of greater or lesser extent; these are almost always fertile, and
generally cultivated when large; when small, they are in pasture. The
origin of these fertile soils, and their perpetual change, is to be
described with a view to show, that vegetation, although most powerful
in stopping the ravages of water, and for accumulating soil retained
by this means, does it only for a time; after which the soil is again
abandoned to the ravages of the running water, when no more protected by
the vegetation.

Let us suppose the river running upon the one side of the haugh (which
is the name we gave those little fertile plains) and close by the side
of the mountain. In this case the bed of the river is deepest at the
side of the mountain, which it undermines, leaving a falling _(un
eboulement)_ on that side; on the other side, the river shelves
gradually from the plain, and leaves soil in its bottom or stony bed
upon the side of the haugh, in proportion as it makes advances in
carrying away the bank at the bottom of the sloping mountain. The part
which vegetation takes in this operation is now to be considered.

When the river has enlarged its bed by preying upon one side, whether of
the mountain or the haugh, the water only covers it in a flood; at other
times, it leaves it dry. Here, among the rocks and stones, the feeds of
plants, left by the water or blown by the wind, spring up and grow; and,
in little floods, some sand and mud is left among those plants; this
encourages the growth of other plants, which more and more retain the
fertile spoils of the river in its floods. At last, this bed of the
river is covered perfectly with plants, which having retained plenty of
fertile soil, although still rooted among the stones, opposes to the
river a resistance which its greatest velocity is not able to overcome.
In this state, the haugh is always deepening or increasing its soil, and
has its surface heightened. At last, when this soil becomes so high as
only to be flooded now and then, it becomes most fertile, as the
heavier parts are carried in the bed of the river, and the lighter soil
deposited upon the plain. The operations of the river, upon the plain,
thus increase at the same time the height and fertility of the haugh.
But this operation, of accumulated soil upon the stony bottom, has a
period, at which time the river must return again upon its steps, and
sweep away the haugh which it had formed. This is the natural course of