538 JRev. T. G. Bonney — Cirque in the Hills of Sky e. 



the comparatively small elevation of the mountain crest behind 

 them showed that they could not be explained by any hypothesis 

 of a long slope of snow pressing downwards upon the ground 

 beneath it. The only lofty slope was that of Ben na Caillicb, and 

 that not only showed no corrie, but was in the wrong position. 



But on looking closely at the cliffs, it was evident that, dry as they 

 were then, this was not always the case ; again and again they are 

 seamed with tiny vertical furrows, streaks, and stains, which show 

 that often — probably after each heavy shower (and Skye is proverbial 

 for its rainy and stormy climate) — they drip with numerous rills. 

 These act both chemically and mechanically : attacking the alkaline 

 and calcareous silicates in the rock, and abrading it by the grit 

 which they sweep along. Heat and frost also act upon the saturated 

 rock ; and so the cliff is sapped slowly back by the agency of these 

 almost invisible but resistless forces. 



Fig. 2. — Rougli Sketch of Cirque in Rothstock, Surenen Pass. 



A. Clouds concealing peaks. B. Limestone cliffs. 



C. SUaly slope, -with small combes and snow-beds. 



D. Shaly cliffs furrowed by streamlets. 



E. Limestone cliffs, occasionally slightly grooved by streamlets. 



F. Floor of Cirque, with talus-heaps at side. 



But there is other evidence : the ice-worn slopes below are strewn 

 with debris, and their junction with the cliff is almost everywhere 

 masked by screes. Beneath each one of these furrows which I have 

 mentioned is its own tiny talus of fresh-fallen debris, showing 

 whence it has come and by what path. 



If it be urged that what I may call mere rain-drip, not yet col- 

 lected into anything more than slender rills, which are dry again 

 after an hour or two's sunshine, is inadequate, when aided by other 

 meteoric agencies, to sap and remove solid rock, and hew back 

 the slopes into a cliff, I would call attention to the mountains 

 throughout all this syenite region. For several hundred feet from 

 their bases their flanks are thickly clothed with sallow, heather, 

 and coarse herbage, and even spotted with not a few patches 



