By theRev. John M'Murtrie, M.A.
Thefollowing article appeared inGood Wordsin August 1883, and is generously contributed to this work by the author, the Rev. John M'Murtrie, lately minister of St Bernard's Church, Edinburgh, and now convener of the Foreign Mission Committee of the General Assembly of the Church of Scotland. Mr M'Murtrie has kindly added an appendix containing a list of shells, prepared by him expressly for this book. The article, which is inserted here with the consent of the Rev. Donald Macleod, D.D., editor ofGood Words, is entitled—
"Spring-tide at Gairloch, West Ross—A study of small shells.
"By the way, some people know as little about spring-tides as about small shells. I lately read, in a thrilling narrative of escape from drowning, 'It was neap-tide, and the sea was very far out.' Evidently the writer supposed that neap-tides are the very low tides, just as spring-tides are the very high ones. Of course, the truth is, that spring-tides both rise very high and fall very low; while neap-tides are the tides of least variation,—when, in short, the tides arenipped, and do not fall very low.[1]Once a fortnight there is a series of spring-tides, but, for reasons astronomical, some are much better than others. The half-hour of lowest recess of a first-rate spring-tide is precious to naturalists. You may chance to find them then at the edge of the sea, working, as if for dear life, under rock ledges and among seaweeds; and, wading as deep as they can, with bare arms they lift great stones from the bottom, and examine them for their living treasures. The sea in calm weather becomes very still during that half hour. When it is ended there occurs a remarkable thing, which I have never seen mentioned in books, but I think many shore-naturalists and bait-gatherers must know it. It is a sort of shudder of the sea, as though it awoke; there is a sudden strongsusurrus,—the sound of that wonderful Latin word tells you its meaning,—the wash-sh of a swift little wave, breaking all along the shore and rising in every crevice at your feet, the first impact of a resistless power. At such a time I found myself at Gairloch, on the shore of Western Ross, beyond that gem of Scottish lakes, Loch Maree.
"Naturalists divide every shore into its upper, middle, and lower 'littoral zone.' I cannot write this paper without using a few hard words;littoral zonejust means the beach between high andlow tide-marks. Those plants and animals which live in the 'upper littoral' want no more of the sea than an occasional bath, or even merely its salt spray. The middle region is inhabited by species which prefer to be half their time under water, and the lower by those which agree with being usually submerged. Below the littoral we come upon the greatlaminarian zone, the region of waving laminaria, or sea-tangle. The best view of this submarine forest is from a boat, and you may have dipped an oar at low-water among its olive-brown fronds. These are not uncovered at ordinary tides, but a low spring-tide reveals them. Changed and weird is then the aspect of the sea, and the searcher has access to what he calls the 'upper laminarian.' It is but little harm after all that he ever does, if we take into account the prodigality with which the shore is furnished with life. But should a storm rage when the spring-tide is low, the waves tear up the tangles by hundreds, and pile them, with their countless freight of living shells and other creatures of God, in irretrievable ruin on the strand.
"At Gairloch I found that the rocky shore, while not precipitous, was yet so steep that the various zones and their subdivisions, which on a level beach may easily occupy a mile, were compressed into a very small space. Every few steps in a downward scramble brought one to a new vegetation and new forms of animal life. In particular, it was obvious that innumerable molluscs of the smaller, and therefore less-known species, found shelter and food among the seaweeds that densely clothed the rocks. These molluscs seemed brought to my hand that I might look at them. It occurred to me that no shell-gatherer, so far as I knew, had ever made it his study to know with exactness a compact little shore like this, to determine all the species of those myriads of living shells, to note their distribution and relative abundance, and to estimate the number of individuals.
"It was necessary first of all to devise a right method of investigation. To examine the whole shore was impossible and unnecessary. Plainly I must take samples. The rocks just below high-water mark were covered with a thick stubble oflichina, a small plant resembling the lichens of the land. Various species of minute sea-shells nestled plentifully at its roots. As much of the lichina as two hands could hold was soon scraped from the rocks, wrapped in paper, and called Parcel No. 1. Though months passed before I had leisure to scrutinize my prize, I may here state the result. When all the lichina and broken plates of barnacles and otherdébrishad been removed, there remained twelve hundred and twenty perfect shells, which had been alive when captured; and when they were all put into a pill-box of the smallest size used by druggists, it was scarcely two-thirds full. The leading shell was a dwarf form of our smallest winkle,Littorina neritoïdes,—a species which may almost be said to dislike the sea, though it cannot live far from it. There were six hundred and three of this tiny winkle. Next camelasaea, a red and white bivalve (L. rubra), with four hundred and thirty-nine, mostly full grown. Small as it is, you may, with care and a good lens, open its valves and count a score of young ones within, each having a shell like that of its parent.Skenea (S. planorbis) was third, with a hundred and six shells, each like a short and not quite flat coil of brown rope. But a large skenea is less than the head of a small pin, and these were all young. The rest were a few specimens of the fry of all our other British winkles, and of the common mussel.Rissoa—so named from a naturalist of Nice, M. Risso—is a genus of humble spiral-shelled molluscs, which feed upon decaying seaweeds. Two specks in the parcel shewed themselves under the lens, by the bands which encircled their whorls, to be the young ofRissoa cingillus,—the rissoa, with the little belts around it.
