n the surface and shell of
the earth.

Before entering on the principal division of this subject, the imbedding
and preservation of animal and vegetable remains, I shall offer a few
remarks on the superficial modifications caused directly by the agency
of organic beings, as when the growth of certain plants covers the slope
of a mountain with peat, or converts a swamp into dry land; or when
vegetation prevents the soil, in certain localities, from being washed
away by running water.

In considering alterations of this kind, brought about in the physical
geography of particular tracts, we are too apt to think exclusively of
that part of the earth's surface which has emerged from beneath the
waters, and with which alone, as terrestrial beings, we are familiar.
Here the direct power of animals and plants to cause any important
variation is, of necessity, very limited, except in checking the
progress of that decay of which the land is the chief theatre. But if we
extend our views, and instead of contemplating the dry land, consider
that larger portion which is assigned to the aquatic tribes, we discover
the great influence of the living creation, in imparting varieties of
conformation to the solid exterior which the agency of inanimate causes
alone could not produce.

Thus, when timber is floated into the sea, it is often drifted to vast
distances, and subsides in spots where there might have been no deposit,
at that time and place, if the earth had not been tenanted by living
beings. If, therefore, in the course of ages, a hill of wood, or
lignite, be thus formed in the subaqueous regions, a change in the
submarine geography may be said to have resulted from the action of
organic powers. So in regard to the growth of coral reefs; it is
probable that a large portion of the matter of which they are composed
is supplied by mineral springs, which often rise up at the bottom of the
sea, and which, on land, abound throughout volcanic regions hundreds of
leagues in extent. The matter thus constantly given out could not go on
accumulating for ever in the waters, but would be precipitated in the
abysses of the sea, even if there were no polyps and testacea; but these
animals arrest and secrete the carbonate of lime on the summits of
submarine mountains, and form reefs many hundred feet in thickness, and
hundreds of miles in length, where, but for them, none might ever have
existed.

_Why the vegetable soil does not augment in