Rosemarkie and its Scaurs—Kaes' Craig—A Jackdaw Settlement—"Rosemarkie Kaes" and "Cromarty Cooties"—"The Danes," a Group of Excavations—At Home in Cromarty—The Boulder-clay of Cromarty "begins to tell its story"—One of its marked Scenic Peculiarities—Hints to Landscape Painters—"Samuel's Well"—A Chain of Bogs geologically accounted for—Another Scenic Peculiarity—"Ha-hasof Nature's digging"—The Author's earliest Field of Hard Labor—Picturesque Cliff of Boulder-clay—Scratchings on the Sandstone—Invariable Characteristic of true Boulder-clay—Scratchings on Pebbles in the line of the longer axis—Illustration from the Boulder-clay of Banff.
Rosemarkie and its Scaurs—Kaes' Craig—A Jackdaw Settlement—"Rosemarkie Kaes" and "Cromarty Cooties"—"The Danes," a Group of Excavations—At Home in Cromarty—The Boulder-clay of Cromarty "begins to tell its story"—One of its marked Scenic Peculiarities—Hints to Landscape Painters—"Samuel's Well"—A Chain of Bogs geologically accounted for—Another Scenic Peculiarity—"Ha-hasof Nature's digging"—The Author's earliest Field of Hard Labor—Picturesque Cliff of Boulder-clay—Scratchings on the Sandstone—Invariable Characteristic of true Boulder-clay—Scratchings on Pebbles in the line of the longer axis—Illustration from the Boulder-clay of Banff.
Rosemarkie, with its long narrow valley and its red abruptscaurs,[14]is chiefly interesting to the geologist for its vast beds of the boulder-clay. I am acquainted with no other locality in the kingdom where this deposit is hollowed into ravines so profound, or presents precipices so imposing and lofty. The clay lies thickly over most part of the Black Isle and the peninsula of Easter Ross,—both soft sandstone districts,—bearing everywhere an obvious relation, as a deposit, to both the form and the conditions of exposure of the existing land,—just as the accumulated snow of a long-lying snow-storm, exposed to the drifting wind, bears relation to the heights and hollows of the tracts which it covers. On the higher eminences the clay forms a comparatively thin stratum, and in not a few instances it has been wholly worn away; while on the lower grounds, immediately over the old coast line, and in the sides of hollow valleys,—exactly such places as we might expect to see thesnow occupying most deeply after a night of drift,—we find it accumulated in vast beds of from eighty to an hundred feet in thickness. One of these occurs in the opening of the narrow valley along which my course this morning lay, and is known far and wide,—for it forms a marked feature in the landscape, and harbors in its recesses a countless multitude of jackdaws,—as the "Kaes' Craig of Rosemarkie." It presents the appearance of a hill that had been cut sheer through the middle from top to base, and exhibits in its abrupt front a broad red perpendicular section of at least a hundred feet in height, barred transversely by thin layers of sand, and scored vertically by the slow action of the rains. Originally it must have stretched its vanished limb across the opening like some huge snow-wreath accumulated athwart a frozen rivulet; but the incessant sweep of the stream that runs through the valley has long since amputated and carried it away; and so only half the hill now remains. The Kaes' Craig resembles in form a lofty chalk cliff, square, massy, abrupt, with no sloping fillet of vegetation bound across its brow, but precipitous direct from the hill-top. The little ancient village of Rosemarkie stretches away from its base on the opposite side of the stream; and on its summit and along its sides, groups of chattering jackdaws, each one of them as reflective and philosophic as the individual immortalized by Cowper, look down high over the chimneys into the streets. The clay presents here, more than in almost any other locality with which I am acquainted, the character of a stratified deposit; and the numerous bands of sand by which the cliff is horizontally streaked from top to bottom we find hollowed, as we approach, into a multitude of circular openings, like shot-holes in an old tower, which form breeding-places for the daw and the sand-martin. The biped inhabitants of the cliff are greatly more numerous than the biped inhabitantsof the quiet little hamlet below; and on Fortrose fair-days, when, in virtue of an old feud, the Rosemarkie boys were wont to engage in formidable bickers with the boys of Cromarty, I remember, as one of the invading belligerents, that, in bandying names with them in the fray, we delighted to bestow upon them, as their hereditary sobriquet, given, of course, in allusion to their feathered neighbors, the designation of the "Rosemarkie kaes." Cromarty, however, is two-thirds surrounded by the waters of a frith abounding in sea-fowl; and the little fellows of Rosemarkie, indignant at being classed with theirkaes, used to designate us with hearty emphasis, in turn, as the "Cromarty cooties,"i.e., coots.