"It would weary the ordinary reader to go through such details in the rest of this paper. I only seek to give him a glimpse into a world of life, of whose existence he was perhaps scarcely aware.
"Parcel No. 2 was an equal quantity of a small seaweed, with a long name,Polysiphonia fastigiata, which fringes common wrack between tides with its thick and branching tufts. Nothing can be simpler than the process of separating thousands of shells from such a handful. You put your seaweeds in a basin of cold fresh water, and all the molluscs instantly let go and fall to the bottom. When those of this parcel were dried, the little pill-box was again in requisition; they exactly filled it. If anybody wants precision, there were forty-two minims of shells. It may give a new thought to some one to read that there were in that box about twelve thousand five hundred shells, each of them a marvel of beauty, and each of them only the external skeleton of a highly organised creature, which secreted and built up that shell bit by bit as its soft body grew larger, and which mixed in the colours and lined it with mother-of-pearl. The little skenea, which began to appear in our first parcel, reached here the extraordinary development of about eleven thousand eight hundred specimens, of which one hundred and thirty-eight were grown up, while all the rest, to the unassisted eye, were like dust, and weighed only eleven and a half grains. The remainder of the parcel consisted of twelve species, ranging in number of examples from one to three hundred and fifty. The shell of which there was but a single specimen wasCyamium minutum, a glittering bivalve, somewhat smaller thanlasaea.
"Parcel No. 3 was made up by scraping from the rock a small strong-smelling seaweed calledLaurencia, which grows near low-water. It yielded about twenty thousand shells, belonging to fourteen species, and they more than filled two of the little boxes. The most remarkable circumstance was, that the shining little bivalvecyamium, which was represented by a solitary specimen in the second parcel, formed here at least three-fifths of the whole. In other words, twelve thousand individuals, old, young, and middle-aged, of thiscyamium—each of them a good walker, a good swimmer, a good spinner when it wished to moor itself by a rope, and each the maker of its own polished shell—were clustered upon a handful of one of their favourite plants. I could not get them till now, because I was not near enough to the edge of the ebb tide. It may be worth noting that there are other shell-gatherers who know where to look forcyamium, for it is told in books upon shells that thirty-five thousand cyamiums were once taken from the stomach of a mullet.
"No. 4 was a parcel of the same size as all the rest, and consisted of various small seaweeds growing at ordinary low water. It proved to contain about eight thousand five hundred shells, of ten species. There was scarcely a bivalve among them. Twolacunæ(cousins to the winkles), and a pearly top-shell (Trochus helicinus), shewed by their abundance that the verge of the accessible shore was nearly reached.
"No. 5 was a parcel of the same kind, from the lowest point of the spring-tide, and produced about thirteen thousand shells. The between-tides species—such asskenea—now visibly began to fail, and a few shells from deeper water, including a youthful scallop, made their appearance.
"The tide was about to turn. Could one more 'parcel' be achieved? From the rock there was visible, far down in the quiet depth, a giant frond oflaminaria, apparently detached, but likely still to have its shelly inhabitants upon it. The day was warm, the spot retired, the water inviting; to swim downwards with the eyes open is easy, if you learned as a boy. Soon thelaminariawas gently laid on dry rock. It was quite ten feet long, and bore one hundred and fifty-seven little shells of nine species, one of them a prize—Rissoa violacea.
"This record is not written for conchologists, but for others to whom its facts are unfamiliar or unknown. Two dozen species, most of them common, and three or four varieties, were all that were found. But, of individual shells there were fifty-five thousand. A calculation, necessarily rough, but as likely to be under the truth as over it, led to the conclusion that, if it were possible to examine all the seaweeds which the lowest tide leaves bare for a stretch of only twenty-five or thirty yards along that shore, a hundred million living shell-bearing molluscs would be found. Of all these not even the smallest would, strictly speaking, be a microscopic object, though certainly requiring a lens for the determination of its species. A hundred millions! How easily we set down the words! And neither the writer nor anybody else has the least conception of what they represent. And if, from that little nook on the Gairloch as a measured base, I tried to estimate the molluscan population of our British shores, making due allowance for the comparative barrenness of many places, I might fill a large part of one of these lines with figures; but who would be any the wiser?
"We are not to suppose that a shore so prolific as that of Gairloch has really only twenty-four kinds of shells. That no more were found among the seaweeds examined, is simply due to the circumstance that all the samples were taken from the same kind of ground. Hard by, round a jutting rock, there is a sandy shell-strewn beach on which, without trouble, fifty species may be gathered,—some of them such rarities that the reading of their names is enough to make an eager collector wish he might forthwith take train for Achnasheen.[2]Let us single out one. Time was whenCrenella decussatawas known to naturalists by a single valve. Here, in a little shell-sand, were six perfect specimens, the valves united and closed, or each what children call a 'box.' Imagine an almost transparent pearl, the size of a grain of mustard seed, suffused with opaline gleams, and covered with exquisite latticed and bead-like sculpture. It wants nothing but size to rival the most splendid exotics.
