35 1 2 ARKAN. GEOLOGY. GRANITE. 



As, in describing the syenite of Sky, I took occa- 

 sion to point out its occasional identity in point of 

 mineral structure, with those granites which occur beneath 

 the primary strata, and also referred to a fuller con- 

 sideration in this place, some peculiarities in the syenite 

 of St. Kilda, I shall terminate these remarks with a nearer 

 approximation of these facts to those which are visible 

 in this island. 



There is a very strong resemblance between the granitic 

 syenite of Sky and many portions of the small grained 

 varieties of granite that are found in Glen Catcol; nor 

 indeed is it easy at times to distinguish them, when 

 in hand specimens. The same striking resemblance exists 

 between the larger grained syenite of St. Kilda and some 

 parts of the granite of Goatfellj while the resemblance 

 here is rendered more striking by the identity of the 

 cavities in both, and by that of the crystallized sub- 

 stances, the felspar and quartz, which they both contain. 

 It is also remarkable that in both, the quartz is smoke 

 coloured, or black, and if Martin's report is trustworthy, 

 the magnitude of the crystals in St. Kilda is equal to 

 that which they attain in Arran.* In neither case have 

 geologists entertained any doubts respecting the geological 

 connexions of these different rocks ; the syenite of Sky 

 lying decidedly over the secondary strata while that of 

 St. Kilda is continuous with trap ; and the granites of Arran, 

 without any exception, being covered by primary schists 

 and successively by the red sandstone. These circum- 

 stances will perhaps only be regarded as striking examples 



on the mountains of Mar and Atholl, and more recently in Mull; but as 

 this subject was then sufficiently discussed, it is unnecessary to take 

 further notice of it here. 



* I must here also add, that I am informed by Mr. Von Buch that the 

 overlying granite which he has described in his work on Norway, re- 

 sembles precisely that now under review, containing similar cavities ; and 

 there is no doubt that his rock is connected with the porphyry, and conse- 

 quently appertains to the syenite of the overlying rocks. 



