The ravine excavated by the mill-dam showed me what I had never so well seen before,—the exact relation borne by the deep red stone of the Cromarty quarries to the ichthyolite beds of the system. It occupies the same place, and belongs to the same period, as those superior beds of the Lower Old Red Sandstone which are so largely developed in the cliffs of Dunnet Head in Caithness, and of Tarbet Ness in Ross-shire, and which were at one time regarded as forming, north of the Grampians, the analogue of the New Red Sandstone. I paced it across the strata this morning, in the line of the ravine, and found its thickness over the upper fish-beds, though I was far from reaching its superior layers, which are buried here in the sea, to be rather more than five hundred feet. The fossiliferous beds occur a few hundred yards below the dwelling-house of Rose Farm. They are not quite uncovered in the ravine; but we find their places indicated by heaps of gray argillaceous shale, mingled with their characteristic ichthyolitic nodules, in one of which I found a small specimen of Cheiracanthus. The projecting edge of some fossil-charged bed had been struck, mayhap, by an iceberg, and dashed into ruins, just as the subsiding land had brought the spot within reach of the attritive ice; and the broken heap thus detached had been shortly afterwards covered up, without mixture of any other deposit, by the red boulder-clay. On the previous day I had detected the fish-beds in another new locality,—one of the ravines of the lawn of Cromarty House,—where the gray shale, concealed by a covering of soil and sward for centuries, had been laid bare during the storm by a swollen runnel, and a small nodule, inclosing a characteristic plate of Pterichthys, washed out. And my next object in to-day's journey, after exploring this ravine of the boulder-clay, was to ascertain whether the beds did not also occur in a ravine of the parish of Avoch, some eight or nine miles away, which, when lying a-bed one night in Edinburgh, I remembered having crossed when a boy, at a point which lies considerably out of the ordinary route of the traveller. I had remarked on this occasion, as the resuscitated recollection intimated, that the precipices of the Avoch ravine bore, at the unfrequented point, the peculiar aspect which I learned many years after to associate with the ichthyolitic member of the system; and I was now quite as curious to test the truth of a sort of vignette landscape, transferred to the mind at an immature period of life, and preserved in it for full thirty years, as desirous to extend my knowledge of the fossiliferous beds of a system to the elucidation of which I had peculiarly devoted myself.
As the traveller reaches the flat moory uplands of the parish, where the water stagnates amid heath and moss over a thin layer of peaty soil, he finds the underlying boulder-clay, as shown in the chance sections, spotted and streaked with patches of a grayish-white. There is the same mixture of arenaceous and aluminous particles in the white as in the red portions of the mass; for, as we see so frequently exemplified in the spots and streaks of the Red Sandstone formations, whether Old or New, the coloring matter has been discharged without any accompanying change of composition in the substance which it pervaded;—evidence enough that the red dye must be something distinct from the substance itself, just as the dye of a handkerchief is a thing distinct from the silk or cotton yarn of which the handkerchief has been woven. The stagnant water above, acidulated by its various vegetable solutions, seems to have been in some way connected with these appearances. In every case in which a crack through the clay gives access to the oozing moisture, we see the sides bleached, for several feet downwards, to nearly the color of pipe-clay; we find the surface, too, when it has been divested of the vegetable soil, presenting for yards together the appearance of sheets of half-bleached linen: the red ground of the clay has been acted upon by the percolating fluid, as the red ground of a Bandanna handkerchief is acted upon through the openings in the perforated lead, by the discharging chloride of lime. The peculiar chemistry through which these changes are effected might be found, carefully studied, to throw much light on similar phenomena in the older formations. There are quarries in the New Red Sandstone in which almost every mass of stone presents a different shade of color from that of its neighboring mass, and quarries in the Old Red the strata of which we find streaked and spotted like pieces of calico. And their variegated aspect seems to have been communicated, in every instance, not during deposition, nor after they had been hardened into stone but when, like the boulder-clay, they existed in an intermediate state. Be it remarked, too, that the red clay here,—evidently derived from the abrasion of the red rocks beneath,—is in dye and composition almost identical with the substance on which, as an unconsolidated sandstone, the bleaching influences, whatever their character, had operated in the Palæozoic period, so many long ages before;—it is a repetition of the ancient experiment in the Old Red, that we now see going on in the boulder-clay. It is further worthy of notice, that the bleached lines of the clay exhibit, viewed horizontally, when the overlying vegetable mould has been removed, and the whitened surface in immediate contact with it paired off, a polygonal arrangement, like that assumed by the cracks in the bottom of clayey pools dried up in summer by the heat of the sun. Can these possibly indicate the ancient rents and fissures of the boulder-clay, formed, immediately after the upheaval of the land, in the first process of drying, and remaining afterwards open enough to receive what the uncracked portions of the surface excluded,—the acidulated bleaching fluid?