"Nothing but size! But, to most people, size is everything; wherefore to them the small shells and their beauty are not. Their minuteness hides them as though they were in a far-off and uninhabited isle. To science bulk is an accident, only one of the many properties which she has to consider. What science does for us—even for those of us who, being otherwise busy, can be naturalists only in our leisure time—is something still more important than providing us with a magnifying lens. She takes away that mental habitude which makes minuteness a barrier to interest,—she puts her hand on the inward eye, and we see. Whosoever has been thustouched, has an 'open-sesame' to a treasure-house, has a slave of the lamp to make rubies common. And, besides all this, who dare say that that hidden world of beauty and adaptation is wasted, is lost, till the scientific observer draws near? Certainly he who has watched the little molluscs at their love and their play will be slow to think that they have not a sense of beauty which can be pleased. He who notes how the shells during life are protected from their enemies by their colours; how they are brown and yellow and red like the seaweed on which they feed; how they are pink and white among those algæ which are encrusted with lime; how they are transparent and iridescent as any jelly-fish in the clear sea-water,—has a glimpse into the process by which the Divine Architect who works through the ages fashioned those manifold species. And I, for one, am of Charles Kingsley's creed in this matter:—'See now,' said the hero of 'Westward Ho!' to his brother, as they looked at flies and flowers and humming-birds in a West Indian island, uninhabited till the white man came,—'See now, God made all these things, and never a man, perhaps, set eyes on them till fifty years agone; and yet they were as pretty as they are now, ever since the making of the world. And why do you think God could have put them here, then, but to please Himself'—and Amyas took off his hat—'with the sight of them?'"
Appendix.
Mr Dixon has kindly sent me a considerable quantity of shell-sand from Gairloch shore. I have examined it, and found the following sea-shells. Those which were somewhat plentiful are marked with an asterisk. It would be easy to name some additional shells which will probably be found on Gairloch shore, though they were absent from the sand examined; but I have preferred not to do so.*Anomia ephippium.* Do. do.,var.imbricata.*Pecten opercularis.P.similis(a valve).*Mytilus edulis.*Modiolaria discors.*Crenella decussata.*Montacuta ferruginosa(single valves).M.bidentata.Kellia suborbiculata.*Cyamium minutum.*Cardium edule.*C.nodosum.C.echinatum.C.Norvegicum.*Cyprina Islandica.Astarte sulcata(a valve).A.triangularis.*Venus gallina.V.lincta.V.exoleta.*V.casina.V.ovata(a valve).*Tapes virgineus.Do. do.,var.alba.*Tellina tenuis.*T.fabula.T.pusilla.*Psammobia ferroënsis.*Donax vittatus.*Mactra stultorum.Do. do.,var.cinerea.M.subtruncata.M.solida.Scrobicularia prismatica.*Solen siliqua.*Thracia papyracea.*Saxicava rugosa.* Do. do.,var.arctica.* Do. do.,var.minuta.*Patella vulgata.* Do. do.,var.picta.* Do. do.,var.cœrulea.*Helcion pellucidum.* Do. do.,var.lævis.Tectura testudinalis.*T.virginea.*Trochus cinerarius.T.umbilicatus.*T.millegranus(young shells).*T.helicinus.*Do. do.,var.fasciata.T.zizyphinus.*Lacuna divaricata.*L.pallidula.*Littorina obtusata.*L.litorea.*L.rudis.*Do. do.,var.saxatilis.*L.neritoides.*Rissoa violacea.* Do. do.,var.ecostata.R.semistriata.*R.striata.* Do. do.,var.arctica.*R.parva.*Do. do.,var.interrupta.R.punctura(a fragment).*R.cingillus.*Hydrobia ulvæ.Do. do.,var.albida.*Skenea planorbis.Cœcum glabrum(one specimen).C.trachea(one specimen).Odostomia rissoïdes.O.indistincta.O.lactea.*O.nitidissima.*Natica Alderi.Velutina lævigata.*Aporrhaïs pes-pelecani.*Cerithium reticulatum.*Purpura lapillus.Do. do.,var.imbricata.Buccinum undatum.Fusus antiquus.*Nassa incrassata.Do. do.,var.minor.Pleurotoma striolata(one specimen).*Cylichna umbilicata.*Utriculus truncatulus.U.obtusus.*U.hyalinus.U.mammillatus(two specimens).Philine catena.P.angulata(one specimen).Melampus bidentatus.Spirialis retroversus.The following are a few notes on the land and fresh-water shells:—Pisidium fontinale—Occurred in the shell-sand, having been washed down to the sea by streams. I found a fine variety—perhapsvar.pulchella—in a pond between Gairloch and Loch Maree.Ancylus fluviatilis—Several among the shell-sand.Succinea putris—Two among the shell-sand.Vitrina pellucida—Not uncommon under stones, &c.Zonites cellarius—Two among the shell-sand. I found it also living among stones.Zonites nitidulus,var.nitens—Living among stones, &c.Zonites purus—Among dead leaves.Zonites radiatulus—Two among the shell-sand. It is probably not rare under stones, &c.Zonites fulvus—Among dead leaves.Helix nemoralis—Among the shell-sand.Helix rotundata—Under stones.Pupa umbilicata—Under stones. The variety edentula occurs.Balia perversa—Common at the foot of walls near the parish church, and probably in other places.Clausilia rugosa—Under stones, &c.Cochlicopa lubrica—Three among the shell-sand.J. M'Murtrie.
