Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/426

316 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 9, Kil-Donnan itself there stands out a wall of hard, whitish, brittle quartz-rock, which forms the Scarabin Hills*. These, which I have visited at intervals, suggested to me the idea that they were the result of intense metamorphism of Lower Silurian rocks.

When I first heard of the Sutherland discovery, in January last, I wrote to my friend Mr. Joass, urging him to examine the tract; for I knew that he combined the powers of a good geological observer with those of a skilful artist, and also that, through his residence at Golspie in the neighbourhood, he would be enabled to give us a better account of the real nature of the deposit than any casual visitor. I then found that he had already anticipated my wishes to a great extent; and since then, being encouraged by the Duke of Sutherland, the liberal-minded proprietor of the grounds, and His Grace's chief agent, Mr. G. Loch, M.P., he has greatly extended his acquaintance with the localities. As, fortunately, he has now come to London to tell us his own tale, I have no doubt that my associates will derive a very clear view of all the relations of these auriferous deposits — the more so as the map and sections which he has prepared are worthy of all commendation, and fully explain the detailed and complicated relations of the different rock-masses, with which I was unacquainted.

A note or two embodying my opinion as to the sources from which the Sutherland gold-detritus has been derived may not be out of place. Seeing, as above explained, that the transport of the great mass of the auriferous materials in question has in all probability been from W.N.W. to E.S.E., we have now to consider the composition of the successive rock-formations which present themselves as the observer proceeds from the west to the east coast, in order to form an opinion as to which of the parent rocks may most probably have furnished the gold-detritus.

1. The Laurentian or fundamental gneiss may be excluded from our consideration, not only from its composition and the absence in it of anything like auriferous quartz-veins, but also because it forms for the most part low buttresses only on the west coast, and scarcely anywhere rises to the height of the mountain watershed.

2. The Cambrian rocks are also excluded from our reasoning, for they are simply hard sandstones, grits, and conglomerates, which, clearly exposed in mountain-masses, never exhibit any metalliferous veins, and scarcely ever show any signs of metamorphism. They are entirely discordant to the Laurentian gneiss on which they rest, and are unconformably surmounted by the lowest Silurian rocks of the Highlands.

3. These lowest Silurian rocks, chiefly hard granular quartzite, which rise into lofty mountains, and contain intercalated masses of fossiliferous limestone, are all so thoroughly exposed in precipitous or highly inclined escarpments, that if they contained any auriferous veins the same must have been detected.

4. The next overlying group, consisting of chloritic micaceous flags and schists, which, as they dip away to the E.S.E., become


 * In Gaelic, Sceirea Beinn.