ccounts an acre
of irrigated soil can be made to yield a far greater return than can
be obtained from land of like chemical composition in humid regions.

In many parts of the world, particularly in the northern and western
portions of the Mississippi Valley, there are widespread areas, which,
though moderately well watered, were in their virgin state almost
without forests. In the prairie region the early settlers found the
country unwooded, except along the margins of the streams. On the
borders of the true prairies, however, they found considerable areas
of a prevailingly forested land, with here and there a tract of
prairie. There were several of these open fields south of the Ohio,
though the country there is in general forested; one of these prairie
areas, in the Green River district of Kentucky, was several thousand
square miles in extent. At first it was supposed that the absence of
trees in the open country of the Mississippi Valley was due to some
peculiarity of the soil, but experience shows that plantations
luxuriantly develop, and that the timber will spread rapidly in the
natural way. In fact, if the seeds of the trees which have been
planted since the settlement of the country were allowed to develop as
they seek to do, it would only be a few centuries before the region
would be forest-clad as far west as the rainfall would permit the
plants to develop. Probably the woods would attain to near the
hundredth meridian.

In the opinion of the writer, the treeless character of the Western
plains is mainly to be accounted for by the habit which our Indians
had of burning the herbage of a lowly sort each year, so that the
large game might obtain better pasturage. It is a well-known fact to
all those who have had to deal with cattle on fields which are in the
natural state that fire betters the pasturage. Beginning this method
of burning in the arid regions to the west of the original forests,
the natural action of the fire has been gradually to destroy these
woods. Although the older and larger trees, on account of their thick
bark and the height of their foliage above the ground, escaped
destruction, all the smaller and younger members of the species were
constantly swept away. Thus when the old trees died they left no
succession, and the country assumed its prairie character. That the
prairies were formed in this manner seems to be proved by the
testimony which we have concerning the open area before mention