emical production has every essential quality, or every
peculiar property, of the fixed and infusible species; although, from
the circumstances of our operation, this caput mortuum may not have
precisely the exterior appearance of the natural coal. But, we have
reason to believe, it is not in the nature of things to change the
infusible species, so as to make it fusible or oily. Now, that this body
was not formed originally in its present state, must appear from this,
that the stratum here considered is perfectly solid; but, without
fusion, this could not have been attained; and the coal is now supposed
to be infusible. Consequently, this fixed substance, which is now,
properly speaking, a perfect coal, had been originally an oily
bituminous or fusible substance. It is now a fixed substance, and an
infusible coal; therefore, it must have been by means of heat and
distillation that it had been changed, from the original state in which
this stratum had been formed.

We have thus, in the examination of coal strata upon chemical
principles, received a certain lesson in geology, although this does not
form a proper distinction by which to specify those strata in general,
or explain the variety of that mineral. For, in this manner, we
could only distinguish properly two species of those strata; the one
bituminous or inflammable; the other proper coal, burning without smoke
or flame. Thus it will appear that, as this quality of being perfectly
charred is not originally in the constitution of the stratum, but an
accident to which some strata of every species may have been subjected,
we could not class them by this property without confounding together
strata which had differences in their composition or formation.
Therefore, we are led to inquire after some other distinction, which may
be general to strata of fossil coal, independent of those changes which
this substance may have undergone after it had been formed in a stratum.

Perfect mineral coal being a body of undistinguishable parts, it is only
in its resolution that we may analyse it, and this is done by burning.
Thus, in analysing coal by burning, we have, in the ashes alone, that by
which one species of coal may be distinguished from another; and, if we
should consider pure coal as having no ashes of itself, we should then,
in the weight of its ashes, have a measure of the purity of the coal,
this being inversely as the quantity of the ashes. Now, though this be
not a