us, 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.
Thus we have this coal commonly in rectangular pieces, in which it
is extremely difficult to distinguish the direction of the bed, or
stratification of the mass. By an expert eye, however, this may be in
general, or at least sometimes, distinguished, and then, by knowing
the habit of the coal in burning, a person perfectly ignorant of the
philosophy of the matter may exhibit a wonderful sagacity, or even of
power over future events, in applying this body to fire; for, at his
pleasure, and unknown to those who are not in the secret; he may
apparently, in equal circumstances, make this coal either kindle
quietly, or with violent cracking and explosions, throwing its splinters
at a distance.

The explanation lies in this, that, though the rectangular mass of coal
appears extremely uniform in its structure, it is truly a stratified
mass; it is therefore affected, by the sudden approach of fire in a very
different manner, according as the edge of the stratum, which is seen in
four of the sides of this supposed cube, shall be applied to the fire,
or the other two sides, which are in the line of the stratum, or
parallel to the bed of coal. The reason of this phenomenon now remains
to be considered.

When the edge of the coal is exposed