Mr Dixon has kindly sent me a considerable quantity of shell-sand from Gairloch shore. I have examined it, and found the following sea-shells. Those which were somewhat plentiful are marked with an asterisk. It would be easy to name some additional shells which will probably be found on Gairloch shore, though they were absent from the sand examined; but I have preferred not to do so.
*Anomia ephippium.* Do. do.,var.imbricata.*Pecten opercularis.P.similis(a valve).*Mytilus edulis.*Modiolaria discors.*Crenella decussata.*Montacuta ferruginosa(single valves).M.bidentata.Kellia suborbiculata.*Cyamium minutum.*Cardium edule.*C.nodosum.C.echinatum.C.Norvegicum.*Cyprina Islandica.Astarte sulcata(a valve).A.triangularis.*Venus gallina.V.lincta.V.exoleta.*V.casina.V.ovata(a valve).*Tapes virgineus.Do. do.,var.alba.*Tellina tenuis.*T.fabula.T.pusilla.*Psammobia ferroënsis.*Donax vittatus.*Mactra stultorum.Do. do.,var.cinerea.M.subtruncata.M.solida.Scrobicularia prismatica.*Solen siliqua.*Thracia papyracea.*Saxicava rugosa.* Do. do.,var.arctica.* Do. do.,var.minuta.*Patella vulgata.* Do. do.,var.picta.* Do. do.,var.cœrulea.*Helcion pellucidum.* Do. do.,var.lævis.Tectura testudinalis.*T.virginea.*Trochus cinerarius.T.umbilicatus.*T.millegranus(young shells).*T.helicinus.*Do. do.,var.fasciata.T.zizyphinus.*Lacuna divaricata.*L.pallidula.*Littorina obtusata.*L.litorea.*L.rudis.*Do. do.,var.saxatilis.*L.neritoides.*Rissoa violacea.* Do. do.,var.ecostata.R.semistriata.*R.striata.* Do. do.,var.arctica.*R.parva.*Do. do.,var.interrupta.R.punctura(a fragment).*R.cingillus.*Hydrobia ulvæ.Do. do.,var.albida.*Skenea planorbis.Cœcum glabrum(one specimen).C.trachea(one specimen).Odostomia rissoïdes.O.indistincta.O.lactea.*O.nitidissima.*Natica Alderi.Velutina lævigata.*Aporrhaïs pes-pelecani.*Cerithium reticulatum.*Purpura lapillus.Do. do.,var.imbricata.Buccinum undatum.Fusus antiquus.*Nassa incrassata.Do. do.,var.minor.Pleurotoma striolata(one specimen).*Cylichna umbilicata.*Utriculus truncatulus.U.obtusus.*U.hyalinus.U.mammillatus(two specimens).Philine catena.P.angulata(one specimen).Melampus bidentatus.Spirialis retroversus.
The following are a few notes on the land and fresh-water shells:—
Pisidium fontinale—Occurred in the shell-sand, having been washed down to the sea by streams. I found a fine variety—perhapsvar.pulchella—in a pond between Gairloch and Loch Maree.Ancylus fluviatilis—Several among the shell-sand.Succinea putris—Two among the shell-sand.Vitrina pellucida—Not uncommon under stones, &c.Zonites cellarius—Two among the shell-sand. I found it also living among stones.Zonites nitidulus,var.nitens—Living among stones, &c.Zonites purus—Among dead leaves.Zonites radiatulus—Two among the shell-sand. It is probably not rare under stones, &c.Zonites fulvus—Among dead leaves.Helix nemoralis—Among the shell-sand.Helix rotundata—Under stones.Pupa umbilicata—Under stones. The variety edentula occurs.Balia perversa—Common at the foot of walls near the parish church, and probably in other places.Clausilia rugosa—Under stones, &c.Cochlicopa lubrica—Three among the shell-sand.
J. M'Murtrie.
ByWilliam Jolly.
