79. That granite has undergone a change from a fluid to a solid state, is evinced from the crystallized structure in which some of its component parts are usually found. This crystallization is particularly to be remarked of the feldspar, and also of the schorl, where there is any admixture of that substance, whether in slender spiculæ, or in larger masses. The quartz itself is in some cases crystallized, and is so, perhaps, more frequently than is generally supposed. The fluidity of granite, in some former period of its existence, is so evident from this, as to make it appear singular that it should ever have been considered as a fossil that had remained always the same, and one, into the origin of which it was needless to inquire. If the regular forms of crystallization are not to be received as proofs of the substance to which they belong having passed from a fluid to a solid state, neither are the figures of shells and of other supposed petrifactions, to be taken as indications of a passage from the animal to the mineral kingdom; so that there is an end of all geological theories, and of all reasonings concerning the ancient condition of the globe. To an argument which strikes equally at the root of all theories, it belongs not to this, in particular, to make any reply. 80. We shall, therefore, consider it as admitted, that the materials of the granite were originally fluid; and, in addition to this, we think it can easily be proved, that this fluidity was not that of the elements taken separately, but of the entire mass. This last conclusion follows, from the structure of those specimens, where one of the substances is impressed by the forms which are peculiar to another. Thus, in the Portsoy granite,[27] which Dr Hutton has so minutely described, the quartz is impressed by the rhomboidal crystals of the feldspar, and the stone thus formed is compact and highly consolidated. Hence, this granite is not a congeries of parts, which, after being separately formed, were somehow brought together and agglutinated; but it is certain that the quartz, at least, was fluid when it was moulded on the feldspar. In other granites, the impressions of the substances on one another are observed in a different order, and the quartz gives its form to the feldspar. This, however, is more unusual; the quartz is commonly the substance which has received the impressions of all the rest; and the spiculæ of schorl often shoot both across it and the feldspar. [Footnote 27: Theory of the Earth, vol. i. p. 104.] The ingredients of granite were therefore fluid when mixed, or at least when in contact with one another. Now, this fluidity was not the effect of solution in a menstruum; for, in that case, one kind of crystal ought not to impress another, but each of them should have its own peculiar shape.