ccurately true, as the purest coal must have some ashes proper to
itself, yet, as this is a small matter compared with the quantity of
earthy matter that may be left in burning some species of coal, this
method of analysis may be considered as not far removed from the truth.

But, in distinguishing fossil coal by this species of chemical analysis,
not only is there to be found a perfect or indefinite gradation from a
body which is perfectly combustible to one that is hardly combustible in
any sensible degree, we should also fall into an inconveniency similar
to that already mentioned, of confounding two things extremely different
in their nature, a bituminous body, and a perfect charcoal. Thus, if we
shall found our distinction upon the fusibility and different degree of
having been charred, we shall confound fossil coals of very different
degrees of value in burning, or of very different compositions as
strata; if, again, we found it upon the purity of composition, in
judging from the ashes, we shall confound fossil bodies of very
different qualities, the one burning with much smoke and flame, the
other without any; the one fusible almost like wax, the other fixed and
infusible as charcoal.

It will now appear, that what cannot be done in either the one or other
of those two methods, may in a great degree, or with considerable
propriety, be performed in employing both.

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 i