GEOLOGY OF ARRAN. 



proximity to the Craig-Dhu mass, of which they are probably 

 injected pieces, and not derived from the disintegration of a 

 granite already exposed. 



(3.) The injection of the granite of the nucleus, whether 

 coarse or fine, in a melted state, amid the slate strata, was 

 certainly posterior to the deposit of the old red sandstone, 

 and may have been posterior also to that of the carboniferous 

 strata. 



(4.) If the granite of the nucleus be thus of later age than 

 the carboniferous strata, then may all the granites be of one 

 age, if such differences of mineral structure, or aggregation 

 of parts, can be admitted to exist in contemporaneous 

 granites. 



(5). But as the coarse-grained granite cannot with certainty 

 be pronounced newer than the carboniferous strata, while 

 the Craig-Dhu and Ploverfield granites undoubtedly are so, 

 then we may have two ages for these outbursts one for 

 that of the coarse granite, and another for that of these 

 latter. 



(6.) The constant character of the fine-grained granite of the 

 interior, through a considerable area, its impenetratiou of the 

 coarse, and of the slate in veins, point to a later origin than that 

 of the latter; while its almost perfect identity in structure and 

 arrangement of parts with the other two granites render 

 very probable the contemporaneity of these three, and their 

 posteriority to the coarse-grained variety. This conclusion 

 seems now warranted by the facts.* 



T/te Trappean Rocks. 



16. Arran is extremely rich in rocks of this class; most of 

 the known species occur, and also those numerous varieties 

 by which these graduate into one another. They form great 



* The conclnsion stated in the text has been embraced by Sir Charles 

 Lyell (loc. cit. ) on a review of the evidence set forth in our last edition, 

 as well as from his own knowledge of Arran. 