A little higher up the valley, on the western side, there occurs in the clay what may be termed agroupof excavations, composing a piece of scenery ruinously broken and dreary, and that bears a specific character of its own which scarce any other deposit could have exhibited. The excavations are of considerable depth and extent,—hollows out of which the materials of pyramids might have been taken. The precipitous sides are fretted by jutting ridges and receding inflections, that present in abundance their diversified alternations of light and shadow. The steep descents form cycloid curves, that flatten at their bases, and over which the ferruginous stratum of mould atop projects like a cornice. Between neighboring excavations there stand up dividing walls, tall and thin as those of our city buildings, and in some cases broken at their upper edges into rows of sharp pinnacles or inaccessible turf-coped turrets; while at the bottom of the hollows, washed by the runnels which, in the slow lapse of years, have been the architects of the whole, we find cairn-like accumulations of water-rolled stones,—the disengaged pebbles and boulders of the deposit. The boulders and pebbles project also from the steep sides, at allheights and of all sizes, like the primary masses inclosed in our ancient conglomerates, when exhibited in wave-worn precipices,—forcing upon the mind the conclusion that the boulder-clay is itself but an unconsolidated conglomerate of the later periods, which occupies nearly the same relative position to the existing vegetable mould, with all its recent productions, that the great conglomerate of the Old Red Sandstone occupies in relation to the lower ichthyolite beds of that system, with their numerous extinct organisms. But its buried stones are fretted with hieroglyphic inscriptions, in the form of strange scratchings and polishings, grooves, ridges, and furrows,—always associated with the boulder-clays,—which those of the more ancient conglomerates want, and which, though difficult to read, seem at length to be yielding up the story which they record. Of this, however, more anon. Viewed by moonlight, when the pale red of the clay where the beam falls direct is relieved by the intense shadows, these excavations of the valley of Rosemarkie form scenes of strange and ghostly wildness: the projecting, buttress-like angles,—the broken walls,—the curved inflections,—the pointed pinnacles,—the turrets, with their masses of projecting coping,—the utter lack of vegetation, save where the heath and the furze rustle far above,—all combine to form assemblages of dreary ruins, amid which, in the solitude of night, one almost expects to see spirits walk. These excavations have been designated, from time immemorial, by the neighboring town's-people, as "the Danes;" but whether the name be, as is most probable, merely a corruption of an appropriate enough Saxon word, "the dens," or derived, as a vague tradition is said to testify, from the ages of Danish invasion, it is not quite the part of the geologist to determine. It may be worth mentioning, however, from its bearing on the point, that there are two excavations in the boulder-claynear Cromarty, one of which has been long known by the name of "the Morial's Den," while the other, greatly smaller in size, rejoices in the double diminutive of "the Little Dennie." For an hour or so the Danes proved agreeable though somewhat silent companions; and then, climbing the opposite side of the valley, I gained the high road, and, walking on to Cromarty, found myself once more among "the old familiar faces."
In a few days the storm blew by; and as the prolonged rains had cleared out the deep ravines of the district, and given to the boulder-clay in which they are scooped a freshness in its section analogous to fresh fracture in rocks of harder consistency, I availed myself of the facilities afforded me in consequence, for exploring it once more. It has long constituted one of the hardest of the many riddles with which our Scottish deposits exercise the patience and ingenuity of the geologist. I remember a time when, after passing a day under its barrenscaurs, or hid in its precipitous ravines, I used to feel in the evening as if I had been travelling under the cloud of night, and had seen nothing. It was a morose and taciturn companion, and had no speculation in it. I might stand in front of its curved precipices, red, yellow or gray, according to the prevailing average color of the rocks on which it rests, and mark their water-rolled boulders, of all qualities and sizes, sticking out in bold relief from the surface, like the rock-like protuberances that roughen the rustic basements of the architect, from the line of the wall; but I had noopen sesameto form vistas through them into the recesses of the past. I saw merely the stiff pastry matrix of which they are composed, and the inclosed pebbles. But the boulder-clay has of late become more sociable; and, though with much hesitancy and irresolution, like old Mr. Spectator on the first formal opening of his mouth,—a consequence, doubtless, in both cases ofprevious habits of silence long indulged,—it begins to tell its story. And a most curious story it is.