Thegeology of Loch Maree is unusually varied, interesting, and representative. It exhibits, in a limited area, the whole debated series of the succession of rocks in the North-West Highlands. This has been a fertile subject of controversy, surpassed only by the world-famous Glen Roy. It has engaged the attention and the pens of some of the most eminent British geologists, including Macculloch, Hugh Miller, Sedgwick, Sir Roderick Murchison, Professor Nicol of Aberdeen, Archibald Geikie, and a host of others not less able. After considerable discussion, chiefly between Murchison and Nicol, the authoritative name of Murchison, along with that of Archibald Geikie, who wrote a joint memoir on the subject, seemed for a time finally to settle the question in Murchison's favour; and his views were not only generally received, but were embodied in the geological maps of the district most in use. But, lately, the whole question has been reopened with greater keenness than ever, and the conclusions of the geological king have been vigorously and uncompromisingly assailed all along the line. The war is, at the present date, in full swing, but with a near prospect of final peace. The geological problem of the Highlands is by no means settled, though much additional light has been thrown on the debatable ground by the researches of the numerous and capable combatants, including recently Peach and Horne, of the Geological Survey; and their investigations will no doubt hasten the final determination of the vexed question. But a firm basis of interpretation has at length been gained, by which the geological structure of the broad tracts of the Highlands, hitherto uniformly coloured as Silurian, will be investigated under new and important lights, and a remapping of the Highland area erelong achieved, with such permanent results as have hitherto been impossible.
The conditions of the problem are extremely well exhibited round Loch Maree. Here we are presented, as Dr Archibald Geikie truly observes, with "a series of sections of singular clearness." He confesses that he knows of "no locality where the geologist may better acquaint himself with the order of superposition of the ancient crystalline rocks of the Highlands, or with the dislocations and metamorphism which they have undergone." These will now be briefly explained. The whole subject may, without much difficulty, be understood by the ordinary reader, if he will use a geological map of Scotland, such as Nicol's or Geikie's, which he will also find useful as a guide.
A.—The Series of Rocks in the North-West Highlands.
The rocks round Loch Maree are shortly the following:—
I.The Hebridean Gneiss.—The Long Island from the Butt of the Lews to Barra Head consists almost entirely of a species of gneiss, very much metamorphosed. It occurs in the Inner Hebrides in Tiree and Coll, in Sleat, in Raasay, and Rona, off Portree, but very little in Skye, one of our youngest isles. It is found in patches on the Mainland on the western shores of Ross and Sutherland, and stretches from Torridon to Cape Wrath, whose contorted cliffs it forms. It has been variously designatedHebridean, from being chiefly found in the Hebrides;Lewisean, from forming the most of the Lewis, a less acceptable name;Archæan, from being the earliest system;Pre-Cambrian, as being earlier than the Cambrian sandstone immediately above it; andFundamental, from its constituting the lowest rock strata in the British Isles. Murchison identified it with the lowest geological series, theLaurentian, which is so named from being extensively developed on the St Lawrence in Canada. It is best, however, to designate the rocks by a geographical and non-theoretical term, like Hebridean.
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 toSlioch, 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 ofBeinn Aridh CharrandBeinn 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 loneLoch Fionnand its darker chamber of theDubh Lochat its head. North ofCoigeach, 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 themap, 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 hasnamed, and by which he seeks to interpret the rest of the Highlands.[3]In America, the Laurentian system contains the celebratedEozoon 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 ofLiathgach. 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 ofSlioch, 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, inSlioch, 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, thesecond 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 ofSlioch, on the right side of a glen watered by a stream called the Fasagh, which separates Slioch from the ridge to the east. In GlenFasagh, 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 ofSlioch, 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 GlenCruaidh 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.
Its capabilities in this way are also well exhibited on the west coast round Loch Assynt, rising there into the summits of Beinn More and Queenaig, above three thousand feet; and also near Loch Carron to the south, and between Assynt and Eriboll to the north. On Loch Torridon, its prevailing tendency to whiteness gives rise to the name Grey Heads, very descriptive of certain contorted peaks near Coulin Lodge.
The Quartzite is interesting as exhibiting the earliest indications of organic life yet discovered in Scotland:—
1.Annelid Borings.—The lower beds next the Torridon contain, on their surface, as described by Murchison, "large round knobs on the top of cylindrical bodies, which pass through several layers," their number being often astonishing. These are, it is safely concluded, "infillings of excavations" made by certain worms called Annelids, and are known asAnnelid Borings. They are noteworthy as "the oldest vestiges of life which can be detected in the North Highlands." They are often very clearly seen, as the filling in has generally been done by a different coloured sand from that in which they had been bored. They sometimes project above the surface like "pipes," and are so numerous as to cause these beds to be called "pipe-rock." Examples are abundant round Kenlochewe, and on the roadside at the entrance to GlenCruaidh Choillie, where they are unusually good. They should be secured by the intelligent visitor from their extraordinary interest.
2.Fucoid Remains.—Interstratified with the Quartzite, are certain brown, mottled, shaly and flaggy bands, with curious impressions of what seem leaves, which have been thought to be fucoids or seaweeds. The recent Survey explorations would seem to point to their being simply very much squeezed annelid "pipes." The shales in which they occur are thus generally known as the Fucoid Beds, and, when found, are very good evidence of the horizon of the rocks. They are often very distinct and easily seen, and are most interesting. They occur on Loch Maree near the top of the east side of GlenFasagh, imbedded in the Quartzite, and run through the Quartzite to GlenCruaidh Choillie.
Other organisms have been found in it elsewhere, such as orthoceratite in Assynt, and certain small conical bodies called serpulites.
