outh Wales, the Kilkenny coal of Ireland, and the blind
coal of Scotland, notwithstanding that these are a perfect coal, or
charred to a coal, have nothing of the porous construction of the
specimen which I have just now mentioned; they are perfectly solid, and
break with a smooth shining surface like those which emit smoke and
flame.

Here is therefore a mineral operation in the preparation of those coals
which we cannot imitate; and here is the clearest evidence of the
operation of mineral fire or heat, although we are ignorant of the
reason why some coal strata are charred, while others are not, and why,
in some particular cases, the charred coal may be porous or spongy like
our coals, while in general those blind coals (as they are called) are
perfectly solid in their structure.

But to what I would call more particularly the attention of mineral
philosophers is this, that it is inconceivable to have this effect
produced by means of water; we might as well say that heat were to be
the cause of ice. The production of coal from vegetable bodies, in which
that phlogistic substance is originally produced, or from animal bodies
which have it from that source, is made by heat, and by no other means,
so far as we know. But, even heat alone is not sufficient to effect that
end, or make a perfect coal; the phlogistic body, which is naturally
compound, consisting of both inflammable and combustible substances,
must be separated chemically, and this must be the operation of heat
under the proper circumstances for distillation or evaporation.

Here is the impossibility which in the last chapter I have alleged the
aqueous theory has to struggle against; and here is one of the absolute
proofs of the igneous theory. Not only must the aqueous part of those
natural phlogistic bodies be evaporated, in order to their becoming
coal, but the oily parts must also, by a still increased degree of heat,
be evaporated, or separated by distillation from the combustible part.
Here, therefore, is evidently the operation of heat, not simply that
of fusion in contradiction to the fluidity of aqueous solution, but
in opposition to any effect of water, as requiring the absence or
separation of that aqueous substance.

But those natural appearances go still farther to confirm our theory,
which, upon all occasions, considers the compression upon the bodies
that are submitted to the operation of heat, in the mineral regions, as
having the greatest