145. The quantity of hornblende and siliceous schistus, necessary to be decomposed, in order to produce the coal strata presently existing, is enormous, and would lead to an estimate of what is worn away from the primeval mountains, far exceeding any thing that Dr Hutton has supposed. It is true, that Mr Kirwan, never at all embarrassed about preserving a similitude between nature as she is now, and as she was heretofore, lays it down, that the part of the primeval mountains which is worn away, contained much more carbon than the part which is left behind. This, however, is an arbitrary supposition; and since, in this system, such suppositions are so easily admitted, why may we not conceive, in the primeval mountains, a more copious source of carbonic matter than hornblende or siliceous schistus? We have but to imagine, that the _diamond_ existed among these mountains in such abundance, as to constitute large rocks. This stone being made up of pure, or highly concentrated carbon, the adamantine summits of a single ridge, by their decomposition, might afford a carbonic basis, sufficient for the coal beds of all the surrounding plains. 146. We may also object to Mr Kirwan, that the siliceous part of the mountains has not been chemically dissolved; it has been only abraded and worn away. Mechanical action has reduced the quartz to gravel and sand, but has not produced on it any chemical change. The carbon, therefore, could not be let loose. Experiment, indeed, might be employed, to determine whether the siliceous matter of the secondary, and of the primary strata contains this substance in the same proportion. Again, a more fatal symptom can hardly be imagined in any theory, than that, when the circumstances of the phenomena to be explained are _a little_ changed, the theory is under the necessity of changing _a great deal_. Now, this is what happens to Mr Kirwan's theory, in the attempt made to explain by it the stratum of coal described in the _Annales de Chimie_,[56] as cutting a mountain of argillaceous strata in two, at about three-fourths of its height. This stratum, Mr Kirwan says, must have been formed by _transudation_ from the superior part of the mountain,[57] Besides that this is a gratuitous supposition of a thing, without example, it involves in it an absurdity, which becomes evident the moment the question is asked, What occupied the place of the coal-bed before the transudation from the upper part of the mountain? Has the _liquid coal_, as it percolated through the upper strata, expelled any substance from the place it now occupies? or has it been powerful enough to raise up, or to float, as it were, the upper part of the mountain? [Footnote 56: Tom. xi. p. 272.] [Footnote 57: Geol. Essays, p. 338.]