the roots of plants, are disposed for vegetation in different degrees; a
mixture of the different earths being, upon the whole, the best suited
to that purpose; and this compound body, mixed with vegetable or animal
substances, becoming a most luxuriant soil.

Soils are thus formed, either by the resolution of the surface of that
land upon which they are to rest, or by the transportation of those
solid parts to be again deposited upon another basis. In this manner
soils are constantly changing upon the same spot; sometimes they are
meliorated, at other times impoverished. From the tops of the mountains
to the shores of the sea, all the soils are subject to be moved from
their places, by the natural operations of the surface, and to be
deposited in a lower situation; thus gradually proceeding from the
mountain to the river, and from the river, step by step, into the sea.
Countries are thus formed at the mouths of rivers in the sea, so long as
the quantities of materials transported from the land exceeds that which
is carried from the shore, by tides and currents, into the deeper water.

The soil, with which the surface of this earth is always covered more or
less, is extremely various, both with respect to quantity and quality;
it is found resting upon the solid parts; and those solid parts are
always more or less affected by the influences of the atmosphere near
the surface of the earth. Those parts of the strata which approach
the surface are always in a decayed state; and this sometimes may be
observed for very considerable depths, according as the quality of the
materials, and the situation of the place dispose to that effect. This
general observation however may be formed, that, _cet. par._ the strata
become always more solid, or are found in their sound and natural state,
more and more in proportion as we sink into the earth, or have proceeded
from the surface.