Remote Antiquity of the Old Red Sandstone — Suggestive of the vast Tracts of Time with which the Geologist has to deal — Its great Depth and Extent in Scotland and England — Peculiarity of its Scenery — Reflection on first discovering the Outline of a Fragment of the Asterolepis traced on one of its Rocks — Consists of Three Distinct Formations — Their Vegetable Organisms — The Caithness Flagstones: how formed — The Fauna of the Old Red Sandstone — The Pterichthys of the Upper or Newest Formation — The Cephalaspis of the Lower Formation — The Middle Formation the most abundant in Organic Remains — Destruction of Animal Life in the Formation sudden and violent — The Asterolepis and Coccosteus — The Silurian the Oldest of the Geologic Systems — That in which Animal and Vegetable Life had their earliest beginnings — The Theologians and Geologists on the Antiquity of the Globe — Extent of the Silurian System in Scotland — The Classic Scenery of the Country situated on it — Comparatively Poor in Animal and Vegetable Organisms — The Unfossiliferous Primary Rocks of Scotland — Its Highland Scenery formed of them — Description of Glencoe — Other Highland Scenery glanced at — Probable Depth of the Primary Stratified Rocks of Scotland — How deposited — Speculations of Philosophers regarding the Processes to which the Earth owes its present Form — The Author's Views on the subject.
I INCIDENTALLY mentioned, when describing the Oolitic productions of our country, that the shrubs and trees of this Secondary period grew, on what is now the east coast of Sutherland, in a soil which rested over rocks of Old Red Sandstone, and was composed mainly, like that of the county of Caithness in the present day, of the broken débris of this ancient system. We detect fragments of the Old Red flagstones still fast jammed among the petrified roots of old Oolitic trees; we find their water-rolled pebbles existing as a breccia, mixed up with the bones of huge Oolitic reptiles and the shells of extinct Oolitic molluscs; we even find some of its rounded masses incrusted over with the corals of the Oolite: the masses had existed in that  remote age of the world as the same grey indurated blocks of stone that we find them now; and busy Madreporites, — Isastræa and Thamnastræa, — whose species have long since perished, built up their stony cells on the solid foundations which the masses furnished. Nay, within the close compressed folds of these flagstones lay their many various fossils, — glittering scale, and sharp spine, and cerebral buckler, — in exactly the same state of keeping as now; and had there been a geologist to take hammer in hand in that Oolitic period, when the spikes of the Pinites Eiggensis were green upon the living tree, and the Equisteum columnare waved its tall head to the breeze, he would have found in these stones the organisms of a time that would have seemed as remote then as it does in the present late age of the world. We may well apply to this incalculably ancient Old Red system what Wordsworth says of his old Cumberland beggar, —
This glimpse, through the medium of the high antiquity of the Oolite, of an antiquity vastly higher still, — that of the Old Red Sandstone, — may well impress us with the enormous extent of those tracts in time with which the geological historian is called on to deal. There are some of the lesser planets that seem to the naked eye quite as distant as many of those fixed stars whose parallax the astronomer has failed to ascertain; but when they come into a state of juxtaposition, and the moveless star is seen dimly through the atmosphere of the moving planet, we are taught how enormous must be those tracts of space which intervene between them, and keep them apart. And it is thus with the periods of the geologist. Even the comparatively near are so distant, that the remote seem scarce more so; but the dead and stony antiquity of one system, seen as if through the living nature of another, enables us, in at least  some degree, to appreciate the vastness of those cycles by which they were separated. It is further interesting, too, thus to find one antiquity curiously inlaid, as it were, in another. We feel as if, amid the ancient relics of a Pompeii or a Herculaneum, we had stumbled on the cabinet of some Roman antiquary, filled with bronze and granite memorials of the first Pharaohs, or of the old hunter king who founded Nineveh ; — things that in times which we now deem ancient had been treasured up as already grown venerably old.'Him from my childhood have I known; and then
He was so old, he seems not older now.'
The Old Red Sandstone underlies the Coal Measures, and is, in Scotland at least, still more largely developed than these, both in depth and lateral extent. In Caithness and Orkney, one of the three great formations of which it consists has attained to a thickness that equals the height of our highest hills over the sea.1 The depth of the entire system in England has been estimated by Sir Roderick Murchison at ten thousand feet; and as these ten thousand feet include three formations so distinct in their groups of animal life that not a species of fish has been found common to both higher and lower, it must represent in the history of the globe an enormously protracted period of time.
The scenery of the Old Red Sandstone we find much affected to the south of the Grampians, like that of the Coal Measures, by the presence of the trap rocks; but in the north, where there is no trap, it bears a character decidedly its own. It is remarkable for rectilinear ridges elongated for miles, that, when they occur in semi-Highland districts, where the primary rocks have been heaved into wave-like hills, or ascend in to boldly-contoured mountains, constitute a feature noticeable for the contrast which it forms to all the other features of the scene. In approaching the eastern coast
1 The Caithness flagstones and their iclithyolites constitute, according to Sir R. Murchison, the central portion of the Old Red group. — W. S. S.
 of Caithness from the south, the voyager first sees a mountain country, — the land piled up stern and high, — the undulations bold and abrupt. He is looking on the High lands of Sutherlandshire. All at once, however, the aspect of the landscape changes ; — the broken and wavy line suddenly descends to a comparatively low level, and, wholly altering its character, stretches away to the north, straight as a tightened cord, or as if described by a ruler. Caithness thus seen in profile reminds one of a long thin proboscis, or mesmerized arm, stretched stiffly out from the Highlands to the distant Orkneys. In sailing upwards along the Moray Firth, the line which defines seawards the plain of Easter Ross from the Hill of Nigg to the low rocky promontory of Tarbat, topped by its lighthouse, presents nearly the same rectilinear character. Another long straight line which meets the eye on entering the bay of Crornarty stretches westwards from the hill of granitic gneiss immediately over the town, and runs for many miles into the interior along the bleak ridge of the Black Isle. Yet another rectilinear line may be seen running on the south side of the Moray Firth, from beyond the Moor of Culloden, which it includes, to the eastern end of Loch Ness. And in all these instances the rectilinear ridges are composed of Old Red Sandstone. On some localities on the seaboard of the country the system is much traversed by firths and bays, and what in Caithness and Orkney are termed goes, — narrow inlets in the line of faults, along which the waves find straight passage far into the interior. From the Hill of Nigg, the centre of an Old Red Sandstone district, the eye at once commands three noble firths, all scooped out of the deposit, — the Firth of Cromarty, the Dornoch Firth, and the upper reaches of the Moray Firth. It commands, too, what is scarce less a feature of the Old Red system, — the rich corn-bearing plains of Moray and of Easter Ross; and from the union which the prospect exhibits of two elements  dissociated elsewhere in the country, — the rich softness of a Lowland scene, with numerous arms of the sea, characteristic elsewhere, as on the western coast, of a Highland one, — it forms a landscape unique among the landscapes of Scotland. But perhaps the most striking scenic peculiarities of the Old Red Sandstone are to be found in its rock-pieces. The Old Man of Hoy, with its mural rampart of precipices, not unfurnished with turret and tower, and wide yawning portals, and that rise a thousand feet over the waves, — the tall stacks of Canisbay, ornately Gothic in their style of ornament, with the dizzy chasms of the neighbouring headland, in which the tides of the Pentland Firth forever eddy and boil, and the surf for ever roars, — and the strangely fractured precipices of Holburn Head, where, through dark crevice and giddy chasm, the gleam of the sun may be seen reflected far below on the green depths of the sea, and, venerable and grey, like some vast cathedral, a dissevered fragment of the coast descried rising beyond, — are all rock-scenes of the Old Red Sandstone. When I last stood on the heights of Holburn, there was a heavy surf toiling far below along the base of the overhanging wall of cliff which lines the coast; and deep under my feet I could hear a muffled roaring amid the long corridorlike caves into which the head land is hollowed, and which, opening to the light and air far inland by narrow vents and chasms, send up at such seasons, high over the blighted sward, clouds of impalpable spray, that resemble the smoke of great chimneys. As I peered into one of these profound gulfs, and dimly marked, hundreds of feet below, the upward dash of the foam, grey in the gloom, — as I looked, and experienced, with the gaze, that mingled emotion natural amid such scenes which Burke so well analyses as a consciousness of great expansiveness and dimension, associated with a sense of danger, — my eye caught, on the verge of the precipce, the outline of part of an old reptile fish traced on the rock. It was the cranial  buckler of one of the hugest ganoids of the Old Red Sand stone, — the Asterolepis. And there it lay, as it had been deposited, far back in the bypast eternity, at the bottom of a muddy sea. But the mud existed now as a dense grey rock, hard as iron; and what had been the bottom of a Palæozoic sea had become the edge of a dizzy precipice, elevated more than a hundred yards over the surf. The world must have been a very different world, I said, when that creature lived, from what it is now. There could have been no such precipices then; a few flat islands comprised, in all probability, the whole dry land of the globe; and that emotion of which I have just been conscious, is it not some thing new in creation also? The deep gloom of these perilous gulfs, — these incessant roarings, — these dizzy precipices, — the sublime roll of these huge waves, — are they not associated in my mind with a certain dim idea of danger, — a feeling of incipient terror, which, in all God's creation, man, and man only, is organized to experience? Is it not an emotion which neither the inferior animals on the one hand, nor the higher spiritual existences on the other, can in the least feel, — an emotion dependent on the union of a living soul with a fragile body of clay, easily broken?
