386 SKY. GEOLOGY. HYPERSTHENE ROCK. 



which impede its examination in many other parts; a 

 stormy climate added to the distance from human habita- 

 tions and the difficulty of access, opposing all investi- 

 gation. Although I have only named the Cuchullin ridge, 

 this rock is not thus limited, since it extends to the moun- 

 tain boundary of the eastern side of Loch Coruisk, as will 

 be seen in the accompanying map. There is even reason 

 to suppose that it forms part of Blaven ; an opinion founded 

 on the similarity of its craggy outline and the remarkable 

 permanence and nakedness of its rocks, which I have 

 never yet had an opportunity of examining. 



Although it forms the principal and fundamental rock 

 of these mountains, it is not the only substance present. 

 Blue felspar porphyry of different aspects, blue claystone, 

 and common greenstone are also to be seen in different 

 places : if we should judge from the fragments of these 

 rocks that are scattered about, their extent would be 

 supposed considerable. But I believe this is one of the 

 fallacies that .not uncommonly arise from trusting to the 

 examination of detached fragments. No extent of such 

 rocks can any where be found in situ, but veins of them 

 may be seen in many places, whence it is natural to con- 

 clude that they are the origin of the fragments in question, 

 being from their inferior hardness more subject to waste 

 than the including rock. 



There is nothing more remarkable in the hypersthene 

 rock than its uncommon power in resisting the effects of 

 time and weather ; the consequence of which has already 

 been mentioned in the general account of the disposition 

 and features of the island. That durability is exhibited 

 not less remarkably in the condition of the rock on the 

 faces of the mountains, than in the spiry and rugged 

 forms of the summits already mentioned. Detached frag- 

 ments of it are indeed found, but as they have fallen 

 so they lie, unchanged, no accumulations of sand or gravel 

 from their decomposition being found in the valley ; the 

 small and partial deposits of clay that here exist having 



