ICE-EROSION IN THE CUILLIN HILLS, SKYE. 225 



is only 250 feet above sea-level, and over this point we may conceive the summit of 

 the ice-cap to have been situated. Some such supposition is necessary to account for 

 the enormous volume of what we may style the interior ice-drainage of the Cuillin 

 district. The ice-streams which found outlet by the three principal interior valleys 

 already mentioned — viz., Coruisk, Camasunary, and Sligachan — were clearly of far 

 greater volume than those which drained the exterior valleys of the Cuillins. The 

 Sligachan ice-stream, for instance (see map below), on emerging from its valley, 

 spread out fan-like through an angle of at least 120°, crossing several minor watersheds 

 and over-riding the hills (sometimes 1300 or 1400 feet high) as well as the lower 

 ground. Its left wing swept round the northern end of the Cuillins into the head of 

 Glen Brittle, penning into the narrow space between there and the mountains the ice 

 from all the northern and north-western corries. Its right wing, moving northward, was 

 for some distance strong enough to prevent the Scottish ice (with that from the eastern 

 Red Hills) from encroaching upon the coast of Skye. All this bespeaks a very great 

 thickness farther back, in the comparatively restricted valley and on the central water- 

 shed. Other features in the movement of the ice of the Cuillins point to the same 

 conclusion, and we shall see that the boulders in the drift accumulations afford strong 

 confirmatory evidence. 



(iii.) Movement of Ice during the Great Glaciation. 



The movement of the ice in and immediately around the Cuillins during the stage 

 of maximum glaciation is sufficiently indicated on the large map below. The chief 

 data are the directions of striae on rock surfaces and the distribution of boulders 

 of recognisable rock- types. These two criteria supplement one another, the former 

 being of most service among the mountains and the latter on the lower ground ; 

 while various other circumstances, such as the moulding of exposed crags, afford 

 additional information. The striae necessarily give the direction of movement of the 

 lower layers of the ice only, and we shall see that this is also true in great measure of 

 the dispersal of boulders. 



It is seen that within the mountain area proper, the natural outward flow was, in 

 general, closely guided, as regards the lower layers of the ice, by the form of the 

 ground. The main ridge-line of the Cuillins and the higher parts of the principal 

 branch ridges everywhere acted, for these lower layers, as an ice-shed. Some of the 

 branch ridges, however, were over-ridden. The most striking example of this is 

 afforded by the ice from Lota Corrie and the upper part of Harta Corrie. These form 

 the interior basin of the northern Cuillins, and now supply the head-waters of the 

 Sligachan River, which turns through a complete semicircle before running northward 

 to Sligachan. The ice-drainage took a more direct line, and found an outlet southward, 

 a large part of it crossing obliquely the ridge of Druim nan Ramh into the Coruisk 



