The more ancient boulder-clays of Scotland seem to have been formed when the land was undergoing a slow process of subsidence, or, as I should perhaps rather say, when a very considerable area of the earth's surface, including the sea-bottom, as well as the eminences that rose over it, was the subject of a gradual depression; for little or no alteration appears to have taken place at the time in the relative levels of the higher and lower portions of the sinking area: the features of the land in the northern part of the kingdom, from the southern flanks of the Grampians to the Pentland Frith, seemed to have been fixed in nearly the existing forms many ages before, at the close, apparently, of the Oölitic period, and at a still earlier age in the Lammermuir district, to the south. And so the sea around our shores must have deepened in the ratio in which the hills sank. The evidence of this process of subsidence is of a character tolerably satisfactory. The dressed surfaces occur in Scotland, most certainly, as I have already stated on the authority of Dr. Fleming, at the height of fourteen hundred feet over the present sea-level; it has been even said, at fully twice that height, on the lofty flanks of Schehallion,—a statement, however, which I have had hitherto no opportunity of verifying. They may be found, too, equally well marked, under the existing high-water line; and it is obviously impossible that the dressing process could have been going on at the higher and lower levels at the same time. When the icebergs were grating along the more elevated rocks, the low-lying ones must have been buried under from three to seven hundred fathoms of water,—a depth from three to seven times greater, be it remembered, than that at which the most ponderous iceberg could possibly have grounded, or have in any degree affected the bottom. The dressing process, then, must have been a bit-and-bit process, carried on during either a period of elevation, in which the rising land was subjected, zone after zone, to the sweep of the armed ice from its higher levels downwards, or during a period of subsidence, in which it was subjected to the ice, zone after zone, from its lower levels upwards. And that it was the lower, not the higher levels, that were first dressed, appears evident from the circumstance, that though on these lower levels we find the rocks covered up by continuous beds of the boulder-clay, varying generally from twenty to a hundred feet in thickness, they are, notwithstanding, as completely dressed under the clay as on the heights above. Had it been a rising land that was subjected to the attrition of the icebergs, the debris and dressings of the higher rocks would have protected the lower from the attrition; and so the thick accumulation of boulder-clay which overlies the old coast line, for instance, would have rested, not on dressed, but on undressed surfaces. The barer rocks of the lower levels might of course exhibit their scratchings and polishings, like those of the higher; but wherever these scratchings and polishings occurred in the inferior zones, no thick protecting stratum of boulder-clay would be found overlying them; and, vice versa, wherever in these zones there occurred thick beds of boulder-clay, there would be detected on the rock beneath no scratchings and polishings. In order to dress the entire surface of a country from the sea-line and under it to the tops of its hills, and at the same time to cover up extensive portions of its low-lying rocks with vast deposits of clay, it seems a necessary condition of the process that it should be carried on piece-meal from the lower level upwards,—not from the higher downwards.
It interested me much to find, that while from one set of appearances I had been inferring the gradual subsidence of the land during the period of the boulder-clay, the Rev. Mr. Cumming of King William's College had arrived, from the consideration of quite a different class of phenomena, at a similar conclusion. "It appears to me highly probable," I find him remarking, in his lately published "Isle of man," "that at the commencement of the boulder period there was a gradual sinking of this area [that of the island]. Successively, therefore, the points at different degrees of elevation were brought within the influence of the sea, and exposed to the rake of the tides, charged with masses of ice which had been floated off from the surrounding shores, and bearing on their under surfaces, mud, gravel, and fragments of hard rock." Mr. Cumming goes on to describe, in his volume, some curious appearances, which seem to bear direct on this point, in connection with a boss of a peculiarly-compounded granite, which occurs in the southern part of the island, about seven hundred feet over the level of the sea. There rise on the western side of the boss two hills, one of which attains to the elevation of nearly seven hundred, and the other of nearly eight hundred feet over it; and yet both hills to their summits are mottled over with granite boulders, furnished by the comparatively low-lying boss. One of these travelled masses, fully two tons in weight, lies not sixty feet from the summit of the loftier hill, at an altitude of nearly fifteen hundred feet over the sea. Now, it seems extremely difficult to conceive of any other agency than that of a rising sea or of a subsiding land, through which these masses could have been rolled up the steep slopes of the hills. Had the boulder period been a period of elevation, or merely a stationary period, during which the land neither rose nor sank, the travelled boulders would not now be found resting at higher levels than that of the parent rock whence they were derived. We occasionally meet on our shores, after violent storms from the sea, stones that have been rolled from their place at low ebb to nearly the line of flood; but we always find that it was by the waves of the rising, not of the falling tide, that their transport was effected. For whatever removals of the kind take place during an ebbing sea are invariably in an opposite direction;—they are removals, not from lower to higher levels, but from higher to lower.
