474 Dr. Mac Culloch on Quarlz Rock, 



character considerably different from that which it exhibits ehher irt ^ 

 Jura, in Assynt, or in the other places which I have described. 

 Its aspect is more uniform, and its texture more compact. Its 

 fracture is rather more splintery than granular, and it rarely con- 

 tains felspar, a mineral seldom absent for a long space in the ge- 

 nerality of the quartz rock. It is here of various colours, brown, 

 grey, yellowish, reddish, and white, but its predominant tint is a 

 blueish grey. lis marks of stratification are obscure, yet they may, 

 however disturbed, be traced, and its true character is I think de- 

 termined by a compact breccia, which in some places may be ob- 

 served separating it from the schistose rocks, the micaceous and ar- 

 gillaceous slate. It occurs again in Sky under another form, namely, 

 in disrupted portions, forming the tops of low hills in the district 

 of Slate, of a snowy aspect and compact texture, with irregular 

 grains of felspar imbedded, and in intimate connexion with the 

 micaceous schistus. 



I have reason to think that the same rock will be found to form 

 a large portion of that ridge of mountains which extends in a 

 curved line to the south of Ben Nevis, so as to constitute the 

 southern boundary of Glen Nevis ; but as this conclusion is only 

 founded on a distant observation, and on the peculiar aspect and 

 mode of decomposition which these hills exhibit, I lay no stress on 

 it. Yet as it actually occurs in that part of the declivity of this 

 group which descends into Loch Eil, and is to be found consti- 

 tuting a considerable mass of mountain at Balahulish, I shall not 

 be surprised if future observers assign to it a very considerable ex- 

 tent in this district. It is at the edges of the road between Balahu- 

 lish and Fort William, that it may be conveniently examined, and 

 it will there also be seen to alternate with a compact argillaceous 

 schist. 



