e of trees from the prairies is the mechanical condition of the
soil, which is, he thinks, too fine,--a coarse, rocky soil being, in his
estimation, a necessary condition of the growth of trees.

Most of these theories seem to be inconsistent with the plain facts of
the case. First, we know that these prairies existed in their present
condition when the first white man visited them, two hundred years ago;
and also that similar treeless plains exist in South America and Central
Africa, and have so existed ever since those countries were known. We
are told by travellers in those regions, that the natives have the same
custom of annually burning the dry grass and herbage for the same reason
that our Indians did it, and that the early white settlers kept up the
custom,--namely, to promote the growth of young and tender feed for the
wild animals which the former hunted and the cattle which the latter
live by grazing.

Another fact, well known to all settlers in the prairie, is, that it is
only necessary to keep out the fires by fences or ditches, and a thick
growth of trees will spring up on the prairies. Many fine groves now
exist all over Illinois, where nothing grew twenty years ago but the
wild grasses and weeds; and we have it on record, that locust-seed, sown
on the prairie near Quincy, in four years produced trees with a diameter
of trunk of four to six inches, and in seven years had become large
enough for posts and rails. So with fruit-trees, which nowhere flourish
with more strength and vigor than in this soil,--too much so, indeed,
since they are apt to run to wood rather than fruit. Moreover, the soil
in the groves and on the river bottoms, where trees naturally grow, is
the same, chemically and mechanically, as that of the open prairie; the
same winds sweep over both, and the same rain falls upon both; so that
it would seem that the absence of trees cannot be attributed wholly to
fire, water, wind, or soil, but is owing to a combination of two or more
of those agencies.

But from whatever cause the prairies originated, they have no doubt been
perpetuated by the fires which annually sweep over their surface. Where
the soil is too wet to sustain a heavy growth of grass, there is no
prairie. Timber is found along the streams, almost invariably,--and,
where the banks are high and dry, will usually be found on the east bank
of those streams whose course is north and south. This is caused by the
fact that the prevai