GRANITES OF THE WEST OF SCOTLAND. 239 



district. Granitic structure alternates with gneiss structure in the 

 southern part of Ben Aigan. In the hill called Little Conval, near 

 Dufftown, the S.E. base is a large-grained rock with red felspar and 

 little mica, but higher up it becomes finer-grained, and at the top is a 

 mixture of small-grained red felspar and quartz. But the felspar is 

 redder than is usual in gneiss, and the quartz is less in amount. 



Grampians. Of the Grampian chain, Professor Judd remarks 

 that where the lower portions of the masses are exposed by extensive 

 denudation, the rock presents the character of a typical granite, such 

 as is well seen in the Ross of Mull ; but where it rises into lofty 

 peaks it becomes more and more hornblendic, and then graduates into 

 felsite, which rock is commonly more or less porphyritic. And it is 

 worthy of notice that a similar series of changes in the character of 

 the rock is often to be observed when the granite is traced from its 

 central portion towards the outer margin. At the junction of the 

 granite and stratified rocks numerous veins, which often include 

 angular fragments of the strata, penetrate the water- formed deposits, 

 and large masses of stratified rocks, altered on their surface, and pene- 

 trated by granite veins, are found enveloped in the igneous mass, so 

 that the granite is entangled with the strata. Granite and felstone 

 dykes are well seen in the Passes of Glencoe and Brander, and are 

 always numerous near the central igneous masses. 



The central mass of Ben Nevis consists of hornblendic granite, 

 passing by insensible gradations into ordinary granite on the one 

 hand and syenite granite on the other. The period at which these 

 granitic protrusions took place was posterior to the deposition of the 

 Cambrian rocks, which were already metamorphosed when the granite 

 penetrated them ; and since this granite never penetrates either the 

 secondary or tertiary strata, it is inferred to belong to the newer 

 palaeozoic period. Professor Haughton describes the granite of the 

 Koss of Mull as coarse-grained, with abundance of quartz, pink 

 orthoclase, and a little black mica. It contains 74 per cent, of silica 

 and 1 6 per cent, of alumina. 



The Granite of Loch Etive is described by Mr. R. H. Scott, F.R.S., 

 as consisting of a fine-grained rock in which the felspar is mainly 

 anorthic. It sometimes contains sphene, and includes many frag- 

 ments of slaty rocks, which are often angular and but little altered ; 

 it is traversed by dykes of red quartz felstone, and has all the char- 

 acters of an elvan. The neighbouring granite is grey, and consists of 

 anorthic felspar, quartz, and black mica. Granite extends on Loch 

 Leven for two and a half miles, and has an elvan character where 

 quarried at Ardsliiel and close to the pier at Ballachulish. It is 

 succeeded in the usual way by gneiss, mica slate, and roofing slate. 

 The gneiss of Loch Linnhe often assumes a granitoid character. Up 

 Glen Tarbert, to within four miles of Strontian village, it is absolutely 

 bare of vegetation, and yet shows no sign of chemical disintegration. 



The Granite of Strontian extends eight miles east and west ; it is 

 dark and coarse-grained, with red orthoclase, white felspar, quartz, a 

 large proportion of black mica and hornblende, with crystals of sphene, 



