328 BATHYMETRICAL SURVEY OF 



the Cambrian system, repeated by folds and reversed faults, and overlaid 

 by slices of Archaean gneiss, which resemble portions of the old floor on 

 which the Cambrian strata rest unconformably west of Loch Eriboll and 

 the Kyle of Durness. 



East of these displaced masses there is a great succession of crystalline 

 schists stretching eastwards to Strath Naver, which, in the north of 

 Sutherland, are everywhere separated from the rocks to the west by a 

 powerful line of disruption, termed the Moine thrust. They consist 

 of two main types flaggy quartzose granulites and garnetiferous 

 muscovite-biotite schists with intermediate varieties the whole 

 evidently representing an altered sedimentary series. Bands of 

 garnetiferous hornblende-schist are intercalated in these granulitic 

 schists, which are, without doubt, deformed intrusive sheets of igneous 

 material. The lithological characters of the strata, the order of succes- 

 sion, and the peculiar system of folding are magnificently displayed 

 on Ben Hope (3040 feet), where the divisional planes generally dip to 

 the east-south-east at angles varying from 12 to 30. But in addition 

 to these members of the Moine series, which are now generally regarded 

 as altered sediments, there are belts of massive, hornblendic, and 

 micaceous gneisses resembling the Lewisian types in the north-west of 

 Sutherland. The precise relationship of these two divisions of the 

 crystalline schists has not been definitely ascertained in this district, 

 but it is sufficiently clear that they have been affected by a common 

 system of folding, and in certain localities by common planes of 

 schistosity. From the north coast, these massive basic and acid gneisses 

 of Archaean type stretch southwards along the west side of the Borgie 

 valley to Loch Creagach, near Loch Laoghal, and another belt of 

 somewhat similar materials has been traced from the village of Tongue 

 northwards by Ribigill to Loch an Dithreibh. 



After the eastern schists had assumed their present crystalline 

 characters, they were pierced by intrusive masses of granite, which 

 form a picturesque group of peaks on Beinn Laoghal, south of Tongue. 

 The mapping of that area leads to the conclusion that the granite there 

 forms a great sill-like intrusion, which, on the north-east side of the 

 loch of that name, branches off into minor sheets, or apophyses. 



On the east side of the Kyle of Tongue there are various small 

 outliers of Old Red Sandstone, largely composed of conglomerate, as, 

 for instance on Cnoc Creagach, on Beinn Bhreac, and on Cnoc an 

 Fhreiceadain, which rest unconformably on the crystalline schists. 

 They contain fragments of the various component members of the 

 underlying platform, together with blocks of Cambrian quartzite and 

 limestone. 



Loch Hope. The lower portion of this lake, measuring about 2 miles 

 in length, is floored by thrust masses of Lewisian gneiss and deformed 

 schistose rocks affected by the Post-Cambrian movements, while the 



