^{page 596 note *} In Glen Gluoy (as Sir Thomas Dick Lauder states) the highest shelf has a width of 100 yards. In Glen Spean Shelf 4, above Inverlair House, has a width of 20 yards. (See fig. 17, p. 51.) In Glen Glaster, on the side next Craig Dhu, this same shelf has a width of nearly 100 yards, as is shown on the Ordnance Survey 6-inch Map.

^{page 597 note *} As this is a point of some importance, it is only fair to state, that a very experienced observer, Professor Nicol of Aberdeen, does not admit that there is evidence of a River Channel from any one Glen into another Glen. He says (“ London Geol. Socy. Journal,” May 12,1869, page 284) “ I examined the various passes carefully, and found that whilst in none of them was there the slightest trace of an ancient river, in all there were distinct indications of the former existence of a narrow Sea Strait.” The valley by which the Gluoy Lake is assumed to have drained into Glen Roy is very narrow, and encumbered with detritus from the hills on the sides. The summit level is flat and marshy, and it appeared to me considerably below the level of the line (i.e., the ‘Road’ ?). On the other hand, a line of stones, as if washed out of the detritus, appeared to show that the sea or loch, had extended quite through the Strait. I observed no indication of any stream of water, larger than the present small rivulet, having ever been there.”

In answer to these statements, I give the following Extracts from the Notes made by me on the occasion of my visit to the place with Robert Chambers, in September 1846.

“ At the head of Glen Gluoy, Shelf 1 almost disappears in the Moss. It is however faintly visible on the North side, about 1 or 2 feet above the Moss, running towards Glen Turrit. The Moss I found to be 5½ feet thick above Boulder Clay. About 1½ miles to Eastward, found rocks in middle of Channel, much worn and smoothed,—their rough edges or faces all pointing Eastward, i.e., towards Glen Roy. This is near Glen Turrit, and about the place where traces of Shelf 1 disappear. About 8 or 10 feet above these smoothed rocks there are other rocks which present no appearance of smoothing.

“ At the side, there are low grassy knolls or hummocks apparently marking edge of a River Course,— which here 40 yards wide.

“Apparently Gluoy Lake continued to discharge, whilst Roy dropped from Shelf 2 to 3, hence additional cutting power given to Gluoy Stream ;—and accordingly there is a deep and rocky ravine, down to Glen Turret.

“ Measured with Robert Chambers (who first drew my attention to fact) depression of Shelf 2 in Glen Roy below Shelf 1, and found that by Spirit-levelling, it was 29 feet; by Sympysometer 35 feet; by Barometer 11 feet.

“ Visited next, head of Glen Roy, in upper Glen Roy. Interesting to observe how uniformly the smooth surfaces of rocks are to West, the rough faces to East.” (Notes p. 47).

The following applies to the Glen Glaster old River course.

“ Discovered debouche of Lake No. 3 in Glen Glaster. A Shelf on both sides runs up to Col, at a level coincident with Moor there.

“ At this place, rocks appear above moss. These are about middle and lowest part of flat.—Evidently, water has rushed over these rocks from West : for their round and smooth faces are to West, their rough faces to East. They form a Channel sloping down towards Loch Laggan for about a mile. By existing burn, they can't have been rounded, as this burn, very small, and 20 feet below them. These rocks occupy a breadth of from 30 to 40 feet, and have evidently occupied bed of a stream, exceeding that width. Walked along this supposed ancient water-course for about a mile, and saw that it extended down towards Loch Laggan, as far as eye could reach. Probably Loch Laggan then stood at level of Shelf 4, discharging itself at Mukkoul, as it continued to do, when Lake Roy sunk to Shelf 4.

“ No sand or gravel in this old Water-course, but numerous granite boulders, very spherical.

“ Remnants of sloping haughs on each side, evidently formed by old River when in flood,—with precipitous cliffs beyond these haughs,—indicating height to which floods reached.”

^{page 600 note *} It may be proper to explain that the lake did not subside at once 81 feet. Two intermediate shelves are visible between Shelves 2 and 3, in Glen Glaster (east side), in Glen Collarig, in Glen Roy on the south side above Achavaddy, and on Ben Erin—i.e., the hill above the Gap. One of these is about 14 feet below Shelf 2, the other about 32 feet above Shelf 3. So also, when the lake subsided from shelf 3 to shelf 4, there was a halt long enough to allow an intermediate shelf to be formed at a height of 990 feet, which is very conspicuous in Glen Collarig. None of these intermediate shelves are marked on the Ordnance Maps ; they were, however, pointed out by me to the Surveyors.

^{page 602 note *} I am told that this Gaelic word means “ Valley of high heaps or banks.”

^{page 603 note *} To this cliff I particularly drew the attention of the Government Surveyors, and of Mr Jolly.

^{page 604 note *} Loch Spey is about 1200 feet above the sea.

^{page 606 note *} Mr Jamieson (page 250, “London Geo. Soc. Pro.,” 21st January 1863), admits Loch Treig, in its outflow, “has not even yet cut its way to the very bottom, for the lake is still partly retained by banks of gravel.”

