[CHAPTER VII.]
Further Discoveries of the Ichthyolite Beds.—Found in one Locality under a Bed of Peat.—Discovered in another beneath an ancient Burying-ground.—In a third underlying the Lias Formation.—In a fourth overtopped by a still older Sandstone Deposit.—Difficulties in ascertaining the true Place of a newly-discovered Formation.—Caution against drawing too hasty Inferences from the mere circumstance of Neighborhood.—The Writer receives his first Assistance from without.—Geological Appendix of the Messrs. Anderson, of Inverness.—Further Assistance from the Researches of Agassiz.—Suggestions.—Dr. John Malcolmson.—His Extensive Discoveries in Moray.—He submits to Agassiz a Drawing of the Pterichthys.—Place of the Ichthyolites in the Scale at length determined.—Two distinct Platforms of Being in the Formation to which they belong.
I commenced forming a small collection, and set myself carefully to examine the neighboring rocks for organisms of a similar character. The eye becomes practised in such researches, and my labors were soon repaid. Directly above the little bay there is a corn-field, and beyond the field a wood of forest trees; and in this wood, in the bottom of a water-course, scooped out of the rock through a bed of peat, I found the stratified clay charged with scales. A few hundred yards farther to the west there is a deep, wooded ravine cut through a thick bed of red diluvial clay. The top of the bank directly above is occupied by the ruins of an ancient chapel, and a group of moss-grown tombstones; and in the gorge of this ravine, underlying the little field of graves by about sixty feet, I discovered a still more ancient place of sepulture—that of the ichthyolites. I explored every bank, rock, and ravine on the northern or Cromarty Frith side of the tongue of land, with its terminal point of granitic gneiss, to which I have had such frequent occasion to refer, and then turned to explore the southern, or Moray Frith side, in the rectilinear line of the great valley. And here I was successful on a larger scale. A range of lofty sandstone cliffs, hollowed by the sea, extends for a distance of about two miles between two of the granitic knobs or wedges of the line—the Southern Sutor and the hill of Eathie. And along well nigh the entire length of this range of cliffs, I succeeded in tracing a continuous ichthyolite bed, abounding in remains, and lying far below the Lias, and unconformable to it. I pursued my researches, and in the sides of a romantic precipitous dell, through which the Burn of Eathie—a small, mossy stream—finds its way to the Moray Frith, I again discovered the fish-beds running deep into the interior of the country, with immense strata of a pale yellow sandstone resting over them, and strata of a chocolate red lying below. But their place in the geological scale was still to fix.
I had seen enough to convince me that they form a continuous convex stratum in the sandstone spear-shaft, covering it saddle-wise from side to side, dipping towards the Moray Frith on the south, and to the Cromarty Frith on the north—that, as in a bona fide spear-shaft, the annual ring or layer of growth of one season is overlaid by the annual rings of succeeding seasons, and underlaid by those of preceding ones; so this huge semi-ring of fossiliferous clays and limestones had its underlying semi-ring of Red Sandstone, and its overlying semi-rings of yellow, of red, and of gray sandstone. I knew, besides, that beneath there was a semi-ring of conglomerate, the base of the system; and that, for more than two hundred yards upwards, ring followed ring in unbroken succession—now sandstone, now limestone, now stratified clay. But though intimately acquainted with these lower rocks for more than a hundred fathoms from their base upwards, and with the upper rocks on both sides the ichthyolitic bed for more than a hundred feet, there was an intervening hiatus, whose extent at this period I found it impossible to ascertain. And hence my uncertainty regarding the place of the ichthyolites, seeing that whole formations might be represented by the occurring gap. On the Moray Frith side, where the sections are of huge extent, a doubtful repeat in the strata at one point of junction, and an abrupt fault at another, cuts off the upper series of beds to which the organisms belong, from the lower to which the great conglomerate belongs. On the Cromarty Frith side the sections are mere detached patches, obscured at every point by diluvium and soil; and, in conceiving of the whole as a continuous line, with the Lias a-top and the granite group at the bottom, I was ever reminded of those coast-lines of the ancient geographers, where a few uncertain dots, a few deeper markings, and here and there a blank space or two, showed the blended results of conjecture and discovery—whether they give a Terra Incognita Australia to the one hemisphere, or a North-Western passage to the other. The ichthyolites in a section so doubtful might be regarded as belonging to either the Old or the New Red Sandstone—to the Coal Measures, or to the Mountain Limestone. All was uncertainty.
