VI. Curious Impressions on Torridon Sandstone near Talladale.—Near Loch Maree Hotel, the stream that forms the Victoria Falls runs over Torridon sandstone. A short distance above the bridge which carries the Gairloch highway over its waters, about three or four hundred yards above the falls, and just beside the last of a succession of lesser falls, on the left bank of the stream, there exists a flat bed of sandstone, some sixteen feet square, on which occur certain remarkable impressions which deserve attention. These were first noticed by the late Mr Walter Carruthers of the Inverness Courier, who directed my attention to them, and published some account of them, along with observations made by me regarding them (July 1, 1880), of which the following is a summary:—
The most distinct of the impressions consists of two continuous flat bands side by side, 1¼ to 1½ inch broad and about a quarter of an inch deep, running quite straight across the flat layers of sandstone in situ, and perfectly distinct for sixteen feet, disappearing on the west side under the superincumbent rock, and broken only where portions of the sandstone have been weathered out. In some places, a third line runs alongside, but this is much less distinct and persistent. The double band resembles nothing more nearly than the hollow impression that would be left by double bars of iron neatly inserted in the rock for clasping some structure on it, if the iron were subsequently removed. The bands, when narrowly looked into, consist of very fine, close, hair-lines, continuous and parallel to their sides, resembling very minute striæ left by glaciation, and they look as if caused by some object drawn along the original red sand, before it became the present indurated rock.
A similar double line runs parallel to this one, about two feet lower down, seven feet long; and a third parallel double line occurs on the upper side, three feet long,—both of the same breadth as the first. Besides those pointed out by Mr Carruthers, which occur on the same flat of sandstone, other lines exist farther down, on the other side of the pool below this rocky flat, on a similar bed of sandstone, part of the same layer,—one three feet in length, another six feet, running more or less parallel to those above. Indications of others may also be seen, and, no doubt, several more may be discovered on more careful examination.
What they are I can scarcely even surmise, having seen nothing of the same kind elsewhere. They do suggest the possibility of their being the indentations of the caudal appendage of some huge creature, similar to the hollow tail lines between the footprints on the sandstone at Tarbatness and along the shores of Morayshire,—a suggestion strengthened by the fact of the existence, on both sides of the line, of numerous rounded hollow marks, very like the footprints on these reptiliferous rocks, occuring, as in them, at intervals. But the continuous even breadth and square section of the lines would seem to render this impossible. They might be the depressions left on the soft sand by the hinder portions of the shell of some huge crustacean,—a more likely cause, rendered more probable by the existence of very good ripple marks on the same sandstone, in the same and neighbouring layers. The striæ-like lines of which the grooves consist would seem to point to some moving agent, organic or physical. They may, however, be the casts or impressions of some great land reed or sea fucoid, the hair-lines being the marks of the fine flutings on its stem or the parallel veins of its leaves. It would be desirable to have the superincumbent layer of rock carefully removed where the bands in question disappear under the upper rock, in order to shed more light on the nature of the strange marks. Whatever they are, they certainly deserve the careful attention of geologists. Dr Heddle, who has examined them since 1880, is of opinion that they are not in any way connected with organisms, but are due to mineralogical and structural causes, but he has not yet published his views.
VII. The Fionn and Dubh Loch.—This double loch is remarkable, and eminently worth visiting, not only for its scenery, elsewhere described, but also for its geology. Both lakes are enclosed in Hebridean gneiss, which here very powerfully exhibits its usual characteristics, reaching its highest in the picturesque peak of Coire Chaoruinn, above the centre of the loch. The Torridon sandstone appears on Ruadh Stac or Red Peak, which bears an appropriate title, and possibly on the very crown of the Maiden. The pale rock which catches the eye from far on the front of Craig an Dubh Loch, at the head of the Fionn Loch, is a remarkable species of granite, known by the French term Pegmatite, which consists of quartz and felspar, often with small quantities of silvery mica. It abounds in the Hebridean gneiss in other parts of the west coast, but in our district, it is comparatively little developed except at the Dubh Loch, where it also appears on the Maiden's shoulders, and on Carn Bhan or the White Cairn, to which it gives name. It should be examined on the great cliff of Craig an Dubh Loch, where it traverses its face and head in serpentine lines and masses, like injected lava. The rare mineral epidote is also found here, and near the top of Beinn a Chaisgean, on the north shore of the lake.
