THE geology 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 Home, 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 meta-morphism 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 designated Hebridean, from being chiefly found in the Hebrides; Lewisean, from forming the most of the Lewis, a less acceptable name; Archcean, from being the earliest system; Pre-Cambrian, as being earlier than the Cambrian sandstone immediately above it; and Fundamental, from its constituting the lowest rock strata in the British Isles. Murchison identified it with the lowest geological series, the Laurentian, 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 to Slioch, and running along its southern side from near Inverasdale on Loch Ewe to Talladale. It stretches northwards from the lake to Loch Gruinard, and westwards to Poolewe and Gairloch, where its characteristics are very well seen on the wave-beaten coast near the hotel there. It forms the rugged outlines of Craig Tollie, at the west end of the loch, and of Beinn Aridh Charr and Beinn Lair, near Letterewe. It shows one of the most magnificent series of furrowed precipices in Britain, at the back of Beinn Lair, which should be visited by all who appreciate the wildly grand; and entirely encloses the lone Loch Fionn and its darker chamber of the Dubh Loch at its head. North of Coigeach, it occupies most of the west coast on the mainland up to Cape Wrath; and southwards, there is a patch of it at the Narrows of Loch Torridon. From recent researches, it will probably be found widely extended over the rest of the Highlands.

It is more or less vertical in dip on the west coast, and has there a general persistent strike from north-west to south-east. The special character of its scenery is very well seen round Loch Assynt, and is well presented in the parish of Gairloch. As shewn on the map, it forms the splendid peak of Alligin, above three thousand feet, which towers above Loch Torridon, from which it passes to the head of the Gairloch, where it is admirably exhibited in structure, dip, and strike on the shore near the Free church and along the picturesque road to Poolewe. It contains some limestone on Loch Maree in a line parallel to the loch, for some miles on both sides of Letterewe. A vigorous attempt has recently been made by Dr Hicks to discriminate this gneiss into certain series or epochs, which he has named, and by which he seeks to interpret the rest of the Highlands.* In America, the Laurentian system contains the celebrated Eozoon Canadense, that is, the Canadian Dawnlife, the lowest organic form yet known. It has as yet proved absolutely barren in Europe, though a flutter was raised by its supposed discovery by Dr Heddle of St Andrews, Dr Carpenter asserting the fact, but its discoverer, on further examination, disclaiming the honour.

II. The Torridon Sandstone.—This is the chocolate-coloured sandstone so splendidly exhibited round Loch Torridon, where it towers into the mural dignity of Liathgach. It is well presented in the mountains of Applecross, as seen from Loch Carron, and from Loch Kishorn which lies at their southern base. This sandstone occurs only at one spot in the Outer Hebrides, round the harbour of Stornoway; it is found in Rum, its southermost position, in Sleat, Scalpa, Raasay, and neighbouring islets; it occurs continuously, except where the Hebridean gneiss appears, from Loch Carron to Coulmore near Loch Inver, and thence in isolated patches, north to the Kyle of Durness. The scenery it presents is uncommonly striking, massive and grand, its mural character, which arises from its horizontal strata, being a special feature, and nothing in style can anywhere surpass the splendid spear-headed crest of Slioch, the monarch of the mountains, worthy though his compeers are, that stand round Loch Maree. The denudation to which this ancient sandstone has been subjected has been extraordinary. This is well seen round our loch, when we consider that Slioch is above three thousand feet in height; but still more impressively, from the sea off Loch Inver, in the sugar-loaf cone of Suilven and its brethren, all isolated stacks of Torridon sandstone,—so remarkable that Murchison selected this scene as the most striking example of denudation he knew, to illustrate the subject in his famous "Silurian Round Loch Maree", it forms its southern shores east of Talladale, where its character can be well examined in the delightful drive from Kenlochewe. On the north side, it touches the loch only at its two extremities, at the one end, near Inveran and along the Ewe, and at the other, in Slioch, stopping short of the head of the lake, as can easily be seen from the south side. It is more or less horizontal, or dips slightly to the south-east, being deposited in thick, well-marked beds, as everywhere exhibited, and thus forms a remarkable contrast to the vertical strata on which it rests. An excellent junction of the two, easily reached and examined, occurs on the shores of Gairloch, at the end of the rocky peninsula on which the Free church stands. There the two are seen, the more or less horizontal Torridon superposed on the vertical Hebridean, in the most striking style, which is rendered all the clearer by the washing of the restless tides. This sandstone about Loch Mar^e is about four thousand feet in thickness.

