98 Prof. Forbes on the Topography and Geology of the 



from that of the fundamental rock." "' This is substantially 

 correct. The little gravel on the shore of Loch Coruisk is 

 almost entirely composed of rolled claystone and trap fel- 

 spar; in vain we look for the numerous loose crystals of 

 hypersthene, which, from their individually indestructible 

 nature, we might expect to find. I do not mean to say that 

 such do not exist ; but, considering the circumstances, they 

 are singularly few. Hence it may fairly be concluded, that 

 a cause which could manipulate this adamantine rock with 

 the freedom which the abrasions so often alluded to display, 

 is one which does not now act, even to the most trifling ex- 

 tent, in our climates. The indefinite mechanical power of 

 glaciers, in this respect, I have elsewhere sufficiently insisted 

 on. 



Secondly, The other striking consideration which the cir- 

 cumstances of the CuchuUin hills presents, is their small ex- 

 tent and insulated position. If we are to attempt to explain 

 these phenomena of abraded rocks and transported blocks 

 in any of the ways which have been proposed (and perhaps 

 not unreasonably), to account for them in other positions, 

 •we are here wholly at fault, for want of a sufficiently exten- 

 sive field of operations. The radiating nature of the lines of 

 abrasion, and of scattering of blocks, which we have already 

 proved to exist, by examples on the south, east, north, and 

 west sides of the Cuchullin, (see the map) but which, in every 

 case, indicate a force emanating from the centre of the group, 

 makes it impossible to conceive feeders of torrents sufficiently 

 powerful, and sufficiently long maintained for producing the 

 least important eff'ect, to have had their origin within so small 

 a space. The steep, confined, short ravines of the Cuchul- 

 lins, terminating in ridges, jagged like a saw, afford no scope 

 *for vast mountain lakes, or even for the generation of pro- 

 digious waves, carrying everything before them : such lakes 

 could not have found a place — such waves, even if generated, 

 could have acted but for a few minutes. The theory of float- 

 ing-ice is obviously of equally little avail. On the other 

 hand, the ravines in question are perfectly fitted for lodging 



* MacCuHoch, Description, i., p. 386. 



