Thus, whether for the economical purposes of life, or the natural
history of fossil coal, those strata should be considered both with
regard to the purity of their composition as inflammable matter
deposited at the bottom of the sea, and to the changes which they
have afterwards undergone by the operation of subterranean heat and
distillation.
We have now considered the original matter of which coal strata are
composed to be of two kinds; the one pure bitumen or coal, as being
perfectly inflammable or combustible; the other an earthy matter,
with which proper coal may be variously mixed in its composition, or
intimately connected, in subsiding from that suspended state by which it
had been carried in the ocean. It is a matter of great importance, in
the physiology of this globe, to know that the proper substance of coal
may be thus mixed with heterogeneous bodies; for, supposing that this
earthy matter, which has subsided in the water along with coal, be no
farther connected with the combustible substance of those strata, than
that it had floated in the waters of the ocean, and subsided _pari
passu_ with the proper materials of the coal, we hence learn a great
deal with regard to the state in which the inflammable matter must have
been at the time of its formation into strata.
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