Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/311

 right ridge of Glen Tilt is part of this great mass, and it in fact constitutes its termination in a southern direction. To ascertain its connection with the quartz rock, it is necessary to compare numerous observations made on the slopes of the hills, and in the channels of the torrents where such connections are visible. I have already mentioned the very conspicuous junction visible at Glen Criny, and it would be tedious to repeat the rest of the observations from which the general conclusion is drawn. That general conclusion is, that the quartz rock is superimposed on the granite, and that every instance of apparent alternation in these rocks may be resolved into this. The confusion which arises in the disposition of these rocks depends on two causes, the discontinuous arrangement of the quartz rock, and the irregular protuberances, into which the surface of the granite is formed. These latter are the cause of the semblance of alternation before noticed, both on the sides of the right ridge, and in the bed of the Tilt. In no instance have I discovered them proceeding to such a distance from the body of the granite as to deserve the name of veins, and assuredly they are not veins traversing the main body of granite, but on the contrary portions of its solid mass. The junctions therefore of the limestone and schist with the granite, which are visible in the bed of the Tilt, are not to be viewed as consisting in the passage of granite veins through those rocks, a phenomenon sufficiently common in other places, but as the points of junction, as I shall soon proceed to show, between a great bed of stratified rocks and a central mass of granite.

It is necessary for that purpose to enquire into the structure of the left ridge or southern side of Glen Tilt.

Beginning from Gow's bridge and ascending the hill at right angles