The morning was clear, but just a little chill; and a soft covering of snow, that had fallen during the storm on the flat summit of Ben-Wevis, and showed its extreme tenuity by the paleness of its tint of watery blue, was still distinctly visible at the distance of full twenty miles. The sun, low in the sky,—for the hour was early,—cast its slant rays athwart the prospect, giving to each nearer bank and hillock, and to the more distant protuberances on the mountain-sides, those well-defined accompaniments of shadow that serve by throwing the minor features of a landscape upon the eye in bold relief, to impart to it an air of higher finish and more careful filling up than it ever bears under a more vertical light. I took the road which, leading westward from the town towards Invergordon Ferry, skirts the Frith on the one hand, and runs immediately under the noble escarpment of green bank formed by the old coast line on the other. Fully two-thirds of the entire height of the rampart here, which rises in all about a hundred feet over the sea-level, is formed of the boulder-clay; and I am acquainted with no locality in which the deposit presents more strongly, for at least the first half mile, one of its marked scenic peculiarities. It is furrowed vertically on the slope, as if by enormous flutings in the more antique Doric style; and the ridges by which these are separated,—each from a hundred to a hundred and fifty feet in length, and from five-and-twenty to thirty feet in average height,—resemble those burial mounds with which the sexton frets the churchyard turf; with this difference, however, that they seem the burial mounds of giants, tall and bulky as those that of old warred against the gods. They are striking enough to have caught the eye of the children of the place, and are known among them as the Giants'Graves. I could fain have taken their portrait in a calotype this morning, as they lay against the green bank,—their feet to the shore, and their heads on the top of the escarpment,—like patients on a reclining bed, and strongly marked, each by its broad bar of yellow light and of dark shadow, like the ebon and ivory buttresses of the poet. This little vignette, I would have said to the landscape painter, represents the boulder-clay, after its precipitous banks—worn down, by the frosts and rains of centuries, into parallel runnels, that gradually widened into these hollow grooves—had sunk into the angle of inclination at which the disintegrating agents ceased to operate, and the green sward covered all up. You must be studying these peculiarities of aspect more than ever you studied them before. There is a time coming when the connoisseur will as rigidly demand the specific character of the various geologic rocks and deposits in your hills,scaurs, and precipices, as he now demands specific character in your shrubs and trees.
It is worthy the notice of the young geologist, who has just set himself to study the various effects produced on the surface of a country by the deposits which lie under it, that for about a quarter of a mile or so, the base of the escarpment here is bordered by a line of bogs, that bear in the driest weather their mantling of green. They are fed with a perennial supply of water, by a range of deep-seated springs, that come bursting out from under the boulder-clay; and one of their number, which bears I know not why, the name of Samuel's Well, and yields its equable flow at an equable temperature, summer and winter, into a stone trough by the way-side, is not a little prized by the town's-people, and the seamen that cast anchor in the opposite roadstead, for the lightness and purity of its water. What is specially worthy of notice in the case is, the very definitebeginning and ending of the chain of bogs. All is dry at the base of the escarpment, up to the point at which they commence; and then all is equally dry at the point at which they terminate. And of exactly the same extent,—beginning where the bogs begin, and ending where they end,—we may trace an ancient stratum of pure sand,—of considerable thickness, intercalated between the base of the clay and the superior surface of the Old Red Sandstone. It is through this permeable sand that the profoundly seated springs find their way to the surface,—for the clay is impermeable; and where it comes in contact with the rock on either side of the arenaceous stratum, the bogs cease. The chain of green bogs is a consequence of the stratum of permeable sand. I have in vain sought this ancient layer of sand,—decidedly of the same era with the argillaceous bed which overlies it,—for aught organic. A single shell, so unequivocally of the period of the boulder-clay as to occur at the base of the deposit, would be worth, I have said, whole drawerfuls of fossils furnished by the better-known deposits. But I have since seen in abundance shells of the boulder-clay.
There is another scenic peculiarity of the clay, which the neighborhood of Cromarty finely illustrates, and of which my walk this morning furnished numerous striking instances. The Giants' Graves—to borrow from the children of the place—occur on the steep slopes of the old coast line, or in the sides of ravines, where the clay, as I have said, had once presented a precipitous front, but had been gradually moulded, under the attritive influences of the elements, into series of alternating ridges and furrows, which, when they had flattened into the proper angle, the green sward covered up from further waste. But the deep dells and narrow ravines in which many ranges of these graves occur are themselves peculiarities of the deposit.Wherever the boulder-clay lies thick and continuous, as in the parish of Cromarty, on a sloping table-land, every minute streamlet cuts its way to the solid rock at the bottom, and runs through a deep dell, either softened into beauty by the disintegrating process, or with all its precipices standing up raw and abrupt over the stream. Four of these ravines, known as the "Old Chapel Burn," the "Ladies' Walk," the "Morial's Den," and the "Red Burn," each of them cutting the escarpment of the ancient coast line from top to base, and winding far into the interior, occur in little more than a mile's space; and they lie still more thickly farther to the west. These dells of the boulder clay, in their lower windings,—for they become shallower and tamer as they ascend, till they terminate in the uplands in meredrains, such as a ditcher might excavate at the rate of a shilling or two per yard,—are eminently picturesque. On those gentler slopes where the vegetable mould has had time and space to accumulate, we find not a few of the finest and tallest trees of the district. There is a bosky luxuriance in their more sheltered hollows, well known to the schoolboy what time the fern begins to pale its fronds, for their store of hips, sloes, and brambles; and red over the foliage we may see, ever and anon as we wend upwards, the abrupt frontage of some precipitousscaur, suited to remind the geologist, from its square form and flat breadth of surface, of the cliffs of the chalk. When viewed from the sea, at the distance of a few miles, these ravines seem to divide the sloping tracts in which they occur into large irregular fields, laid out considerably more in accordance with the principles of the landscape gardener than the stiffly squared rectilinear fields of the agriculturist. They areha-hasof Nature's digging; and their bottom and sides in this part of the country we still find occupied in a few cases—though in many more they have been ravagedby the wasteful axe—by noble forest-hedges, tall enough to overtop, in at least their middle reaches, the tracts of table-land which they divide.
