Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/346



In terminating this description I may remark, that the topographical deficiencies which may be found in it are irremediable until an accurate geographical survey of this country shall be made, but that these deficiencies can not materially affect the arguments about to follow, whatever additions they may chance to make to them.

In as far as the mineralogical structure of the country is concerned in the description of the lines of Glen Roy, I have already noticed the principal facts in describing the nature of the alluvia which form the surfaces of the hills. I may however proceed to say, that the natural rock is not often visible on their faces, although it may be observed in most parts of the bed of the river. I have already briefly remarked that at the upper part of the valley it consists of a hard micaceous schist traversed by veins of red granite. The same rock is continued upwards towards the source of the Spey till the granite itself appears; which forms the most elevated part, and that only, of the country between the sources of the Spey and of the Roy. But in proceeding from the head of Glen Roy to its mouth, the granite veins gradually disappear; various sorts of schist, micaceous, quartzose, and argillaceous, occurring in an irregular order and at various elevations. The beds are sometimes to be seen absolutely horizontal, and at others as completely vertical; and I need hardly say that they occupy all the intermediate angles. A similar construction extends through Glen Gloy, and along the sides of Loch Lochy, as well as the skirts of Ben Nevis.

The different opinions which have been entertained relative to the origin of these lines, or Roads, as they have most commonly been supposed, render it necessary to describe their form and materials; which the accompanying sections, with the aid of a few