488 Alfred Harher — 8uhaenal Erosion of Skye. 



in length) of Garbh-choive. In their situation and condition these 

 coarse screes often differ markedly from true stone-falls or from the 

 waste of an escarpment in more ordinary circumstances. Some of 

 the blocks have evidently fallen upon some soft cushion, such as 

 snow ; others could not reach their actual position by merely falling 

 and rolling; others, again, have been derived from the rock upon 

 which they rest. Screes of this kind must be regarded as, in a sense, 

 Glacial accumulations, and, indeed, it is sometimes impossible to 

 separate them in mapping from true ice-borne debris. The additions 

 from later stone-falls are quite insignificant. What is true of the 

 Cuillins, the gabbro mountains, seems to be true also of the Red 

 Hills, formed of granite, though it is less easily demonstrated. The 

 screes which conceal much of the slopes of these hills are not to be 

 separated from the boulders which often cover the flat or gently 

 rounded tops, and these are much more regularly distributed than, 

 e.g., the blocks which build the tors of Dartmoor and other granite 

 plateaux. Chemical, co-operating with mechanical, degradation has 

 caused a sensibly greater post-GIacial waste of the general surface 

 here than elsewhere in the district, but it is probably still of trivial 

 amount, being measured by the slight projection of the occasional 

 basalt dykes above the granite which they traverse. 



Assigning, then, to the screes in general a Glacial age, it may be 

 stated that post-Glacial erosion in the district is almost limited to 

 the clearing out of the pre-Glacial channels by the removal of the 

 boulder-clay which filled them. Not the valleys, but only the water- 

 courses have been cleared, and these not always completely. On the 

 lower ground, where the declivities are slight and the drift in places 

 thick, streams seem in a few instances to have been diverted for 

 some distance into a new course, but in no case is a new channel cut 

 into rock. It will also be shown below that, when we speak of 

 boulder-clay being removed, this is to be ui:iderstood of the clay 

 itself, not of the contained boulders. The courses of the minor 

 streams in the drift-covered counti-y are detei-mined by the super- 

 ficial features of the drift itself, which remain practically without 

 change. Here and there a burn, winding its way among the 

 tumulus-like mounds of the ' kettle moraine,' has trenched upon the 

 steep slope of one of the mounds, but the smaller streams usually 

 flow over turf or peat. The mountain torrents, which drain the bare 

 rocks of the higher corries and fall in cascades over their rocky 

 barriers, give even less indication of post-Glacial erosion. Some- 

 times they are guided by dyke-fissures, but as a rule there is no 

 channel at all : the water glides over the polished rocks in a spreading 

 sheet, through which the glacial scorings appear as distinct as else- 

 where on the smooth surface. As might be inferred, the streams 

 throughout the district are found to be wholly free from sand, or 

 other detritus. 



Two localities in the district are worthy of special notice as 

 illustrating the foregoing remarks. One is Eas Mor, the most 

 consideral)le waterfall in the Cuillins, on the lower part of the burn 

 draining Coire na Banachdich. Here the burn plunges over a nearly 



