Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/140

 a tract far removed, yet possibly not unconnected with this, is also composed of granite; and among this are found perfect granitic conglomerates, in which fragments of mica schist, equalling in quantity the substance which connects them, are seen imbedded in a paste of granite.

Occasionally the fragments are confounded with the mass at their edges, but at times they are so defined, and even so separable, that I procured a specimen with the distinct vacant impression of a rectangular fragment which had probably been detached. Cavities left in this way by the wearing out of the schist occur frequently in the rocks throughout the moor of Rannoch. The union between granite and the schists which it touches when passing through them in the form of veins, is known to be subject to similar variations. I may here add that the same appearances, though more rarely, may be found in Mar, and in the granite which occurs near Comrie.

It is well known that the passage of granite veins through schist is commonly well defined, and that the two are generally easily separable by the action of the weather. But the district of Rannoch, offers a multiplicity of veins which are so confounded with each other and with the rocks which they traverse, that their appearances cannot be described. They frequently vanish so imperceptibly both in the quartz rock and the mica slate, that a perfect passage from the one to the other is visible, while the accessions of additional veins, traversing and often shifting the already intricate structure, increase the unexampled confusion which reigns among them. The granite is often found imbedded in detached lumps in the schist, and I must remark of these lumps and veins, however minute they may be, that contrary to the granite veins and detached masses of Glen-Tilt or Corpach, their character is perfect even to the minutest division.