These imperfect hexagonal cases of quartz, filled with feldspar, certainly indicate the crystallization of substances, which all assumed their solidity at the same time, and, in doing so, constrained the figures of one another. To use the words of Dr Hutton, "whether crystallizing quartz inclose a body of feltspar, or concreting feltspar determine the shape of fluid quartz, particularly if we have, as is here the case, two solid bodies including and included, it amounts to a demonstration, that those bodies have concreted from a fluid state of fusion, have not crystallized, in the manner of salts, from a solution."[150] [Footnote 150: Trans. Royal Society Edin. _ubi supra_, p. 84.] 291. The quartz in granite so generally receives the impressions of all the other substances, particularly of the feldspar and schorl, and appears to be so passive a body, that it has been doubted by some mineralogists, whether in this stone it ever assumes its own figure, except where cavities afford room for its crystallization. But it is certain that, beside the Daourian granite just mentioned, there are others, in which the quartz is completely crystallized. Of this sort are some specimens, found in a granite vein on the west side of the hill of St Agnes, in Cornwall. The vein traverses the primitive schistus, of which that hill consists, from south to north nearly: the stone is much decomposed, and the feldspar in general is almost reduced to the state of clay. In this decomposed mass, quartz crystals are found, having the shape of double hexagonal pyramids, perfectly regular and complete. The side of the hexagon, which is the base of the two opposite pyramids, varies from half a tenth to a tenth of an inch in length, and is the same with the altitude of each of the pyramids. In some few specimens, the two pyramids do not rest on the same base, but are separated by a very short, though regular, hexagonal prism. The surfaces of these crystals are rough, and somewhat opaque, with slender spiculæ of schorl frequently traversing them. This roughness is occasioned by slight furrows on the surface of the crystal, very regularly disposed, and parallel to one another, being without doubt impressions from the thin plates of the feldspar, which surrounded the crystal, and slightly indented it. They very much resemble some impressions, remarked by Dr Hutton in the granite of Portsoy, and ascribed by him also to a similar cause. He has represented these in his Theory of the Earth, vol. i. plate ii. fig. 4. The action and reaction of two crystallizing bodies, hardly admits of a stronger and more unequivocal expression, than in these two instances.