The Old Red Sandstone consists, as I have said, of three great formations, furnished each, in Scotland at least, with its peculiar group of fossils. In the upper division, — that which rests immediately under the Carboniferous system, — a few straggling plants of the Coal Measures have been occasionally found; but, so far as I know, no plant peculiar to itself. In the middle (lower) division we find traces of a peculiar but very meagre flora. I detected about ten years ago, among the grey micaceous sandstones of Forfarshire, a fucoid furnished with a thick, squat stem, that branches into numerous divergent leaflets or fronds of a slim, grass-like form, and which, as a whole, somewhat resembles the scourge of cords attached to a handle with which a boy whips his  top. And Professor Fleming describes a still more remarkable vegetable organism of the same formation, which, to employ his own well-selected words, 'occurs in the form of circular flat patches, composed each of numerous smaller contiguous circular pieces, altogether not unlike what might be expected to result from a compressed berry, such as the bramble or rasp.'1 In the lowest (middle) division of the Old Red traces of land plants become very rare. Many years ago, at Cromarty, I detected, in one of its oldest fossiliferous beds, a fragment of a cone-bearing tree, remarkable as being the oldest piece of wood ever found, that, when subjected to the microscope, exhibits the true ligneous structure; and I possess a small specimen from Skaill, in the mainland of Orkney, also detected in one of the lower beds, which formed apparently a portion of some nameless fern; but the other vegetable remains of the lower (middle) division, though sufficiently abundant in some localities to give a fissile character to the rock in which they occur, are, with one doubtful exception, all marine. They were the weeds of a widely extended sea, in which land was at once very unfrequent and of very limited extent. In the neighbourhood of Thurso my attention has been attracted for several years past by a curious appearance among the flagstones of the district, — there enormously developed, — which I am disposed to regard as indications of the existence of vast mud flats of the Old Red Sandstone, that occasionally showed their surfaces above water for perhaps weeks and months at a time, but which were in every instance submerged ere they acquired coverings of terrestrial vegetation. The flagstones, now known very extensively over Europe as the Caithness flag of commerce, must have been deposited at the bottom of a shallow sea,
1 Parka decipens. See Testimony of the Rocks, latest edition. For notice of a Lepidodendron occuring in the Forfarshire sandstone see likewise Testimony of the Rocks, page 466-7. — L. M.
 in the form of beds of arenaceous mud, largely charged with organic matter. They abound in minute ripple-markings, which could have been formed only a few feet, or at most a few fathoms, under the surface; and between these rippled bands, for a series of beds together, there occur bands which had been evidently subjected to a drying process, so that, as happens with the bottom of a muddy pool laid dry during the summer droughts, they cracked into irregularly polygonal divisions, and as, when again submerged, a sudden deposition filled up the cracks, we can still trace these marks of desiccation as distinctly in the stone as if they had been made by the sun of the previous week. Hall of Leicester spoke, in one of his illustrations, of 'a continent of mud;' and it would seem that in the earlier ages of the Old Red Sandstone continents of mud were not mere figures of speech; but that over dark-hued and shallow seas, mud-banks of vast extent occasionally raised their flat dingy backs, and remained hardening in the hot sun until their oozy surfaces had cracked and warped, and become hard as the sun-baked brick of eastern countries; and that then, ere the seeds of terrestrial plants, floated from some distant island, or wafted in the air, had found time to strike root into the crevices of the soil, some of the frequent earth-tremors of the age shook the flat expanse under the water out of which it had arisen, and the waves rippled over it as before. The features of a scene so tame and unattractive, — features which none of the poets, save perhaps the truthful Crabbe, would have ventured to portray, — will not strike you as very worthy of preservation: there is certainly not much to excite or gratify the fancy in a scene of wide yet shallow seas, here and there darkened by forests of algae, and here and there cumbered by archipelagos of flat verdure less islands of mud that harden in the sun; but, regarded as embryo and rudimentary land, even these mud-banks may be found to possess their modicum of interest. And  we know that in the shallows of that muddy sea, the Creator wrought with all His wonted wisdom and inexhaustible fertility of resource, in the production of a dynasty of fishes of very extraordinary form, but high type, and which manifested exquisite faculties of adaptation to the circumstances in which they were placed.
In glancing at the fauna of the Old Red Sandstone, let us imagine three great platforms from which the sea has just retired, leaving them strewn over with its spoils, — chiefly fishes. These platforms represent the three great periods of the system; and in each do we find the group specifically, and in several instances generically, distinct. In the upper or newer platform, — that immediately under the Coal Measures, — there occur several species of Holoptychius, all of them of smaller dimensions than the giant of the Carboniferous system, but, in proportion to their bulk and size, even more strongly armed. With the Holoptychius there was associated a fish of the same Coelacanth family, the Bathriolepis, and several curious fishes of what is known as the Dipterian family, such as the Stagonolepis1 and Glyptolepis. It contains also at least three species of Pterichthys. One of these, the Pterichthys major, which occurs in the upper sandstones of Moray, is of greater size than any of the others its contemporaries, or than any of the older species; as if, in at least point of bulk, the creature received its fullest development just when on the eve of passing away.2
1 The Stagonolepis is now under examination as to whether it is to be ranked as fish or reptile. Sir R. Murchison mentions this in his last address to the Leeds British Association as still undetermined. — L. M.
2 Associated with this large Pterichthys are now found not only the Telerpeton Elginense, a small tortoise, but footprints of larger reptiles, some only of greater size than the Telerpeton, others considered to approach more nearly in bulk and conformation to some of those of the succeeding eras. When I lately visited the Museum at Elgin, I was gratified by seeing sandstone slabs bearing the traces of each of these; but I was told that the best specimens had been sent to London [204f] for examination. It is probable that they will have been lawfully named and surnamed by the savants ere the next edition of this work is ready for the press. — L. M.
[204 ] This strange Pterichthyan genus first appears at the base of the Old Red Sandstone, and disappears with its upper beds. It is peculiarly and characteristically the distinctive organism of the system, for in no other system does it occur; and it has a yet further claim on our notice here, from the extreme singularity of its construction. 'It is impossible,' says Agassiz, in his great work on fossil fishes, — 'it is impossible to find anything more eccentric in the whole creation than this genus. The same astonishment which Cuvier felt on examining for the first time the Plesiosauri, I myself experienced when Mr. Hugh Miller, the original discoverer of these fossils, showed me the specimens which he had collected from the Old Red Sandstone of Cromarty.' And we find Humboldt referring, in his Cosmos, to this strange Pterichthyan genus in nearly the same terms. This, I suspect, is no place for strict anatomical demonstration; and so, instead of elaborately describing the Pterichthys, I shall merely attempt sketching its general outlines by the aid of a few simple illustrations. When, in laying open the rock in which it lies, the under part is presented, as usually happens, we are struck with its resemblance to a human figure, with the arms expanded, as in the act of swimming, and the legs transformed, as in the ordinary figures of the mermaid, into a tapering tail. On further examination, we ascertain that the creature was cased in a complete armature of solid bone, but that the armour was of different construction over the different parts. The head was covered by a strong helmet, perforated in front by two circular holes, through which the eyes looked out. The chest and back were protected by a curiously constructed cuirass, formed of plates; and the tail sheathed in a flexible mail of osseous scales. The arms, which were also covered with plates, were articulated  rather to the lower part of the head than to the shoulders; and this by what at first appears to be simply a ball-and-socket joint, like that of the human thigh, but which, on further examination, proves to be of a more complex character, as we find a pin-like protuberance from the socket finding, in turn, a socket in the ball. The abdomen of the creature was flat; the dorsal portions strongly arched; and not in our Gothic roofs, constructed on strictly mathematical principles, do we discover more admirable contrivances for combining in the greatest degree lightness with strength, than in the arch of osseous plates which protected the Pterichthys. Nay, we find in it the two leading peculiarities of the Gothic roof anticipated, — the contrivance of a series of ribs that radiate from certain centres, and the contrivance of the groin. The helmet was united to the cuirass by a curious and yet very simple joining, that united the principle of the dovetail of the carpenter to that of the keystone of the architect. Further, the creature, with its inflexible cuirass and its flexible tail, and with its two arms, that combined the broad blade of the paddle with the sharp point of the spear, might be regarded, when in motion, as a little subaqueous boat, mounted on two oars and a scull. And such was the Pterichthys, — the characteristic organism of the Old Red Sandstone. I may remark, in connexion with this fish, — a remark, however, which bears equally on all its ganoidal contemporaries, — that the development of its dermal or skin-skeleton, compared with that of its internal one, was singularly great. In the present creation, with but a few exceptions, such as the Pangolin and Armadillo among quadrupeds, the crocodiles and tortoises among reptiles, and the Lepidosteus and Polyopterus among fishes, the dermal skeleton is but very slenderly represented. In our own species, for instance, it is represented by but the teeth, the hair, and the nails; and were there no other portions of us to survive in the fossil state, each of the male  animals among us would be represented by but ten toe and ten finger nails, one set of teeth, a periwig, and a pair of whiskers. But so complete, on the other hand, was the development of the derrnal skeleton among the fishes of the Old Red Sandstone, that, though in many instances no other parts of them survive, we find their outlines complete in the rock from head to tail. Dermal plates of enamelled bone represent the head; dermal scales, also of enamelled bone, lie ranged side by side, like tiles on a roof; in the lines in which they originally covered the body; and thickly-set enamelled rays of bone indicate the place and outline of the fins. As a set-off, however, against this great development of dermal skeleton in the ganoids of the Old Red Sandstone, their internal skeletons were exceedingly slight, and in whole families entirely cartilaginous.