The kind of ferruginous pavement of the boulder-clay known to the agriculturist as pan, which may be found extending in some cases its iron cover over whole districts,—sealing them down to barrenness, as the iron and brass sealed down the stump of Nebuchadnezzar's tree,—is, like the white strips and blotches of the deposit, worthy the careful notice of the geologist. It serves to throw some light on the origin of those continuous bands of clayey or arenaceous ironstone, which in the older formations in which vegetable matter abounds, whether Oölitic or Carboniferous, are of such common occurrence. The pan is a stony stratum, scarcely less indurated in some localities than sandstone of the average hardness, that rests like a pavement on the surface of the boulder-clay, and that generally bears atop a thin layer of sterile soil, darkened by a russet covering of stunted heath. The binding cement of the pan is, as I have said, ferruginous, and seems to have been derived from the vegetable covering above. Of all plants, the heaths are found to contain most iron. Nor is it difficult to conceive how, in comparatively flat tracts of heathy moor, where the surface water sinks to the stiff subsoil, and on which one generation of plants after another has been growing and decaying for many centuries, the minute metallic particles, disengaged in the process of decomposition, and carried down by the rains to the impermeable clay, should, by accumulating there, bind the layer on which they rest, as is the nature of ferruginous oxide, into a continuous stony crust. Wherever this pan occurs, we find the superincumbent soil doomed to barrenness,—arid and sun-baked during the summer and autumn months, and, from the same cause, overcharged with moisture in winter and spring. My friend Mr. Swanson, when schoolmaster of Nigg, found a large garden attached to the school-house so inveterately sterile as to be scarce worth cultivation; a thin stratum of mould rested on a hard impermeable pavement of pan, through which not a single root could penetrate to the tenacious but not unkindly subsoil below. He set himself to work in his leisure hours, and bit by bit laid bare and broke up the pavement. The upper mould, long divorced from the clay on which it had once rested, was again united to it; the piece of ground began gradually to alter its character for the better; and when I last passed the way, I found it, though in a state of sad neglect, covered by a richer vegetation than it had ever borne under the more careful management of my friend. This ferruginous pavement of the boulder-clay may be deemed of interest to the geologist, as a curious instance of deposition in a dense medium, and as illustrative of the changes which may be effected on previously existing strata, through the agency of an overlying vegetation.
I passed, on my way, through the ancient battle-field to which I have incidentally referred in the story of the Miller of Resolis.[17] Modern improvement has not yet marred it by the plough; and so it still bears on its brown surface many a swelling tumulus and flat oblong mound, and—where the high road of the district passes along its eastern edge—the huge gray cairn, raised, says tradition, over the body of an ancient Pictish king. But the contest of which it was the scene belongs to a profoundly dark period, ere the gray dawn of Scottish history began. As shown by the remains of ancient art occasionally dug up on the moor, it was a conflict of the times of the stone battle-axe, the flint arrow-head, and the unglazed sepulchral urn, unindebted for aught of its symmetry to the turning-lathe,—times when there were heroes in abundance, but no scribes. And the cairn, about a hundred feet in length and breadth, by about twenty in height, with its long hoary hair of overgrown lichen waving in the breeze, and the trailing club-moss shooting upwards from its base along its sides, bears in its every lineament full mark of its great age. It is a mound striding across the stream of centuries, to connect the past with the present. And yet, after all, what a mere matter of yesterday its extreme antiquity is! My explorations this morning bore reference to but the later eras of the geologist; the portion of the geologic volume which I was attempting to decipher and translate formed the few terminal paragraphs of its concluding chapter. And yet the finis had been added to them for thousands of years ere this latter antiquity began. The boulder-clay had been formed and deposited; the land, in rising over the waves, had had many a huge pebble washed out of its last formed red stratum, or dropped upon it by ice-floes from above; and these pebbles lay mottling the surface of this barren moor for mile after mile, bleaching pale to the rains and the sun, as the meagre and mossy soil received, in the lapse of centuries, its slow accessions of organic matter, and darkened around them. And then, for a few brief hours, the heath, no longer solitary, became a wild scene of savage warfare,—of waving arms and threatening faces,—and of human lives violently spilled, gushing forth in blood; and, when all was over, the old weathered boulders were heaped up above the slain, and there began a new antiquity in relation to the pile in its gathered state, that bore reference to man's short lifetime, and to the recent introduction of the species. The child of a few summers speaks of the events of last year as long gone by; while his father advanced into middle life, regards them as still fresh and recent.
