ition,
as well as that which is most impure or earthy; and we have shown that
there is a gradation, from the most bituminous state in which those
strata had been formed in being deposited at the bottom of the sea,
to the most perfect state of a chemical coal, to which they have been
brought by the operation of subterranean fire or heat.

We have been hitherto considering fossil coal as formed of the
impalpable parts of inflammable bodies, united together by pressure, and
made to approach in various degrees to the nature of a chemical coal,
by means of subterranean heat; because, from the examination of those
strata, many of them have evidently been formed in this manner.
But vegetable bodies macerated in water, and then consolidated by
compression, form a substance of the same kind, almost undistinguishable
from some species of fossil coal. We have an example of this in our turf
pits or peat mosses; when this vegetable substance has been compressed
under a great load of earth, which sometimes happens, it is much
consolidated, and hardens, by drying, into a black body, not afterwards
dilutable or penetrated by water, and almost undistinguishable in
burning from mineralised bodies of the same kind.

Also, when fossil wood has been condensed by compression and changed by
the operation of heat, as it is frequently found in argillaceous strata,
particularly in the aluminous rock upon the coast of Yorkshire, it
becomes a jet almost undistinguishable from some species of fossil coal.

There cannot therefore be a doubt, that if this vegetable substance,
which is formed by the collection of wood and plants in water upon the
surface of the earth, were to be found in the place of fossil coal, and
to undergo the mineral operations of the globe, it must at least augment
the quantity of those strata, though it should not form distinct strata
by itself.

It may perhaps be thought that vegetable bodies and their impalpable
parts are things too far distant in the scale of magnitude to be
supposed as subsiding together in the ocean; and this would certainly be
a just observation with regard to any other species of bodies: But the
nature of vegetable bodies is to be floatant in water; so that we may
suppose them carried at any distance from the shore; consequently, the
size of the body here makes no difference with regard to the place or
order in which these are to be deposited.

The examination of fossil coal fully confirms those re