﻿1861.] 



MTTB.CHISON" AND GEIKIE HIGHLANDS. 



193 



strata, and abounding in so many deep gorges and ravines, there 

 were yet no lines of extensive faulting. Such lines must almost 

 necessarily exist. But what are the conditions needful for their 

 discovery ? Must we not have at least certain persistent strata of 

 well-defined lithological characters, and trace them in their windings 

 among the mountains ? Such strata, however, are not well repre- 

 sented among the Silurian rocks of these regions. The limestones, 

 as we have seen, are subject, as in Wales and Siluria, to sudden 

 and capricious changes, amounting even to entire disappearance. 

 The upper gneissose series has no distinguishing band, and, where 

 the limestone is wanting, passes down imperceptibly into the quartz- 

 rock. The quartz-rock, too, has a more or less uniform aspect 

 throughout ; so that faults, repeating one part of it against another, 

 might easily escape observation. If, however, we could find it on 

 some exposed hillside, faulted along with its subjacent Cambrian 

 sandstones, there would then be every probability of detecting the 

 fractures ; for the quartz-rock being white, and the Cambrian dark 

 reddish-brown, any alternation of these two formations would be 

 observable even at a distance. This desideratum is admirably sup- 

 plied among the craggy mountains of Beann Taobhliath, which, from 

 within four or five miles of Loch Maree, extend southwards almost to 

 Loch Doule, on the road between Dingwall and Skye. The hillsides 

 along the deep glens in that region afford the clearest and most 

 startling proofs of dislocation ; and yet, but for the contrasting co- 

 lours of the two series of rocks, these fractures would probably never 

 have been detected, unless, with a good map in his hand, a geologist 

 had set out purposely to seek for them. Hence it is in the highest 

 degree probable, that among the gneissose rocks there may exist many 

 large faults, which have not been even suspeeted. 



Having made this admission, however, it by no means follows that 

 over the region we have examined any kind of fault may occur, and 

 along any part of the line. In the sections already described in 

 this paper there is certainly no fault, but a clear order of superpo- 

 sition from the lower quartz-rock into the upper quartzose or gneiss- 

 ose series. But between the points which we have selected for 

 description in detail, it is far from improbable that faults may inter- 

 vene, limited in their extent and in their amount of throw. They 

 can only be local ; and their character is probably sufficiently shown 

 in the region, one or two sections in which we shall now describe. 



Beann Taobhliath, or "the Grey Heads.'''' — About 5 or 6 miles south- 

 west from Kinloch Ewe, on the road to Loch Torridon, lies the water- 

 shed between that arm of the sea and the freshwater Loch Maree. 

 On the north side of the valley the mountains of Leagach and Ben 

 Eay, already referred to (fig. 9), show their capping of white quartz- 

 rock on the sombre-hued Cambrian sandstones which form their 

 mass. It was the southern side of the valley, however, that chiefly 

 attracted our attention. There the quartz-rock on the mountains, 

 when seen from the road, appeared interbanded with some dark rock, 

 as if sheets of greenstone had been thrust between its strata. This 

 seemed the more inexplicable as we had seen no such rock in any 



