Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/302

 to the same order of rocks as mica slate, and clay slate, it will only serve to point out their concurrence in another common circumstance. It is perhaps almost superfluous to say that the transition, which I am now describing, of quartz rock into granite, is by no means a dubious one, and that it does not bear the least resemblance to the common variety above referred to, which has so often been mistaken for granite. It is perfectly crystallized throughout, the felspar, the quartz, and the mica, having that aspect and relation to each other which cannot for a moment be mistaken by any one acquainted with the characters of rocks. The aspect of the mica alone is so remarkable, and so different from its appearance when found in quartz rock, that it is sufficient of itself to distinguish this modification from every other. Before quitting this subject it is necessary to remark, that one of the transitions between the granite and quartz rock takes place at the junction of the latter with the great body of granite.

I have been thus particular in describing this singular rock, because it has often been confounded with gneiss, from which it is strongly distinguished in its mineral character, and because it is important that a substance of so much consequence in the system of rocks as this is should have its relations accurately ascertained, and should not from laxity of definition be introduced into a series with which it has no geological connection. Many of the Western islands offer examples of it in its most genuine form.

From the point last described, following still the course of the stream, nothing is seen for the space of a mile and upwards, but a continued succession of the same varieties of schist. These rocks are also found occupying the hills on both sides of the glen, as far as they are within sight of the river.

If there are any other remarkable varieties, or any peculiar circumstances