The middle (lower) platform of the Old Red Sandstone has for its characteristic organism the Cephalaspis, or Bucklerhead, — a curiously formed, bone-covered fish, with a thin triangular body, and crescent-shaped head, somewhat resembling in outline a shoemaker's cutting-knife. It had for its contemporaries several fishes armed with dorsal spines, of which only the spines remain, and of a gigantic Crustacean, akin, as shown by some of its plates, to our existing lobsters, but which in some specimens must have exceeded four feet in length.
It is, however, on the lower (middle) platform of the system that we find its organic remains at once most abundant and most characteristic. The flagstones of Caithness and Orkney, and the nodule-bearing beds of Ross, Cromarty, and Moray, contain more fossil fish than all the other formations of not only Scotland, but of Great Britain, from the Tertiary deposits down to the Mountain Limestone. There are strata in which they lie as thickly as herrings on our better fishing banks in autumn, when the fisherman's harvest is at its best; and, strange to say, not unfrequently do the fish of  a whole platform give evidence, both in their state of keeping and in their contorted attitude, that they all died at once, and died by violent death. We see them still presenting over wide areas the stiff curved outline, — a result of the unequal contraction of the muscles, — which, as in the case of recently netted herrings, marks that dissolution had been sudden. We find, too, that their remains did not suffer from the predatory attacks of other fishes: it would seem as if all the finny inhabitants of wide tracts of sea had been at once cast dead to the bottom, so that not an individual survived, to prey upon the remains of his deceased neighbours. It was the first remark of Agassiz, when introduced to a collection of fossil fish from Orkney, — ' All these fish died by violent death,' — a remark which he again and yet again repeated when introduced to the Old Red ichthyolites of Cromarty and Moray. We have already seen that the oldest plant-covered land of which the geologist finds distinct and certain trace in this country was a land subject to incessant fluctuations of level, and to sudden and disastrous invasions of the sea; and that, though suited for the production of a rank and luxuriant flora, whose numerous denizens lived without consciousness and died without suffering, or for animals fitted to enjoy the present without thought or fear of the future, and to whom life, so long as they lived, was pleasure, and death merely a ceasing to be, we conclude that it could have been no fitting home for creatures of a higher order, whose nature it is to look before and behind them, — before them with hope or with fear, behind them with satisfaction or regret. And these strange platforms of sudden death, — of no rare occurrence in the marine depths of the Old Red Sandstone, — show that the sea in these early times was not less subject to disastrous catastrophe than the land, — that that order of nature which we now term its fixed order, and on whose permanency our minds have been framed to calculate, was, if I may venture the expression,  enacted, but not enforced, and so the breaches of it were scarce more exceptional than the observance, — that life, greatly more emphatically than now, was the least certain of all things, — and that both in sea and on the land the young and immature earth, like an inexperienced and careless nurse, was ever and anon overlaying and smothering its offspring.
Among the various ichthyic families and genera of the Lower and Middle Old Red Sandstone, — Acanths, Dipterians, Cœlacanths, and Cephalaspians, — I shall refer to only two, and that in but a few brief words; the one remarkable for its great size, the other for its extraordinary organization. The Asferolepis seems to have been one of at once the earliest and bulkiest of the ganoids. Cranial bucklers of this creature have been found in the flagstones of Caithness large enough to cover the front skull of an elephant, and strong enough to have sent back a musket-bullet as if from a stone wall. The Asterolepis must have at least equalled in size the largest alligators; and there were several points in which it must have resembled that genus of reptiles. Its head was covered with strong osseous plates, ornately fretted by starlike markings, and its body by closely imbricated and delicately-carved osseous scales. But it is chiefly in its jaws that we trace a reptilian relationship to the alligators. The alligators among existing reptiles, and the Lepidostei among existing reptile-fishes, are remarkable for a peculiar organization of tooth and maxillary, through which certain long teeth in the anterior part of the nether jaw are received into certain scabbard-like hollows in the anterior part of the upper jaw. The hollows receive the teeth when the mouth is shut, as the scabbard receives the sword. Now, in the Asterolepis this reptilian peculiarity was not restricted to a small group of the anterior teeth, but pervaded the entire jaw. Beside each of the creature's reptile teeth, in both jaws, there was a deep pit, which received the reptile tooth  opposite; and thus, when the animal closed its formidable mouth, the jaws would have been locked together by their long teeth and deep recipient hollows, as the crenellated jaws of a fox-trap lock into each other when we release the spring. The other ichthyolite of the Old Red Sandstone to which I shall refer is the Coccosteus, — a ganoid that, so far as we yet know, was restricted to this formation. Like the Pterichthys, with which it has been classed, it was provided with a helmet and cuirass of bony plate; but its caudal portion seems to have been naked, — a peculiarity of which we find no other example among the ganoids of this early time. The Coccosteus was, however, chiefly remarkable for the form of its jaws.1 More than ten years ago I ventured to state, in the first edition of a little work on the Old Red Sandstone, that the jaws of this ancient fish seemed, like those of some of the crustaceans, and of some of the insects, to have possessed a horizontal action. Aware, however, that I was on dangerous ground, I exercised, in making the statement, some little share of Scotch caution: the thing was, I stated, too anomalous to be regarded as proven by the evidence of the specimens yet found; and I mentioned it, I said, only with the view of directing attention to it. It was a question, I thought, worthy of being entertained, and so I craved that it should be entertained, and specimens carefully examined. But specimens were not examined, at least no specimens that threw any light on the subject; and my very modified statement respecting it was written down a blunder on the very highest authority. I kept, however, a steady eye on the rocks, as the real authorities in the case; and, deeming myself bound as a geologist to observe carefully and record truthfully whatever they revealed, but as not in the least responsible for the anomalies of the revelation, I persisted in quietly collecting their evidence in a
1 The Coccosteus possessed also true bony vertebræ. See Siluria, p. 504, new edition. — W. S. S.
 suite of fossils, which has now fully convinced our first comparative anatomists that there was an anomaly in the structure of the jaws of this ancient fish, unique among the vertebrata; and that, in calling to it the attention of the scientific world, I was in the right, not in the wrong. The under jaws contained two distinct sets of teeth; the one set or group in the line of the symphysis, the other set or group on the upper edge of the jaw, and placed on such different planes, that they could not possibly have been brought into action by the same movement of the condyles. And there are on the table specimens which show, that while the group in the customary place, the upper edge of the under jaw, were made to act against a group placed in the nether edge of the upper one by the usual vertical action, the groups so strangely placed in the symphysis, if brought into action at all, must have acted against each other through a lateral motion altogether unique. The jaws of the Coccosteus are interesting in another point of view, as being perhaps the oldest portions of any internal skeleton that have presented their structure to the microscope. And it is surely not uninteresting to see the osseous substance, destined to perform so important a part in the animal economy, presenting in so early an age its distinguishing characteristics; in especial, those arterial Haversian canals through which the ancient blood must have flowed for its nourishment, and those numerous corpuscles or life-points from which its organization began, and which continued to remain open as the sheltering cells in which its vitality resided. Was it impossible, in the nature of things, we ask, that life could be equally diffused over hard and rigid earth built up into this new animal substance, bone? and was it therefore merely sown over it in hollow microscopic points? Is bone rather a thing strongly garrisoned by vitality, than itself vital? Direct questions cannot always, in the present imperfect state of our knowledge, receive answers equally direct; and  these are questions to which our first physiologists might hesitate to reply. But we may at least safely infer, from the thorough identity of the osseous material throughout all ages, that it was a material compounded at all times by the same Architect, according to a predetermined recipe; that it is He who built up the corpuscles and arranged the canals in that ancient jaw which so excites our curiosity, that now maketh in the human subject 'the bones to grow ;' and that, in his eternal purposes, the existences of the most ancient times may be woven into the tissue of one great plan, with all that now exists, and with all that shall exist in the future.
In retiring into the remote past, and descending from formation to formation as we retire, we have now reached that great Silurian group of rocks in which, so far as the geologist yet knows, fossils first appear, and which represents a period of incalculable vastness, in which life, animal and vegetable, seems to have had its earliest beginnings on our planet. Enormous as is the depth of some of the other systems, — such as the Old Red and the Carboniferous systems, — they shrink into moderate dimensions when we compare them with the truly vast Silurian deposit. It was estimated only a few years ago, that the entire depth of all the fossiliferous strata did not much exceed six miles: it is now found by the geologists of the Government Survey, that the Lower Silurian strata of North Wales are of themselves about five miles in depth, while the Upper Silurian, as estimated by Sir Roderick Murchison, are about a mile more. Many of the beds, too, of both the Upper and Lower divisions, must have been of exceedingly slow deposition, — formed far from land, and at the bottom of deep seas: nay, there are Silurian limestones that can scarce be regarded as deposits at all, seeing that every calcareous particle of which they are composed was at one time associated with animal life, as the joints of crinoidea, the calcareous framework of corals, or the shells of molluscs, all  of which lived and died upon the spot that the rocks now occupy. And rocks of this character, when of any considerable thickness, must have been very many years in the forming. The sagacious Chalmers saw and taught, at the beginning of the present century, that 'the writings of Moses do not fix the antiquity of the globe:' 'if they fix anything at all,' he said, 'it is only the antiquity of the species. But there were few among either teachers or pupils who saw so clearly as Chalmers; and when the geologist first began to demand a long tale of years for the production of all the stony volumes of his record, it was, like the long price which the ancient sibyl demanded for all her volumes, very decidedly refused him. Instead, however, of bating in the demand, or acquiescing in the denial, the geologists have been ever and anon returning, sibyl-like, to drive harder and yet harder bargains, and even to ask, as they do now, as much for a single volume as they formerly asked for the whole; but their library, unlike that offered in sale to the old Roman, is undergoing no diminution in bulk; on the contrary, its volumes increase in number as the demand made for each is raised. But it is at least something to be made to feel, by means of these time-marks in the remote distance, that eternity is not a mere idle name, which at times children employ in their catechisms, but a great and awful fact; and that its unmeasurable amplitude of duration closes as completely around the systems of the geologist in time, as the infinity of extension closes around the systems of the astronomer in space. It is one of the revealed characteristics of the adorable Creator, that 'from everlasting to everlasting he is God.'
