304 GEOLOGICAL APPEARANCES 



in height to Ben Nevis *, are said to be mostly of granite ; and, 

 it is probable, that either granite, or substances akin to it, oc- 

 cur in many places between these mountains and Glen Tilt. 

 From the south-east, round by the south, to west, there is little 

 room to doubt that the rock is almost wholly stratified, and 

 that its chief components are gneiss, mica-slate, granular lime- 

 stone, and granular quartz, with their intermediate gradations; 

 This opinion was supported by our own observations, at the 

 Pass of Killicranky, a few miles to the south-east of Blair, 

 where there is a fine transverse section of the strata, and by 

 others upon the rocks in the channels of the Garry and the- 

 Bruar, to^he west and north-west of Blair. Without dwelling 

 upon these f, I shall enter upon a detailed description of what 

 appears nearer Blair, and proceed with it up Glen Tilt J. 



3. In- 



* Their height is about 4000 feet ; that of Cairngorm, one of the highest, is 

 4060. 



f See Note A, at the end of the paper. 



J The miniitp details, whirh ront.inually orrnr in flip following pages, must, 

 to most readers, appear tedious and useless. It is necessary, therefore, to men- 

 tion, that Glen Tilt was the first scene, in which Dr Hutton met with what he 

 considered as a confirmation of his views, respecting the relations that subsist 

 between granite and the strata adjacent to it ; and, in the controversy that has. 

 since prevailed, between his followers and those of Werner, the former have in- 

 sisted much upon the phenomena in this Glen, while the latter have repelled 

 their arguments by a very different account of the structure of the rocks, and of 

 the substances that compose them. It became of importance, therefore, to ascer- 

 tain the facts more precisely. With this intention, Mr Playfair and myself 

 passed some days in examining Glen Tilt, in the autumn of 1807 ; and I return- 

 ed again, for a short time, in 1808. In my description, I have endeavoured to 

 avoid the language of theory as much as possible. When any thing has been no- 

 ticed which is trivial, and does not immediately bear upon the main question, ife 



will; 