One remark in the passing: it may teach the young geologist to be cautious in his inferences, and illustrate, besides, those gaps which occur in the geological scale. I had now discovered the ichthyolite beds in five different localities; in one of these—the first discovered—there is no overlying stratum; it seems as if the bed formed the top of the formation: in all the others the overlying stratum is different, and belongs to distant and widely separated ages. We cut in one locality through a peat moss—part of the ruins, perhaps, of one of those forests which covered, about the commencement of the Christian era, well nigh the entire surface of the island, and sheltered the naked inhabitants from the legions of Agricola. We find, as we dig, huge trunks of oak and elm, cones of the Scotch fir, handfuls of hazel-nuts, and bones and horns of the roe and the red deer. The writer, when a boy, found among the peat the horn of a gigantic elk. And, forming the bottom of this recent deposit, and lying conformably to it, we find the ichthyolite beds, with their antique organisms. The remains of oak and elm leaves, and of the spikes and cones of the pine, lie within half a foot of the remains of the Coccosteus and Diplopterus. We dig in another locality through an ancient burying-ground; we pass through a superior stratum of skulls and coffins, and an inferior stratum, barren in organic remains, and then arrive at the stratified clays, with their ichthyolites. In a third locality we find these in junction with the Lias, and underlying its lignites, ammonites, and belemnites, just as we see them underlying, in the other two, the human bones and the peat moss. And in yet a fourth locality we see them overlaid by immense arenaceous beds, that belong evidently, as their mineralogical character testifies, to either the Old or the New Red Sandstone. The convulsions and revolutions of the geological world, like those of the political, are sad confounders of place and station, and bring into close fellowship the high and the low; nor is it safe in either world,—such have been the effects of the disturbing agencies,—to judge of ancient relations by existing neighborhoods, or of original situations by present places of occupancy. "Misery," says Shakspeare, "makes strange bedfellows." The changes and convulsions of the geological world have made strange bedfellows too. I have seen fossils of the Upper Lias and of the Lower Old Red Sandstone washed together by the same wave, out of what might be taken, on a cursory survey, for the same bed, and then mingled with recent shells, algæ, branches of trees, and fragments of wrecks on the same sea-beach.
Years passed, and in 1834 I received my first assistance from without, through the kindness of the Messrs. Anderson, of Inverness, who this year published their Guide to the Highlands and Islands of Scotland—a work which has never received half its due measure of praise. It contains, in a condensed and very pleasing form, the accumulated gleanings, for half a lifetime, of two very superior men, skilled in science, and of highly cultivated taste and literary ability; whose remarks, from their intimate acquaintance with every foot-breadth of country which they describe, invariably exhibit that freshness of actual observation, recorded on the spot, which Gray regarded as "worth whole cart-loads of recollection." But what chiefly interested me in their work was its dissertative appendices—admirable digests of the Natural History, Antiquities, and Geology of the country. The appendix devoted to Geology, consisting of fifty closely printed pages,—abridged in part from the highest geological authorities, and in much greater part the result of original observation,—contains, beyond comparison, the completest description of the rocks, fossils, and formations of the Northern and Western Highlands, which has yet been given to the public in a popular form. I perused it with intense interest, and learned from it, for the first time, of the fossil fishes of Caithness and Gamrie.
