THE NORTH-WESTERN HIGHLANDS. 38^ 



consists of gneiss with veins of granite. Professor Nicol remarks that 

 the whole series seems to be conformable, and as though the gneiss 

 were the more metamorphosed lower portion, and the quartzite the 

 less metarnorphic higher portion of one formation, which rests on the 

 granite of Ben Macdhui and the Cairngorm mountains, without evidence 

 of disturbance at the junction. 



Gneiss of the North- West Highlands of Scotland. The North- 

 West Highlands of Scotland comprise a strip of about a hundred miles 

 of country, running from N.N.K to S.S.W. through the west of 

 Sutherland and Eoss. This region is formed almost entirely of gneiss 

 and similar metarnorphic rocks which were fully described by Sir K. 

 I. Murchison and Professor Nicol. The succession of rocks from the 

 west to the east is first fundamental gneiss, sometimes diversified by 

 patches of igneous rocks ; second, quartzite with limestone ; and 

 thirdly, the eastern gneiss. Whether this is a true succession has 

 seemed doubtful since the discovery of fossils in the limestone at 

 Durness. The succession has been accepted by experienced sur- 

 veyors Murchison, Eamsay, Geikie, and Harkness. It was contested 

 by Nicol, who regarded the eastern gneiss as a repetition of the western 

 gneiss consequent upon faulting, so that the occurrence of fossils of 

 the genera, Maclurea, Murchisonia, and Orthoceras in the Durness 

 limestone, and similar fossils in the limestones of Assynt and the 

 quartzite of Loch Erriboll, would present no anomalies. The sections 

 are such that considerable latitude in opinion may be allowed to all 

 observers ; for the contortions, the slips, the changes in mineral 

 character, the occurrence of igneous rocks which break the succession, 

 and such-like phenomena, impose caution. Dr. Hicks, who has exa- 

 mined the southern part of this country, accepts the view of the younger 

 gneiss being a separate formation, and regards the older stratified rocks 

 as resting unconformably on gneissic and pre-Cambrian rocks, which 

 have a different strike and with him the unconformity stands in place 

 of the fault, while the western gneiss is made to reappear to the east. 



Hebridean Gneiss. Dr. Galloway has examined the sequence in 

 Loch Broom, Assynt, and Loch Erriboll, and regards the eastern 

 gneiss as newer than the western gneiss, but older than the Assynt 

 series. The lower rocks of this region, called fundamental gneiss or 

 western gneiss, are also termed the Hebridean. 



The Hebridean gneiss, according to Heddle, is composed almost 

 entirely of pink orthoclase, dark-green hornblende, small-flaked black 

 mica, and quartz with a greasy lustre. The hornblende and mica are 

 especially aggregated into broadly-banded stripes. At the south-west 

 of Sutherland, at Loch Iiiver, and towards Loch Polly, the gneiss is 

 greatly convoluted ; its layers become smaller, and the banding is less 

 prevalent. Where the rock is exposed to the sea, near Cape Wrath, 

 the felspar bands weather out, leaving the hornblende standing 

 isolated. At Cape Wrath the gneiss dips south-east ; its prevalent 

 strike is north-west to south-east ; but in Sutherland its dip is south- 

 west. 



Caledonian Gneiss. The eastern gneiss is termed the Cale- 

 VOL. i. 2 B 



