'242 MR ALFRED HARKER ON 



bold range of cliff, partly enclosing a come, to the north and a gentler slope to the 

 south, though the dip, which is northerly, would lead us to anticipate the reverse. 



If, as I believe, the asymmetric character of the ridges and valleys in the outer 

 parts of the mountain area is really significant, and depends upon the different aspects 

 of the slopes relatively to the sun, it seems clear that this influence was exerted, not 

 at the stage of maximum glaciation, but when the ice-cap had shrunk so as to occupy 

 the valleys alone, and during the later glaciation, which was effected by glaciers only. 

 In the preceding sections I have not attempted to apportion the work of erosion 

 between the ice-cap and the glaciers. I have in more than one place postulated a 

 great thickness of ice over the centre of the area, and it is to be inferred that some 

 of the most characteristic features of the district, especially in its interior part, were 

 developed under such conditions ; but we may still allow no inconsiderable role as 

 agents of erosion to the glaciers, more particularly in the middle and lower courses of 

 the mountain-glens. It is possible that a more thorough analysis might enable us to 

 discriminate, by means of the resulting surface-relief, between the sculpture of a valley 

 by a limb of an ice-cap on the one hand and by a glacier on the other, both being- 

 assumed to move down the valley. At present we are only concerned in distinguishing 

 these two jointly from a foreign ice-sheet forced across the face of the country with 

 scant regard to the pre-existing form of the ground. From the foregoing brief 

 examination of the peculiar type of surface-configuration presented by the Cuillins, 

 it has been made sufficiently clear that most of the positive characteristics, i.e., those 

 involving the development as distinguished from the obliteration of features of relief, 

 depend upon the fact that the flow of the ice followed, in general and upon a broad 

 scale, the natural direction of drainage. That in other circumstances the results miarht 

 be very different is suggested by several of the phenomena described above. A good 

 illustration is afforded by the small pre-Glacial glen of Allt a' Coir' an Lochain, a type 

 of numerous others in the district. Here, as we have seen, the movement of the ice 

 in the upper part of the valley was down-stream, but in the lower part directly at 

 right angles to it. The result has been that the head of the glen is enlarged and the 

 lower portion completely obliterated. 



III. The Glacial Accumulations and their Testimony to Ice- and 



Frost-Erosion. 



(x.) Drift Deposits. 



We turn now from erosion to the complementary process of deposition ; but, in 

 accordance with the general design of this contribution, the glacial accumulations will 

 be considered chiefly as throwing light upon the subject of ice-erosion. Drift deposits 

 are found, though not as an unbroken sheet, over the whole of the tract that lies 

 beyond the mountains. The continuous deposits — i.e., excluding scattered erratics — 



