ICE-EROSION IN THE CUILLIN HILLS, SKYE. 229 



role. The latter agent, following upon the former, has replaced the forms character- 

 istic of aqueous erosion by those proper to itself ; and it is in the peculiar topography 

 thus developed that we find the most convincing proofs of the important part played 

 by glacial erosion in this district. 



The most palpable evidence of the abrasive power of ice, fortified by included 

 de'bris, is seen in the rounded, grooved, striated, and polished rock-surfaces throughout 

 the gabbro mountains. Excluding only the higher parts of the summit-ridges, where 

 this characteristic appearance has been obliterated by subsequent frost-weathering, it 

 is scarcely too much to say that almost every square foot of the surface bears in this 

 way the stamp of glaciation. Very striking are the shores of Loch na Creitheach and 

 Loch Coruisk and the sea-loch Scavaig, localities known to many tourists ; but an 

 equally remarkable display is seen on the floor of any of the higher corries or on a 

 steep smooth mountain-slope such as the west faces of Blath-bheinn, Sgurr na Stri, 

 and Druim nan Ramh. The same smoothing, fluting, and polishing is found on the 

 vertical walls of gullies and on the undercut and overhanging rock-surfaces, which are 



o DO 7 



not uncommon in some parts of the Cuillins. It is clear that the ice has been in 

 close contact, throughout its whole extent, with the subjacent rocks, and has forced 

 its way into hollows and openings, vertically and horizontally, in a fashion which 

 argues effective plasticity in its lower layers. The conditions were totally different 

 from those which obtain beneath an Alpine glacier near its termination. 



In this connection it is instructive to turn from the mountains proper to the belt 

 of country a little beyond them, where the ice has evidently had much less erosive 

 power. Here we find that the bottoms of certain deep gorges have escaped glacial 

 erosion. The best example is the gorge of Allt Coire na Banachdich, just below 

 Eas M5r, where for some distance the gabbro is so rotten that it can be dug with a 

 spade. Something similar is seen in the gorge of Allt a' Coire Ghreadaidh. These 

 few places preserve the only relics in the district of the pre-G-lacial weathered surface. 



Another difference between the mountains and the bordering tract is seen in 

 the form of the roches moutonnees. In the sub-montane belt these exhibit the well- 

 known contrast between "Stossseite" and " Leeseite," but among the mountains each 

 knoll and ridge is commonly as well rounded and polished on the lee as on the weather 

 side. It is not to be supposed, however, that in the former case the craggy shape of 

 the lee side is an indication that ice-erosion has not operated on it : only the mode 

 of operation was different, taking the form of fracture instead of abrasion. This point 

 will be considered later. 



The impression of a smooth rounded outline upon every prominence, implying as 

 it does the removal of a considerable amount of material, is enough to show that the 

 work of the ice was something more than a mere excoriation of the surface. It is very 

 far, however, from affording a measure of the actual amount of glacial erosion. An 

 idea of this is to be gained only by an analysis of the physical features of the 

 mountain-district, distinguishing those due to glacial from those due to aqueous 



VOL. XL. PAET II. (NO. 12). 2 M 