I reached the Burn of Killein,—the scene of my purposed explorations,—where it bisects the Inverness road; and struck down the rocky ravine, in the line of the descending strata and the falling streamlet, towards the point at which I had crossed it so many years before. First I passed along a thick bed of yellow stone,—next over a bed of stratified clay. "The little boy," I said, "took correct note of what he saw, though without special aim at the time, and as much under the guidance of a mere observative instinct as Dame Quickly, when she took note of the sea-coal fire, the round table, the parcel-gilt goblet, and goodwife Keech's dish of prawns dressed in vinegar, as adjuncts of her interview with old Sir John when he promised to marry her. These are unequivocally the ichthyolitic beds, whether they contain ichthyolites or no." The first nodule I laid open presented inside merely a pale oblong patch in the centre, which I examined in vain with the lens, though convinced of its organic origin, for a single scale. Proceeding farther down the stream, I picked a nodule out of a second and lower bed, which contained more evidently its organism,—a finely-reticulated fragment, that at first sight reminded me of some delicate festinella of the Silurian system. It proved, however, to be part of the tail of a Cheiracanthus, exhibiting—what is rarely shown—the interior surfaces of those minute rectangular scales which in this genus lie over the caudal fin, ranged in right lines. A second nodule presented me with the spines of Diplacanthus striatus; and still farther down the stream,—for the beds are numerous here, and occupy in vertical extent very considerable space in the system,—I detected a stratum of bulky nodules charged with fragments of Coccosteus, belonging chiefly to two species,—Coccosteus decipiens and Coccosteus cuspidatus. All the specimens bore conclusive evidence regarding the geologic place and character of the beds in which they occur; and in one of the number, a specimen of Coccosteus decipiens, sufficiently fine to be transferred to my knapsack, and which now occupies its corner in my little collection, the head exhibits all its plates in their proper order, and the large dorsal plate, though dissociated from the nail-like attachment of the nape, presents its characteristic breadth entire. It was the plates of this species, first found in the flagstones of Caithness, which were taken for those of a fresh-water tortoise; and hence apparently its specific name, decipiens;—it is the deceiving Coccosteus. I disinterred, in the course of my explorations, as many nodules as lay within reach,—now and then longing for a pickaxe, and a companion robust and persevering enough to employ it with effect; and after seeing all that was to be seen in the bed of the stream and the precipices, I retraced my steps up the dell to the highway. And then, striking off across the moor to the north,—ascending in the system as I climbed the eminence, which forms here the central ridge of the old Maolbuie Common,—I spent some little time in a quarry of pale red sandstone, known, from the moory height on which it has been opened, as the quarry of the Maolbuie. But here, as elsewhere, the folds of that upper division of the Lower Old Red in which it has been excavated contain nothing organic. Why this should be so universally the case,—for in Caithness, Orkney, Cromarty, and Ross, wherever, in short, this member of the system is unequivocally developed, it is invariably barren of remains,—cannot, I suspect, be very satisfactorily explained. Fossils occur both over and under it, in rocks that seem as little favorable to their preservation; but during that intervening period which its blank strata represent, at least the species of all the ichthyolites of the system seem to have changed, and, so far as is yet known, the genus Coccosteus died out entirely.
The Black Isle has been elaborately described in the last Statistical Account of the Parish of Avoch as comprising at least the analogues of three vast geologic systems. The Great Conglomerate, and the thick bed of coarse sandstone of corresponding character that lies over it, compose all which is not primary rock of that south-eastern ridge of the district which forms the shores of the Moray Frith; and they are represented in the Account as Old Red Sandstone proper. Then, next in order,—forming the base of a parallel ridge,—come those sandstone and argillaceous bands to which the ichthyolite beds belong; and these though at the time the work appeared their existence in the locality could be but guessed at, are described as representatives of the Coal Measures. Last of all there occur those superior sandstones of the Lower Old Red formation in which the quarry of the Maolbuie has been opened, and which are largely developed in the central or backbone ridge of the district. "And these," says the writer, "we have little hesitation in assigning to the New Red, or variegated Sandstone formation." I remember that some thirteen years ago,—in part misled by authority, and in part really afraid to represent beds of such an enormous aggregate thickness as all belonging to one inconsiderable formation,—for such was the character of the Old Red Sandstone at the time,—I ventured, though hesitatingly, and with less of detail, on a somewhat similar statement regarding the sandstone deposits of the parish of Cromarty. But true it is, notwithstanding, that the stratified rocks of the Black Isle are composed generally, not of the analogues of three systems, but of merely a fractional portion of a single system,—a fact previously established in other parts of the district, and which my discovery of this day in the Burn of Killein served yet farther to confirm in relation to that middle portion of the tract in which the parish of Avoch is situated. The geologic records, unlike the Sybilline books, grow in volume and number as one pauses and hesitates over them; demanding, however, with every addition to their bulk, a larger and yet larger sum of epochs and of ages.
