81. The perfect consolidation of many granites, furnishes an argument to the same effect. For, agreeably to what was already observed, in treating of the strata, a substance, when crystallizing, or passing from a fluid to a solid state, cannot be free from porosity, much less fill up completely a space of a given form, if, at the same time, any solvent is separated from it; because the solvent so separated would still occupy a certain space, and, when removed by evaporation or otherwise, would leave that space empty. The perfect adjustment, therefore, of the shape of one set of crystallizing bodies, to the shape of another set, as in the Portsoy granite, and their consolidation into one mass, is as strong a proof as could be desired, that they crystallized from a state of simple fluidity, such as, of all known causes, heat alone is able to produce. 82. This conclusion, however, does not rest on a single class of facts. It has been observed in many instances, that where granite and stratified rocks, such as primary schistus, are in contact, the latter are penetrated by veins of the former, which traverse them in various directions. These veins are of different dimensions, some being of the breadth of several yards, others of a few inches, or even tenths of an inch; they diminish as they recede from the main body of the granite, to which they are always firmly united, constituting, indeed, a part of the same continued rock. These phenomena, which were first distinctly observed by Dr Hutton, are of great importance in geology, and afford a clear solution of the two chief questions concerning the relation between granite and schistus. As every vein must be of a date posterior to the body in which it is contained, it follows, that the schistus was not super-imposed on the granite, after the formation of this last. If it be argued, that these veins, though posterior to the schisti, are also posterior to the granite, and were formed by the infiltration of water in which the granite was dissolved or suspended; it may be replied, _1mo_, That the power of water to dissolve granite, is a postulatum of the same kind that we have so often, and for such good reason, refused to concede; and, _2do_, That in many instances the veins proceed from the main body of the granite _upwards_ into the schistus; so that they are in planes much elevated in respect of the horizon, and have a direction quite opposite to that which the hypothesis of infiltration requires. It remains certain, therefore, that the whole mass of granite, and the veins proceeding from it, are coeval, and both of later formation than the strata.