On the western coast of Ross and Sutherland, on a general basement of broken primaly hills of no great altitude, we find the (Cambrian) deposit occurring as a series of noble mountains, now entirely insulated from each other, and that yet give evidence, in their lines of nearly horizontal strata,  that they once formed parts of a continuous bed, which ere the operation of the denuding agencies, had overlaid, to the depth of from two to three thousand feet, the gneiss and quartz deposits below. They now exist, however, as a group of magnificent pyramids, compared with which those of Egypt are but the toy erections of children; and yet, from the rectilinear character of their abrupt and mural precipices, coursed as if with tiers of ashlar, — from their general regularity of form, their utter bareness of vegetation, and their rich warm colour, which contrasts as strongly with the cold grey tints of the rocky platform on which they rest, as the warm colour of our fresher public buildings with the cold grey of our paved streets or squares, — they seem rather works of human contrivance than productions of Nature. Seen from the west in a clear summer evening, when the red level light falls on the still redder stone, but at a sufficient distance to admit of those softening influences of the atmosphere which mellow the harsher reds into crimson and purple, there is a gorgeous beauty in these pieces of Nature's masonry which it is scarce possible to exaggerate in description. Beneath and in front we see a tumbling sea of craggy hills, which even the warm gleam of sunset scarce relieves from their sober tint of neutral grey; while rising over them abrupt and bold, and lined with their horizontal bars, appear the noble pyramids in their rich vestures of regal purple, — the monuments of an antiquity compared with which that of Nineveh and Babylon belong to the morning hours of a day not yet come to its close.1
But it is peculiarly in the southern Silurian portions of the kingdom that 'scarce a mountain lifts its head unsung.'
1 The above description of the scenery of the West Highlands is, in fact, that of the Silurian, although written before Sir Roderick Murchison discovered his error in laying down these mountains as Old Red. It is inserted here to fill up the hiatus in description which would else occur. — L. M.
 Yarrow, Ettrick, St. Mary's Loch, Leader Haughs, Tweedside, — especially along those upper reaches of the river where it mirrors, in its calmer pools, the classic ruins of Melrose and Dryburgh, and the young woods of Abbotsford, — the Gala-water, Teviotdale, Lammermuir, Galloway, and Niths dale, the springs of the Doon, the hills that rise over the source of Dee, and the 'moors and mosses many' where the 'Stinchar flows,' — are all to be sought and found in the Silurian region of Scotland. It will scarce do now to estimate the scenic merit associated with these names at its actual value. The words of sober truth would seem, according to Wordsworth, 'strange words of slight and scorn,' —
Even the indomitable good-nature of Sir Walter was scarce proof against what he deemed the disparaging, but, I doubt not, truthful, estimate of Washington Irving. 'Our ramble,' says this accomplished writer, in his Abbotsford, 'took us on the hills, commanding an extensive prospect. "Now," said Scott, "I have brought you, like the pilgrim in the Pilgrim's Progress, to the top of the Delectable Mountains, that I may show you all the goodly regions hereabouts. Yonder is Lammermuir and Smailholme; and there you have Galashiels, and Torwoodlee, and Gala-water; and in that direction you see Teviotdale and the braes of Yarrow, and Ettrick stream winding along, like a silver thread, to throw itself into the Tweed." He went on thus to call over names celebrated in Scottish song, and most of which had recently received a romantic interest from his own pen. In fact, I saw a great part of the border country spread out before me, and could trace the scenes of those poems and romances which had in a manner bewitched the world. I gazed about me for a time with mute surprise, I may almost say with  disappointment. I beheld a mere succession of grey, waving hills, line beyond line, as far as my eye could reach, monotonous in their aspect, and so destitute of trees, that one could almost see a stout fly walking along their profile; and the farfamed Tweed appeared a naked stream, flowing between bare hills, without a tree or thicket on its banks. I could not help giving utterance to my thoughts. Scott hummed for a moment to himself, and looked grave. He had no idea of having his muse complimented at the expense of his native hills. "It may be partiality," said he at length ; "but to my eye these grey hills, and all this wild border country, have beauties peculiar to themselves. I like the very nakedness of the land: it has something bold, and stem, and solitary about it."' Yes; there is no question that, had not the poets thought so, they could not have sung so honestly and warmly, and, of consequence, so successfully:'What 's Yarrow but a river bare,
That glides the dark hills under?
There are a thousand such elsewhere,
As worthy of our wonder.'
and so let us with a good grace acquiesce in their decision. The border land, with its Silurian groundwork, has its peculiar beauties; and no one could portray them at once so graphically and so discriminately as Scott himself. Take, for instance, the passage in Guy Mannering where he describes his hero, Brown, and the redoubtable Dandie Dinmont, approaching Charlieshope after the rencontre with the gipsies on Bewcastle Moor : — ' Night was now falling, when they came in sight of a pretty river winding its way through a pastoral country. The hills were greener and more abrupt than those which Brown had lately passed, sinking their grassy sides at once upon the stream. They had no pretensions to magnificence of height or to romantic shapes, nor did their smooth swelling slopes exhibit either rocks or woods; yet the view was wild, solitary, and pleasingly rural. No enclosures, no roads, almost no tillage: it seemed a land  where a patriarch would have chosen to feed his flocks and herds.' This is faithful description, at once beautiful and characteristic; and such of my audience as remember the exquisite landscape of the 'Enterkin' of our countryman Harvey, as exhibited at the Royal Institution here, in, if I remember aright, the year 1846, with its grey rocks, its green swelling hills of softish outline, and its recluse and houseless valley of deepest loneliness, will be convinced, as I am, that where there is in the mind a certain prominent requisite present, the region of the Silurians is as available for the purposes of the painter as for those of the poet, — that one requisite being the not very definable and many-sided faculty represented by the single magic word genius.'The poet's lyre, to fix his theme,
Must be the poet's heart ~'
The Silurians of Scotland, though of very considerable depth, are greatly less rich in organic remains than the contemporary deposits of England and the Continent. Vast beds of grey slaty rock, hundreds of feet in thickness, seem to have been formed at the bottom of profound seas beyond the zero line of animal or vegetable life. And even in the cases in which organisms of both kingdoms were present, we find their remains very imperfectly preserved.1 The flora of the system in Scotland is represented merely by a few dark-coloured carbonaceous beds, which occasionally pass into an impure anthracite or blind coal, and which are probably identical in their origin with the anthracite schists of Scandina via, regarded by Sir Roderick Murchison as the remains of large forests of algae and fuci, which originally existed in the
1 As mentioned in the preface, it is stated by Sir Roderick Murchison, in his Leeds address to the British Association, that twenty species of Silurian fossils have been discovered by Mr. Peach in a limestone band above the Silurian conglomerate of the Western Highlands, determined by Mr. Salter, and carefully examined by Sir Roderick himself. They are Maclurea, Murchisonia, Cephileta, and Orthoceras, with an Orthis, etc. — L. M.
Silurian seas, and which, from their perishable nature, have lost all trace of their original forms. In the ashes of an an thracite of our Scottish Silurians which occurs near Traquair, Professor Nicol of Cork observed, under the microscope, tubular fibres unquestionably vegetable, but which he thought indicative of vegetation of a higher class than our existing algæ. There is, however, a family of marine plants, now represented on our coasts by a single species, which had, I am inclined to think, its representatives at a very early period in our seas; and which, had it existed during the Silurian ages, could have furnished the tubular cells. I refer to the Zostera, or grass-wrack, a plant of the pond-weed family, which, unlike any of the algæ, has true roots, true flowers, true seeds, tough fibrous stems, and grass-like leaves, traversed by parallel veins, and that yet lives in the sea among laminariœ and floridiœ, far below the fall of our lowest stream tides. It is worthy of notice, too, that the Zostera marina, our recent British species, when driven ashore on parts of our coasts at certain seasons, as it always is in great abundance, decomposes into a substance much resembling peat, that, unlike the brown pulpy mass into which the algæ in similar circumstances resolve, retains distinct trace of the vegetable fibre. It is further noticeable, that some of the vegetable remains of the Old Red Sandstone, — the oldest specimens furnished by our Scottish flora that present aught approaching distinctness of outline, — exhibit several traits that remind us of the leaves of gigantic Zostera. The vegetable impressions of some of the Caithness flagstones have rectilinear edges, and are traversed by parallel lines, scarce less strongly marked than the ridges of the Calamite ; but, from the extreme thinness of the impression left in the rock, they seem rather the veins of leaves than the fluted markings of stems. It is quite possible, therefore, that though the anthracite beds of our Scottish Silurian system give evidence of the existence of a higher vegetation than that of the algæ,  it may have been a marine vegetation notwithstanding. No terrestrial plant has yet been detected in the Silurians of either England or Scotland: the flora of the time, within at least the area of the British islands, seems to have been a poverty-stricken flora of the sea, consisting mainly of Fuci and Algæ, and including as its highest forms a species or two of Zostera, or, as is more probable, of some extinct analogous family.