I passed, a little farther on, the quarry of Old Red Sandstone, with a huge bank of boulder-clay resting over it, in which I first experienced the evils of hard labor, and first set myself to lessen their weight by becoming an observer of geological phenomena. It had been deserted apparently for many years; and the debris of the clay partially covered up, in a sloping talus, the frontage of rock beneath. Old Red Sandstone and boulder-clay, a broad bar of each!—such was the compound problem which the excavation propounded to me when I first plied the tool in it,—a problem equally dark at the time in both its parts. I have since got on a very little way with the Old Red portion of the task; but alas for the boulder-clay portion of it! A bar of impenetrable shadow has rested long and obstinately over the newer deposit; and I scarce know whether the light which is at length beginning to play on its pebbly front be that of the sun or of a delusive meteor. But courage, patient hearts! the boulder-clay will one day yield upitssecret too. Still further on by a few hundred yards, I could have again found use for the calotype, in transferring to paper the likeness of a protuberant picturesque cliff, which, like the Giants' Graves, could have belonged, of all our Scotch deposits, to only the boulder-clay. It stands out, on the steep acclivity of a furze-covered bank, abrupt as a precipice of solid rock, and yet seamed by the rain into numerous divergent channels, with pyramidal peaks between; and, combining the perpendicularity of a true cliff with the water-scooped furrows of a yielding clay, it presents a peculiarity of aspect which strikes, by its grotesqueness, eyes little accustomed to detect the picturesque in landscape. I rememberstanding to gaze upon it when a mere child; and the fisher children of the neighboring town still tell that "it has been prophesied" it will one day fall, "and kill a man and a horse on the road below,"—a legend which shows it must have attractedtheirnotice too.
I selected as the special scene of exploration this morning, a deep ravine of the boulder-clay, which had been recently deepened still more by the waters of a mill-pond, that had burst during a thunder-shower, and, after scooping out for themselves a bed in the clay some twelve or fifteen feet deep, where there had been formerly merely a shallow drain, had then tumbled into the ravine, and bared it to the rock. The sandstones of the district, soft and not very durable, show the scratched and polished surfaces but indifferently well, and, when exposed to the weather, soon lose them; but in the bottom of the runnel by which the ravine is swept I found them exceedingly well marked,—the polish as decided as the soft red stone could receive, and the lines of scratching running in their general bearing due east and west, at nearly right angles with the course of the stream. Wherever the rock had been laid bare during the last few months,therewere the markings; wherever it had been laid bare for a few twelvemonths, they were gone. I next marked a circumstance which has now for several years been attracting my attention, and which I have found an invariable characteristic of the true boulder-clay. Not only do the rocks on which the deposit rests bear the scratched and polished surfaces, but in every instance the fragments of stone which it incloses bear the scratchings also, if from their character capable of receiving and retaining such markings, and neither of too coarse a grain nor of too hard a quality. If of limestone, or of a coherent shale, or of a close, finely-grained sandstone, or of a yielding trap, theyare scratched and polished,—invariably on one, most commonly on both their sides; and it is a noticeable circumstance, that the lines of the scratchings occur, in at least nine cases out of every ten, in the lines of their longer axes. When decidedly oblong or spindle-shaped, the scratchings run lengthwise, preserving in most cases, on the under and upper sides, when both surfaces are scratched, a parallelism singularly exact; whereas, when of a broader form, so that the length and breadth nearly approximate,—though the lines generally find out the longer axis, and run in that direction,—they are less exact in their parallelism, and are occasionally traversed by cross furrows. Of such certain occurrence is this longitudinal lining on the softer and finer-grained pebbles of the boulder-clay, that I have come to regard it as that special characteristic of the deposit on which I can most surely rely for purposes of identification. I am never quite certain of the boulder-clay when I do not detect it, nor doubtful of the true character of the deposit when I do. When examining, for instance, the accumulation of broken Liasic materials in the neighborhood of Banff, I made it my first care to ascertain whether the bank inclosed fragments of stone or shale bearing the longitudinal markings; and felt satisfied, on finding that it did, that I had discovered the period of its re-formation.
