190 
BATHYMETRICAL SURVEY OF 
Loch. The soundings also prove that there is a steep cliff along the 
south shore parallel to this line of shearing, which is continued west- 
north-west beyond the lake towards the Fionn Loch. 
Of all the lakes within the Archaean plateau, Loch SkinasTdnk 
presents the most irregular outlines. Still, it is obvious that its 
southern portion lies along a consequent valley, which rises between 
Cul Mor and Cul Beag. The lake is now drained by the river Polly, 
which, where it leaves the loch, flows over a barrier of Archaean gneiss. 
The longer axis of the loch south-west of Eilean Mor coincides with the 
trend of the early foliation of the gneiss and of certain intrusive dykes. 
The north-west margin of the loch has been determined by a pre- 
Torridonian line of fault, which shifts the outcrops of the intrusive 
dykes. 
Numerous rocky islets rise above the level of the loch, which, 
together with the soundings, reflect the varying character of the 
Archaean gneiss and intrusive dykes. Various faults enter the loch, 
which in many cases have given rise to well-marked inlets. The deepest 
sounding is 216 feet, which occurs not far to the south of Eilean Mor, 
in the line of the longest axis from south-east to north-v/est, and 
where that axis is intersected by a north-east and south-west fault. 
Loch Lurgain lies wholly within the Torridon Sandstone area, and 
is a true rock-basin, for at its outlet it flows over a barrier of rock into 
Loch Bada na h-Achlaise. The trend of the upper part obliquely 
crosses the strike of the Torridon Sandstone, while that of the lower 
is more or less parallel to it. About midway down the loch, roches 
moutonnees appear, and the soundings there vary from 20 to 56 feet. 
Above these islands there is a simple basin, the deepest sounding being 
156 feet north-east of Beinn Eun. Below the islands the basin is 
comparatively simple, the greatest depth being 148 feet. At the foot 
of the loch, immediately in front of the rocky barrier, the basin 
enclosed by the 100-feet contour-line is broader than further up the 
lake. 
Loch Bad a’ Ghaill is a true rock-basin, which, save at its lower 
end, where the rocky barrier is composed of Archsean gneiss, is floored 
by Torridon Sandstone. The soundings show that this lake forms two 
well-marked basins. The greatest depth of the upper one is 180 feet, 
which is a few feet below sea-level, and the deepest sounding of the 
lower basin is 153 feet. The ice-movement, as indicated by the striae, 
seems to have coincided generally with the direction of this lake and 
Loch Lurgain. Morainic drift is met with at intervals along the shores 
of these lakes. 
T^och Oiuskeich is likewise a rock-basin, the barrier being formed of 
Torridon Sandstone. The loch, save at its upper end, where there 
is a ridge of Archaean gneiss, is floored by Torridon Sandstone. The 
soundings show that this lake has been modified by a powerful north- 