The Silurian fauna in Scotland consisted also, so far as we can now judge from the broken remains, of but a few marine forms. In the Silurian deposits of England fishes appear; but in our Scotch Silurians we find nothing higher than a Trilobite or a cephalopodous mollusc. The Trilobite was perhaps the most characteristic organic form of the system. It occurred also, though in types specifically distinct, in the Old Red Sandstones of England and the Continent; and I have found well-marked specimens even in the Mountain Limestone of this neighbourhood, — the formation in which the family finally disappears; but it was in the Silurian system that it received its fullest development both in size and number; and portions of at least five species have been detected in the Silurian deposits of Scotland. The Trilobite was a many-jointed crustacean, which, since the close of the Carboniferous period, has had no adequate representative in creation, but whose nearest allies we have now to seek among the minute Entomostraca, especially among the genus Branchipus, — little insect-like creatures, occasionally found in stagnant pools, furnished with fin-like legs, fitted for swimming, but not for walking with, and that, spending happy lives, darting hither and thither through the upper reaches of the water, now swim along the surface on their backs and now on their abdomens. The Trilobites, like the Entomostraca, seem to have been furnished with merely membranaceous, oarlike limbs, and must have led a purely aquatic life as swimmers, — at one  time oaring their way, back below, along the surface of the sea, at an other, back above, along the bottom. But some of these Entomostraca of the old Silurian ocean were, compared with their modern representatives, of great size. The Homalonotus delphinocephalus had a carapace as large as that of an ordinary market-crab, and the Asaphus tyrannus and Isoletus megistos were each of them as large animals, though different in their proportions, as ordinary market-lobsters. But it seems to have been characteristic of both the flora and fauna of these ancient times, that many of their characteristic forms should unite great size to a humility of organization restricted in the present ages to forms comparatively minute. The Trilobites of the Silurian system, like the Club-mosses and Equisetaceæ of the Coal Measures, were of a Brobdingnagian cast; and, regarded as Entornostraca, we must hold — to return to a former illustration — that we look upon them with eyes sharpened by an experience acquired among the productions of Lilliput. So far as we yet know, the higher contemporaries of the Trilobite in Scotland were chambered shells of two well-marked genera, — that of the Orthoceratite, a long, straight, horn-shaped shell; and that of the Lituite, which may be described as an Orthoceratite curled up into a scroll. And, associated with these, we find some of the low brachiopodous molluscs of the more ancient types, such as Leptenæ, Orthes, and Spirifers. But by far the most characteristic organisms of our Scottish Silurians belonged to a low zoophytic family, allied by some of their affinities, in some of their genera, to the sea-pens, and by certain other affinities, in some of their other genera, to the Sertularia. They are known to the geologist by the general name of Graptolites. The Sertularia, compound, plant-like animals, that resemble miniature bushes in spring, just as the buds are bursting into leaf, are attached always, by their seeming roots, to rocks, shells, or sea-weed, and so require  a hard bottom; whereas the sea-pens, compound, feather like Zoophytes, whose every fibre contains its rows of living creatures, affect soft muddy bottoms, in which they may be found sticking by their quill-like points, like arrows in the soft sward around a target. I have seen them brought up by scores on the lines of the fisherman, out of a muddy ravine in the Moray Firth that sinks abruptly from beside the edge of a hard submarine bank, to the depth of thirty fathoms; and have often admired their graceful, quill-like forms, and their delicate hues, that range from pink to crimson, and from crimson to purple. And, judging from the character of those grey carbonaceous deposits in which the Graptolites of our Silurian rocks most abound, it is probable that they also were mud-loving animals, and more resembled in their habitats, if not in their structure, the sea-pens than the Sertularia. It is a curious circumstance that, in the group at least, the Graptolites of Scotland are more obviously allied to the Graptolites of the vast Silurian deposits of Canada and the United States, than to those of the Silurians of England. With this curious zoophyte we take farewell in Scotland of life and organization, and the record of the palæontologist closes. The remains of no plant or of no animal have been detected in this country underlying the rocks in which the oldest Graptolites occur.
Beneath the SILURIAN deposits of Scotland there rest, to an enormous thickness, what, with the elder geologists, I shall persist in terming the primary deposits, consisting, in the descending order, of clay-slates, mica-schists, quartz rocks, primary limestones, and the two varieties of gneiss, — the granitic and the schistose.1 In retaining the old name, I must, however, be regarded as merely holding that
1 Hugh Miller evidently MORE THAN SUSPECTED the history of the geology of the north and north-west of Scotland, as developed by Mr. Peach and Sir Roderick Murchison in 1858. — W. S. S.
 these rocks were actually the first-formed rocks of what is now Scotland; — that the gneiss was gneiss, and the slate was slate, ere ever our oldest fossiliferous formations began to be deposited, or the organisms which they contain had lived or died. Into the question raised regarding the form in which they were deposited, or the condition of our planet during the period of their deposition, I do not at present enter. On the other point, however, — the comparative antiquity of these unfossiliferous rocks in Scotland, — the evidence seems very conclusive: the base of some of the oldest deposits in which we find organisms enclosed consists of broken, and in most cases water-rolled, fragments of the gneisses, quartz-rocks, clay-slates, and mica-schists of the primary regions of the country.1 These primary regions are of great extent. The gneiss region contains nearly ten thousand square miles of surface; the mica-schists, fully three thousand; and the quartz-rock and clay-slate united about fourteen hundred miles more. Comprising almost all the Highlands of Scotland, with the greater part of two of our Lowland counties, Banffshire and Aberdeen, their entire area, if we add about fifteen hundred miles additional of granite and primary porphyry, does not fall short of sixteen thousand square miles. It would be a bold and perilous task for one who has in some degree appreciated those sublimely impressive word-paintings of the Highlands which have added so largely to the well-earned celebrity of your distinguished President, and which seem invested with the very atmosphere of our hills, or who has seen with admiration and delight not only the very features, but all the poetry, of our noble mountain scenery, glowing from the canvas of Macculloch and of Hill, — it would, I say, be a perilous task, under the recollection of achievements such as theirs, to attempt a dull analysis of the geologic principles on which the peculiarities of our Highland
1 See Murchison's Siluria, 2d edition, App. 553, 554, and 556.
 landscape depend. I would feel as if I were bringing you from the studio of some heaven-taught sculptor, crowded with shapes of manly beauty and feminine loveliness, to lecture, amid the melancholy rubbish of a dissecting-room, on the articulations and proportions of the bones, and the form and position of the muscles. I shall venture, therefore, on merely a few desultory remarks, and shall request you, in order to lighten them as much as possible, to accompany me, first, in a sort of mesmeric expedition to the western extremity of Glencoe; at which, after having journeyed as only the clairvoyant can journey, let us now deem ourselves all safely arrived, and just set out on our way back again by the Loch Lomond road. In the course of our journey we shall pass, in the ascending order, over all the great Primary formations.1
Let us first mark the character of the Glen, — not less famous for the severe and terrible sublimity of its natural features, than for that dark incident in its history which associates in such melancholy harmony with the terrible and the severe. We are in a region of primary porphyry, — in the main a dark-coloured rock, though it is one of its peculiar traits, that in the course of a few yards it some times changes its hue from dark green to black or a deep neutral tint, and from these again to chocolate colour, to brick red, or to iron grey. But the prevailing hues are dingy and sombre; and hence, independently of the brown heath and ling, and those deep shadows which always
1 According to a diagram which I have had the honour of receiving from the hand of Sir Roderick Murchison, illustrating his latest explorations in the north, there are two distinct gneisses, — an older and a younger; the first underlying the Cambrian conglomerate and Silurian fossil-bearing band of the west; the other or younger gneiss forming part of the central nucleus, and underlying the Old Red Sandstone conglomerates and ascending fossiliferous series of the east. Of course, the Cambrian will contain fragments of the older, and the Old Red conglomerate fragments of the younger gneiss. — L. M.
 accompany steep rocks and narrow ravines, a sombre tone in the colouring of the landscape. When, however, for a few days the atmosphere has been dry and the sky serene, the dark rocks seem in many parts as if strewed over with an exceedingly slight covering of new-fallen snow, — the effect of the weathering of a thin film of the compact feld spar, which forms the basis of the porphyry into a white porcelanic earth. It is, however, in the form of the rocks that we detect the more striking peculiarities of the porphyritic formation. They betray their igneous origin in their semi-columnar structure. Every precipice is scarred vertically by the thick-set lines which define the thin irregular columns into which the whole is divided; and as the columnar arrangement is favourable to the production of tall steep precipices, deep narrow corries, and jagged and peaked summits, the precipices on either side are tall and steep, the corries are deep and narrow, and the summits are sharp, spine-like, and uneven. A hill of primary porphyry, where not too much pressed upon by its neighbour hills, as trees press upon one another in a thick wood, so that each checks the development of each, generally affects a pyramidal form; and we find fine specimens of the regularly pyramidal hill in the upper part of' the valley, just as we enter on the open moor. I may mention, ere we quit Glencoe, that the more savagely sublime scenery of Scotland is almost all porphyritic. There is only one other rock, — hypersthene, — which at all equals the primary porphyry in this respect; and hypersthene is of comparatively rare occurrence in Scotland. It furnishes, however, one very noble scene in the Isle of Skye : the stern and solitary valley of Corriskin, so powerfully described in the Lord of the Isles, is a hypersthene valley.
