38 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 19, 



Tlie termination of the quartzite-period seems again to have been 

 marked by convulsions. To these we must ascribe the action by 

 which the higher portions were converted into gneiss ; or this gneiss, 

 if a pre-existing rock, forced over the quartzite. At the same time 

 we may suppose that those serpentinous felspar-rocks were formed 

 w^hich we have mentioned as occurring at Loch Alsh, Ullapool, and 

 Assynt, and which probably exist in other places. In the same period 

 also we may place the serpentinous rocks mixed with the gneiss of 

 Loch Greinord. The effect of this action has been to raise up the strata 

 along a N.E. and S.W. line, running nearly parallel to the west coast, 

 from a point between Cape Wrath and Durness on the north, by 

 Loch Greinord and Loch Keeshorn, to near Kyle Rhea in Skye. 

 The red sandstone dips west from this axis on the west side, and on 

 the east side east, with all the superior strata. The watershed of 

 the country is a parallel line, but lies much farther in the interior ; 

 and the influence of this line of elevation may also be traced in many 

 other physical features of the north-west Highlands*. 



The next great action to which this region was exposed has been 

 that process of denudation by which the mountains have been cut 

 out into their present forms. If the newer red sandstone on Loch 

 Greinord be, as Macculloch supposed, red marls or triassic, this 

 action must have begun shortly after this elevation, as it is chiefly 

 made up of fragments of these older strata. At the same time, or 

 soon after, the lias of Skye may have been forming in the deeper and 

 more distant parts of the sea. But at whatever time this denudation 

 took place, we may form some idea of the manner in which it was 

 effected. The whole west coast seems to have been slowly and 

 uniformly rising, until it stood like a long mural ridge above the 

 waters. But these waters were not idle, — breaching this rampart 

 from point to point along the old lines of fracture, and hollowing out 

 those great sea- and land-lochs by which the country is now inter- 

 sected. Even after this process was completed, the elevation seems 

 still to have gone on, — carrying the mountains far up into the regions 

 of ice and snow, when those enormous glaciers were produced which 

 filled their deepest valleys, and polished their hardest rocks, from the 

 sea-level to many hundred feet above it, as with a lapidary's tool. 



But the land must have again gone down, even below its present 

 level, leaving only the mountains, like islands, rising up out of the 

 ocean. In no other way can we explain the peculiar forms of the 

 low rounded gneiss hills between Loch Enard and Loch Inchard, and 

 the singular detritus with which they are covered. The innumerable 

 islands lying off the coast of Edderachyllis are only a portion of such 



* These two lines of elevation which I have thus noted in the rocks of this 

 region, Jt will be observed, correspond with two of the most ancient lines described 

 by M. Elie de Beaumont, in his " Notice sur les Systcmes de Montagues. " The 

 N.W. line may be referred to the system of Morbihan, which at Milford has the 

 direction of W. 36° 35' N. ; the N.E. line to the Longmynd System, with a direc- 

 tion N. 21° 24' E. at Milford. The order of succession is not, however, the same, 

 and my observations are not sufficiently numerous to make a more precise com- 

 parison worth while. So far as they go, these coincidences may be regarded as 

 favourable to the more ancient date of tlie beds. 