It was correlated by Murchison with the Cambrian system, the second in the geologic series, and was so named by him,—a name now recognised by the chief authorities. It is well, however, to designate it by a neutral geographical term, and to retain the title given it by Professor Nicol, that of Torridon Sandstone, or Torridon Red. In Scotland, it has as yet yielded no organic remains, though these are abundant and good in Wales, after whose ancient name of Cambria it is called, and also in Scandinavia, which remained united to Scotland till post-glacial times. It was long thought to be a western representative of the Old Red Sandstone of the east coast, Hugh Miller, among others, looking on it as a worthy example of his pet rocks; but in his day, the geology of the Highlands was but dimly and imperfectly known, and their great problems were not even surmised.

Like the Old Red, a fact that tended to mislead early observers. its lowest bed is a thick massy conglomerate or breccia, which is very well seen at the junction at Gairloch, and which is generally persistent throughout the system on the west coast. It consists of varied pieces, sometimes rounded, often angular, and some of them large, of the under-lying Hebridean rocks, enclosed in a finer matrix of the same materials. Portions of the " Eastern rocks" have, it seems, also been detected in it,—a fact which, if established, indicates the true age and succession of these "Eastern rocks."

III. The Quartzite.—Above the Torridon Red, lies a thick-bedded whitish rock, called from its general appearance Quartzite. This French word is, however, a partly misleading term, as the rock is not quartz, though much made up of quartz grains; but it is a highly metamorphosed fine sandstone. It is here sometimes coincident in dip with the underlying Red, but it is generally non-conformable. It can be easily seen, looking from the south side of Loch Maree, at a point east of Slioch, on the right side of a glen watered by a stream called the Fasagh, which separates Slioch from the ridge to the east. In Glen Fasagh, the Torridon Red is clearly observed to rest horizontally on the Hebridean gneiss below, on both sides of the glen; the Torridon forming the most of the western side of the valley up to the summit of Slioch, but rising, on the eastern side, only half-way up, being then surmounted by the strongly contrasted Quartzite to the top of the ridge. The Quartzite continues eastwards to the wide glen beyond, generally but erroneously called "Glen Laggan," or " Glen Logan," though its real name is Glen Cruaidh Choillie. [Pronounced Croocholee. The wrong name occurred in the common maps, and from them, being much used by geological writers, will, it is to be feared, continue to be employed.]

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 wray 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 as Annelid 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 Glen Cruaidh 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 Glen Fasagh, imbedded in the Quartzite, and run through the Quartzite to Glen Cruaidh Choillie.

Other organisms have been found in it elsewhere, such as ortho-ceratite 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 the map, it will be seen that this 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 unfossili-ferous, tike 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.* 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 Ordovi-cian 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 Glen Cruaidh Choillie and 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 Glen Cruaidh 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 Glen Cruaidh 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," inter-bedded with and resting directly upon the limestone; by Dr Hicks and 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 Glen Cruaidh Choillie at 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,* 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 meta-morphic forms of the western gneiss reappearing.

Murchison, at last associated with I)r Archibald Geikie, who in 1858 wrote a joint memoir with him on the subject of great value, f 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, J 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 declare against the theory of his former chief. In a remarkable declaration, published in Nature of November 13, 1884, prefacing a paper on "The Geology of North-West Sutherland," by the two Survey geologists Peach and Home, 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, triey 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 Glen Cruaidh 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 Glen Fasagh. 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" generally are 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 Archaean 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 Archaean (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, "Archaean;" 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 be granitic 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,* 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 in Beinn Aridh Charr and Beinn Lair, and wTith its own height in Slioch. The same remarkable faulting holds good of other lakes. Loch Assynt to the north, being in much the same position as Loch Maree to these controverted rocks, lies also in the line of another great fault; Loch Ness also runs in the line, and occupies the place of a stupendous crack in the rocks there, shewn by a great anticline which runs from the Moray Firth to Loch Linnhe, and which has also in some way given rise to the enormous hollow occupied by Loch Ness,—a hollow twice the depth of the German Ocean, being nearly a thousand feet deep, while the North Sea is nowhere deeper than five hundred. The great Loch Maree fault can be seen in Glen Dochartie, and is there exhibited on both sides of the glen, where the unsymmetrical relations of the rocks may be studied.

