But one line occurs in this upper valley, and it is most easily seen on the left bank of the stream, from the junction upwards towards the elevation that contains Loch Spey. This, when examined by the level, and duly prolonged, is found to correspond with the uppermost of the three principal lines in Lower Glen Roy, of which it is an interrupted continuation. None of the lower lines which are found in this latter glen exist in this upper di vision.
The flat rock just mentioned, which forms the narrow entrance at the upper end of Lower Glen Roy, or which divides the upper from the lower part of the general val ley, projects at right angles from the hill on the right, and then turns westward so as to form a promontory pa rallel to the side of the glen ; thus producing a cal de sac on one side, and giving passage to the river on the other. The rock itself exhibits no trace of a line ; but the two uppermost commence at its junction with the hill or side of the glen, whence they are seen running westward far along the faces of the mountains. The uppermost of the two, if prolonged, would just be even with the flat parts of the surface of that rock. 'Wherever, in a few places, it rises higher than the place where the line ought to be, it still bears no marks of it ; as is an invariable rule wherever any of these lines traverse hard rocks.
It requires some previous information, or an acquaint ance with these lines where they are most distinct, to dis cover them at first sight at the point just mentioned. They are often so faint when viewed from above, as to be scarcely distinguishable on the face of the hills. In pro file they are seen somewhat more easily ; but they are al ways distinguishable from below, or in any position in which their breadth is foreshortened to the spectator's eye, when they assume the shadowy form of strong lines We may here remark, that in this place the lines are nar rower than they are in many others, and that the declina tion of their surfaces from the horizontal plane is very considerable. Hence it is, that, coinciding in a great measure with the declivity of the hill, they are only easily visible under the peculiar circumstances just men tioned.
This ground is rocky and irregular ; the natural rock, which consists of gneiss, being visible in many places ; while, in the rest of the glen, it seldom breaks through the surface; and in all such cases, wherever they occur, these lines are always least discernible ; being, as in this place, less distinguished from the natural slope of the ground, and more narrow The loose materials at this point con sist of fragments that have descended from the hill, not of transported alluvia. This is rendered evident by their
angular forms, and by their absolute identity with the na tural fixed rock. Wherever any rock happens to inter fere in the course of the lines, it interrupts them ; or they are absent from that particular spot. It is evident in these cases that they have not been overwhelmed by rubbish or alluvia from the hills above, but that their ab sence is the result of the refractory nature of the materials in their course.
On the left side of the glen at this place, there are also seen two lines obscurely traced, but not visible on those projecting parts of the hill which are covered with allu vial matter. These correspond, both in level and relative distance, with the two on the right, as happens through out the whole course of the valley. But besides these, some imperfect traces, or fragments of similar lines, are here seen at other levels—an appearance which is repeat ed also in some other places lower down.
In proceeding down the valley, we arrive at a river equal in size to the Roy, which it joins by a cascade rush ing over a rocky bed. A great series of terraces here occurs, similar to those so frequent in the course of High land rivers, forming a large alluvium in the nature of a terre !item at the top of this glen. These are of different levels, and the highest of them is on a level with the third or lowest line of Glen Roy, yet undescribed. This principal one, however, declines by many successive stages of similar terraces ; while numerous smaller ones are also found descending down to the very bed of the river; skirting its banks, and accompanying its course. Here the bottom of the glen is an alluvial flat. In this place also is found one of the supernumerary lines just men tioned ; appearing to be nearly intermediate between the first and second lines formerly described. These princi pal ones here continue their courses along the alluvial slopes of the declivities, where they also acquire their greatest breadth and distinctness.