THE PEAIEIES 217 



to the prairie for the purpose of furnishing pasture for the 

 buffalo, but the view is considered not proven by Schimper 

 (1903). Over-grazing by the buffalo has also been offered to 

 the writer privately by several speculators as a cause of the 

 prairie on the well-known ground that overgrazing destroys for- 

 ests and groves. However, cause and eft'ect are here reversed, 

 for the prairie in all probability made the bison possible. 



Prairie Fires 



Fire has been considered the cause of the treelessness of 

 prairies more frequently than any other factor. It was so con- 

 sidered in some of the earliest known references, and has re- 

 ceived a varying degree of attention to the present time. To 

 those who have seen a prairie fire in all its fury this does not 

 even now seem wholly without reason, for surely no seedlings, 

 and few large trees could withstand the furious onslaught of 

 the flames. Some writers^^ assumed that the prairies had been 

 tree-covered, and that the forests were destroyed by fire, but 

 there is no warrant for this statement. "We have in the loess^^ 

 some e^'idence that there were forests where we now find prairie, 

 but this evidence merely suggests that there were local groves 

 which became exterminated probably through exposure due to 

 change in topography incident to the uuecjual piling up of loess. 

 There is certainly no evidence that such forests were of wide ex- 

 tent, or that they extended over the flatter prairies. 



The probability is that prairie fires were possible because of 

 the condition of the prairie, and that when they consumed the 

 grass and herbs of the prairie they encountered no tree seedlings, 

 except perhaps at the very edges of the groves. 



The fire-theory seemed to be supported by the presence of 

 prairie on the drier areas, where it was assumed that fires would 

 be more readily kindled, but such places often have a vegetation 

 so scant that it would furnish but little fuel for the flames, and 

 in the fall and early spring the denser vegetation of the more 

 protected slopes is always sufficiently dry to burn, and hence 

 should have suffered more from fires. 



isGleason (1909). 



i^See Journal of Geology, 1899, p. 133, and Proceedings of the Iowa 

 Academy of Sciences, vol. "ST!, 1899, p. 108. 



VOL. VI 1. 16 



