Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/128



Except in the rolled fragments however, no appearance of granite is visible as we skirt the sides of Cruachan from Dalmally to Inverawe.

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, varying 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 schistose 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