1858.] MUKCHISON NOETHEEN HIGHLANDS, ETC. 365 



The upland longitudinal depression separating Suilven from Canisp 

 is in its lowest part occupied by Loch Ganiveh, the old gneiss hills 

 on the sides of which oifer many fine examples of the polishing, 

 scratching, and rounding action of a glacier which must have passed 

 along the gorge. In proof that the movement was towards the sea, 

 we found at Loch Inver many blocks of that large crystallized fel- 

 spathic porphyry which my active and zealous companion, Mr. Peach, 

 had in the previous year traced around the fiank of Canisp. As seen 

 from the shepherd's hut called Clacharie, the chocolate-coloured 

 bands of the lofty Suilven are partially fi'etted by pendent stalactites 

 like icicles, whilst a few green grassy slopes occur at intervals, to 

 give greater effect to the marked horizontality of the whole, which 

 is strikingly contrasted with the highly inclined gneiss on which it 

 rests. Here the base of the sandstone is a coarse brecciated conglome- 

 rate. The fault traversing this mountain, and which at a rough esti- 

 mate seemed to me to be an upcast to the south of from 800 to 1000 

 feet, is, as far as I could judge, parallel to a great fault in the adjacent 

 mountain of Canisp, observed by Mr. Peach. 



"WTiilst the unconformability of the Old Gneiss to the Cambrian 

 Sandstone is everywhere manifest, an equally clear discordance is 

 exhibited between the latter and the overlying quartz-rocks ; and 

 of this feature many examples will be presently given. 



In the depression between Canisp and Suilven, Mr. Peach detected 

 the existence of the strong band of red porphyry, with large crystals 

 of felspar, which is interposed between the gneiss and the great 

 conglomerate*. Thus, one of the earliest coarse sedimentary accu- 

 mulations in the cnist of the globe seems to have been ushered 

 in by the eruption and spreading out of porphyry associated with 

 red conglomerate, — a phenomenon which has been repeated at in- 

 tervals through the Silurian and Devonian periods to the conclusion 

 of the great Palaeozoic era, and strikingly during the accumulation of 

 the Permian deposits. The pebble-beds of the North-western High- 

 lands, though traceable for a considerable distance along a given 

 north and south zone (evidently an ancient line of shore), diminish 

 rapidly if followed on their dip, and are thus seen to be accumula- 

 tions, which, though of great thickness in some spots, thin out and 

 disappear in the course of a few miles. In no countiy is this feature 

 better seen than in following these Cambrian conglomerates of the 

 ^.W. Highlands to the E.S.E., when we distinctly see, as has just 

 been said, the fundamental or old gneiss at once covered by the 

 quartz-rock series, to the entire exclusion of any remnant of the 

 old shore pebbles with their coarse grits and sands, which, at a few 

 miles only to the west, clearly underlie all the quartz-rock series. 

 The range of these conglomerates southwards along the western 

 shores of Eoss-shire has already been well detailed by Prof. Nicol ; 

 and his sections are so clear that I have simply to refer the reader 

 to themf. 



* Prof. Nieol has also noticed the presence of porphyry associated with the 

 same rocks in Loch Broom. See Quart. Jom-n. Geol. Soc. vol. xiii. pp. 20, 21, 35. 

 t See Quart. Journ. Geol. Soc. vol. xiii. p. 23. 