This Quartzite, with its annelid borings and fucoid beds, is placed by Murchison in the Silurian series, the third in the geological record. By others, such as Dr Hicks, it is considered possibly Cambrian.
IV.The Limestone.—On the western side of Glen Cruaidh Choillie, resting on the Quartzite, and generally conformable with it, is found a limestone. By examining themap, it will be seen thatthis limestone runs more or less continuously from Loch Carron to Loch Eriboll. It receives its greatest development at Inchnadamph, at the east end of Loch Assynt, where it forms splendid cliffs. It is of commercial value, and has been worked at various places along its outcrop. It will also be observed that there is a wide isolated patch of limestone at Durness, between Loch Eriboll and Cape Wrath.
In this Durness limestone, which was long considered unfossiliferous, like the other rocks of the North-West Highlands, shells were discovered in 1854 by Mr Peach, the eminent geologist, and friend of Dick of Thurso. These were determined to be Silurian by Mr Salter, a great specialist in such matters, and were described and figured in a paper by Sir Roderick Murchison in 1858.[5]Since then finer specimens have been discovered. Their likeness to British Silurian fossils is very remote, and they are more related to American forms; but they are generally now accepted as of Silurian or Ordovician age. This discovery of fossils gave a great impetus to the study of these rocks, and formed the basis of the theory propounded by Sir Roderick Murchison.
The Durness limestone turns out, however, to be, as a whole, of a different type from the great strike of limestone which goes through GlenCruaidh Choillieand terminates at Loch Eriboll. This Durness limestone is held by Dr Heddle, who first ascertained the fact, and by other competent authorities, to be non-dolomitic, while that of the great strike to the east is dolomitic; dolomite (so called from the French geologist Dolomieu) being a variety of limestone, which, in addition to the carbonate of lime of which common limestone mainly consists, contains more or less carbonate of magnesia,—in this dolomite, forty-eight per cent. Dolomitic beds have, however, lately been discovered in the Durness basin by the Survey. For long, no fossils were obtained from the great dolomitic strike, except an orthoceratite at Assynt by Mr Peach, and a possible organic mass by myself at the same place; but recently a varied and important suite of fossils has been gathered by the Survey, which has clearly decided the age of the Dolomite to be Silurian. Of its position above the Quartzite there is no doubt.
It is pretty well exhibited in GlenCruaidh Choillie, where it has been worked at various places, and where its superposed junction with the Quartzite can be seen.
V.The "Logan Rock."—Immediately to the east of the Limestone, and in contact with it, is found a remarkable rock, which appears at various parts in the middle of GlenCruaidh Choillie, and which has caused great discussion in regard to its character, relative position, and age. By Professor Nicol, it was held to be igneous, serpentinous, felspathic, porphyritic, and intrusive, and was named by him "Igneous rock;" by Murchison, to be here a "syenite," and elsewhere a "greenstone," and "serpentinous and felspathic," interbedded with and resting directly upon the limestone; by Dr Hicksand others, to be a "syenite," or a "granitic" and "quartz diorite," and igneous, faulted, and intrusive, like Nicol; and by Dr Callaway, as the Hebridean gneiss "brought up by a fault." It is well here, as in all other cases, to designate it geographically, and call it the "Logan Rock," as first suggested by Heddle, and now generally used.
In "Glen Logan," it is best exposed in the bed of the river about two miles above the school. At a point about halfway up the glen it runs up the hill on the west side, and is seen to overlie the limestone.
This rock appears, as maintained by Nicol, more or less continuously associated with the limestone strike, and assumes a great variety of forms, as shewn by the different characterisations it has received. It has played an important part in the history of the theories of the succession of these Highland rocks. In Sutherland, it sometimes receives a broad development.
VI.The "Eastern Gneiss."—Immediately to the east of this rock, rising in GlenCruaidh Choillieat once from contact with the "Logan Rock," and forming the whole of the eastern wall of the glen, there stretches a long series of shales, schists, gneiss, and other rocks. These appear on both sides of Glen Dochartie, and thence on eastwards through Ross and the main body of the Highlands, till they are overlaid by the Old Red Sandstone of the east coast. The position and interpretation of these rocks have caused extraordinary investigation and discussion, which is still being carried on. They are variously known as the "Eastern gneiss," "Eastern schists," by Murchison and others; the term "Caledonian" has also been proposed by Dr Callaway,—all to distinguish them from the Hebridean of the west coast.
B.—The Controversy regarding the Succession of these Rocks.
Up to the Limestone, the order of succession of the rocks may be regarded as settled, all parties agreeing as to their relations though differing as to their classification under the early geological systems. It is held that the order is,—lowest, the Hebridean gneiss; above that, very unconformably, the Torridon Red; above that, less unconformably, the Quartzite, with its embedded organic remains; and above that, more or less conformably, the Limestone, with its numerous fossils. At this point, begins the controversy which has so long been waged regarding the nature and succession of the rocks in the North-West Highlands, and which has passed through many phases of opinion, and even disturbed the long-tried friendship between the chief combatants, Murchison and Nicol.
