THE ECONOMIC ASPECTS OF SOIL EROSION 
373 
that the wooded shore advances while that which is defenseless 
is worn away. Many of the stream-swingings are readily ex- 
plained by alternations in the development of the water-loving 
trees. Thus, while the oscillations of rivers cannot be altogether 
controlled by the planting of these trees, these changes can be 
considerably reduced by the proper use of such defenses. 
From a large economic point of view, it will readil}^ be seen 
that the changes in the -courses of the great rivers are not very 
serious, and this for the reason that the area removed on the one 
side of the channel is in a manner compensated for b}'’ a growth 
on the other side. It is otherwise with the smaller streams which 
have slight alluvial jjlains, and which often have their channels 
pressed in against either bank. In these cases the water cuts 
away the base of the declivity and brings about the rapid move- 
ment of the soil down the slope. The loss of tillage area due to 
this action is considerable ; from certain studies which I have 
made in the countiy in the basin of the Ohio river, especially in 
that part of it which lies to the south of the main stream, it ma}' 
be reckoned that since the general removal of the forests an area 
of not less than 150 square miles, outside of the torrent section 
of this river system, has parti j'- or completel}^ lost its soil through 
this action. 
We have now glanced at the several modes in which the solar 
energy, operating through the instrumentalit}" of the winds, the 
waves, and the rain, tends to remove the detrital covering of the 
earth on Avhich the substance of all land life depends. We may 
note in summing-up the matter that the attack of the waves is 
practically irresistible, but that its effect is graduall}' to diminish 
the area of the lands, the process going on so slowly that the 
immediate effect on human interests is veiy small. ^Moreover, 
as one part of the lands is worn away, compensation is generally 
made by the uplifting of other areas above the ocean level. The 
work of the winds in blowing away the friable earth coating is 
slight, and that for the reason that the surfiice is well ])rotected 
by the coating of vegetation. It is when we come to consider 
the action of the rain that we find ourselves face to face with the 
really important economic ])rohlems of erosion. ^Ve have seen 
that in the state of nature the lands are provided against the 
destruction of tlie soil which the rainfall would otherwise cause 
b\' the admirably contrived ]>rotection afforded by the vegetal 
coating. If man occupied the earth under the same conditions 
as the other creatures of the land, he would not disturb the an- 