The upper subsoils of Scotland bear frequent mark of the elevatory period which succeeded this period of depression. The boulder-clay has its numerous intercalated arenaceous and gravelly beds, which belong evidently to its own era; but the numerous surface-beds of stratified sand and gravel by which in so many localities it is overlaid belong evidently to a later time. When, after possibly a long protracted period, the land again began to rise, or the sea to fall, the superior portions of the boulder-clay must have been exposed to the action of the tides and waves; and the same process of separation of parts must have taken place on a large scale, which one occasionally sees taking place in the present time on a comparatively small one, in ravines of the same clay swept by a streamlet. After every shower, the stream comes down red and turbid with the finer and more argillaceous portions of the deposit; minute accumulations of sand are swept to the gorge of the ravine, or cast down in ripple-marked patches in its deeper pools; beds of pebbles and gravel are heaped up in every inflection of its banks; and boulders are laid bare along its sides. Now, a separation, by a sort of washing process of an analogous character, must have taken place in the materials of the more exposed portions of the boulder-clay, during the gradual emergence of the land; and hence, apparently, those extensive beds of sand and gravel which in so many parts of the kingdom exist, in relation to the clay, as a superior or upper subsoil; hence, too, occasional beds of a purer clay than that beneath, divested of a considerable portion of its arenaceous components, and of almost all its pebbles and boulders. This washed clay,—a re-formation of the boulder deposit, cast down, mostly in insulated beds in quiet localities, where the absence of currents suffered the purer particles held in suspension by the water to settle,—forms, in Scotland at least, with, of course, the exception of the ancient fire-clays of the Coal Measures, the true brick and tile clays of the agriculturist and architect.
It is to these superior beds that all the recent shells yet found above the existing sea-level in Scotland, from the Dornoch Frith and beyond it, to beyond the Frith of Forth, seem to belong. Their period is much less remote than that of the shells of the boulder-clay, and they rarely occur in the same comminuted condition. They existed, it would appear, not during the chill twilight period, when the land was in a state of subsidence, but during the after period of cheerful dawn, when hill-top after hill-top was emerging from the deep, and the close of each passing century witnessed a broader area of dry land in what is now Scotland, than the close of the century which had gone before. Scandinavia is similarly rising at the present day, and presents with every succeeding age a more extended breadth of surface. Many of the boulder-stones seem to have been cast down where they now lie, during this latter time. When they occur, as in many instances, high on bare hill-tops, from five to fifteen hundred feet over the sea-level, with neither gravel nor boulder-clay beside them, we of course cannot fix their period. They may have been dropped by ice-floes or shore-ice, where we now find them, at the commencement of the period of elevation, after the clay had been formed; or they may have been deposited by more ponderous icebergs during its formation, when the land was yet sinking, though during the subsequent rise the clay may have been washed from around them to lower levels. The boulders, however, which we find scattered over the plains and less elevated hill-sides, with beds of the washed gravel or sand interposed between them and the clay, must have been cast down where they lie, during the elevatory ages. For, had they been washed out of the clay, they would have lain, not over the greatly lighter sands and gravels, but under them. Would that they could write their own histories! The autobiography of a single boulder, with notes on the various floras which had sprung up around it, and the various classes of birds, beasts, and insects by which it had been visited, would be worth nine-tenths of all the autobiographies ever published, and a moiety of the remainder to boot.
