186 
BATHYMETRICAL SURVEY OF 
ill the course of the movement. On Cul Mor, north of Cul Beag, our 
colleague Mr. Hinxman found a boulder of nepheline-oegirine syenite 
just below the 2000-feet contour-line, which must have been derived 
from the Cnoc na Sroine and Aultnacallagach igneous mass (see 
Geological Map). No part of that mass reaches an elevation greater 
than 1306 feet, so that this boulder, during the westerly movement of 
the ice, must have been raised at least about 600 feet above its parent 
source. 
There is hardly any trace of boulder clay within the mountainous 
part of Assynt. This deposit appears in some of the valleys occupied 
by the Moine schists, as for instance, in the catchment basins of the 
Cassley and the Oykell, and in the valleys of the Cromalt hills. The 
drift deposits consist chiefly of moraines which have indeed a wide 
distribution. An examination of the morainic material, and of the 
boulders on the mounds, points to a period of confluent glaciers when 
the mountainous part of Assynt, together with the Cromalt hills, 
Cul Mor, Cul Beag, and the Coigach mountains, became independent 
centres of dispersion. The feathered arrows on the geological map 
indicate this later movement, and show a marked contrast from the 
persistent westerly trend of the earlier glaciation. A glance at the 
map will show, for instance, how from the north-east slope of the 
Glas Bheinn and Ben More Assynt range the later ice spread over the 
moorland plateau east of Gorm Loch Mor and Fionn Loch Mor onwards 
in the direction of Loch Shin. This plateau is covered with moraine 
mounds which contain boulders and debris of Cambrian quartzite, 
borne from the mountains to the west on to the area occupied by the 
Moine schists. Again, in the valley of the Cassley that drains the 
great corries east of Ben More Assynt and Cam na Convaroan, boulders 
of Cambrian quartzite have been traced for about 15 miles down to 
Invercassley. Again, on the Moine schist plateau east of Loch Ailsh 
and south-east of Sgonnan Mor, moraines occur containing blocks 
of Cambrian quartzite and thrust Archaean gneiss from that area. 
Further, on the west side of Glas Bheinn and Ben More Assynt, in 
the neighbourhood of Inchnadamph, part of this confluent glacier ice 
streamed northwards up the Skiag valley, carrying boulders of the 
intrusive porphyrite of Beinn Gharbh in its train. Local ice streamed 
off the eastern slopes of Canisp and Beinn Gharbh, which coalesced with 
that radiating from Breabag. In like manner, from the eastern slopes 
of Cul Mor and Cul Beag, local glaciers diverged which united with 
that moving off the Cromalt hills, and were deflected westwards towards 
the Archaean plateau and northwards towards Strath Kanaird. 
On referring to the geological map, it will be seen that most of the 
lochs lie within the area occupied by the Archaean gneiss. As the 
region is remarkably free of drift, the lochs lie in hollows in the solid 
rock, and are therefore rock-basins. Indeed, any one who visits the 
