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 Archsean 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 Bed 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 
