1878.] Distribution of Timber and the Origin of Prairies. 93 
HI. 
These are the observed facts; wnat is their bearing on some of 
the theories advanced by different writers? 
(1.) We find in Dr. White’s report on the Geology of Iowa, 
Vol. 1, page 133, these words: “It now remains to say without 
the least hesitation that żke real cause of the present existence of 
the prairies in Towa is the prevalence of annual fires. If these had 
been prevented fifty years ago, Ilowa would now be a timbered, 
instead of a prairie state. This view was fully endorsed by his 
assistant, Professor St. John. Although the distribution of trees 
as given above may seem to favor this theory, when we remem- 
ber that fires occur mainly while the north-west winds prevail, 
‘and though it may be a slight factor in the problem, yet its inad- 
equacy is clearly proved, not only by the constancy of timber 
areas whether the fires burn or not, but also indirectly, by their 
failing to make prairies of Ohio and New York, when the princi- 
ple is made of general application. Dr. Newberry from a general 
survey of the subject, pronounces the idea “simply pees 
(Geology of Ohio, Vol. 1, page 30). 
(2.) Professor J. D. Whitney has recently taken pains to reit- 
erate his theory published some years ago, viz: that the cause of 
prairies, at least in states east of the Missouri river, is mainly 
in the fineness and depth of the soil, which he further ascribes to 
_ the nature and position of the rocks underlying. This theory is 
sufficiently disproved by the. observations given above. In 
exactly the same soil totally different results are discovered, 
_(3.) The theory that ‘the absence of trees is mainly dependent 
on the rain-fail, as is very generally held, is also proved to be 
faulty, if not false, for there is every reason to believe the rain- 
fall the same over most of the area under consideration. There 
American NATURALIST (October, 1876), in which he shows from 
Smithsonian rain-charts that the forest region of several States 
receives the least rain-fall, and the prairie region the greatest. 
 (4.) The theory advocated, as we understand, by Colonel J. W. 
Foster, and more recently by Dr. Newberry (Geology of Ohio, 
Vol. 1, page 30), is, that forests to flourish need “not so mucha 
profuse as a constant supply of water,” that a deficiency of winter 
