186 BATHYMETRICAL SURVEY OF 



in the course of the movement. On Cul Mor, north of Cul Beag, our 

 colleague Mr. Hinxman found a boulder of nepheline-aegiriiie 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 moraiiiic 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 Carn 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 Bheimi 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 Beimi 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 



