•240 MR ALFRED HARKER ON 



by water; but the soundings taken are not numerous enough to bring this out in the 

 lower and deeper of the two basins. 



In the Camasunary valley there are two lakes, the upper and smaller Loch an 

 Athain and the lower and larger Loch na Oreitheach. The latter is visibly rock-bound 

 except at its head, where a gravel flat intervenes, which extends up to Loch an Athain 

 and some three-quarters of a mile further. The form of the rock-surface is thus obscured, 

 but it seems almost certain that the two lakes lie in separate basins. The proprietor, 

 ^\lr R. L. Thomson, had some soundings taken, and has kindly communicated the result. 

 The greatest depth found in Loch na Creitheach was 91 feet, at a point about one- 

 third up the loch from the S. end and a quarter across from the W. side. As the 

 water-surface is 85 feet above the Ordnance Datum, the loch descends about 6 feet 

 below this. Loch an Athain (111 feet above O.D.) has only about half the depth of 

 its larger neighbour. 



(ix.) Asymmetric Element in the Surf ace- Relief . 



The last peculiarity to be mentioned in the topography of the Cuillins is one 

 which is very evident when once pointed out. It is observable, not in the central, 

 but in the peripheral parts of the mountain-area ; and takes the form of a decided 

 asymmetry, as between the northerly and southerly aspects, in the transverse section 

 of any element of the relief (ridge or valley) which has something of an E. to W. 

 trend. The northward-facing slopes are invariably steeper than those facing in the 

 opposite direction. There is nothing in the geological structure of the ground to 

 account for this, and it is certainly too prevalent a phenomenon to be dismissed as 

 fortuitous. The only reason which suggests itself for this dependence of the character 

 of a mountain-slope upon its aspect, is one which connects it with the direction of 

 incidence of solar radiation. 



The asymmetric character is almost lost in the central parts of the area, but 

 declares itself more and more as we approach the margin. This is shown, e.g., in the 

 two sections across Coir' a' Ghreadaidh given above (fig. 5) ; but the point perhaps 

 comes out more clearly if we consider, not the valleys, but the ridges, i.e., those of the 

 exterior branch ridges which have (as is mostly the case) something of an easterly or 

 westerly direction. Any one of these in its higher or proximal portion, where it 

 forms the boundary between two cirques, shows the same general shape as the main 

 ridge. Farther away it changes its character. It may or may not abate something of 

 its steepness, and in some cases it becomes round-backed, though still with relatively 

 steep flanks; but in every case the contrast between the two faces declares itself in 

 the distal portion of the ridge (fig. 9). The westerly spurs of the Cuillins are Sgiirr 

 Thiiihn. Sgiirr' nan Gobhar with its offshoot An Diallaid, Sgiirr Dearg (west ridge), 

 and Sgiirr Sgmnain, to which we. may add the west ridge of Gars-bheinn. On the 

 opposite side of the gabbro mountains we have Belig, Sgiirr nan Each, and the 



