In the Bovey coal too, I must observe, though its beds have the ligneous structure very distinct, the clay interposed between these beds, which is but little indurated, contains a great deal of coaly matter, in the form of thin flakes, interspersed through it. So far as I know, there are no mineral reins nor shifts, nor any bed of indurated stone, that accompany this coal; so that, though one can not doubt of its vegetable origin, some doubt may be entertained concerning the nature of the mineralizing operations, to which it has been subjected The consideration of these, however, does not belong to the present argument; and the peculiarities of this semi-mineralized coal, as it may be called, have nothing to do with the general question, whether wood coal and mineral coal are the same substance; about which question, if the gradations are properly considered, I think, no reasonable doubt can remain. 142. One of Mr Kirwan's objections to the vegetable origin of coal, is founded on this fact, that there is, in the museum at Florence, a cellular sandstone, the cells of which are filled with genuine mineral coal. "Could this (adds he) have been originally wood?"[53] The answer to the interrogatory proposed here as a _reductio ad absurdum_, is, that most undoubtedly it may have been wood. Sandstone with charred wood, that is, with wood coal in it, is not an uncommon phenomenon in coal countries. I have seen a specimen of this kind from the Hales Quarry, near Edinburgh, consisting of a piece of charred wood, imbedded in sandstone; the wood was much altered, but the remains of its fibrous structure were distinctly visible. This affords a perfect commentary on the specimen in the Florence cabinet. [Footnote 53: Geol. Essays, p. 321.] 143. If then it be granted, as I think it must, that the two kinds of coal we have been speaking of are of the same origin, it is not very necessary to enter on a refutation of Mr Kirwan's theory with respect to either of them. His account of the formation of mineral coal, however, is so singular, that it cannot be passed over without remark. Mr Kirwan supposes, 1mo, That natural carbon was originally contained in many mountains of the granite and porphyritic order, and also in siliceous schistus; and might, by disintegration and decomposition, be separated from the stony particles. 2do, That both petrol and carbon are often contained in trap, since hornblende, which has lately been found to contain carbon, very frequently enters into its composition.