Organisms of the Boulder-clay not unequivocal—First Impressions of the Boulder-clay—Difficulty of accounting for its barrenness of Remains—Sir Charles Lyell's reasoning—A Fact to the contrary—Human Skull dug from a Clay-bank—The Author's Change of Belief respecting Organic Remains of the Boulder-clay—Shells from the Clay at Wick—Questions respecting them settled—Conclusions confirmed by Mr. Dick's Discoveries at Thurso—Sir John Sinclair's Discovery of Boulder-clay Shells in 1802—Comminution of the Shells illustrated—Cyprina islandica—Its Preservation in larger Proportions than those of other Shells accounted for—Boulder-clays of Scotland reformed during the existing Geological Epoch—Scotland in the Period of the Boulder-clay "merely three detached groups of Islands"—Evidence of the Subsidence of the Land in Scotland—Confirmed by Rev. Mr. Cumming's conclusion—High-lying Granite Boulders—Marks of a succeeding elevatory Period—Scandinavia now rising—Autobiography of a Boulder desirable—A Story of the Supernatural.
Organisms of the Boulder-clay not unequivocal—First Impressions of the Boulder-clay—Difficulty of accounting for its barrenness of Remains—Sir Charles Lyell's reasoning—A Fact to the contrary—Human Skull dug from a Clay-bank—The Author's Change of Belief respecting Organic Remains of the Boulder-clay—Shells from the Clay at Wick—Questions respecting them settled—Conclusions confirmed by Mr. Dick's Discoveries at Thurso—Sir John Sinclair's Discovery of Boulder-clay Shells in 1802—Comminution of the Shells illustrated—Cyprina islandica—Its Preservation in larger Proportions than those of other Shells accounted for—Boulder-clays of Scotland reformed during the existing Geological Epoch—Scotland in the Period of the Boulder-clay "merely three detached groups of Islands"—Evidence of the Subsidence of the Land in Scotland—Confirmed by Rev. Mr. Cumming's conclusion—High-lying Granite Boulders—Marks of a succeeding elevatory Period—Scandinavia now rising—Autobiography of a Boulder desirable—A Story of the Supernatural.
Forthe greater part of a quarter of a century I had been finding organisms in abundance in the boulder-clay, but never anything organic that unequivocally belonged to its own period. I had ascertained that it contains in Ross and Cromarty nodules of the Old Red Sandstone, which bear inside, like so many stone coffins, their well laid out skeletons of the dead; but then the markings on their surface told me that when the boulder-clay was in the course of deposition, they had been exactly the same kind of nodules that they are now. In Moray, it incloses, I had found, organisms of the Lias; buttheyalso testify that they present an appearance in no degree more ancient at the present time than they did when first enveloped by the clay. In East and West Lothian too, and in the neighborhood of Edinburgh, I had detected in it occasional organismsof the Mountain Limestone and the Coal Measures; but these, not less surely than its Liasic fossils in Moray, and its Old Red ichthyolites in Cromarty and Ross, belonged to an incalculably more ancient state of things than itself; and—like those shrivelled manuscripts of Pompeii or Herculaneum, which, whatever else they may record, cannot be expected to tell aught of the catastrophe that buried them up—they throw no light whatever on the deposit in which they occur. I at length came to regard the boulder-clay—for it is difficult to keep the mind in a purely blank state on any subject on which one thinks a good deal—as representative of a chaotic period of death and darkness, introductory, mayhap, to the existing scene of things.
After, however, I had begun to mark the invariable connection of the clay, as a deposit, with the dressed surfaces on which it rests, and the longitudinal linings of the pebbles and boulders which it incloses, and to associate it, in consequence, with an ice-charged sea and the Great Gulf Stream, it seemed to me extremely difficult to assign a reason why it should be thus barren of remains. Sir Charles Lyell states, in his "Elements," that the "stranding of ice-islands in the bays of Iceland since 1835 has driven away the fish for several successive seasons, and thereby caused a famine among the inhabitants of the country;" and he argues from the fact, "that a sea habitually infested with melting ice, which would chill and freshen the water, might render the same uninhabitable by marine mollusca." But then, on the other hand, it is equally a fact that half a million of seals have been killed in a single season on the meadow-ice a little to the north of Newfoundland, and that many millions of cod, besides other fish, are captured yearly on the shores of that island, though grooved and furrowed by ice-floes almost every spring. Of the seal family it is speciallyrecorded by naturalists, that many of the species "are from choice inhabitants of the margins of the frozen seas towards both poles; and, of course, in localities in which many such animals live, some must occasionally die." And though the grinding process would certainly have disjointed, and might probably have worn down and partially mutilated, the bones of the amphibious carnivora of the boulder period, it seems not in the least probable, judging from the fragments of loose-grained sandstone and soft shale which it has spared, that it would have wholly destroyed them. So it happened, however, that from North Berwick to the Ord Hill of Caithness, I had never found in the boulder-clay the slightest trace of an organism that could be held to belong to itself; and as it seems natural to build on negative evidence, if very extensive, considerably more than mere negative evidence, whatever the circumstances, will carry, I became somewhat skeptical regarding the very existence of boulder-fossils,—a skepticism which the worse than doubtful character of several supposed discoveries in the deposit served considerably to strengthen. The clay forms, when cut by a water-course, or assailed on the coast by some unusually high tide, a perpendicular precipice, which in the course of years slopes into a talus; and as it exhibits in most instances no marks of stratification, the clay of the talus—a mere re-formation of fragments detached by the frosts and rains from the exposed frontage—can rarely be distinguished from that of the original deposit. Now, in these consolidated slopes it is not unusual to find remains, animal and vegetable, of no very remote antiquity. I have seen a human skull dug out of the reclining base of a clay-bank once a precipice, fully six feet from under the surface. It might have been deemed the skull of some long-lived contemporary of Enoch,—one of the accursed race, mayhap,
"Who sinned and died before the avenging flood."
