Page:A Treatise on Geology, volume 2.djvu/122

 108 character of granite, and its peculiar effects on the adjoining rocks, to be the fruit of the local circumstances of its deep 'plutonic' origin? It is a 'hypogene' rock very slowly cooled; in other circumstances it would not appear as granite. In thin veins and parts remote from the great body it becomes a fine-grained or even compact mass, hardly different from the base of porphyry. What then prevents us from believing that many felspathic dykes, like the elvans of Cornwall and Cumberland, which are so very generally found on the borders of granitic districts, are really of granitic origin? This is a view which has become familiar to our minds, while traversing the vale of St. John's, Wastdale, and Shapfells, and which has already been advanced by MM. Oeynhausen and Von Dechen, while speaking of the geology of Cornwall. (Geol. Proceedings, vol. i.)

Amorphous Masses under all the Strata.—If granitic veins surprise us by their smallness and the perfection with which they have been injected into all the ramifications of a stratified rock, the vastness of the masses from which they arise is even more remarkable. For it is certainly true, that in every place, yet completely explored, the veins end downwards in granite formations, so extensive and unbounded, and appearing at so many points beneath the lowest strata, as to deserve, more than any other assemblages of mineral masses yet made known, the title of an universal formation. The differences which obtain between different sorts of granite are more striking to the eye than important in reasoning; for it has already appeared, that even when one of the constituent minerals, mica, is wholly absent, the chemical contents of this remarkable stone vary almost imperceptibly. (See p. 92.)

On this head it has not been found necessary to add to the remarks which will be found in Vol. I. p. 62.