II. Glaciation.—The phenomena of the Glacial Period are exceedingly well exhibited round Loch Maree. On the surfaces of the flat Torridon sandstone, at many places along the southern shores, especially on the higher parts of the road a little to the east of Talladale hotel, the scratchings are very good, distinct, and continuous, extending, on some of the slabs, for hundreds of feet in unbroken line. They run generally parallel to the longer axis of the lake, and prove the existence of an immense glacier that moved to the sea down the deep hollow now filled by its waters. The Stoss seite, or rubbed side, of the roches 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 passed increasingly from north to south, as exceedingly well seen on certain exposed rock surfaces above and to the west of the road between Gairloch and Poolewe. There the glacier movement seems to have been from Loch Ewe to Gairloch, showing that the ice stream from Loch Maree had probably expanded fan-wise on its exit from the narrow glen near Inveran, where its pressure had been greatest and where its effects are so well shewn.

Another striking evidence of glacial work, and a telling proof of the existence of this mighty glacier, should be visited. This is the series of lateral moraines that lie between Loch Ewe and Loch Gruinard, more or less parallel to their coasts. They are cut across by the high road at its most elevated portion, and run interruptedly out to sea, along the peninsula between these lochs. They consist of irregular lines, more or less continuous, of rough 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 moutonne'e, 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 rate intruder.

A most interesting feature connected with the glaciation of the district is the probable existence of a glacial period before the Tor-ridon 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 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 the breccia may here be easily examined, from its wrave-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 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 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 Apple-cross 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 Ken-lochewe 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 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 unitiated, 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 i, 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 \\ inch broad and about a quarter of an inch deep, running quite straight across the flat layers of sandstone in stilly 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 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 shores of Morayshire,—a suggestion strengthened by the fact of the existence, on both sides of the line, of numerous rounded hollow marks, very like the footprints on these reptiliferous rocks, occuring, as in them, at intervals. But the continuous even breadth and square section of the lines would seem to render this impossible. They might be the depressions left on the soft sand by the hinder portions of the shell of some huge crustacean,—a more likely cause, rendered more probable by the existence of very good ripple marks on the same sandstone, in the same and neighbouring layers. The 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 superincumbent layer of rock carefully removed where the bands in question disappear under the upper rock, in order to shed more light on the nature of the strange marks. Whatever they are, they certainly deserve the careful attention of geologists. Dr Heddle, who has examined them since 1880, is of opinion that they are not in any way connected with organisms, but are due to mineralogical and structural causes, but he has not yet published his views.

VII. The Fionn and Dubh Loch.—This double loch is remarkable, and eminently worth visiting, not only for its scenery, elsewhere described, but also for its geology. Both lakes are enclosed in Hebridean gneiss, which here very powerfully exhibits its usual characteristics, reaching its highest in the picturesque peak of Coire Chaoruinn, above the centre of the loch. The Torridon sandstone appears on Ruadh Stac or Red Peak, which bears an appropriate title, and possibly on the very crown of the Maiden. The pale rock which catches the eye from far on the front of Craig an Dubh Loch, at the head of the Fionn Loch, is a remarkable species of granite, known by the French term Pegmatite, which consists of quartz and felspar, often with small quantities of silvery mica. It abounds in the Hebridean gneiss in other parts of the west coast, but in our district, it is comparatively little developed except at the Dubh Loch, where it also appears on the Maiden's shoulders, and on Cam Bhan or the White Cairn, to which it gives name. It should be examined on the great cliff of Craig an Dubh Loch, where it traverses its face and head in serpentine lines and masses, like injected lava. The rare mineral epidote is also found here, and near the top of Beinn a Chaisgean, on the north shore of the lake.

