The upper line becomes also invisible on the right, op posite to this place, and shortly after the whole disappear together on this side, although no material alteration takes place in the form or structure of the hills. About a mile before the junction of the Roy and Spean, thc val ley expands, and here the lowest line again makes its ap pearance, continuing its course round to the 'I side of Glen Spean, where it disappears. The same line shortly after re-appears on the right side, and hence it On the left bank of this river, near the junction of the Roy, a line is visible, which was found by the spirit-level to correspond with the lowest line of Glen Roy. It runs about three or four miles down the valley, over a surface ' of moderate inclination, yet, though the curvature and structure of the opposite hills which bound the Spean are similar, it is not always found on the other bank. It con tinues to hold its course westward, with more or less ob• scurity, from the junction of the Roy and the Spam along the declivities of the high mountains, Ben na 'Chlianach, Scuir Rinish, and Carts Derig, which bound this wide valley to the south, finally disappearing opposite to Tein drish, and nearly in the meridional direction. The valley here is of such dimensions, that the opposite lines are about four miles asunder. Its bottom is extremely irre gular, offering rather an accumulation of low hills than a valley, properly so called. But in no place does the alti tude of these low hills rise above the level of the lowest line, a fact which it will be necessary to keep in mind when we inquire into the causes which have led to the forma tion of these. It is also necessary to remark, that through this wide and irregular space there are no streams of any note, but that the whole is drained in a manna' almost im perceptible into the only river which traverses it, namely, the Spean. The opening of this valley is wider than its mean dimensions, since it gradually loses itself in the great val ley of the Lochy, a part of the Caledonian Glen, which, forming a wide plain, at length terminates in the sea, at Loch Eil.
On the north side of this part of the valley of the Spean, or on its right bank, the lowest line of Glen Roy can also be traced with more or less difficulty, round the hill of Bohuntine, which forms the angle that separates the low valleys ; entering Glen Collarig, and proceeding round the base of Ben y Vaan, when it at last disappears, as nearly as possible on the same point with respect to the meridian as that on the southern side which runs along the skirts of Ben Nevis.
Near Craig Dhu, forming the angle at-which Glen Roy turns round eastward into Glen Spean, the entrance of this latter valley is much contracted, and the opposite sides are steep. The hills here are not a mile asunder ; but farther up they recede considerably, while their ele vation also apparently diminishes. The whole length of this valley, from the point under review, to the pass of Mackull, at the eastern end of Loch Laggan, is about twenty miles, including that lake, which occupies about half this space. This pass, which we formerly mention ed in the table of altitudes, forms the summit level for the waters which here flow east and west ; and if our compu tations from the comparisons of different measurements are correct, its highest point is about ten feet above the level of the lowest line of Glen Roy, which is the one that extends up this valley. We had no opportunity of
making an actual measurement of it, and have reason to think that this distance is overrated, a circumstance not to be wondered at, from the circuitous mode of computa tion by barometers, to which we were compelled.
The mountains on the north side of Loch Laggan are, can be traced with more or less difficulty as far Tcindrish, over a various surface of very slight inclination, till it finally vanishes. .1t Keppoch, the Roy falls into the Spean, issuing from Loch Laggan, and here it loses its name; while the Spean holds its course westward for five or six miles, till it falls into the Loch)-.
Ifaving thus examined the lines of Glen Roy, it is necessary to turn our addition to those found in Glen Spean.
n some places, of a moderate acclivity, but in a few they ise suddenly to a considerable height. Though not on the south side, they are bold and rocky to the vater's edge, %%Inch is indeed the general character of :he sides of the lake everywhere. After the Spean is ales from the lake, course is gentle for about two stiles, and through an alluvial bottom. After that it re ;elves the water of Gulbran, and then that which runs From Loch Treig. After its union with the last, it be Lames skirted with alluvial terraces, similar to those al ready described in Glen Roy, at various distances from its course, and in one place inclosing a considerable plain. Where this plain terminates by the approximation of these terraces below, the river enters a deep and rocky ravine; after which it again passes through another plain, similar to the former, to be again contracted lower down; and near the mouth of this part of Glen Spean, or the upper and proper valley of that river, by another rocky interruption, through which it escapes in various falls, of which that of monossie is the most remarkable. Shortly after this it joins the Roy, as formerly describsd.
Now, the lowest line of Glen Roy, which passes round Craig Dhu, runs up the valley of the Spean, but interrupt edly, along its right bank, or on the north side, ind so along the shores of Loch Laggan, even round its upper extremity. Near the lake it is elevated to a very small distance, not exceeding a few feet above its waters; and when it meets the alluvial terrace near the exit of the Spean, it coincides with many of them, as some of the. lines of Glen Roy have been shown to do with the terraces in that valley.
From this it may be traced in a similar manner, and at the same level, along the smith side or left bank of Loch Laggan and of the Spean; entering into the wide mouth of the valley that brings down the water of Gulbran for a short space, and still more perfectly extensively into that of the Treig, which we shall presently describe. Tracing it from this place, we are conducted towards the hills formerly described under the skirts or Ben Nevis, where its existence and course have already been men tioned.