Thus, we have a species of coal in which we shall find but a small
degree of fusibility, although it may not be charred in any degree.
Such an infusible coal may therefore contain a great deal of aqueous
substance, and volatile oily matter; consequently may burn with smoke
and flame. But this same species of coal may also occasionally be
charred more or less by the operation of subterranean heat; and, in
that case, we should have a variety of coal which could only be
distinguished, from a similar state of pure bituminous coal, by the
ashes which they leave in burning. At least, this must be the case, when
both species are, by sufficient distillation, reduced to the state of
what may be properly termed a chemical coal.
But in the natural state of its composition, we find those strata of
kennel or parrot coal, possessing a peculiar property, which deserves to
be considered, as still throwing more light upon the subject.
We have been representing these strata of coal as homogeneous to
appearance, and as breaking indifferently in all directions; this last,
perhaps, is not so accurate; for they would seem to break chiefly into
two directions, that is, either parallel or perpendicular to the bed.
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