Mineralogy of sky. 63 



characters of the southern part of the group, Garsven and Blaven, 

 since I was unable to procure access to the other portions of it. 



In other parts of Sky we have seen that the greenstones as well 

 as the other varieties of trap, are disposed in a flat or apparently- 

 stratified manner by which the general aspect and outline of all these 

 portions of the island are determined. Here on the contrary the 

 external outline and general features are those of granite, and I may 

 say that to its forms they appear also to add its permanence and du- 

 rability. They are disposed in huge curved beds of which the 

 external angles are, like those of granite in similar cases, slightly 

 rounded, and they extend over considerable spaces, offering smooth 

 sheets of rock unmarked by a single fissure or indication of past or 

 future fractures. No eye could distinguish them from granite except 

 by examining their composition. Their resemblance to this rock in 

 disposition, and their dissimilarity to the greenstones of the stratified 

 parts of the island, are in every way so decided that no position can 

 be assumed, nor any view taken of them, however general, or on a 

 scale however comprehensive, which can convey the slightest idea 

 of a tendency to stratification. Nor do they in any case that I have 

 seen shew the tendency to vertical fracture so common among green- 

 stones, being in every respect, except that of mineral structure, en- 

 tirely different from the ordinary varieties of this substance. Their 

 granitic aspect is still further expressed in a most striking manner 

 by the spiry forms of the summits, by their hard serrated outline 

 and their overhanging masses, a disposition by which they are ren- 

 dered 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 masses of the granitic 