Emerging from Glencoe, we enter upon a scene that, in simple outline, abstracted from the dingy tone of the colouring, and the bleak and scanty vegetation common to both,  contrasts with it more strongly than perhaps any other in Scotland. We have quitted the porphyritic region, and entered upon a region of granite and gneiss. Looking back from that most solitary of Scottish inns, King's House, we find that we can determine with much exactness, from the form of the hills, where the porphyry ends and the granite or gneiss begins. The last of the porphyritic hills is a noble pyramid, broken into dizzy precipices, and lined vertically, like some of our semi-columnar traps; whereas the first of the granitic hills, placed immediately beside it, with but a narrow valley between, is of rounded outline, — a mere hummock magnified into a mountain, and wrapped round by a continuous caul of brown heath. On the other hand, we see the granite rolling out into a moory plain, — one of the dreariest in Scotland, — and forming a basin for a long, flat-shored loch, whose brown waters do not reflect a single human dwelling. Granite, however, does not always present features so little attractive. It is, in truth, a many-charactered rock. In general, the feldspar, which enters so largely into its composition, contains a considerable percentage of potash, and so decomposes readily; and hence the rounded forms of many of our granite hills and boulders. It affects, too, on the large scale, though unstratified, a tabular arrangement, and sometimes exists, as in this instance, and in those dreary parts of the lowlands of Aberdeen where the patrimony of the redoubtable Sir Dugald Dalgetty lay, as extensive and usually very barren plains. But in other parts it has little or no potash in its composition; and forming, in these circumstances, one of the most durable of rocks, its peaks and precipices stand up, as in Goatfell in Arran, with all the porphyritic sharpness of outline, unweathered for ages, or present, as in Ben Muich Dhui and its Titanic compeers, features at once bold, broad, and sublimely impressive. Humboldt, generally so correct, in his Views of Nature, seems to have seized on the granite in  but one of its aspects. 'All formations,' we find him saying, are common to every quarter of the globe, and assume the like forms. Everywhere basalt rises in twin mountains and truncated cones; everywhere trap porphyry presents itself to the eye under the form of grotesquely-shaped masses of rock; while granite terminates in gently rounded summits.' We pursue our journey, and enter on a great gneiss district. And in its swelling hills, rolled, like pieces of plain drapery, into but a few folds, and in its long withdrawing valleys, more imposing from an element of simple extent than from aught peculiarly striking in their contour, we recognise the staple scenery of the Scotch Highlands, — the scenery of ten thousand square miles. A gneiss hill is usually massive, rounded, broad of base, and withal somewhat squat, as if it were a mountain well begun, but interdicted some how in the building, rather than a finished mountain. It seems almost always to lack the upper storeys and the pinnacles. It is, if I may so express myself, a hill of one heave; whereas all our more imposing Scottish hills, — such as Ben Nevis and Ben Lomond, — are hills of at least two heaves; and hence, in journeying through a gneiss district, there is a frequent feeling on the part of the traveller that the scenery is incomplete, but that a few hills, judiciously set down upon the tops of the other hills, would give it the proper finish. No hill, however, accomplishes more with a single heave than a gneiss one; the broad-based Ben Wyvis, that raises its head, white with other snows than those of age, more than three thousand feet over the sea, and looks down on all the other mountains of Ross-shire, is a characteristic gneiss hill of a single heave. Quitting the gneiss region, we cross a comparatively narrow strip of quartz rock. The quartz hills in its course are, however, not very characteristic. Such of you as may have sailed over the upper reaches of Loch Maree, with its precipitous, weatherbleached pyramidal hills, so bare of vegetation atop that their peaks  may be seen gleaming white in the autumnal moonlight for miles, as if covered with snow, or who may have threaded your way through the deep and sterile valleys that open their long vistas towards the head of the lake, will be better able to conceive, than from aught witnessed in the course of our present day's journey, of the savage wildness of scenery, — savage and wild, but grand withal, — which is the proper characteristic of a quartz-rock district.
And now, the strip of quartz rock passed over, we enter into an extensive region of mica-schist, — a formation so favourable to the development of a picturesque beauty, — ever and anon rising into the sublime, — that what is peculiarly the classic ground of Highland scenery is to be found within its precincts. Loch Awe, Loch Long, Loch Goil, Loch Tay, by much the larger and finer part of Loch Lomond, all Loch Katrine, Ben Venue, Ben Ledi, Ben Lomond, and the Trossachs, with many a fine lake and stream besides, and many a noble hill, are included in this rich province of the mica-schist.
We first become aware that we are nearing the formation, by the peculiar contour of its hills, as seen at a distance of several miles. As we approach their grey rocks of silky lustre, we find that they are curved, wrinkled, contorted, so as to remind us of pieces of ill-laid-by satin, that bear on their crushed surfaces the creases and crumplings of a thousand careless foldings; and mark further, that it is to these curves and contortions of the strata that the tubercled outlines of the hills are owing, and, with these, the bold projecting knobs and sudden recesses which break up their surfaces into so many picturesque wildernesses of light and shade. Not unfrequently, however, vast masses of schist, of a structure as dense and solid as that of granite, occur in the micaceous districts; and these form hills of a simpler outline, which, like the rock which composes them, seem intermediate in character between the mica-schist and the  gneiss hills. All the mica-schists, however, decompose into soils, which, though light and thin, are more favourable to the production of the grasses and the common dicotyledonous shrubs and trees of the Highlands, than any of the gneisses or granites, and greatly more so than the porphyries or quartz rocks; and so the micaceous regions are not only more picturesque in outline than any of the others, but also richer in foliage and softer in colour. A tangled profusion of vegetation forms quite as marked a feature in the living and breathing description of the Lady of the Lake, as the mural picturesqueness of the crags and precipices which the vegetation half-conceals; and this, be it remembered, is not an ordinary characteristic of the Scottish Highlands, though true to nature in the mica-schist region selected by Scott as the scene of his story. After employing, in describing the rocks near Loch Katrine, well-nigh half the vocabulary of the architect, — spires, pyramids, and pinnacles, — towers, turrets, domes, and battlements, — cupolas, minarets, pagodas, and mosques, — he goes on to say,
Here is there a description of the characteristic vegetation of our richer mica-schist valleys, not more remarkable for its poetic luxuriance than for its strict truth, — truth so strict and literal, that I question whether even the hypercritic, who looked for but a typical catalogue, could enumerate more than two forms of vegetation prevalent in such districts which it does not include. The ferns grow at once singularly rank and delicate in the shade, amid the bosky recesses of the mica-schist; and every damper recess of the rock we find thickly tapestried over by the mosses and the liverworts.'Nor were these earth-born castles bare,
Nor lacked they many a banner fair;
For from their shivered brows displayed,
Far o'er the unfathomable glade,
All twinkling with the dewdrop's sheen,
The brierrose fell in streamers green,
And creeping shrubs of thousand dyes
Waved in the west wood's summer sighs.
Boon nature scattered free and wild
Each plant or flower, the mountain's child.
Here eglantine embalmed the air,
Hawthorn and hazel mingled there,
The primrose pale and violet flower
Found in each cliff a narrow bower;
Foxglove and nightshade, side by side,
Emblems of punishment and pride,
Grouped their dark hues with every stain
The weatherbeaten crags retain, 
With boughs that quaked with every breath;
Grey birch and aspen wept beneath;
Aloft the ash and warrior oak
Cast anchor in the rifted rock;
And higher yet the pine-tree hung
His shattered trunk, and frequent flung,
Where seemed the cliffs to meet on high,
His boughs athwart the narrow sky.'