The smaller upper part of the loch is almost entirely separated from the lower, and forms an Alpine chamber, strongly contrasting with the rest in form, feature, colour, and surroundings, which has given rise to its most appropriate name of the Dubh or Black Loch. This loch is an excellent example—none better—of a moraine-dammed lake, being held in by an uncommonly pronounced moraine, which marks the last boundary of the ancient glacier that filled its deep pot. This moraine begins on the left side, under the grand cliff of Craig an Dubh Loch, curves finely round the lower end of the Dubh Loch,. crosses the loch to the other side, forming in its passage the narrow waist that separates the two lakes, and then runs along two-thirds of the Dubh Loch till it gets lost in the general rubbish of the hills, the path to Loch Broom which crosses the causeway taking advantage of its terraced line for some distance. The moraine consists of a long circular ridge of loose 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, Cam na Paite, some three hundred feet high, which has formed a huge roche moutonnee. Over this the ice of the old glacier has passed, and smoothed it, the same ice having crushed and striated the steep front of Craig an Dubh Loch, on the other side of the glen. Other telling proofs are apparent all round of the more general glaciation of Scotland, when it was a veritable Greenland, with a huge ice sheet enveloping mountain and glen, in the numerous perched blocks placed in most striking positions. One large boulder is set right on the very head of Scuir a Laocainn. Others crest the surface of Cam Bhan and the Maiden, and give the sky-line of their summits the appearance of a broken-toothed saw, so numerous are these deposits of the great ice sheet of the severer Glacial Period. The remarkable gathering of blocks seen from the lower end of Fionn Loch has already been noted, and the height near the stable there should certainly be climbed to view them. The jutting capes and islands, as well as many exposed surfaces on the way back to Poolewe, all tell the same tale.

VIII. The Trias at Loch Gruinard.—Another series of rocks —the comparatively recent Trias—may be seen by the traveller not far from Loch Maree, on Loch Gruinard, some miles to the north of the moraines already described. On' the way to Aultbea, the road rises to a considerable height above Loch Ewe, and overlooks its waters. Here, from the Torridon sandstone, a magnificent view may be had of the whole remarkable country, with its striking scenery and interesting geology, exhibited at a glance. In front, stretches a rolling plateau of the bare Hebridean gneiss, which attains its greatest altitude in the graceful Maiden and her powerful fellows at the head of the Fionn Loch, and in the pointed Beinn Aridh Charr, Beinn Lair, and Beinn Alligin. Beyond, rise the dark domes of the Torridon Red, in Slioch and his compeers; and then the bright peaks of the Quartzite, in the shining Beinn Eay and other mountains, the Quartzite being seen finely cresting masses of the lower red sandstone. Behind these, stretch the undulating hills of the Eastern gneiss far into the background of the wonderful picture.

On the shore of Loch Gruinard, to the east and west of where the road touches the loch, are found two isolated patches of the Lower Trias, the lowest of the Mesozoic series, and the second above the second rarest series in the Hebrides, —rarer than the next strata, the Lias and Oolite of Skye, Mull and Brora, and than even the Cretaceous or Chalk, on the shores of Mull and Morven. The only rarer, if not unique, rock in the Hebrides is the one patch of Carboniferous on the tide line of Ardtomish in Morven, opposite Oban.

The Trias here consists chiefly of a thick-bedded sandstone of uncommon redness, which recalls the bright tints of the Old Red of Fochabers and the Permian of Dumfries. It is well exhibited in cliffs and reefs along the shore, by breccias and conglomerates, thin shales, yellow and greenish sandstones and flags, and concretionary limestone.

These Triassic 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. [For an interesting and valuable account of these Gruinard rocks and their correlations, by the greatest authority, Professor Judd, see Quart, Jour. Geolog, Soc. for 1878, pp. 670, 671, 688-690, where they are called Poikilitic, or Variegated, their varied colouring being well shewn on Loch Gruinard.