388 SKY.' GEOLOGY. HYPERSTHENE ROCK. 



of mineral structure, entirely different from the ordinary 

 varieties of this substance. Its granitic aspect is still 

 further displayed in a most striking manner in the spiry 

 forms of the summits, in their hard serrated outline, and 

 their overhanging masses, by which they are rendered 

 inaccessible even to the stags and the wild goats that 

 roam over this region of solitude and rocks. To this is 

 owing their highly picturesque aspect, which bears a 

 striking resemblance to that of the granite hills of Arran, 

 or the more stupendous granitic masses of the Alps. It 

 offers one instance, among a thousand others, of the little 

 dependence to be placed on the characters of the outline 

 in determining the nature of mountains ; and shows how 

 easily geologists, who have assumed the certainty of such 

 a criterion and used it in their investigations, have been 

 led to deceive themselves, and have contributed to mis- 

 lead their readers. 



The appearance produced by the fallen fragments 

 is very remarkable, and cannot fail to strike a visitor 

 on his first entrance into the valley of Coruisk. The 

 interval between the borders of the lake and the side 

 of Garsven is strewed with them ; the whole, of what- 

 ever size, lying on the surface in a state of uniform 

 freshness and integrity, unattended by a single plant or 

 atom of soil, as if they had all but recently fallen in a 

 single shower. The mode in which they lie is no less 

 remarkable. The bottom of the valley is covered with 

 rocky eminences, of which the summits are not only bare 

 but often very narrow, while their declivities are always 

 steep and sometimes perpendicular. Upon these rocks 

 the fragments lie just as on the more level ground, and 

 in positions so extraordinary that it is scarcely possible 

 to conceive how they have risen so high after the rebound, 

 or how they have remained balanced on the very verge of 

 a precipice. One, weighing about ten tons, has become a 

 rocking stone ; another, of not less than fifty, stands on 

 the narrow edge of a rock an hundred feet higher than 