But, alas! the laborer dug a little further, and struck his pickaxe against an old rybat that lay deeper still. There could be no mistaking the character of the champfered edge, that still bore the marks of the tool, nor that of the square perforation for the lock-bolt; and a rising theory, that would have referred the boulder-clay to a period in which the polar ice, set loose by the waters of the Noachian deluge, came floating southwards over the foundered land, straightway stumbled against it, and fell. Both rybat and skull had come from an ancient burying-ground, that occupies a projecting angle of the table-land above. I must now state, however, that my skepticism has thoroughly given way; and that, slowly yielding to the force of positive evidence, I have become as assured a believer in thecomminuted recent shellsof the boulder-clay as in the belemnites of the Oölite and Lias, or the ganoid ichthyolites of the Old Red Sandstone.
I had marked, when at Wick, on several occasions, a thick boulder-clay deposit occupying the southern side of the harbor, and forming an elevated platform, on which the higher parts of Pulteneytown are built; but I had noted little else regarding it than that it bears the average dark-gray color of the flagstones of the district, and that some of the granitic boulders which protrude from its top and sides are of vast size. On my last visit, however, rather more than two years ago, when sauntering along its base, after a very wet morning, awaiting the Orkney steamer, I was surprised to find, where a small slip had taken place during the rain, that it was mottled over with minute fragments of shells. These I examined, and found, so far as, in their extremely broken condition, I dared determine the point, that they belonged in such large proportion toone species,—theCyprina islandicaof Dr. Fleming,—that I could detect among them only a single fragment of any other shell,—the pillar, apparently, of a large specimen ofPurpura lapillus. Both shells belong to that class of old existences,—long descended, without the pride of ancient descent,—which link on the extinct to the recent scenes of being.Cyprina islandicaandPurpura lapillusnot only exist as living molluscs in the British seas, but they occur also as crag-shells, side by side with the dead races that have no place in the present fauna. At this time, however, I could but think of them simply in their character as recent molluscs; and as it seemed quite startling enough to find them in a deposit which I had once deemed representative of a period of death, and still continued to regard as obstinately unfossiliferous, I next set myself to determine whether it reallywasthe boulder-clay in which they occurred. Almost the first pebble which I disengaged from the mass, however, settled the point, by furnishing the evidence on which for several years past I have been accustomed to settle it;—it bore in the line of its longer axis, on a polished surface, the freshly-marked grooves and scratchings of the iceberg era. Still, however, I had my doubts, not regarding the deposit, but the shells. Might they not belong merely to the talus of this bank of boulder-clay?—a re-formation, in all probability, notmoreancient than the elevation of the most recent of the old coast lines,—perhaps greatly less so. Meeting with an intelligent citizen of Wick, Mr. John Cleghorn, I requested him to keep a vigilant eye on the shells, and to ascertain for me, when opportunity offered, whether they occurred deep in the deposit, or were restricted to merely the base of its exposed front. On my return from Orkney, he kindly brought me a small collection of fragments, exclusively, so far as I could judge, ofCyprina islandica, picked up infresh sections of the clay; at the same time expressing his belief that they really belonged to the deposit as such, and were not accidental introductions into it from the adjacent shore. And at this point for nearly two years the matter rested, when my attention was again called to it by finding, in the publication of Mr. Keith Johnston's admirable Geological Map of the British Islands, edited by Professor Edward Forbes, that other eyes than mine had detected shells in the boulder-clay of Caithness. "Cliffs of Pleistocene," says the Professor, in one of his notes attached to the map, "occur at Wick, containing boreal shells, especiallyAstarte borealis."
