Gairloch in North-West Ross-Shire / Its Records, Traditions, Inhabitants, and Natural History, with a Guide to Gairloch and Loch Maree, and a Map and Illustrations

by John H. Dixon

Great honour has lately been done Professor Nicol for his enlightened perception of the true solution of this difficult problem at so early a date, "against a phalanx of eminent geological authorities." Professor Judd, at the meeting of the British Association at Aberdeen last year (1885), in reviewing this geological problem in a masterly address, justly observes, and in so doing felicitously expresses general opinion:—"Calmly reviewing, in the light of our present knowledge, the grand work accomplished single-handed by Nicol, I have no hesitation in asserting that, twenty-six years ago, he had mastered the great Highland problem in all its essential details." "The Murchisonian theory of Highland succession," he finally concludes, "is now, by general consent, abandoned."

C.—Other Noteworthy Geological Phenomena.

There are other noteworthy phenomena connected with the geology of Loch Maree deserving attention, which will be now shortly described:—

I. Faults.—Several faults have already been pointed out. The greatest, however, is that which runs parallel to Loch Maree itself, the loch lying in and along this huge fault. It extends from Loch Ewe, along Loch Maree and up through Glen Dochartie to its head, and so on eastwards. It runs parallel to the strike of the Hebridean gneiss, and has thrown down the rocks on the south side of Loch Maree by a south-west downthrow of considerable magnitude, as compared with the rocks on the north side of the lake. It has not, however, interfered with the strike of the rocks or their relations to each other, which remain the same on both sides of the fault. The formation of Loch Maree, which lies exactly in the line of this great fault, is due in some way, no doubt, to the presence of the fault at this place and in this direction. The existence of this fault is proved, among other facts, by the general want of symmetry between the rocks on the two sides of Loch Maree, and by the low horizon at which the Torridon lies in the islands of Loch Maree and round Talladale, as compared with that at which the Hebridean stands in Beinn Aridh Charr and Beinn Lair, and with its own height in Slioch.

The same remarkable faulting holds good of other lakes. Loch Assynt to the north, being in much the same position as Loch Maree to these controverted rocks, lies also in the line of another great fault; Loch Ness also runs in the line, and occupies the place of a stupendous crack in the rocks there, shewn by a great anticline which runs from the Moray Firth to Loch Linnhe, and which has also in some way given rise to the enormous hollow occupied by Loch Ness,—a hollow twice the depth of the German Ocean, being nearly a thousand feet deep, while the North Sea is nowhere deeper than five hundred. The great Loch Maree fault can be seen in Glen Dochartie, and is there exhibited on both sides of the glen, where the unsymmetrical relations of the rocks may be studied.

II. Glaciation.—The phenomena of the Glacial Period are exceedingly well exhibited round Loch Maree. On the surfaces of the flat Torridon sandstone, at many places along the southern shores, especially on the higher parts of the road a little to the east of Talladale hotel, the scratchings are very good, distinct, and continuous, extending, on some of the slabs, for hundreds of feet in unbroken line. They run generally parallel to the longer axis of the lake, and prove the existence of an immense glacier that moved to the sea down the deep hollow now filled by its waters. The Stoss seite, or rubbed side, of the roches moutonnées is everywhere apparent, looking up the loch; which shows that the ice moved seawards, and pressed hard against the landward faces of all projecting rocks, while leaving their seaward faces, or lee sides, greatly untouched. This is very well seen on the islands and projecting capes in the loch itself, especially where the lake narrows at its western extremity, and markedly, on the east front and north face of the splendid Craig Tollie opposite Inveran, along and above water-level. There the smoothing, grooving, and scratching are remarkably good, and worth going far to see. The visitor should make a special point to see them also on the flat surfaces of the red sandstone to the west of Talladale, already mentioned. At both these places, the lateral pressure of the ice is also very well shewn, as well as, at not a few points, its upward pressure on projecting rocks, the under side of which are well glaciated. This glaciation also extends all the way down the river Ewe and out to sea, and is exhibited at many places.

The course of the ice stream has undergone several deflections, arising chiefly from the nature of the ground. Between Gairloch and Loch Ewe it has passed increasingly from north to south, as exceedingly well seen on certain exposed rock surfaces above and to the west of the road between Gairloch and Poolewe. There the glacier movement seems to have been from Loch Ewe to Gairloch, showing that the ice stream from Loch Maree had probably expanded fan-wise on its exit from the narrow glen near Inveran, where its pressure had been greatest and where its effects are so well shewn.

Another striking evidence of glacial work, and a telling proof of the existence of this mighty glacier, should be visited. This is the series of lateral moraines that lie between Loch Ewe and Loch Gruinard, more or less parallel to their coasts. They are cut across by the high road at its most elevated portion, and run interruptedly out to sea, along the peninsula between these lochs. They consist of irregular lines, more or less continuous, of rough débris, enclosing angular and sub-angular stones, and they mark the later boundaries of the ice-sheet which filled Loch Ewe from side to side, flowing over Eilean Ewe, out to the Minch, and glaciating the rock faces in its course, as well seen at many points between Poolewe and Inverasdale on the south, and between Poolewe and Aultbea on the north. No glacier in Scotland is more proved than the great Loch Maree glacier. The ice markings near Udrigil to the north of Loch Ewe, and beyond Inverasdale on the south, are very good, on the well-preserving red sandstone that forms these bounding rocky peninsulas. Good scratches also occur along the road between Talladale and Gairloch. At one time Craig Tollie itself had been an immense roche moutonnée, over which the ice sheet, here at least fifteen hundred feet thick, had triumphantly ridden.

Still another evidence of glaciation is the number of "Carried Blocks" everywhere seen, borne by the ice sheet, and dropped far from their parent rocks in the line of the ice movement. At many points, they are finely perched on conspicuous elevations, and often on the summit of the higher peaks, as well exhibited on the road between Gairloch and Poolewe, and, indeed, all over the district. But nowhere are they shown in such multitude as round the Fionn Loch, and especially from a low eminence near the stable at the foot of the loch, where they are scattered over the whole surface in surprising abundance, and look like sheep or goats in lines along the ridges, gazing on the rare intruder.

A most interesting feature connected with the glaciation of the district is the probable existence of a glacial period before the Torridon sandstone was laid down upon the Hebridean gneiss! As suggested by Archibald Geikie (Nature, 26th August 1880), there are evidences of ice action on the Hebridean floor on which the Torridon conglomerates were deposited, and the idea is coincided in by Dr Hicks, who also pleads for the existence of pre-Cambrian volcanoes, as well as glaciers, as exhibited round Loch Maree. Dr Hicks thinks that the immense amount of broken rocky matter necessary to form the Cambrian conglomerates was probably produced in part by pre-Cambrian glaciers, combined with sea action (Geolog. Mag., Nov. 1880).