The "Logan Rock" Murchison considered to rest on the Limestone, and not to be intrusive and igneous as thought by Nicol. He also maintained that the "Eastern gneisses and schists" lay more or less conformably above the limestone or interbedded syenite, and were therefore more recent,—in fact, were a continuation of the Silurian system, of which the limestone was the representative example.
Professor Nicol held to the last,[6]that the Limestone is the highest rock in the whole series of the North-West Highlands; that faulting or igneous action exists along the line of the "Igneous rocks," associated with the Limestone; that these "Eastern gneisses and schists" do not overlie the Limestone; that where they seem to do this, the appearance is caused by an overlapping of these "Eastern rocks" through pressure from the east; and that these rocks are probably the Hebridean, or, as he called it, the "Fundamental," gneiss reappearing. Latterly, he did not condescend to identify any of these rocks of the North-West with the received geological epochs, leaving this to be settled by subsequent investigation; but he held strenuously that the succession was as he declared,—Fundamental gneiss, Torridon Red, Quartzite, and Limestone, the rocks east of this point being metamorphic forms of the western gneiss reappearing.
Murchison, at last associated with Dr Archibald Geikie, who in 1858 wrote a joint memoir with him on the subject of great value,[7]held, on the other hand, that there exists an unbroken series from the Fundamental or Laurentian gneiss to these "Eastern gneisses and schists," and that they succeed each other in superposition and age. They, moreover, classified them as Laurentian, Cambrian, and Silurian; the Silurian beginning with the Quartzite, and continuing eastwards in various folds and reduplications till overlaid by the Old Red Sandstone. Other points of difference existed between these eminent geologists, particularly as to the existence of two Quartzites, and two Limestones, as apparently exhibited at Assynt and elsewhere; but as these do not occur in our district, they need not be further described.
For twenty years Murchison's theory dominated over Nicol's, with scarcely a dissentient voice. The brave old professor maintained to the end, against the geological world, opinions to which, while seemingly less probable, he had been led both by years of unusually careful examination of the whole field, which he knew better than any, and by general considerations regarding metamorphism and other matters affecting these ancient rocks; while his opponents were so confident of their position, that Geikie, in his "Life of Murchison," headed one of his chapters "The Geological Conquest of the Highlands." But in 1878, Murchison's conclusions began to be vigorously assailed, the attack being led by Dr Henry Hicks,[8]and has been strenuously maintained by him and other eminent geologists, of London, such as Bonney, Huddleston, Callaway, Heddle, Lapworth, Etheridge, Judd, and many others. These have written numerous papers advocating conclusions more or less adverse to those of Murchison, and agreeing in the main with those of Nicol.
Even Geikie has had to abandon his early position, and declareagainst the theory of his former chief. In a remarkable declaration, published inNatureof November 13, 1884, prefacing a paper on "The Geology of North-West Sutherland," by the two Survey geologists Peach and Horne, Geikie made a brave and honourable retractation of these opinions, which he had so long and so ably advocated with Murchison. He there declares: "With every desire to follow the interpretation of my late chief, I criticised minutely each detail of the work upon the ground, but I found the evidence altogether overwhelming against the upward succession which Murchison believed to exist in Eriboll from the base of the Silurian strata into an upper conformable series of schists and gneisses." He found the same true all along the strike of these controverted rocks. "The clear coast sections of Eriboll have now taught me that the parallelism between the Silurian strata and the overlying schists is not due to conformable deposition." He traced the same kind of evidence southwards for more than ninety miles, and found it "as well marked above Loch Carron as it is at Loch Eriboll."
These "Eastern gneisses" not only frequently appear to be superposed upon the rocks beneath, but, as Geikie says, the parallelism of dip and strike between them and the rocks below them is so complete in some of the Ross-shire sections, that he asserts "had these sections been planned for the purposes of deception, they could not have been more skilfully devised." These Survey geologists explain these extraordinary phenomena by a system of "reversed faults" and "pushes from the east," by which the "Eastern rocks" have been driven westwards, in some cases ten miles, and are thus made to overlie the older rocks, through "prodigious terrestrial displacements, to which there is certainly no parallel in Britain,"—displacements which Nicol, against the evidence of his eyes, had insisted on as factors, nearly thirty years before.
Evidences of these dislocations are not so apparent round Loch Maree as elsewhere, especially near Loch Eriboll, but they are sufficiently marked round Kenlochewe as to appeal even to a non-scientific visitor. In GlenCruaidh Choillie, at a point already noted, the "Logan Rock" is seen superposed right upon the Limestone up to the crest of the west side of the glen; according to Heddle, it also lies over it, with a slight hiatus, as far as GlenFasagh. It is to be remembered, following recent conclusions, that this rock did not naturally have this position, but has been pushed violently into it by unparalleled "terrestrial displacements;" and that both this and the long series that form the eastern side of the glen are portions of the Hebridean again coming to the surface, and appearing in such mass and extent up Glen Dochartie and on to Achnasheen.
