498 GENERAL COMPARISON OF 



both passing through Bute with an undisturbed regu- 

 larity, and extending also through Arran ; but there 

 subject to a derangement of which the cause has already 

 been pointed out. That sandstone is the*first of the 

 secondary strata, and is covered by various portions of 

 trap rocks of greater or less extent, which, notwithstand- 

 ing, maintain a certain general parallelism to its north- 

 western margin. Thus, as the northern portions of Bute 

 and of Arran appertain to the primary strata of the 

 continent, the Cumbrays and Sanda belong to the se- 

 condary ; the greater Cumbray and Sanda containing 

 the sandstone alone, while the lesser Cumbray presents 

 an example of the trap which covers that rock on the 

 mainland, and which forms so conspicuous a feature in the 

 adjoining district of Ayrshire. By this comparison, the mu- 

 tual dependence of the whole group is established ; and 

 it becomes easy in imagination so to fill up the present 

 vacuities caused by the sea, as to restore the original 

 connexions of all the islands. 



It will be apparent on inspecting the general map, that 

 the principal deficiency occurs in the space that should 

 be occupied by the sandstone ; and, in examining the con- 

 nexions of these several rocks in a more detailed man- 

 ner, the principal attention will be directed to that portion 

 of the whole. 



The granite of Arran presents, as before remarked, a 

 solitary feature that admits of no comparison ; as no 

 analogous rock occurs on the mainland, in any position 

 which would lead us to suppose a connexion existing 

 between portions so widely separated. Nor are any 

 further remarks on this rock necessary ; its peculiar 

 effect in disturbing the regularity of the strata having 

 already been pointed out. As the general connexion of 

 the schistose rocks was also necessarily discussed in 

 illustrating the structure of Bute, any further remarks 

 on these would be equally superfluous. 



The peculiar circumstances of separation under which 



