118 Br. Mac Culloch's observations 



Except in the rolled fragments however, no appearance of granite 

 is visible as we skirt the sides of Cruachan from Dalmally to In- 

 verawe. Every where we observe schistose rocks, which have been 

 laid bare, sometimes by the operation of natural causes, but more 

 generally by the process of making the road. This schistus possesses 

 in different places different features. Sometimes it is a compact mica 

 slate, where the mica and the quartz predominate by turns, but 

 its more general tendency is toward clay slate, of which it often 

 exhibits very well characterized examples of various colours, vary- 

 ing from dark lead-grey to pale greyish -green. These in many 

 places, and particularly where in contact with the veins about to be 

 described, assume an extreme degree of hardness, putting on the 

 aspect of that which is called Lydian stone and flinty slate. It is 

 impossible to assign the breadth of the zone occupied by these schis- 

 tose rocks, as, independently of the turf upon the sides of the hills, 

 the lower skirt is clothed to a very considerable elevation with an 

 impenetrable covering of mixed coppice and underwood. It is 

 probable however, that the incumbent schistus does not any where 

 extend very high, as it may be found terminating at a low elevation 

 on that part of the hill which is naked and accessible, and which 

 impends over the course of the river Awe. 



Numerous veins, of very variable but generally large dimensions, 

 appear traversing this schistus throughout the course I have described. 

 They are of various composition, but consist in general of different 

 coloured porphyries. Their directions are as various as their colours, 

 but their position is generally perpendicular, or nearly so. Together 

 with these veins of porphyry, a few veins of trap, exhibiting the 

 several aspects of greenstone, greenstone-porphyry, and even of 

 genuine basalt, may be observed; and, from some fragments of 

 amygdaloid which I picked up by the road side, it is probable that 