I had seen the boulder-clay characteristically developed in the neighborhood of Thurso; but, during a rather hurried visit, had lacked time to examine it. The omission mattered the less, however, as my friend Mr. Robert Dick is resident in the locality; and there are few men who examine more carefully or more perseveringly than he, or who can enjoy with higher relish the sweets of scientific research. I wrote him regarding Professor Forbes's decision on the boulder-clay of Wick and its shells; urging him to ascertain whether the boulder-clay of Thurso had not its shells also. And almost by return of post I received from him, in reply, a little packet of comminuted shells, dug out of a deposit of the boulder-clay, laid open by the river Thorsa, a full mile from the sea, and from eighty to a hundred feet over its level. He had detected minute fragments of shell in the clay about a twelvemonth before; but a skepticism somewhat similar to my own, added to the dread of being deceived by mere surface shells, recently derived from the shore in the characterofshell-sand, or of the edible species carried inland for food, and then transferred from the ash-pit to the fields, had not only prevented him from following up the discovery,but even from thinking of it as such. But he eagerly followed it up now, by visiting every bank of the boulder-clay in his locality within twenty miles of Thurso, and found them all charged, from top to bottom, with comminuted shells, however great their distance from the sea, or their elevation over it. The fragments lie thick along the course of the Thorsa, where the encroaching stream is scooping out the clay for the first time since its deposition, and laying bare the scratched and furrowed pebbles. They occur, too, in the depths of solitary ravines far amid the moors, and underlie heath, and moss, and vegetable mould, on the exposed hill-sides. The farm-house of Dalemore, twelve miles from Thurso as the crow flies, and rather more than thirteen miles from Wick, occupies, as nearly as may be, the centre of the county; and yet there, as on the sea-shore, the boulder-clay is charged with its fragments of marine shells. Though so barren elsewhere on the east coast of Scotland, the clay is everywhere in Caithness a shell-bearing deposit; and no sooner had Mr. Dick determined the fact for himself, at the expense of many a fatiguing journey, and many an hour's hard digging, than he found that it had been ascertained long before, though, from the very inadequate style in which it had been recorded, science had in scarce any degree benefited by the discovery. In 1802 the late Sir John Sinclair, distinguished for his enlightened zeal in developing the agricultural resources of the country, and for originating its statistics, employed a mineralogical surveyor to explore the underground treasures of the district; and the surveyor's journal he had printed under the title of "Minutes and Observations drawn up in the course of a Mineralogical Survey of the County of Caithness, ann. 1802, by John Busby, Edinburgh." Now, in this journal there are frequent references made to the occurrence of marineshells in the blue clay. Mr. Dick has copied for me the two following entries,—for the work itself I have never seen:—"1802, Sept. 7th.—Surveyed down the river [Thorsa] to Geize; found blue clay-marl,intermixed with marine shellsin great abundance." "Sept. 12th.—Set off this morning for Dalemore. Bored for shell-marl in the 'grass-park;' found it in one of the quagmires, but to no great extent. Bored for shell-marl in the 'house-park.' Surveyed by the side of the river, and found blue clay-marl in great plenty,intermixed with marine shells, such as those found at Geize. This place is supposed to be about twenty miles from the sea; and is one instance, among many in Caithness, ofthe ocean's covering the inland country at some former period of time."
The state of keeping in which the boulder-shells of Caithness occur is exactly what, on the iceberg theory, might be premised. The ponderous ice-rafts that went grating over the deep-sea bottom, grinding down its rocks into clay, and deeply furrowing its pebbles, must have borne heavily on its comparatively fragile shells. If rocks and pebbles did not escape, the shells must have fared but hardly. And very hardly they have fared: the rather unpleasant casualty of being crushed to death must have been a greatly more common one in those days than in even the present age of railways and machinery. The reader, by passing half a bushel of the common shells of our shores through a barley-mill, as a preliminary operation in the process, and by next subjecting the broken fragments thus obtained to the attritive influence of the waves on some storm-beaten beach for a twelvemonth or two, as a finishing operation, may produce, when he pleases, exactly such a water-worn shelly debris as mottles the blue boulder-clays of Caithness. The proportion borne by the fragments of one species of shell to that ofall the others is very extraordinary. TheCyprina islandicais still by no means a rare mollusc on our Scottish shores, and may, on an exposed coast, after a storm, be picked up by dozens, attached to the roots of the deep-sea tangle. It is greatly less abundant, however, than such shells asPurpura lapillus,Mytilus edule,Cardium edule,Littorina littorea, and several others; whereas in the boulder-clay it is, in the proportion of at least ten to one, more abundant than all the others put together. The great strength of the shell, however, may have in part led to this result; as I find that its stronger and massier portions,—those of the umbo and hinge-joint,—are exceedingly numerous in proportion to its slimmer and weaker fragments. "TheCyprina islandica," says Dr. Fleming, in his "British Animals," "is the largest British bivalve shell, measuring sometimes thirteen inches in circumference, and, exclusively of the animal, weighing upwards of nine ounces." Now, in a collection of fragments