The sun had got low in the western sky, and I had at least some eight or nine miles of rough road still before me; but the day had been a happy and not unsuccessful one, and so its hard work had failed to fatigue. The shadows, however, were falling brown and deep on the bleak Maolbuie, as I passed, on my return, the solitary cairn; and it was dark night long ere I reached Cromarty. Next morning I quitted the town for the upper reaches of the Frith, to examine yet further the superficial deposits and travelled boulders of the district.
I landed at Invergordon a little after noon, from the Leith steamer, that, on its way to the upper ports of the Moray and Dingwall Friths, stops at Cromarty for passengers every Wednesday; and then passing direct through the village, I took the western road which winds along the shore towards Strathpeffer, skirting on the right the ancient province of the Munroes. The day was clear and genial; and the wide-spreading woods of this part of the country, a little touched by their autumnal tints of brown and yellow, gave a warmth of hue to the landscape, which at an earlier season it wanted. A few slim streaks of semi-transparent mist, that barred the distant hill-peaks, and a few towering piles of intensely white cloud, that shot across the deep blue of the heavens, gave warning that the earlier part of the day was to be in all probability the better part of it, and that the harvest of observation which it was ultimately to yield might be found to depend on the prompt use made of the passing hour. What first attracts the attention of the geologist, in journeying westwards, is the altered color of the boulder-clay, as exhibited in ditches by the way-side, or along the shore. It no longer presents that characteristic red tint,—borrowed from the red sandstone beneath,—so prevalent over the Black Isle, and in Easter Ross generally; but is of a cold leaden hue, not unlike that which it wears above the Coal Measures of the south, or over the flagstones of Caithness. The altered color here is evidently a consequence of the large development, in Ferindonald and Strathpeffer, of the ichthyolitic members of the Old Red, existing chiefly as fetid bituminous breccias and dark-colored sandstones: the boulder-clay of the locality forms the dressings, not of red, but of blackish-gray rocks; and, as almost everywhere else in Scotland, its trail lies to the east of the strata, from which it was detached in the character of an impalpable mud by the age-protracted grindings of the denuding agent. It abounds in masses of bituminous breccia, some of which, of great size, seem to have been drifted direct from the valley of Strathpeffer, and are identical in structure and composition with the rock in which the mineral springs of the Strath have their rise, and to which they owe their peculiar qualities.
After walking on for about eight miles, through noble woods and a lovely country, I struck from off the high road at the pretty little village of Evanton, and pursued the course of the river Auldgrande, first through intermingled fields and patches of copsewood, and then through a thick fir wood, to where the bed of the stream contracts from a boulder-strewed bottom of ample breadth, to a gloomy fissure, so deep and dark, that in many places the water cannot be seen, and so narrow, that the trees which shoot out from the opposite sides interlace their branches atop. Large banks of the gray boulder-clay, laid open by the river, and charged with fragments of dingy sandstone and dark-colored breccia, testify, along the lower reaches of the stream, to the near neighborhood of the ichthyolitic member of the Old Red; but where the banks contract, we find only its lowest member, the Great Conglomerate. This last is by far the most picturesque member of the system,—abrupt and bold of outline in its hills, and mural in its precipices. And nowhere does it exhibit a wilder or more characteristic beauty than at the tall narrow portal of the Auldgrande, where the river,—after wailing for miles in a pent-up channel, narrow as one of the lanes of old Edinburgh, and hemmed in by walls quite as perpendicular, and nearly twice as lofty,—suddenly expands, first into a deep brown pool, and then into a broad tumbling stream, that, as if permanently affected in temper by the strict severity of the discipline to which its early life had been subjected, frets and chafes in all its after course, till it loses itself in the sea. The banks, ere we reach the opening of the chasm, have become steep, and wild, and densely wooded; and there stand out on either hand, giant crags, that plant their iron feet in the stream; here girdled with belts of rank succulent shrubs, that love the damp shade and the frequent drizzle of the spray; and there hollow and bare, with their round pebbles sticking out from the partially decomposed surface, like the piled-up skulls in the great underground cemetery of the Parisians. Massy trees, with their green fantastic roots rising high over the scanty soil, and forming many a labyrinthine recess for the frog, the toad, and the newt, stretch forth their gnarled arms athwart the stream. In front of the opening, with but a black deep pool between, there lies a midway bank of huge stones. Of these, not a few of the more angular masses still bear, though sorely worn