9. Again, it is certain, as Dr Hutton remarks, that there are few considerable bodies of schistus, even the most decidedly primitive, where sand and gravel may not in some parts be observed. Indeed, it is not only true that they are to be found in some parts of them; but, in fact, among many of the primitive mountains, we find large tracts, composed entirely of a schistose and much indurated sandstone, in beds highly inclined, sometimes alone, sometimes alternated with other schisti. In many of them, the sand of which they consist appears to be entirely of granite, from the detritus of which rock it should seem that they were chiefly formed.
10. Thus we conclude, that the strata both primary and secondary, both those of ancient and those of more recent origin, have had their materials furnished from the ruins of former continents, from the dissolution of rocks, or the destruction of animal or vegetable bodies, similar, at least in some respects, to those that now occupy the surface of the earth. This conclusion is not indeed proved of every individual portion of rock, but it is demonstrated of many and large parts, and those scattered indifferently through all the varieties of the strata; and therefore, from the rules of the strictest reasoning, we must infer, that the whole is derived from the same origin.[6]
Thus far concerning the materials of the strata; and, as these were originally loose and unconnected, we must next consider by what means they were consolidated into stone.
2. Consolidation of the Strata.
11. Though Dr Hutton has no where defined the meaning of the term consolidation, he has been scrupulously exact in using it constantly in the same sense. He understands by it, not merely that quality in a hard body, by which its parts cohere together, but also that by which it fills up the space comprehended within its surface, being to sense without porosity, and impervious to air and moisture.
Now, a porous mass of unconnected materials, such as the strata appear originally to have been, can acquire hardness and solidity only in two ways, that is, either when it is first reduced by heat into a state of fusion, or at least of softness, and afterwards permitted to cool; or when matter that is dissolved in some fluid menstruum, is introduced along with that menstruum into the porous mass, and, being deposited, forms a cement by which the whole is rendered firm and compact. Fire and water, therefore, are the only two physical agents to which we can ascribe the consolidation of the strata; and, in order to determine to which of them that effect is to be attributed, we must inquire whether there are any certain characters that distinguish the action of the one from that of the other, and which may be compared with the phenomena actually observed among mineral substances.
12. First, then, it is evident, that the consolidation produced by the action of water, or of another fluid menstruum, in the manner just referred to, must necessarily be imperfect, and can never entirely banish the porosity of the mass. For the bulk of the solvent, and of the matter it contained in solution, being greater than the bulk of either taken singly, when the latter was deposited, the former would have sufficient room left, and would continue to occupy a certain space in the interior of the strata. A liquid solvent, therefore, could never shut up the pores of a body to the entire exclusion of itself; and, had mineral substances been consolidated, as here supposed, the solvent ought either to remain within them in a liquid state, or if evaporated, should have left the pores empty and the body pervious to water. Neither of these however, is the fact; many stratified bodies are perfectly impervious to water, and few mineral substances contain water in a liquid state. That they sometimes contain it, chemically united to them, is no proof of their solidity having been brought about by that fluid; for such chemical union is as consistent with the supposition of igneous as of aqueous consolidation, since the region in which the fire was applied, on every hypothesis must have abounded with humidity.
13. Again, if water was the solvent by which the consolidating matter was introduced into the interstices of the strata, that matter could consist only of such substances as are soluble in water, whereas it consists of a vast variety of substances, altogether insoluble either in it, or in any single menstruum whatsoever. The strata are consolidated, for example, by quartz, by fluor, by feldspar, and by all the metals, in their endless combinations with sulphureous bodies. To affirm that water was ever capable of dissolving these substances, is to ascribe to it powers which it confessedly has not at present; and, therefore, it is to introduce an hypothesis, not merely gratuitous, but one which, physically speaking, is absurd and impossible.
This is not all, however; for, even if this difficulty were to be passed over, it would still be required to explain, how the water, which, together with the matter which it held in solution, had insinuated itself into the pores of the strata, became suddenly disposed to deposit that matter, and to allow it, by crystallization or concretion, to assume a solid form.[7] The Neptunists must either assign a sufficient reason for this great and universal change, or must expect to see their system treated as an inartificial accumulation of hypotheses which assigns opposite virtues to the same subject, and is alike at variance with nature and with itself; in a word, a system that might pass for the invention of an age, when as yet sound philosophy had not alighted on the earth, nor taught man that he is but the minister and interpreter of nature, and can neither extend his power nor his knowledge a hair's-breadth beyond his experience and observation of the present order of things.[8]