of Cyprina sent me by Mr. Dick, disinterred from the boulder-clay in various localities in the neighborhood of Thurso, and weighing in all about four ounces, I have detected the broken remains of no fewer thansixteenhinge joints. And on the same principle through which the stronger fragments of Cyprina were preserved in so much larger proportion than the weaker ones, may Cyprina itself have been preserved in much larger proportion than its more fragile neighbors. Occasionally, however,—escaped, as if by accident,—characteristic fragments are found of shells by no means very strong,—such asMytilus,Tellina, andAstarte. Among the univalves I can distinguishDentalium entale,Purpura lapillus,Turritella terebra, andLittorina littorea, all existing shells, but all common also to at least the later deposits of the Crag. And among the bivalves Mr. Dick enumerates,—besidesthe prevailingCyprina islandica,—Venus casina,Cardium edule,Cardium echinatum,Mytilus edule,Astarte danmoniensis(sulcata), andAstarte compressa, with aMactra,Artemis, andTellina.[15]All the determined species here, with the exception ofMytilus edule, have, with many others, been found by the Rev. Mr. Cumming in the boulder-clays of the Isle of Man; and all of them are living shells at the present day on our Scottish coasts. It seems scarce possible to fix the age of a deposit so broken in its organisms, on the principle that would first seek to determine its per centage of extinct shells as the data on which to found. One has to search sedulously and long ere a fragment turns up sufficiently entire for the purpose of specific identification, even when it belongs to a well-known living shell; and did the clay contain some six or eight per cent. of the extinct in a similarly broken condition (and there is no evidence that it contains a single per cent. of extinct shells), I know not how, in the circumstances, the fact could ever be determined. A lifetime might be devoted to the task of fixing their real proportion, and yet be devoted to it in vain. All that at present can be said is, that, judging from what appears, the boulder-clays of Caithness, and with them the boulder-clays of Scotland generally, and of the Isle of Man,—for they are all palpably connected with the same iceberg phenomena, and occur along the same zone in reference to the sea-level,—were formed during theexistinggeological epoch.
These details may appear tediously minute; but let the reader mark how very much they involve. The occurrence of recent shells largely diffused throughout the boulder-clays of Caithness, at all heights and distances from the seaat which the clay itself occurs, and not only connected with the iceberg phenomena by the closest juxtaposition, but also testifying distinctly to its agency by the extremely comminuted state in which we find them, tell us, not only according to old John Busby, "that the ocean covered the inland country at some former period of time," but that it covered it to a great height at a time geologically recent, when our seas were inhabited by exactly the same mollusca as inhabit them now, and so far as yet appears, by none others. I have not yet detected the boulder-clay at more than from six to eight hundred feet over the level of the sea; but the travelled boulders I have often found at more than a thousand feet over it; and Dr. John Fleming, the correctness of whose observations few men acquainted with the character of his researches or of his mind will be disposed to challenge, has informed me that he has detected the dressed and polished surfaces at least four hundred feet higher. There occurs a greenstone boulder, of from twelve to fourteen tons weight, says Mr. M'Laren, in his "Geology of Fife and the Lothians," on the south side of Black Hill (one of the Pentland range), at about fourteen hundred feet over the sea. Now fourteen or fifteen hundred feet, taken as the extreme height of the dressings, though they are said to occur greatly higher, would serve to submerge in the iceberg ocean almost the whole agricultural region of Scotland. The common hazel (Corylus avellana) ceases to grow in the latitude of the Grampians, at from one thousand two hundred to one thousand five hundred feet over the sea level; the common bracken (Pteris aquilina) at about the same height; and corn is never successfully cultivated at a greater altitude. Where the hazel and bracken cease to grow, it is in vain to attempt growing corn.[16]In the periodof the boulder-clay, then, when the existing shells of our coasts lived in those inland sounds and friths of the country that now exist as broad plains or fertile valleys, the sub-aërial superficies of Scotland was restricted to what are now its barren and mossy regions, and formed, instead of one continuous land, merely three detached groups of islands,—the small Cheviot and Hartfell group,—the greatly larger Grampian and Ben Nevis group,—and a group intermediate in size, extending from Mealfourvonny, on the northern shores of Loch Ness, to the Maiden Paps of Caithness.
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 therelativelevels 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, atfully 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 levelsdownwards, or during a period of subsidence, in which it was subjected to the ice, zone after zone, from its lower levelsupwards. 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 stratumof 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 todressthe 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. Thiswashedclay,—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 isnow 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, notoverthe greatly lighter sands and gravels, butunderthem. 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, andwhich 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 thewater, 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 theoccasionalcause 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.