prairies of the 
Mississippi valley. 
4, A theory often urged is the considerable humidity of the 
soil of certain prairies,” and especially the wetness of the subsoil 
in contrast with the dryness of the soil during summer.” It is 
singular that such an opinion could be entertained when it is so 
well known that there is no situation so wet but certain trees 
will flourish on it—the willow, the cottonwood, the beach, the 
ash, the alder, the cypress, the tupelo, the water-oak, the tama- 
rack, the American arbor-vite or some other tree—some of them 
- 
delayed by the circumstance that neighboring forests are gener- 
t 
5. Prof. 
extreme fineness of the prairie soil is the cause of the absence of 
trees; and the author of the article on “Plains,” in the New 
“ 
opted t 
Against this theory we see several weighty objections. Many 
31. Th 
'rof, Dana allude to the prairies of the 
F Geol ) 
America] has her t prairies and pampas?” See also Cooper, hson. Rep., 
aa: Ser am 1859; Lambert, Pacific R. R. Rep., 
p. 166. 
— * Atwater, this Journal, i, 116; Bourne, Jé., ii, 30; Lesquereux, 2d Ark. Geol. 
ep.; Western Monthly Magazine, Feb., 1836 : 
 Bogelmann, this Journal, {2} xxxvi, 384. > Jowa Geol. Rep., vol. i, p. 24. 