It would be out of place here to enter into the various opinions offered to explain the remarkable facts connected with these "Eastern rocks," their nature, and their relations to the western. The papers on Loch Maree are already very numerous, and opinions are still conflicting; and the Survey has not yet published its memoir on the Loch Maree district.
Dr Hicks, for example, held that these "Eastern rocks" generallyare metamorphosed forms of the Hebridean reappearing, but that the Hebridean occurs at the junction of Glen "Logan" and Glen Dochartie, and that along the floor of the latter, the Hebridean, but not the limestone, is overlaid by certain "blue flags and sandstones, and argillaceous, quartziferous, and micaceous flaggy beds" in succession, up to the head of Glen Dochartie. These along with the Limestone he classes as Silurian, placing the underlying Quartzite with the Cambrian. At the head of Glen Dochartie, the Silurians disappear, he held, by a possible fault, and the Hebridean or "Pre-Cambrian" as he prefers to call it, again reasserts itself up to the summit of Ben Fyn and eastwards. He writes me, however (1886), that in the light of recent investigations, he is prepared to class the Glen Dochartie rocks with the Hebridean, like those at the head of the glen; though he would not yet affirm their exact place in the broad Pre-Cambrian series, which he has lately attempted to classify.
In his recent utterance, Geikie maintains that these "Eastern rocks" have undergone such intense alteration that their original characters have been in great measure effaced. Some of them are "unquestionably part of the Archæan gneiss," others are the western Quartzite, &c.; but traced eastwards, "the crystalline characters become more and more pronounced, until we cannot tell, at least from examination in the field, what the rocks may have originally been. They are now fine flaggy micaceous gneisses and mica-schists, which certainly could not have been developed out of any such Archæan (that is Hebridean) gneiss as is now visible to the west. Whether they consist in part of higher members of the Silurian series in a metamorphic condition remains to be seen."
We have now described the whole succession of rocks in our district, from Gairloch and Poolewe to the head of Glen Dochartie, and given some idea of the difficult problems they present and the theories offered for their solution. The succession up to the Limestone is accepted. The Hebridean is now variously designated "Pre-Cambrian;" and by Callaway, Geikie, and others, "Archæan;" the determination of Murchison as "Laurentian" being generally avoided. The Torridon Red is accepted as "Cambrian" by most, and recently by Geikie and his colleagues; though there are differences of opinion as to the precise period in that series to which they belong. The Quartzite and its associated beds are placed by Hicks and others with the "Cambrian;" and by others, including Geikie, with the Lower Silurian or Ordovician: but their position above the Torridon and below the Limestone is undoubted. The Limestone is conceded to lie above the Quartzite, but its nature and age are not yet settled, some holding it to be dolomitic and unlike the Durness limestone; Heddle for a time heading these, though now agreeing with the Survey; others, like Hicks, holding the limestones to be the same or, like the Survey geologists, so related as to form one system, which they call "Durness-Eriboll limestone." The "Logan rock" is variously interpreted,—some reckoning it to be igneous and intrusive; others, to be metamorphosed Hebridean; and others, to begranitic and syenitic. The "Eastern gneisses and schists" are still undetermined as to character, relations, or age, opinions being very various and conflicting; though there is a general agreement as to their belonging to some portion of the Hebridean series. Attempts have been made to classify the Hebridean, especially by Hicks,[9]but into this, space prevents our entering here.
My own opinion on this much controverted succession, during nigh twenty years' careful study of the whole field from Skye to Eriboll and more or less minute examination of the disputed sections, has been increasingly in favour of Nicol's general position. The proofs of Murchison's contention of the superposition and newer age of the "Eastern gneisses" I always regarded imperfect, as often expressed both privately and publicly. Nicol's general contentions as to the unlikelihood of highly metamorphic schistose and gneissic rocks, like the Eastern, being transformed, while older rocks remained so little affected as the Cambrian and others beneath, gained growing weight. Every fresh examination of the ground increased the probability of their apparent superposition being merely overfoldings of the western rocks. The displacements, the investigations of more recent observers have shewn to be much greater than all earlier students, including myself, ever imagined.
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 inBeinn Aridh CharrandBeinn 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. TheStoss seite, or rubbed side, of theroches moutonnéesis 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, thelateralpressure of the ice is also very well shewn, as well as, at not a few points, itsupwardpressure on projecting rocks, theunderside 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 Gairlochand 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 roughdébris, 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 immenseroche 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).
III.Denudation.—One of the most striking geological featuresof 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 altitude 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 shore 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 thebrecciamay 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 pass, 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 formedof 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 scraped 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 mass 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 unsurpassed 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 masses, mighty, mural, precipitous, and profoundly impressive.
About halfway to Torridon, on the left hand, the eye is arrested by an extraordinary, if not unique, assemblage 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 stonydébris. 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 fromBeinn 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 thedébristhat constantly falls on the glacier from its enclosing walls. These streamlets thus deposit a series of conical hummocks of thisdébris, 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 glaciersin 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 superabundantdébrisof 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 theInverness 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 sandstonein 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 thesamekind 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 footprintson 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. Thestriæ-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.