5. Among bituminous bodies, pit-coal is the only one which constitutes regular and extensive strata; and no fossil has its origin from the waste of former continents, marked by stronger and more distinct characters. Not to mention that the coal strata are alternated with those that have been already enumerated, and that they often contain shells and corals, perfectly mineralized, it is sufficient to remark, that there are entire beds of this fossil, which appear to consist wholly of wood, and in which the fibrous structure is perfectly preserved. From these instances, the appearances of vegetable structure may be traced through all possible gradations, down to an evanescent state. This last state is undoubtedly the most common; and though coal does not then, on bare inspection, make known its vegetable origin, yet, if we take it in connection with the other terms of the series, as we may call them; if we consider that the two extremes, viz. coal, with the vegetable structure perfect, and coal without any such structure visible, are often found in the same or in contiguous beds; and, if we remark, that through all these gradations coal contains nearly the same chemical elements, and yields, on analysis, bitumen and charcoal, combined with a greater or less proportion of earth: if we take all these circumstances into account, we cannot doubt that this fossil is every where the same, and derives its origin from the trees and plants that grew on the surface of the earth before the formation of the present land.
6. Dr Hutton has further observed, that if those ancient continents were at all similar to the present, we can be at no loss to account for the want of any distinct mark of vegetable organization in the greater part of the coal strata. It is plain, that the daily waste of animal and vegetable substances on the surface of the earth, must disengage a great quantity of oily as well as carbonic matter, which, with whatever element it is at first combined, is ultimately delivered into the ocean. Thus, the oily or fuliginous parts of animal and vegetable substances, let loose by burning, first ascend into the atmosphere, but are at length precipitated, and either fall immediately into the sea, or are, in part at least, washed down into it from the land. From other causes also, much vegetable matter is carried down by the rivers; and the whole quantity of animal and vegetable substances thus delivered into the sea, must be very considerable, amounting annually to the whole residuum of those substances, not employed in the maintenance or reproduction of animal and vegetable bodies. Whether chemically united to the waters of the ocean, or simply suspended in them, this matter is at last precipitated, and, mingling with earthy substances, is formed into strata, the place of which will be determined by the currents, the position of the present continents, and many other circumstances not easily enumerated.
If, then, an order of things similar to what we now see, existed before the formation of the present strata, it would necessarily happen, that the animal and vegetable substances, diffused through the ocean, being separated from the water, would be deposited at the bottom of the sea, and, in the course of ages, would form beds, less or more pure, according to the quantity of earth and other substances deposited at the same time. These beds being consolidated and mineralized by operations that are afterwards to be considered, have been converted into pit-coal, the parts of which are impalpable, and retain nothing of their primitive structure.[3]
If, then, the formation of coal from animal and vegetable bodies be admitted, the general position which derives the origin of the strata from the waste of former land, as it is applicable to all the kinds already enumerated, and of course to all those with which they are alternated, comprehends a very large portion of the earth's surface. It comprehends, indeed, all the strata usually distinguished by the name of Secondary; but there is another great division of the mineral kingdom, viz. the rocks, called Primitive, which, as they are never alternated with the secondary, but are always inferior to them, must be further examined, before we can decide whether the same conclusion extends to them or not.
7. Here it must be carefully observed, that, among the primary rocks, the granite is not meant to be included, except where that stone is stratified, and either coincides with veined granite or with gneiss. The primitive strata, in Dr Hutton's theory, comprehend, besides gneiss, the micaceous, chlorite, hornblende, and siliceous schistus, together with slate, and some other kinds of argillite; to which we must add, serpentine, micaceous limestone, and the greater part of marbles. These are mostly distinguished by their laminated structure, by having their planes much elevated with respect to the horizon, and by belonging more to the mountainous than the level parts of the earth's surface. They rarely contain vestiges of organized bodies; so rarely, indeed, that they were called primitive by the geologists who first distinguished them from other rocks, on the supposition of their being part of the primeval nucleus of the globe, which had never undergone any change whatsoever; but this, I believe, has now almost ceased to be the opinion of any geologist.[4] The Neptunists hold the rocks, here enumerated, and also granite, to be produced by aqueous deposition; but maintain them to be in the strictest sense primeval, and of a formation antecedent to all organized bodies.
8. In opposition to this, Dr Hutton maintained, that the primary schistus, like all the other strata, was formed of materials deposited at the bottom of the sea, and collected from the waste of rocks still more ancient. When, therefore, he conformed to the received language of mineralogists, by calling these strata primitive, he only meant to describe them as more ancient than any other strata now existing, but not as more ancient than any that ever had existed. They are distinguished, in his system, by the name of Primary, rather than of Primitive strata.
That the account now given of their origin is well founded, may be proved by unquestionable facts. For, first, though, agreeably to the observation just made, the ancient strata do but rarely contain any remains of organized bodies, they are not entirely destitute of them. Different places in this island have been pointed out by Dr Hutton, where marine objects have been discovered in primary limestone, either by himself or others, and it would not be difficult to add more instances of the same kind.[5] In Dauphine, coal, which is certainly a derivative substance, has been found among mountains which have a title to the character of primitive, such as no one will dispute. These facts put the composition of such rocks from loose materials, beyond all doubt, and also prove their formation to be posterior to the existence of an animal and vegetable system. They do indeed prove this in the strictest sense, only of the particular beds in which they are found; but as these beds are in all other respects as much to be accounted primary as any part of the mineral kingdom, it is evident that the negative instances are here of no force, and that nothing can be gained to the adversaries of this opinion by denying it in general, if they are obliged to admit it in a single case.