^{page 607 note *} A few years ago, when at Killin, at the west end of Loch Tay, I made some ascents of the hills adjoining, and saw traces of several lines of terrace up to a height of 890 feet above the lake, and 1240 feet above the sea. Along the north side of the lake there is an extensive flat at a height of about 400 feet, which seemed to have its counterpart along the south side of the lake I mention this only as a suggestion for farther inquiry. I believe that the late Mr M'Laren described some terraces at the east end of the lake, about 40 feet above it, but I have not his papers to refer to.

^{page 612 note *} I have already explained, that the subsidence of the lake from Shelf 3 to 4 did not take place all at once. It sank at first only about 78 feet, and formed an intermediate road visible in Glen Collarig, at its north end, on both sides.

^{page 614 note *} No. 1 is Ruiske. No. 2, Lein. No. 3, Urquhart. No. 4, Foyers. No. 5, Inverfarrigaig.

^{page 615 note *} In all the valleys adjoining or near the “ Great Glen,” there are still enormous deposits of drift, much of which evidently has been removed by rivers. Thus, in a valley called Flichity (about 12 miles S. W. of Inverness) drift covers the hill sides up to the height of 2000 feet ; and in that valley there are traces of horizontal terraces, on the sides of the valley, more than 100 feet above the bottom, with a blockage of drift, at the lower or east end of the valley, which before it was cut through by the River Nairn must have been the means of causing the valley to be filled with water.

At Rosemarkie, a few miles N.E. of Inverness, which Mr Jolly of Inverness took me to visit, there are magnificent sections of boulder clay, forming cliffs about 300 feet high. If the adjoining hills are, as they seemed to be, from their shape, composed of the same material, this deposit reaches to a height above the sea of 800 or 900 feet. How far down below the sea-level this clay deposit goes, it is impossible to tell, but at Fort George on the opposite side of the Firth, about three miles distant, a bore was sunk 100 feet in the same sort of clay, without reaching the bottom. Here then a clay deposit exists about 1000 feet in thickness. Judging from the beds of sand in the clay, and from the pebbles in it being in nearly horizontal lines, I had no doubt that this Rosemarkie clay bed was a water deposit.

^{page 616 note *} Since this passage was written, I have again examined the Spean. The banks and cliffs referred to in the text, are situated on the east side of the river, about half a mile below Kilmonivaig church. There are similar banks on the west side of the river. I could not make out at this second visit, very clearly, whether the base of the banks sloped with the river or was horizontal If horizontal, they would of course indicate a lake, with a river running through it. In a higher part of the river, viz., above the Roman Catholic Chapel, there are old river cliffs, which show that the river had formerly ran 180 feet higher than it now runs at that place.

^{page 624 note *} Since this paper was read, I have had an opportunity of walking along the line, shown on the 6-inch Ordnance Map at a height of 1306 feet on Craig Dhu. It extends for about half a mile on the part of the valley above Achleureuch and Mullaggan. It certainly has none of the characters of a Parallel Road, but several features which indicate sea action. There is an accumulation of debris from the rocks above, forming a sort of terrace. The terrace is not horizontal towards the valley. It slopes rapidly from the hill.

^{page 626 note *} If Loch Spean existed at this time, of which there can be no doubt, it is difficult to understand how a glacier could protrude across it, in the very middle of the Loch.

^{page 626 note †} To do this, the glacier must have filled Glen Glaster, and crossed the valley of the Roy.

^{page 626 note ‡} The level here referred to is that of Shelf 3. If the ice shrunk back from Glen Glaster, there would be no ice barrier across Glen Roy for Shelf 3, which extends down that Glen, beyond the mouth of Glen Glaster.

^{page 627 note *} There is a very instructive paper “ On the Parallel Roads,” by Mr James Bryce, junior, F.G.S. (published by the Philosophical Society of Glasgow in 1850). Mr Bryce shows from the geographical position of Loch Arkaig that even supposing a glacier to have been formed in that valley, any moraines which it might have produced, ould not have been so situated as to block Glen Gluoy. He does not think it necessary even to entertain the question of a blockage by the glacier itself.

^{page 635 note *} See Plate XLIII.

^{page 636 note *} Mr Jamieson admits that in this valley the gravel is water worn. He says “ at a deep section of one of these banks at the mouth of Corry Laire, I noticed that the mass consisted of coarse water worn gravel, very pebbly; the pebbles indicated a certain amount of water rolling.”

^{page 637 note *} See Plates XLI. and XLIII.

^{page 642 note *} Mr Jolly informs me that red porphyry rocks occur on the hill called Ben Dearg, so called from its red colour. Ben Dearg is distant some miles from Glen Treig, to the west.

^{page 646 note *} See p. 41 hereof.

^{page 646 note †} See p. 640 hereof. For an interesting account of the agency of Pack Ice, not only in transporting boulders, but in making “ horizontal grooves and scratches” on cliffs of rock, see a paper by Professor John Milne, F.C.S., in the Geological Magazine for September 1876.

^{page 647 note *} It is not unimportant to observe that all these abnormal lines, in Glen Spean and Glen Roy, are in level above the highest of the “ Parallel Roads.” The sea may have formed these lines at a period antecedent to the formation of the lakes. The lakes, of course, could not be formed till the sea had sunk to a level below the highest shelf.