330 
Proceedings of the Royal Society of Edinburgh. [Sess. 
The group of isolated hills from Spidean Coinich to Canisp are com- 
posed of Cambrian quartzites with intrusive sheets of igneous material, 
resting partly on Torridon Sandstone, and partly on the ancient platform 
of Lewisian Gneiss, all in normal sequence. 
The range of mountainous ground extending from Glas Bheinn by 
Conamheall to Ben More is composed of thrust masses of Cambrian 
quartzite, Lewisian Gneiss, and, to a limited extent, on Ben More of 
Torridon Sandstone, which have been driven westwards by the Glencoul 
and Ben More thrusts. The Breabag range consists mainly of displaced 
Cambrian quartzites (fig. 4, p. 336) with intrusive sheets of igneous material. 
Further east on Sgonnan Mor, a core of Lewisian Gneiss is laid bare in 
association with Torridon Sandstone and Cambrian quartzite, the whole 
succession on that mountain overlying the Ben More thrust-plane. 
The undulating plateau lying between the central depression and the 
eastern range of mountains consists mainly of Cambrian dolomite and 
limestone, repeated by numerous thrusts and folds. It stretches from 
Achumore to Inchnadamff, thence up the Traligill river for a distance 
of 2 miles, and southwards to Allt nan Uamh and the Ledbeg river. 
Beyond the granitic intrusion of Cnoc na Sroine it has an extensive 
development, for it spreads over the peaty flat, about 4 miles in width, 
south-east of the hamlets of Elphin and Knockan. In the plateau 
between Inchnadamff and Allt nan Uamh the three lowest groups of the 
Durness sequence of Cambrian dolomites and limestones (1, Ghrudaidh, 
2, Eilean Dubh ; 3, Sail Mhor) are represented ; in the peaty moorland 
south-east of Elphin, only the two lowest have been recorded. 
The accompanying section (fig. 2) shows the complicated arrangement 
of the Cambrian dolomites and limestones between the Traligill river and 
Allt nan Uamh, where the zones have been heaped up by major and minor 
thrusts. These piled-up calcareous masses are resting on a sole or thrust- 
plane that truncates the underlying strata. Of special interest are the two 
outliers of displaced materials above the Ben More thrust-plane which have 
been left on the limestone plateau. They form Beinn an Fhuarain and 
Beinn nan Cnairnhseag to the south and north of Allt nan Uamh. With 
the exception of a core of Lewisian Gneiss on the west face of Beinn an 
Fhuarain, these outliers are composed of Torridon Sandstone with a small 
development of basal quartzite and pipe-rock. They clearly point to the 
original westward extension of the materials overlying the Ben More thrust- 
plane, and to their isolation by prolonged denudation from the main mass 
to the east of Breabag (fig. 2). 
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