The length of the valley of the Treig, from its exit to the lake, is about two miles, and the lake itself is suppos ed to be about four in length. This is a very romantic spot, and the shores are bold and rocky, and interspersed with scattered birch. The course of the water of Treig is rapid; and near its junction with the Spezia, it runs through a deep ravine, forming many falls. The line which we formerly mentioned, as entering this valley, may be traced round the lake, and so down on the oppo site side, till it again meets with that which properly be longs to the Spean; and throughout this course it is suffi ciently well marked to permit of no doubt. In one place, a small insulated hill, called Tom na Fersit, with a double summit, near the end of the lake, rises so high as to per mit the line to be marked upon it all round. In conclud ing this account of Loch Treig, we need only farther re mark, that the line is very obscure on the eastern side, and is easiest seen on the western, and at the northern and southern extremities.
It remains to describe Glen Roy. The general direc tion of this valley is about north-east, and its length is nearly eight miles. It opens into the Great Caledonian Glen, as we formerly observed, so as to pour its waters into the middle of Loch Lochy, passing by the village called Lowbridge. The hills by which this valley is bounded approach so near, and the bottom of the Glen is so narrow, that in general it merely leaves room for the passage of the river. They are also very steep, particu larly near Lowbridge. At about three miles upwards from its mouth, it is joined by Glen Fintec, of which the part concerned with Glen Roy was formerly described, and this little valley discharges itself into the water of Gloy. Farther above this its course is somewhat tortu ous, and here it terminates after a time, by joining with Glen Turit formerly mentioned, through the intervention of which it communicates with Glen Roy.
The bottom of Glen Gloy rises rapidly to the place where it joins Glen Turit, so that it may in some measure be divided into an upper and lower valley, the upper stand ing at a considerably higher level than the lower. It is here that the Gloy, coming down through a deep ravine from the southern mountains, joins another in an oppo site direction ; their united waters forming the stream which we had traced thus far upwards from Lowbri .ge. But we must yet mention respecting Glen Turit, that which was deferred to this place as the account of Glen Roy. It forms a communication, as we have seen, be tween this valley and Glen Cloy, in such a manner that its waters are discharged oh both sides. When it falls
into Glen Roy it is at so high a level as to exclude the lowest of the three lines. But traces of the two upper ones enter its mouth, on the right hand side of which, (according to the course of the water) they speedily and suddenly disappear. But on the left, besides a short trace of the second, a line is to be seen, extending for the space of a mile or more, on a level with the upper one, until it is cut off by the rising of the bottom of the Glen. This line is very strongly marked; its breadth being not less than seventy feet, and its horizontal inclination being like wise very small. It is important to notice, that the oppo site sides of Glen Turit are very similar both in shape and composition, although so unequally marked by the lines; and it is also essential to remark, that the bottom of this glen is of solid rock, and not of alluvial formation. It will be important to remember, in the course of the fol lowing examination, that the operation of ordinary causes tends to diminish, not to augment its height.
Where this solitary line disappears in consequence of the rising of the bout, • of the glen, a level space occurs without any stream; but shortly afterwards we meet with one running westward to join the Gloy, as already describ ed. The bottom of Glen Turn may therefore be consi dered as a hill interrupting the communication, which might otherwise take place at an inferior level between Glen Roy and Glen Cloy. If the upper line of the for mer, and that of the latter were on the same level, that communication would have been formed by means of these. Respecting this we must now inquire.
On entering Glen Cloy from Lowbridge, no trace of a line can be perceived for about three miles The marks of three then become visible in the salient angle of a green hill on the left bank of the stream, but the upper and lower soon terminate, while the middle one continues for sonic way up the valley. On the right side of the stream, opposite to Chew, a very strongly marked line occurs, and this may be considered as the only one which prevails iu Glen Cloy, being continued, with occasional obscurities and interruptions, up to its extremity on both sides. Whet., it meets the higher part of the glen that is con nected with Glen Turit, it sweeps round it, being dilated in one place into a considerable plain, analogous in its nature to the terraces occurring in other situations in the course of these lines. Between this and the lines of Glen Tnrit, there is a blank space of about three or four miles.