This gneiss is more largely exhibited on the shores of Loch Maree than any other rock, forming the greater part of its northern side from the exit of the Ewe to Slioch, and running along its southern side from near Inverasdale on Loch Ewe to Talladale. It stretches northwards from the lake to Loch Gruinard, and westwards to Poolewe and Gairloch, where its characteristics are very well seen on the wave-beaten coast near the hotel there. It forms the rugged outlines of Craig Tollie, at the west end of the loch, and of Beinn Aridh Charr and Beinn Lair, near Letterewe. It shows one of the most magnificent series of furrowed precipices in Britain, at the back of Beinn Lair, which should be visited by all who appreciate the wildly grand; and entirely encloses the lone Loch Fionn and its darker chamber of the Dubh Loch at its head. North of Coigeach, it occupies most of the west coast on the mainland up to Cape Wrath; and southwards, there is a patch of it at the Narrows of Loch Torridon. From recent researches, it will probably be found widely extended over the rest of the Highlands.
It is more or less vertical in dip on the west coast, and has there a general persistent strike from north-west to south-east. The special character of its scenery is very well seen round Loch Assynt, and is well presented in the parish of Gairloch. As shewn on the [map], it forms the splendid peak of Alligin, above three thousand feet, which towers above Loch Torridon, from which it passes to the head of the Gairloch, where it is admirably exhibited in structure, dip, and strike on the shore near the Free church and along the picturesque road to Poolewe. It contains some limestone on Loch Maree in a line parallel to the loch, for some miles on both sides of Letterewe. A vigorous attempt has recently been made by Dr Hicks to discriminate this gneiss into certain series or epochs, which he has named, and by which he seeks to interpret the rest of the Highlands.[3] In America, the Laurentian system contains the celebrated Eozoon Canadense, that is, the Canadian Dawnlife, the lowest organic form yet known. It has as yet proved absolutely barren in Europe, though a flutter was raised by its supposed discovery by Dr Heddle of St Andrews, Dr Carpenter asserting the fact, but its discoverer, on further examination, disclaiming the honour.
II. The Torridon Sandstone.—This is the chocolate-coloured sandstone so splendidly exhibited round Loch Torridon, where it towers into the mural dignity of Liathgach. It is well presented in the mountains of Applecross, as seen from Loch Carron, and from Loch Kishorn which lies at their southern base. This sandstone occurs only at one spot in the Outer Hebrides, round the harbour of Stornoway; it is found in Rum, its southermost position, in Sleat, Scalpa, Raasay, and neighbouring islets; it occurs continuously, except where the Hebridean gneiss appears, from Loch Carron to Coulmore near Loch Inver, and thence in isolated patches, north to the Kyle of Durness. The scenery it presents is uncommonly striking, massive and grand, its mural character, which arises from its horizontal strata, being a special feature, and nothing in style can anywhere surpass the splendid spear-headed crest of Slioch, the monarch of the mountains, worthy though his compeers are, that stand round Loch Maree. The denudation to which this ancient sandstone has been subjected has been extraordinary. This is well seen round our loch, when we consider that Slioch is above three thousand feet in height; but still more impressively, from the sea off Loch Inver, in the sugar-loaf cone of Suilven and its brethren, all isolated stacks of Torridon sandstone,—so remarkable that Murchison selected this scene as the most striking example of denudation he knew, to illustrate the subject in his famous "Siluria."
Round Loch Maree, it forms its southern shores east of Talladale, where its character can be well examined in the delightful drive from Kenlochewe. On the north side, it touches the loch only at its two extremities, at the one end, near Inveran and along the Ewe, and at the other, in Slioch, stopping short of the head of the lake, as can easily be seen from the south side. It is more or less horizontal, or dips slightly to the south-east, being deposited in thick, well-marked beds, as everywhere exhibited, and thus forms a remarkable contrast to the vertical strata on which it rests. An excellent junction of the two, easily reached and examined, occurs on the shores of Gairloch, at the end of the rocky peninsula on which the Free church stands. There the two are seen, the more or less horizontal Torridon superposed on the vertical Hebridean, in the most striking style, which is rendered all the clearer by the washing of the restless tides. This sandstone about Loch Maree is about four thousand feet in thickness.
It was correlated by Murchison with the Cambrian system, the second in the geologic series, and was so named by him,—a name now recognised by the chief authorities. It is well, however, to designate it by a neutral geographical term, and to retain the title given it by Professor Nicol, that of Torridon Sandstone, or Torridon Red. In Scotland, it has as yet yielded no organic remains, though these are abundant and good in Wales, after whose ancient name of Cambria it is called, and also in Scandinavia, which remained united to Scotland till post-glacial times. It was long thought to be a western representative of the Old Red Sandstone of the east coast, Hugh Miller, among others, looking on it as a worthy example of his pet rocks; but in his day, the geology of the Highlands was but dimly and imperfectly known, and their great problems were not even surmised.
Like the Old Red, a fact that tended to mislead early observers, its lowest bed is a thick massy conglomerate or breccia, which is very well seen at the junction at Gairloch, and which is generally persistent throughout the system on the west coast. It consists of varied pieces, sometimes rounded, often angular, and some of them large, of the under-lying Hebridean rocks, enclosed in a finer matrix of the same materials. Portions of the "Eastern rocks" have, it seems, also been detected in it,—a fact which, if established, indicates the true age and succession of these "Eastern rocks."
III. The Quartzite.—Above the Torridon Red, lies a thick-bedded whitish rock, called from its general appearance Quartzite. This French word is, however, a partly misleading term, as the rock is not quartz, though much made up of quartz grains; but it is a highly metamorphosed fine sandstone. It is here sometimes coincident in dip with the underlying Red, but it is generally non-conformable. It can be easily seen, looking from the south side of Loch Maree, at a point east of Slioch, on the right side of a glen watered by a stream called the Fasagh, which separates Slioch from the ridge to the east. In Glen Fasagh, the Torridon Red is clearly observed to rest horizontally on the Hebridean gneiss below, on both sides of the glen; the Torridon forming the most of the western side of the valley up to the summit of Slioch, but rising, on the eastern side, only half-way up, being then surmounted by the strongly contrasted Quartzite to the top of the ridge. The Quartzite continues eastwards to the wide glen beyond, generally but erroneously called "Glen Laggan," or "Glen Logan," though its real name is Glen Cruaidh Choillie.[4]
A vertical fault exists in the middle of this Quartzite ridge, situated halfway between the two glens, and is easily distinguished by the eye from the other side of Loch Maree. It has thrown down the rocks on the eastern half of the ridge some distance, and affects both the Quartzite and the Torridon Red below.
This Quartzite is devoid of mica. It passes from pale pinkish to pure white in colour, and occurs in thick, uncommonly regular beds, with rectangular joints. It is well developed at the head of Loch Maree, and rises into the white, glistening, barren peaks and ridges of Beinn Eay. It forms some admirable scenery, not only here but wherever it occurs, for it is widely distributed over the Highlands.