by the torrent, the mark of the blasting iron, and were evidently tumbled into the chasm from the fields above. But in the chasm there was no rest for them, and so the arrowy rush of the water in the confined channel swept them down till they dropped where they now lie, just where the widening bottom first served to dissipate the force of the current. And over the sullen pool in front we may see the stern pillars of the portal rising from eighty to a hundred feet in height, and scarce twelve feet apart, like the massive obelisks of some Egyptian temple; while, in gloomy vista within, projection starts out beyond projection, like column beyond column in some narrow avenue of approach to Luxor or Carnac. The precipices are green, with some moss or byssus, that like the miner, chooses a subterranean habitat,—for here the rays of the sun never fall; the dead, mossy water beneath, from which the cliffs rise so abruptly, bears the hue of molten pitch; the trees, fast anchored in the rock, shoot out their branches across the opening, to form a thick tangled roof, at the height of a hundred and fifty feet overhead; while from the recesses within, where the eye fails to penetrate, there issues a combination of the strangest and wildest sounds ever yet produced by water: there is the deafening rush of the torrent, blent as if with the clang of hammers, the roar of vast bellows, and the confused gabble of a thousand voices. The sun, hastening to its setting, shone red, yet mellow, through the foliage of the wooded banks on the west, where, high above, they first curve from the sloping level of the fields, to bend over the stream; or fell more direct on the jutting cliffs and bosky dingles opposite, burnishing them as if with gold and fire; but all was coldly-hued at the bottom, where the torrent foamed gray and chill under the brown shadow of the banks; and where the narrow portal opened an untrodden way into the mysterious recesses beyond, the shadow deepened almost into blackness. The scene lacked but a ghost to render it perfect. An apparition walking from within like the genius in one of Goldsmith's essays "along the surface of the water," would have completed it at once.
Laying hold of an overhanging branch, I warped myself upwards from the bed of the stream along the face of a precipice, and, reaching its sloping top, forced my way to the wood above, over a steep bank covered with tangled underwood, and a slim succulent herbage, that sickened for want of the sun. The yellow light was streaming through many a shaggy vista, as, threading my way along the narrow ravine as near the steep edge as the brokenness of the ground permitted, I reached a huge mass of travelled rock, that had been dropped in the old boulder period within a yard's length of the brink. It is composed of a characteristic granitic gneiss of a pale flesh-color, streaked with black, that, in the hand specimen, can scarce be distinguished from a true granite, but which, viewed in the mass, presents, in the arrangement of its intensely dark mica, evident marks of stratification, and which is remarkable, among other things, for furnishing almost all the very large boulders of this part of the country. Unlike many of the granitic gneisses, it is a fine solid stone, and would cut well. When I had last the pleasure of spending a few hours with the late Mr. William Laidlaw, the trusted friend of Sir Walter Scott, he intimated to me his intention,—pointing to a boulder of this species of gneiss,—of having it cut into two oblong pedestals, with which he purposed flanking the entrance to the mansion-house of the chief of the Rosses,—the gentleman whose property he at that time superintended. It was, he said, both in appearance and history, the most remarkable stone on the lands of Balnagown; and so he was desirous that it should be exhibited at Balnagown Castle to the best advantage. But as he fell shortly after into infirm health, and resigned his situation, I know not that he ever carried his purpose into effect. The boulder here, beside the chasm, measures about twelve feet in length and breadth, by from five to six in height, and contains from eight to nine hundred cubic feet of stone. On its upper table-like surface I found a few patches of moss and lichen, and a slim reddening tuft of the Vaccinium myrtillus, still bearing, late as was the season, its half-dozen blaeberries. This pretty little plant occurs in great profusion along the steep edges of the Auldgrande, where its delicate bushes, springing up amid long heath and ling, and crimsoned by the autumnal tinge, gave a peculiar warmth and richness this evening to those bosky spots under the brown trees, or in immediate contact with the dark chasm on which the sunlight fell most strongly; and on all the more perilous projections, I found the dark berries still shrivelling on their stems. Thirty years earlier I would scarce have left them there; and the more perilous the crag on which they had grown, the more deliciously would they have eaten. But every period of life has its own playthings; and I was now chiefly engaged with the deep chasm and the huge boulder. Chasm and boulder had come to have greatly more of interest to me than the delicate berries, or than even that sovereign dispeller of ennui and low spirits, an adventurous scramble among the cliffs.