Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/484

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Dr. Mac Culloch on Quartz Rock.

character considerably different from that which it exhibits either in Jura, in Assynt, or in the other places which I have described. Its aspect is more uniform, and its texture more compact. Its fracture is rather more splintery than granular, and it rarely contains felspar, a mineral seldom absent for a long space in the generality of the quartz rock. It is here of various colours, brown, grey, yellowish, reddish, and white, but its predominant tint is a blueish grey. Its marks of stratification are obscure, yet they may, however disturbed, be traced, and its true character is I think determined by a compact breccia, which in some places may be observed separating it from the schistose rocks, the micaceous and argillaceous slate. It occurs again in Sky under another form, namely, in disrupted portions, forming the tops of low hills in the district of Slate, of a snowy aspect and compact texture, with irregular grains of felspar imbedded, and in intimate connexion with the micaceous schistus.

I have reason to think that the same rock will be found to form a large portion of that ridge of mountains which extends in a curved line to the south of Ben Nevis, so as to constitute the southern boundary of Glen Nevis; but as this conclusion is only founded on a distant observation, and on the peculiar aspect and mode of decomposition which these hills exhibit, I lay no stress on it. Yet as it actually occurs in that part of the declivity of this group which descends into Loch Eil, and is to be found constituting a considerable mass of mountain at Balahulish, I shall not be surprised if future observers assign to it a very considerable extent in this district. It is at the edges of the road between Balahulish and Fort William, that it may be conveniently examined, and it will there also be seen to alternate with a compact argillaceous schist.