Passing southwards along the dark surface of Loch Lomond, skirted for rather more than two-thirds of its length by these hills of mica-schist, which confer on its upper reaches a character of mingled picturesqueness and sublimity, we enter, nearly opposite the pastoral village of Luss, on a band of clay-slate, — the last or most modern of the primary formations. It is of no great breadth, — some three or four miles at most; but it runs diagonally across the entire kingdom, from the western shores of Bute, where it disappears under the outer waters of the Firth of Clyde, to near Stonehaven, where we lose it in the German Ocean. We find it associated with a softer style of scenery than the mica-schist. Lacking the multitudinous contortions, and consequent knobs and protuberances, of the schist, it is less picturesque, though scarce less beautiful; nor is its beauty devoid of an ennobling mixture of the sublime. The grace fully-contoured hills that rise immediately behind Luss,  with their recluse withdrawing valley, — the green rolling meadow on which the village is built, — and in front the bolder and finer islands of the lake, — belong all to the clay- slate, and compose a very characteristic landscape. Dunkeld, Comrie, and the fine country to the north and west of Callander, including Loch Vennachar, with many a scene besides of a character intermediate, as becomes their place, between the Highlands and Lowlands, occur in the belt of clay-slate that sweeps in its diagonal course from sea to sea. Leaving Luss behind us, we enter, ere quitting the lakes, on what is unmistakably the low country. The framework of the land before us and on either hand, with that of about one-half the lower islands of Loch Lomond, is all formed of the Old Red Sandstone; and what Byron would perhaps term the 'domestic beauties' of the prospect, — swelling hills ploughed to the top, green lanes, rich meadows, and woods whose rectilinear edges still tell of the planter's line, — bear evidence to the fact. The land, however, is that of Buchanan and of Smollett. Both were born on the Old Red Sandstone here; and the latter, in his well-known description of the lake, in Humphrey Clinker, — the product of a time when descriptions of Scottish scenery were less common than they are now, — places in the foreground, in a style unmistakable from their truth, the features of this Lowland formation, which, in his age, was unfurnished with a name. 'I have seen,' he says, 'the Lago di Garda, Albano, De Vico, Bolsena, and Geneva, and, upon my honour, prefer Loch Lomond to them all, — a preference which is certainly owing to the verdant islands that seem to float upon its surface, affording the most enchanting objects of repose to the excursive view. Nor are the banks destitute of beauties which even partake of the sublime. On this side they display a variety of woodland, corn-fields, and pasture, with several agreeable villas emerging, as it were, out of the lake, till, at some distance, the prospect terminates in huge  mountains covered with heath. Everything here is romantic beyond imagination: the country is justly termed the Arcadia of Scotland.' In the corn-fields here, the woodlands, and the pastures, we recognise the Lowland features of the Old Red placed prominently in the foreground; and in the huge mountains in the distance, the bolder Highland features of the clay-slate and the mica-schist. In still journeying southwards, we skirt the banks of the Leven, — the stream which connects the waters of the lake with those of the Clyde, and which, for the greater part of its course, runs over an Old Red Sandstone of the same age as that of Balruddery, Carmylie, and Turin, and which presents as its characteristic organism, the Cephalaspis. And nowhere in Scotland, as is well shown in Smollett's classical Ode, is there a more thoroughly Lowland river.
Ere, however, closing our journey of a day, which introduces us to so interesting an epitome of the scenery of the primary rocks and the Scottish Highlands, we are startled in the midst of the low country by scenery which seems to be that of the Highlands repeated, but on a smaller scale, and, if I may so express myself, in a more mannered style. We pass over a narrow belt of the trap-rocks, which, like the stratified deposits of this part of the kingdom, — clay-slate and Old Red Sandstone, — runs from sea to sea, and which, including in its range the Campsie and the Ochil hills, is here represented by the picturesque  double-peaked rock which bears the ancient fortalice of Dumbarton, — the castle which, according to Jeanie Deans's friend Mr. Archibald, was always given in keeping to the best man in Scotland, — at one time to Sir William Wallace, at another to the Duke of Argyll.'Pure stream, in whose transparent wrave
My youthful limbs I wont to lave;
No torrents stain thy limpid source,
No rocks impede thy dimpling course,
That sweetly warbles o'er its bed,
With white, round, polished pebbles spread.
Devolving from thy parent lake,
A charming maze thy waters make,
By bowers of birch and groves of pine,
And hedges flower'd with eglantine.'
The depth of the primary stratified rocks, which in Scotland must be very great, has been variously estimated by geologists, — as low as five and as high as ten miles, — evidence enough, did we require any such, that there must be some degree of obscurity in the data on which the calculations regarding it have been founded. It is always extremely difficult to estimate the thickness of even a clay-slate or quartz-rock deposit in a mountainous country, where the centres of disturbance are numerous and involved; and in gneiss and mica-schist, — always greatly contorted deposits, — the difficulty is so enhanced, that what begins as calculation usually ends as guess. But we at least know that it can be no thin series of deposits, however much their strata may be contorted, or however often repeated, that covers, in highly inclined positions, tracts of country so extended as even those which we find covered by them in the Scotch Highlands. In crossing the four primary stratified deposits, — clay-slate, mica-schist, quartz-rock, and gneiss, — at right angles with the line in which they traverse the country in the southern division of the Highlands, we find them occupying, as from near Crieff to Fort-Augustus, a tract rather more than sixty miles across; and in crossing at the same angle the northern division of the Highlands, — as from Glen Urquhart to the middle reaches of Loch Carron, — we find a tract of nearly forty miles occupied by the gneiss alone. The question is one on which I would not choose to dogmatize; but an estimate that gave to our Scottish primary rocks an aggregate thickness of from six to eight miles I would not regard as by any means too high. A more vexed question, however, and a still more  doubtful one, respects their formation. In what form, and under what circumstances, it has been often asked, and very variously answered, were these stratified primary rocks deposited?
They exhibit with almost equal prominence two distinct classes of phenomena, — an igneous class and an aqueous class; and are as intimately associated with the Pleistocene rocks by the one, as with the sedimentary rocks by the other. I have seen in the same quarry of quartz-rock, one set of strata as decidedly chemical in their texture as porphyry or hypersthene, and another intermingling set as decidedly mechanical as grauwacke or conglomerate. I have seen, too, in the same gneiss rock, the minute plates of mica, so abundant in this formation, arranged between the layers as decidedly on the sedimentary principle as in a micaceous sandstone, and in the layers themselves as decidedly on the crystalline principle as in granite. And this compound character of the gneiss may be regarded as the general one, with, of course, certain exceptions in all the primary stratified rocks: the condition of their stratification is mechanical and sedimentary, but the condition of the strata themselves igneous and chemical. How were these variously-blended characters first induced? The geologists of one school tell us that the primary formations originally existed as ordinary sedimentary rocks, but that they have since been altered by the action of intense heat, and that, while the stratification remains as an evidence of their first condition, the texture of the strata indicates the igneous change which has passed over them; while the geologists of another school hold that their first deposition took place under circumstances essentially unlike any which now exist, on at least the surface of our planet, and that their mineralogical conditions were, in consequence, originally different from those of any deposition taking place at the present time, or in any of the later geological ages. I  am inclined to hold that there is a wide segment of truth embodied in the views of the metamorphists; but there seems to be also a segment of truth on the other side; and so I must likewise hold with their antagonists, that there existed long periods in the history of the earth in which there obtained conditions of things entirely different from any which obtain now, — periods during which life, either animal or vegetable, could not have existed on our planet; and further, that the sedimentary rocks of this early age may have derived, even in the forming, a constitution and texture which, in present circumstances, sedimentary rocks cannot receive.
The scientific world is subject, like the worlds of politics and trade, to its periods of action and re-action. Those who hold that the earth was once a molten mass through out, — nay, that at a certain not very profound depth its matter may be still in an incandescent state, — may have perhaps driven their theory too far; and the current at present seems to have set in against them. Mr. Hopkins' profound deductions on the phenomena of Precession and Nutation have been held to establish that the crust of the earth is at present a solid unyielding mass to the depth of at least a thousand miles from the surface. 'Nay, there is nothing in this inquiry,' says Professor Nichol, in referring, in his late admirable work, The Planetary System, to the problem of Mr. Hopkins, — ' there is nothing in this inquiry rendering it impossible that the globe is solid throughout; and assuredly a distinct negative is given to a whole class of prevalent geological conceptions, on grounds vastly more solid than any which appear to sustain them.' And I find Sir Charles Lyell, in the latest edition of his Principles, — that of last year, — suggesting the existence of a circle of superficial action in the earth's crust, quite sufficient to account for an intermittent igneous activity altogether in dependent of central heat, and which might go on by fits  and starts for ever, and be as powerful a million of years hence as in those incalculably ancient times when our Scottish gneiss was in the forming. Accepting the theory of Sir Humphrey Davy, of an unoxidized metallic nucleus of the globe, capable of being oxidized all around its periphery by the percolation of water, and of evolving heat enough in the process to melt the surrounding rocks, he thus provides plutonic, metamorphic, volcanic agencies; and whereas Sir Humphrey Davy held, that when a thick crust of oxide had once formed in this way, it served to shut out the water, and the chemical action became in consequence more and more languid, till it altogether ceased, Sir Charles finds, in another but harmonizing theory, an expedient for re-invigorating the slumbering plutonic forces, and thus, after a period of repose, renewing their activity. The oxygen of the water is, of course, the oxidizing agent; but water also contains hydrogen, and hydrogen is a de-oxidizing agent. 'When the oxidizing process was going on,' says Sir Charles, 'much hydrogen would of necessity be evolved: it would permeate the crust of the earth, and be stored up for ages in fissures and caverns; and whenever it happened to come in contact with the metallic oxides at a high temperature, the reduction of these oxides would be the necessary result.' And we have thus a circle of forces, — oxidization of the metallic basis to evolve the plutonic agencies, and de-oxidization of the oxides to produce the metallic basis again. The process would somewhat resemble that on which the movement of the steam-engine depends, and in which water is first expanded into steam, and then the steam in turn condensed into water, and thus the action of the engine kept up.
Now, I need not here say how thoroughly I respect the judgment and admire the genius of Sir Charles Lyell, — one of the greatest of geologists, and a man of whom Scotland may well be proud; nor need I say how much of pleasure  and instruction I owe to the rich and eloquent writings of Professor Nichol. But, like Job's younger friend, I too must take the liberty of showing forth my opinion, and of giving expression to a conviction, on grounds of which my audience must judge, that both Sir Charles and the Professor have suffered the re-action wave to carry them too far.
