236 MR ALFRED HARKER ON 



A common incident of the cirque is a small rock-basin on its floor, occupied of 

 course by a tarn. The altitudes of the principal examples in the Cuillins are as 

 follows : — 



Coir a' Bhasteir, ..... 2250 feet. 



Coir' a' Ghrunnda, . . . 2220 „ 



Coir' an Lochain, . . . . . 1815 ,, 



Coire Labain, ..... 1805 ,, 



These high-level tarn-basins, a consequence of that excessive erosion in the head 

 portion of the valleys to which we have adverted, are of different significance from the 

 elongated lake-basins to be noticed below. They are of small dimensions, and approxi- 

 mate to the circular form. Though we have not sounded any of them, it is clear that 

 they are of comparatively small depth. Tn a cirque approaching most nearly to the 

 ideal form the tarn occupies the exact centre ; but if there is any tendency to 

 elongation in the direction of the valley, the tarn is found a little further down 

 (compare figs. 3 and 4). 



The concave upward sweep of the cirque continues, as has been said, to the actual 

 crest-line. Hence arises the characteristic cuspate form in cross-section of the main 

 lost) ridge of the Cuillins, and the adjoining 



portions of the chief branch ridges ; a 

 form illustrated by a rather extreme 

 example in fig. 7. In every place the 

 ridges are very narrow and the slopes 

 very steep. Here we must make a 

 remark of considerable importance in this 

 connection. The erosion in the higher 

 corries of which we have been speaking 

 NNE SSwImnw S c; F was °^ course dependent upon an adequate 



„ Z ~Z~7. . , „ , . ~ ~ r n ■ > . x» T • supply of abrading material at the under 



Fig. 7. — Section across the Basteir ridge from Coir a Bhasteir i. I J o 



on the north to Lota Corrie on the south ; scale, about 4J Surface of the ice. On the principal 

 inches to a mile. . , , . . . . . 



ridges, which we have shown acted as 

 ice-sheds, ice-erosion necessarily failed for want of a tool to work with. Hence, as 

 the excavation of the cirques proceeded, the dividing ridges were left standing out in 

 more and more salient relief. Thus arises that knife-edge form of the ridges which 

 makes them the delight of climbers. Hence, too, the peculiarly unbroken character of 

 the main ridge as a whole. From Sgiirr nan Gillean to Gars-bheinn it extends seven 

 miles, and nowhere presents anything that can be called a pass in the usual sense. 

 Although only the higher peaks rise above 3000 feet, the ridge never falls below 2500. 

 A stranger ascending one of the valleys, where he looks for a pass at the head, is 

 confronted by a precipitous rock-face, viz., the back wall of the cirque. 



Just as each portion of the main watershed — once the ice-shed — is merely the 



21 SO 



