on the Mountain Cruachan. 131 



I shall add but one remark more on this subject. Although the 

 schistose rocks are seen only at the two ends of this prolonged tract 

 of granite, the imbedded fragments can be traced throughout the 

 whole. Hence it might be supposed that they were independent 

 of the vicinity of the great schistose masses, whereas in the view 

 which I have taken of them I consider them as connected with and 

 dependent on them. It is plain that the absence of schist at present 

 from the surface of the granite which forms the moor of Rannoch, 

 proves no negative in this case, as we have abundant examples every 

 where of the removal of great tracts of rock from parts of the earth's 

 surface, and of the consequent denudation of the inferior substances ; 

 a change which may easily be conceived to have occurred here, thus 

 leaving exposed that very surface of the granite which once was in 

 contact with the superincumbent beds of schist. 



Having thus traced the granite district of which Cruachan 

 forms the most conspicuous portion as far as means of observation 

 were afforded, I shall point out, under similar limitations, the por- 

 phyry which fell under my notice, since it will tend to illustrate the 

 great predominance of the porphyritic veins in that mountain, as 

 already described. I must however say that I consider the few fol- 

 lowing remarks, like those on the granite of Balahulish and Rannoch, 

 in no other light, since they cannot be viewed even as a sketch of 

 one of the most complicated and interesting districts in the whole 

 range of Scottish geology. It will presently be seen that the great 

 extent, the divided disposition, and the almost impracticable nature 

 of the country throughout which these rocks are scattered, would 

 require a very different investigation from that which a few distant 

 and rapid visits permitted me to bestow on it. 



The various schistose rocks, consisting of quartz rock, mica slate, 



