If, therefore, in mineral bodies, we find the two extreme states of this combustible substance, and also the intermediate states, we must either conclude, that this particular operation of heat has been thus actually employed in nature, or we must explain those appearances by some other means, in as satisfactory a manner, and so as shall be consistent with other appearances.

In this case, it will avail nothing to have recourse to the false analogy of water dissolving and crystallising salts, which has been so much employed for the explanation of other mineral appearances.  The operation here in question is of a different nature, and necessarily requires both the powers of heat and proper conditions for evaporation.

Therefore, in order to decide the point, with regard to what is the power in nature by which mineral bodies have become solid, we have but to find bituminous substance in the most complete state of coal, intimately connected with some other substance, which is more generally found consolidating the strata, and assisting in the concretion of mineral substances.  But I have in my possession the most undoubted proof of this kind.  It is a mineral vein, or cavity, in which are blended together coal of the most fixed kind, quartz and marmor metallicum.  Nor is this all; for the specimen now referred to is contained in a rock of this kind, which every naturalist now-a-days will allow to have congealed from a fluid state of fusion.  I have also similar specimens from the same place, in which the coal is not of that fixed and infusible kind which burns without flame or smoke, but is bituminous or inflammable coal.

We have hitherto been resting the argument upon a single point, for the sake of simplicity or clearness, not for want of those circumstances which shall be found to corroborate the theory.  The strata of fossil coal are found in almost every intermediate state, as well as in those of bitumen and charcoal.  Of the one kind is that fossil coal which melts or becomes fluid upon receiving heat; of the other, is that species of coal, found both in Wales and Scotland, which is perfectly infusible in the fire, and burns like coals, without flame or smoke.  The one species abounds in oily matter, the other has been distilled by heat, until it has become a caput mortuum, or perfect coal.

The more volatile parts of these bituminous bodies are found in their separate state on some occasions.  There is a stratum of limestone in Fifeshire, near Raith, which, though but slightly tinged with a black colour, contains bituminous matter, like pitch, in many cavities, which are lined with calcareous spar crystallised.  I have a specimen of such a cavity, in which the bitumen is in sphericles, or rounded drops, immersed in the calcareous spar.