Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/141



I shall add but one remark more on this subject. Although the schistose rocks are seen only at the two ends of this prolonged tract of granite, the imbedded fragments can be traced throughout the whole. Hence it might be supposed that they were independent of the vicinity of the great schistose masses, whereas in the view which I have taken of them I consider them as connected with and dependent on them. It is plain that the absence of schist at present from the surface of the granite which forms the moor of Rannoch, proves no negative in this case, as we have abundant examples every where of the removal of great tracts of rock from parts of the earth's surface, and of the consequent denudation of the inferior substances; a change which may easily be conceived to have occurred here, thus leaving exposed that very surface of the granite which once was in contact with the superincumbent beds of schist.

Having thus traced the granite district of which Cruachan forms the most conspicuous portion as far as means of observation were afforded, I shall point out, under similar limitations, the porphyry which fell under my notice, since it will tend to illustrate the great predominance of the porphyritic veins in that mountain, as already described. I must however say that I consider the few following remarks, like those on the granite of Balahulish and Rannoch, in no other light, since they cannot be viewed even as a sketch of one of the most complicated and interesting districts in the whole range of Scottish geology. It will presently be seen that the great extent, the divided disposition, and the almost impracticable nature of the country throughout which these rocks are scattered, would require a very different investigation from that which a few distant and rapid visits permitted me to bestow on it.

The various schistose rocks, consisting of quartz rock, mica slate,