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1876 ] Plain, Prairie, and Forest. 581 
goes, unless the hand of man comes in to interfere with nature. 
Mr. N. H. Winchell, although an advocate of the prairie fire 
theory, seems much impressed with one of the difficulties which 
it presents, namely, the irregularity with which prairie and for- 
est are intermingled. Speaking of the “ Big Woods” of Min- 
nesota, a belt of timber some forty-five miles wide, running 
from the centre of the State to the northern boundary of Iowa, 
he says, “ The existence of this great spur of timber, shooting so 
far south from the northern forests, and its successful resistance 
against the fires that formerly must have raged annually on both 
sides, is a phenomenon in the natural history of the State that 
challenges the scrutiny of all observers.” We wonder that it 
had not led him to scrutinize his own theoretical ideas. Of the 
real cause of the existence of these “ Big Woods” we will speak 
farther on. 
By some writers on the theory of the prairies it is held that, 
as trees can be artificially made to grow upon them, therefore 
they must originally have been covered by a forest vegetation. 
This is as if one should argue that because the western part of 
the State of New York is covered with flourishing wheat fields, 
and because grain can be raised there with ease, therefore that 
region must have been always a treeless one ! 
Let us turn now to the other and by far the most prominent 
theory advanced to account for the existence of the prairies. It 
is this: that these treeless plains are in some way a product. of 
the climatological conditions of the country. The only causes 
connected with climate which we can conceive of as likely to 
influence the growth of forests are temperature, force of the 
winds, and moisture; if the latter be the effective agent in de- 
termining the position of the wooded regions, then it may 
be through either excess, deficiency, or irregular distribution of 
the moisture that the result is attained. In regard to the first 
ot these causes, namely, temperature, we are not aware that this 
has ever been suggested as having anything to do with the phe- 
nomenon in question. ‘There seems to be nothing in the distri- 
bution of the isothermal lines in the Mississippi Valley which 
could be in any way connected with the presence or absence of 
forests, and certainly nothing connected with the details of the 
distribution of woodland and prairie could be at all explained 
y reference to temperature. In regard to the winds, it will be 
admitted that these do sweep pretty severely over the prairie 
egion, for the reason that it is mostly flat, and therefore unshel- 