The smaller upper part of the loch is almost entirely separated from the lower, and forms an Alpine chamber, strongly contrasting with the rest in form, feature, colour, and surroundings, which has given rise to its most appropriate name of the Dubh or Black Loch. This loch is an excellent example—none better—of a moraine-dammed lake, being held in by an uncommonly pronounced moraine, which marks the last boundary of the ancient glacier that filled its deep pot. This moraine begins on the left side, under the grand cliff of Craig an Dubh Loch, curves finely round the lower end of the Dubh Loch, crosses the loch to the other side, forming in its passage the narrow waist that separates the two lakes, and then runs along two-thirds of the Dubh Loch till it gets lost in the general rubbish of the hills, the path to Loch Broom which crosses the causeway taking advantage of its terraced line for some distance. The moraine consists of a long circular ridge of loose débris, enclosing large protruding blocks, having a general height of from twenty to thirty feet, with steep sides, like a kaim or esker, and considerable breadth. It is quite continuous, except for three hundred yards at the union of the lakes, where it has been cut through to water-level, but descends so little below the surface that stepping-stones, forming a causeway, are carried across the strait. On the north side, the moraine widens greatly, and encloses a lochan, beyond which rises an isolated steep hill, Carn na Paite, some three hundred feet high, which has formed a huge roche moutonnée. Over this the ice of the old glacier has passed, and smoothed it, the same ice having crushed and striated the steep front of Craig an Dubh Loch, on the other side of the glen.
Other telling proofs are apparent all round of the more general glaciation of Scotland, when it was a veritable Greenland, with a huge ice sheet enveloping mountain and glen, in the numerous perched blocks placed in most striking positions. One large boulder is set right on the very head of Scuir a Laocainn. Others crest the surface of Carn Bhan and the Maiden, and give the sky-line of their summits the appearance of a broken-toothed saw, so numerous are these deposits of the great ice sheet of the severer Glacial Period. The remarkable gathering of blocks seen from the lower end of Fionn Loch has already been noted, and the height near the stable there should certainly be climbed to view them. The jutting capes and islands, as well as many exposed surfaces on the way back to Poolewe, all tell the same tale.
VIII. The Trias at Loch Gruinard.—Another series of rocks—the comparatively recent Trias—may be seen by the traveller not far from Loch Maree, on Loch Gruinard, some miles to the north of the moraines already described. On the way to Aultbea, the road rises to a considerable height above Loch Ewe, and overlooks its waters. Here, from the Torridon sandstone, a magnificent view may be had of the whole remarkable country, with its striking scenery and interesting geology, exhibited at a glance. In front, stretches a rolling plateau of the bare Hebridean gneiss, which attains its greatest altitude in the graceful Maiden and her powerful fellows at the head of the Fionn Loch, and in the pointed Beinn Aridh Charr, Beinn Lair, and Beinn Alligin. Beyond, rise the dark domes of the Torridon Red, in Slioch and his compeers; and then the bright peaks of the Quartzite, in the shining Beinn Eay and other mountains, the Quartzite being seen finely cresting masses of the lower red sandstone. Behind these, stretch the undulating hills of the Eastern gneiss far into the background of the wonderful picture.
On the shore of Loch Gruinard, to the east and west of where the road touches the loch, are found two isolated patches of the Lower Trias, the lowest of the Mesozoic series, and the second above the Carboniferous. This Trias is the second rarest series in the Hebrides,—rarer than the next strata, the Lias and Oolite of Skye, Mull and Brora, and than even the Cretaceous or Chalk, on the shores of Mull and Morven. The only rarer, if not unique, rock in the Hebrides is the one patch of Carboniferous on the tide line of Ardtornish in Morven, opposite Oban.
The Trias here consists chiefly of a thick-bedded sandstone of uncommon redness, which recalls the bright tints of the Old Red of Fochabers and the Permian of Dumfries. It is well exhibited in cliffs and reefs along the shore, by breccias and conglomerates, thin shales, yellow and greenish sandstones and flags, and concretionary limestone.