74 Dr. Ma.c Cul lock's Shtch of the 



manence by which it appears to brave the external war of the ele- 

 ments which surround it, it is no less distinguished from the 

 stratified trap than it is from the neighbouring Red mountains, 

 whose rapidly decomposing summits covered with fragments have 

 long lost their characteristic forms, hastening with daily and visible 

 waste to the level of the plain below. It is equally distinguished 

 by its general aspect, being commonly separated by marked features 

 from the terraced trap with which it is associated, and no less so from 

 the Red hills, with which, however associated in almost a common 

 group, it forms no union. In mineral composition it also differs 

 widely from these, hornblende forming its predominant and charac- 

 teristic ingredient, as felspar does that of the latter. From the 

 terraced trap it differs less in composition, since hornblende is the 

 predominant ingredient of both, but it never like this contains amyg- 

 daloids and beds of tufo, neither does it entangle coal, sandstone or 

 ironstone, or exhibit the beautiful zeolites so abundant in the 

 terraced trap. 



If there were any theory of the formation of the rocks of this 

 class on which we could rely, it would not be useless to examine 

 how far their distinctness of character and appearance was consonant 

 to it, or how far they differed. Although my chief object has been ta 

 describe the geological features of the island, yet I may suggest that 

 such an independence of character and form seems to imply at least 

 that some independence in circumstances, as well as in time, has 

 accompanied the formation of these several portions of a rock 

 associated in so many other essential parts of their leading characters. 

 But the time for discussing questions -of this nature does not appear 

 yet to have arrived, and conjectures may be left to the ingenuity of 

 those to whom they afford a source of gratification. 

 . With this rock I terminate the history of the principal rocks 

 of Sky. " „, ,,•; 