A few hundred yards from the opening of this dell of the boulder-clay, in which I have so long detained the reader, there is a wooded inflection of the bank, formed by the old coast line, in which there stood, about two centuries ago, a meal-mill, with the cottage of the miller, and which was once known as the scene of one of those supernaturalities that belong to the times of the witch and the fairy. The upper anchoring-place of the bay lies nearly opposite the inflection. A shipmaster, who had moored his vessel in this part of the roadstead, some time in the latter days of the first Charles, was one fine evening sitting alone on deck, awaiting the return of his seamen, who had gone ashore, and amusing himself in watching the lights that twinkled from the scattered farm-houses, and in listening, in the extreme stillness of the calm, to the distant lowing of cattle, or the abrupt bark of the herdsman's dog. As the hour wore later, the sounds ceased, and the lights disappeared,—all but one solitary taper, that twinkled from the window of the miller's cottage. At length, however, it also disappeared, and all was dark around the shores of the bay, as a belt of black velvet. Suddenly a hissing noise was heard overhead; the shipmaster looked up, and saw what seemed to be one of those meteors known as falling stars, slanting athwart the heavens in the direction of the cottage, and increasing in size and brilliancy as it neared the earth, until the wooded ridge and the shore could be seen as distinctly from the ship-deck as by day. A dog howled piteously from one of the out-houses,—an owl whooped from the wood. The meteor descended until it almost touched the roof, when a cock crew from within; its progress seemed instantly arrested; it stood still, rose about the height of a ship's mast, and then began again to descend. The cock crew a second time; it rose as before; and, after mounting considerably higher than at first, again sank in the line of the cottage, to be again arrested by the crowing of the cock. It mounted yet a third time, rising higher still; and, in its last descent, had almost touched the roof, when the faint clap of wings was heard as if whispered over the water, followed by a still louder note of defiance from the cock. The meteor rose with a bound, and, continuing to ascend until it seemed lost among the stars, did not again appear. Next night, however, at the same hour, the same scene was repeated in all its circumstances: the meteor descended, the dog howled, the owl whooped, the cock crew. On the following morning the shipmaster visited the miller's, and, curious to ascertain how the cottage would fare when the cock was away, he purchased the bird; and, sailing from the bay before nightfall, did not return until about a month after.
On his voyage inwards, he had no sooner doubled an intervening headland, than he stepped forward to the bows to take a peep at the cottage: it had vanished. As he approached the anchoring ground, he could discern a heap of blackened stones occupying the place where it had stood; and he was informed on going ashore, that it had been burnt to the ground, no one knew how, on the very night he had quitted the bay. He had it re-built and furnished, says the story, deeming himself what one of the old schoolmen perhaps term the occasional cause of the disaster. He also returned the cock,—probably a not less important benefit,—and no after accident befel the cottage. About fifteen years ago there was a human skeleton dug up near the scene of the tradition, with the skull, and the bones of the legs and feet, lying close together, as if the body had been huddled up twofold in a hole; and this discovery led to that of the story, which, though at one time often repeated and extensively believed, had been suffered to sleep in the memories of a few elderly people for nearly sixty years.
CHAPTER VII.
Relation of the deep red stone of Cromarty to the Ichthyolite Beds of the System—Ruins of a Fossil-charged Bed—Journey to Avoch—Red Dye of the Boulder-clay distinct from the substance itself—Variation of Coloring in the Boulder-clay Red Sandstone accounted for—Hard-pan how formed—A reformed Garden—An ancient Battle-field—Antiquity of Geologic and Human History compared—Burn of Killein—Observation made in boyhood confirmed—Fossil-nodules—Fine Specimen of Coccosteus decipiens—Blank strata of Old Red—New View respecting the Rocks of Black Isle—A Trip up Moray and Dingwall Friths—Altered color of the Boulder-clay—Up the Auldgrande River—Scenery of the great Conglomerate—Graphic Description—Laidlaw's Boulder—Vaccinium myrtillus—Profusion of Travelled Boulders—The Boulder Clach Malloch—Its zones of Animal and Vegetable Life.