Gairloch In North-West Ross-Shire Part 43

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 a.s.synt 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 sh.o.r.es, 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 moutonnees_ 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 pa.s.sed 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 _debris_, 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 moutonnee_, 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 mult.i.tude 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).

III. DENUDATION.--One of the most striking geological features of the district is the amount of denudation to which the rocks have been subjected. Slioch itself is a splendid monument of denudation, standing, as it does, a gigantic cone, in isolated grandeur, the rocks that once reached the same alt.i.tude around him having been swept off by gigantic denuding forces, of which we have now little conception. The same denuding processes have been at work, as already remarked, on the Torridon peaks round Loch Torridon and Loch Inver. But Scotland has been subjected to extraordinary denuding forces all over its surface, from John o' Groats to Galloway; such peaks remaining as wonderful monuments both of what once existed and of what has been swept away. Other remarkable examples of denudation are given in this work. Such forces have been active since the birth of time.

IV. ROCK JUNCTIONS.--In the district, there are several noteworthy junctions of the rocks of the great geological epochs deserving examination.

One has already been mentioned, that on the sh.o.r.e near the Free church at Gairloch, between the Torridon and the Cambrian, strikingly clear and impressive from the perfect unconformability between the two series, and their extraordinary dissimilarity in character. The composition of the breccia may here be easily examined, from its wave-worn bareness, and the fact perceived that it has been formed of pieces of the Hebridean floor immediately beneath, with foreign matters included.

Another equally remarkable junction of the same two systems, hitherto unnoticed, occurs three miles from this one, across the Gairloch, at a beautiful spot called Shieldaig of Gairloch. Just before descending on the mansion, the road enters a narrow pa.s.s, having a steep cliff on the right. This precipice consists, in the lower portion, of the Hebridean, and in the upper, of Torridon conglomerate. The line of union, halfway up the cliff, is clear from the road, and on reaching it, you can insert your hand between the two systems and crawl along their junction. The components of the conglomerate are here much more rounded than at Gairloch. This Torridon forms an isolated patch, on both sides of the road, about a quarter of a mile in length and two or three hundred yards in breadth. It is eminently worth a visit, and is easily reached by the pedestrian.

Another striking junction, also undescribed and little known, occurs between the road and the sea, about a mile from Poolewe, not far from Tournaig. There, in a peat bog, an isolated patch of Hebridean rises to the surface, through the Torridon, which surrounds it. It is not more than three or four hundred square yards in area, and is the only gneiss in the broad expanse of Torridon sandstone, which lies on this side of Loch Ewe between Inveran and Greenstone Point. A fine conglomerate of the Torridon firmly adheres to the surface of the rough gneiss, on the outer edges of the bare Hebridean, and fills up its irregularities in a telling way.

Another junction of the same rocks occurs on a small cape formed of gneiss, called Craig an t' Shabhail, which juts into Loch Maree about a hundred yards from Inveran. There a still finer conglomerate is seen, in a thin hard layer, sticking to the surface of the gneiss, evidently the tenacious remnants of a thick bed that has been sc.r.a.ped off by the powerful denuding forces once so active in this region.

Another capital very unconformable junction between the gneiss and the conglomerate is found on Loch Torridon, where the isolated patch of Hebridean that towers into Alligin crosses the loch and forms its Narrows. In the bed of a burn, not far from the school, and in a ridge above it, the two rocks may be easily traced in contact for a considerable distance, and the composition of the brecciated conglomerate easily examined. Similar junctions exist on both sides of this loch at the Narrows, some of them near Shieldaig of Applecross being very good,--all examined by me many years ago.

Between Gairloch and Poolewe, in a hollow to the west, just before the road rises to its summit level, a detached ma.s.s of Torridon sandstone, referred to elsewhere, may be easily observed by the traveller. It forms a thick deposit, with a bold precipitous front facing the south and east, the horizontally bedded red sandstone contrasting well with the grey gneiss that surrounds and underlies it. It also bears well-marked traces of the lateral pressure of ice on its sides next the road.

V. THE VALLEY OF THE HUNDRED HILLS.--No geologist or traveller should miss traversing the picturesque road between Kenlochewe and Loch Torridon, for its wonderful scenery of unsurpa.s.sed grandeur and loneliness, and its splendid exhibitions of the Torridon sandstone, crested by the contrasting pale Quartzite, as seen in Beinn Eay, the Grey Heads, and Liathgach. No sea loch in the Highlands is encircled by such mountain ma.s.ses, mighty, mural, precipitous, and profoundly impressive.