Mr. Charles M'Laren, in a popular digest of Mr. Hopkins' deductions, which first appeared, if I remember aright, in the Scotsman newspaper, and then in Jameson's Philosophical Journal referred, with his characteristic caution, to the narrowness of the base on which they rested. 'Mr. Hopkins' conclusion no doubt rests,' he said, 'on a narrow enough basis. It is somewhat like an estimate of the distance of the stars deduced from a difference of one or two seconds in their apparent position, — a difference scarcely distinguishable from errors of observation.' Let us, how ever, waive the doubt implied in this remark, however important we may deem it, and grant, for the argument's sake, that the base is sufficiently broad for the superstructure erected upon it. Let us freely grant, after first availing ourselves of Mr. M'Laren's protest, and placing it on record, that that equatorial ring, thirteen miles in thickness, which, by disturbing the balance of the earth, is the cause of the phenomena of Precession and Nutation, must be attached to a consolidated crust of at least a thousand miles in thickness, in order to account for the extreme slowness of the peculiar movement which it induces. But let us then inquire how it happens that this equatorial ring at all exists. If our earth was always the stiff, rigid, unyielding mass that it is now, — a huge metallic ball, bearing, like the rusty ball of a cannon, its crust of oxide, — how comes it that its form so entirely belies its history? Its form tells that it also, like the cannon-ball, was once in a viscid state, and that its diurnal motion on its axis, when in, this state of viscidity, elongated it, through the operation of a well-known law, at  the equator, and flattened it at the poles, and made it alto gether the oblate spheroid which all experience demonstrates it to be. It may be urged, however, that this form of our planet, which seems to speak so unequivocally of law, may, after all, be but accident. If so, it must be singular. What say the other planets? Of these, the form of three may be at least approximately, and that of one exactly, ascertained. Venus, Mars, Saturn, are all, like our earth, oblate spheroids, flattened at their poles, and elongated at their equators. Their substance must have been spun out by their rotatory motion in exactly the line in which, as in the earth, that motion is greatest. But while we can only approximately determine the values of the equatorial and polar diameters of these three planets, in one great planet, Jupiter, we can ascertain them scarce less exactly than in our own earth; we can gauge, and measure, and fix the proportions which his equatorial ring bears to his general mass. With a diameter about eleven times larger than that of our planet, and rotating on his axis in less than half the time, the motion of the surface at his equator must be more than twenty times greater than that of the earth's equatorial surface, and his equatorial ring ought, even in proportion to his huge bulk, to be more than twenty times as massive. And what is the fact? While the thickness of the equatorial ring of the earth is only equal to about one three-hundredth part of the earth's diameter, the equatorial ring of Jupiter is equal to about the one fourteenth or fifteenth part of his diameter. It is, as the integrity of the law demands, more than twenty times greater in proportion to his mass than the earth's equatorial ring, and absolutely more than two thousand times greater. Here, then, is demonstration that the oblate sphericity of the earth is a consequence of the earth's diurnal motion on its axis; nor is it possible that it could have received this form when in a solid state. A glass ball made to revolve on a spindle when in  a state of viscidity elongates equatorially, and flattens at its poles; but if allowed to cool in its original form as a sphere, it retains its perfect sphericity without change, let us whirl it as rapidly as we may; and no mechanic ever dreams of increasing the disk of a grindstone simply by turning it round. The earth, then, when it assumed its present form, could not have been a solidified mass, like the glass sphere when cooled down, or like the grindstone.
But is it not possible, it may be asked, that the diurnal motion may so act on the depositions taking place in the sea and forming sedimentary rock, or on a region of igneous action interposed between the oxidized crust of the earth and its solid metallic nucleus, and forming plutonic or igne ous rock, — is it not possible that, in the course of vastly-extended periods, the earth may have taken its form under the influence of the motion exerted on sedimentary deposi tion and plutonic intrusion and upheaval? Nay, what, we ask in reply, are the facts? Does the diurnal motion exercise any influence, even the slightest, on deposition or plutonic intrusion? The laws of deposition are few, simple, and well known. The denuding and transporting agencies are floods, tides, waves, icebergs. The sea has its currents, the land its rivers; but while some of these flow from the poles towards the equator, others flow from the equator towards the poles, uninfluenced by the rotatory motion; and the vast depth and extent of the equatorial seas show that the ratio of deposition is not greater in them than in the seas of the temperate regions. We have, indeed, in the arctic and antarctic currents, and the icebergs which they bear, agents of denudation and transport permanent in the present state of things, which bring detrital matter from the higher towards the lower latitudes; but they stop far short of the tropics; they have no connexion with the rotatory motion; and their influence on the form of the earth must be infinitely slight; nay, even were the case otherwise, instead of tending  to the formation of an equatorial ring, they would lead to the production of two rings widely distinct from the equator. And, judging from what appears, we must hold that the laws of plutonic intrusion or upheaval, though more obscure than those of deposition, operate quite as independently of the earth's rotatory motion. Were the case otherwise, the mountain systems of the world, and all the great continents, would be clustered at the equator; and the great lands and great oceans of our planet, instead of running, as they do, in so remarkable a manner, from south to north, would range, like the belts of Jupiter, from east to west. There is no escape for us from the inevitable conclusion that our globe received its form as an oblate spheroid at a time when it existed throughout as a viscid mass. Nor is it unworthy of remark, that the same arrangement through which a fluid earth was moulded into this shape under the impulsion of the rotatory motion, also secured that when that earth came to be covered by a fluid sea, placed under the same impulsive influence, it should cling to it equably, like a well-fitted cloak, without falling off to the poles on the one hand, or accumulating in a belt round the equator at the other.
But time fails, and I cannot follow up this subject to its legitimate conclusions. Allow me, therefore, simply to state, that I must continue to hold, with Humboldt and with Hutton, with Playfair and with Hall, that this solid earth was at one time, from the centre to the circumference, a mass of molten matter. Let us remember, — I employ here the words of Humboldt, — that the great chemist Sir Humphrey Davy, to whom we are indebted for the knowledge of the most combustible metallic substances, renounced his bold chemical hypothesis in his last work (Consolations of Travel) as 'inadequate and untenable;' and further, that, with the oblate sphericity of the earth and the planets to be accounted for, those who continue to hold what he rejected will be reduced, if they persist, to the unphilosophical  necessity of regarding as a consequence of miracle, a peculiarity of shape easily explicable on the principles of known law.
Now, the fact of a molten earth involves a long series of conditions, each different from all the others, and from the conditions of the present time. It involves the existence of a period in the history of our planet when life, animal or vegetable, was not, and of a succeeding period, when life began to be. It involves, too, the ripening of the earth from ages in which its suiface was a thin, earthquake-shaken crust, subject to continual sinkings, and to fiery outbursts of the plutonic matter, to ages in which it is the very nature of its noblest inhabitant to calculate on its stability as the surest and most certain of all things. It involves, in short, those successive conditions of life in the geologic ages which, in connexion with what is now Scotland, I have, I am afraid, all too inadequately attempted to set before you in my present course. In fine, the primary rocks, when they underlie to a great thickness, as in our own country, the Palæozoic deposits, I regard as the deposits of a period in which the earth's crust had sufficiently cooled down to permit the existence of a sea, with the necessary denuding agencies, — waves and currents, — and, in consequence, of deposition also; but in which the internal heat acted so near the surface, that whatever was deposited came, as a matter of course, to be metamorphosed into semi-plutonic forms, that retained only the stratification. I dare not speak of the scenery of the period. We may imagine, however, a dark atmosphere of steam and vapour, which for age after age conceals the face of the sun, and through which the light of moon or star never penetrates; oceans of thermal water heated in a thousand centres to the boiling point; low half-molten islands, dim through the fog, and scarce more fixed than the waves themselves, that heave and tremble under the impulsions of the igneous agencies;  roaring geysers, that ever and anon throw up their intermittent jets of boiling fluid, vapour, and thick steam, from these tremulous lands; and, in the dim outskirts of the scene, the red gleam of fire, shot forth from yawning cracks and deep chasms, and that bears aloft fragments of molten rock and clouds of ashes. But should we continue to linger amid a scene so featureless and wild, or venture adown some yawning opening into the abyss beneath, where all is fiery and yet dark, — a solitary hell, without suffering or sin, — we would do well to commit ourselves to the guidance of a living poet of true faculty, — Thomas Aird, — and see with his eyes, and describe in his verse
'The awful walls of shadows round might
dusky mountains seem,
But never holy light hath touched an
outline with its gleam
'Tis but the eye's bewildered sense that
fain would rest on form,
And make night's thick blind presence to
created shapes conform.
No stone is moved on mountain here by
creeping creature cross'd,
No lonely harper comes to harp
upon this fiery coast;
Here all is solemn idleness; no
music here, no jars,
Where silence guards the coast ere
thrill her everlasting bars;
No sun here shines on wanton isles; but
o'er the burning sheet
A rim of restless halo shakes, which
marks the internal heat;
As in the days of beauteous earth we
see, with dazzled sight,
The red and setting sun o'erflow with
rings of welling light.'
END OF THE LECTURES.
'The only shells I ever detected in the brick-clay of Scotland occurred in a deposit in the neighbourhood of St. Andrews, of apparently the same age as the beds at Portobello. ' — Lecture Second, page 64.NOTE. — Some time after this statement was made, Mr. Miller devoted himself to a further investigation of the brick-clay beds in the neighbourhood of Portobello, and discovered several species of shells in situ, especially great abundance of Scrobicularia piperata, which he has described in a paper on the brick-clays, to be published hereafter. They form a very interesting portion of his Museum, now in the University of Edinburgh. 'But for him,' said an accomplished geologist, in talking with me on the subject, 'we would have known nothing whatever of the brick clays.' — L. M.