Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/457

Rh point in various places round by the east coast to Troup Head. It is visible at the pass of Aberfoyle, and possesses a character and situation similar to that which it exhibits at Drymen.

A ridge, parallel to that of Ben Lomond, is separated from it by the valley which includes the Forth. A second parallel valley contains Loch Ard and Loch Chon, which pour into the Forth at Aberfoyle a tributary stream of equal magnitude. To the east this is again bounded by a second ridge, nearly parallel to the first, of which Ben Venu is the principal elevation. The valley which lies at the foot of this ridge, contains Loch Ketterin, having for its eastern boundary a double ridge, of which Ben Ledi is the chief eminence. These four ridges appear to ramify from a central point, situated between the top of Loch Ketterin and that of Loch Lomond.

The whole of this country has been supposed to be of the same formation as Ben Lomond, namely micaceous schistus, a supposition which I have found to be groundless. I am ignorant of the nature of the ridge which separates the vale of Loch Ard from that of the Forth, the nearest in order to the ridge of Ben Lomond. But on examining the vale of Aberfoyle, as far as from the breccia to the bottom of Loch Chon, I found it to consist of alternations of graywacke, and graywacke slate, with clay slate, similar to those I have described as occurring at Crinan, and placed with equal irregularity of alternation. The beds are also elevated to high angles, but I believe that the positions are various. In traversing the ridge which separates Loch Ard from Loch Ketterin, the same rocks appear, and quarries of fine roofing clay slate are wrought in various parts of it. These, I believe, are of the same class, and belong to the transition clay slates, but the whole ridge is so extensive and broken, that it is extremely difficult, if not impossible, to obtain access to it, except in a few places. On reaching the shores of Loch