301. The stratification of granite, though it made no part of Dr Hutton's system, does by no means embarrass his theory with any new difficulty. Rocks, of which the parts are highly crystallized, are already admitted as belonging to the strata, and are exemplified in marble, gneiss, and veined granite. In the two last, we have not only stratification, but a schistose, united with a crystallized structure, and the effects of deposition by water, and of fluidity by fire, are certainly no where more singularly combined. The stratification of these substances is therefore more extraordinary than even that of the most highly crystallized granite. Neither the one nor the other can be explained but by supposing, that while such a degree of fluidity was produced by heat, as enabled the body when it cooled to crystallize, the whole mass was kept in its place by great pressure acting on all sides, so that the shape was preserved as originally given to it by the sea. As we cannot, however, suppose, that the intensity of the heat, or the fusibility of the substance through all the parts of a stratum, were precisely the same, we may expect to find in the same stratum, or in the same body of strata, that in some parts the marks of stratification are completely obliterated while in others they remain entire. It is thus that _veined granite_, of what I think should be called granitic schistus, often graduates into granite _in mass_, that is, granite without any schistose or fissile texture. Saussure says, that to be veined or not veined, is an affection of granite, that seems, in many cases, accidental;[155] as, in the midst of rocks of that substance, most clearly fissile, large portions appear without any vestige of stratification. Of this phenomenon, which is frequent in the Alps, instances are also to be met with in the granite rocks of Scotland, and the adjacent isles; and I know that Dr Hope, in a mineralogical excursion which he lately made among the Hebrides, observed many interesting and curious examples of it. Indeed, when rocks were so much fused as to crystallize, and so compressed, at the same time, as to remain stratified, they were evidently on the verge of change; two opposite forces were very nearly balanced, and each carried as far as it could go without entirely overcoming the other; so that a small alteration in the conditions may have made a great alteration in the effects. Hence a sudden transition from a stratified to an unstratified texture, which is only found in rocks highly crystallized, and such as have endured the most violent action of the mineralizing powers. [Footnote 155: Voyages aux Alpes, tom. iv. § 2143.]