About halfway to Torridon, on the left hand, the eye is arrested by an extraordinary, if not unique, a.s.semblage of hillocks, closely set along the bottom of a glen which opens on the road. These are generally round and peaked, and consist of loose stony _debris_. They caught the eyes of the observing Celts of old, who named the place the Coire Cheud Cnoc, the "Corrie of a Hundred Hillocks." The explanation of their number and character seems not far to seek. It will be observed that, opposite this valley, on the right, lies the steep narrow glen that separates Liathgach from Beinn Eay. Out of this has issued an immense glacier, as proved by the abundant scratches that point into it, which pushed its ice right across the strath we are in, against the hills on the other side and up into the valley with the hillocks. As is well known, the surface of a glacier is traversed by numerous runnels, which gush over its icy front, bearing with them the _debris_ that constantly falls on the glacier from its enclosing walls. These streamlets thus deposit a series of conical hummocks of this _debris_, which gradually cover the ground as the ice retreats, similar to those in the corrie in question.

Examples of such glacial hillocks may be found, by the uninitiated, in the sketches of Norwegian glaciers in Campbell's "Frost and Fire." On the Liathgach glacier, the amount of detritus would be unusually large, from the steepness of the hillsides and the constant waste of the sandstone, and still more, from the superabundant _debris_ of the rapidly disintegrating Quartzite in the precipitous Beinn Eay.

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, 1 to 1 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 superinc.u.mbent 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 striae 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 sh.o.r.es 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 sh.e.l.l 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 striae-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 superinc.u.mbent 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 t.i.tle, 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 Pegmat.i.te, which consists of quartz and felspar, often with small quant.i.ties 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 ma.s.ses, like injected lava. The rare mineral epidote is also found here, and near the top of Beinn a Chaisgean, on the north sh.o.r.e 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 p.r.o.nounced 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 pa.s.sage 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 _debris_, 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 moutonnee_. Over this the ice of the old glacier has pa.s.sed, 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 alt.i.tude 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 ma.s.ses 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 sh.o.r.e 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 sh.o.r.es 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 sh.o.r.e, by breccias and conglomerates, thin shales, yellow and greenish sandstones and flags, and concretionary limestone.

These Tria.s.sic rocks extend for about three miles, from Sand, on the east, to a point beyond Udrigil House, on the west. They are continuous, except near Udrigil, where the Torridon sandstone that encloses them comes to the surface. They are reckoned to be about a thousand feet thick. No fossils have as yet been found in them, but their age has otherwise been satisfactorily determined.

These rocks are extraordinarily interesting. They are the most northerly examples of the Secondary Geological Period on the west coast, and they form an isolated fragment of the deposits of this period, which once extended from Gruinard to the Ross of Mull to a depth of over a thousand feet, and which have been entirely swept away by enormous denuding forces, except at a few scattered points. Their protection has, in all cases, except at Gruinard, been due to being covered by volcanic outbursts on the grandest scale, which took place in the late Tertiary Period, and mainly formed the beautiful islands of Skye and Mull. At Gruinard, they were preserved from destruction by enormous faulting, by which they were dropped down at least a thousand feet into the Torridon Red. They are represented on the east coast of Sutherland, and, according to Professor Judd, by the famous reptiliferous sandstones of Elgin.[10]

Chapter X.

MINERALS OF GAIRLOCH.

By Professor W. IVISON MACADAM, F.C.S., F.I.C., M.M.S., &c., Edinburgh.

The following minerals were obtained in the localities mentioned, but the list is very incomplete. Time has not permitted of a.n.a.lyses being made of many samples, but such are now under examination, and will be available for a further edition of this work:--

Agalmatolite--Black Rock, Tollie.

Albite feldspar--Loch Fionn.

Agaric limestone--Coppachy.

Agate--Tollie Rock.

Barytes--Black Rock, Tollie.

Biot.i.te--Loch Fionn.

Calcite--Black Rock, Tollie, &c.

Chalcedony--Glen Logan, &c.

Chalcopyrite--Coppachy.

Chlorite--Loch Gruinard, &c.

Dolomite--Glen Logan, Slioch, &c.

Epidote--Loch Fionn, Tollie Rock.

Galenite--Glen Logan limestone.

Garnet--Loch Fionn.

Heliotrope, or Bloodstone--Glen Logan, &c.

Hornblende--Loch Gruinard, Loch Fionn, &c.

Limestone (Ma.s.sive)--Glen Logan, &c.

Limonite (Bog iron ore)--South Erradale, &c. &c.