There was almost nothing known, at the period, of the oryctology of the older rocks—little, indeed, of that of the Old Red Sandstone, in its proper character as such; and with no such guiding clew as has since been furnished by Agassiz, and the later researches of Mr. Murchison, the writer of the appendix had recorded as his ultimate conclusion, that "the middle schistoze system of Caithness, containing the fossil fish, was intermediate in geological character and position between the Old and New Red Sandstone formations." The ichthyolites of Gamrie he described as resembling those of Caithness; and I at once recognized, in his minute descriptions of both, the fossil fish of Cromarty. The mineralogical accompaniments, too, seemed nearly the same. In Caithness, the animal remains are mixed up in some places with a black bituminous matter like tar. I had but lately found among the beds of the little bay a mass of soft adhesive bitumen, hermetically sealed up in the limestone, which, when broken open, reminded me, from the powerful odor it cast, and which filled for several days the room in which I kept it, of the old Gaulish mummy of which we find so minute account in the Natural History of Goldsmith. The nodules which enclosed the organisms at Gamrie were described as of a sub-crystalline, radiating, fibrous structure. So much was this the case with some of the nodules at Cromarty, that they had often reminded me, when freshly broken, though composed of pure carbonate of lime, of masses of asbestos. The scales and bones of the Caithness ichthyolites were blended, it was stated, with the fragments of a "supposed tortoise nearly allied to trionyx;" one of the ichthyolites, a Dipterus, was characterized by large scales, a double dorsal, and a one-sided tail; the entire lack of shells and zoöphytes was remarked, and the abundance of obscure vegetable impressions. In short, had the accomplished writer of the appendix been briefly describing the beds at Cromarty, instead of those of Caithness and Gamrie, he might have employed the same terms, and remarked the same circumstances—the striated nodules, the mineral tar, the vegetable impressions, the absence of shells and zoöphytes, the large-scaled, and double-finned ichthyolites—the peculiarities of which applied equally to the Dipterus and Diplopterus—and the supposed tortoise, in which I once recognized the Coccosteus. It was much to know, that this doubtful formation—for as doubtful I still regarded it—was of such considerable extent, and occurred in localities so widely separated. I corresponded with the courteous author of the appendix, at that time General Secretary to the Northern Institution for the Promotion of Science and Literature, and Conservator of its Museum; and, forwarding to him duplicates of some of my better specimens, had, as I had anticipated, the generic identity of the Cromarty ichthyolites with those of Caithness and Gamrie fully confirmed.
My narrative is, I am afraid, becoming tedious; but it embodies somewhat more than the mere history of a sort of Robinson Crusoe in Geology, cut off for years from all intercourse with his kind. It contains, also, the history of a formation in its connection with science; and the reader will, I trust, bear with me for a few pages more. Seasons passed; and I received new light from the researches of Agassiz, which, if it did not show me my way more clearly, rendered it at least more interesting, by associating with it one of those wonderful truths, stranger that fictions, which rise ever and anon from the profounder depths of science, and whose use, in their connection with the human intellect, seems to be to stimulate the faculties. I have often had occasion to refer to the one-sided condition of tail characteristic of the ichthyolites of the Old Red Sandstone. It characterizes, says Agassiz, the fish of all the more ancient formations. At one certain point in the descending scale Nature entirely alters her plan in the formation of the tail. All the ichthyolites above are fashioned after one particular type—all below after another and different type. The bibliographer can tell at what periods in the history of letters one character ceased to be employed and another came into use. Black letter, for instance, in our own country, was scarce ever resorted to for purposes of general literature after the reign of James VI.; and in manuscript writing the Italian hand superseded the Saxon about the close of the seventeenth century. Now, is it not truly wonderful to find an analogous change of character in that pictorial history of the past which Geology furnishes? From the first appearance of vertebrated existences to the middle beds of the New Red Sandstone,—a space including the Upper Ludlow rocks, the Old Red Sandstone in all its members, the Mountain Limestone, with the Limestone of Burdie House, the Coal Measures, the Lower New Red, and the Magnesian Limestone,—we find only the ancient or unequally lobed type of tail. In all the formations above, including the Lias, the Oolite, Middle, Upper, and Lower, the Wealden, the Green-Sand, the Chalk, and the Tertiary, we find only the equally-lobed condition of tail. And it is more than probable, that, with the tail, the character of the skeleton also changed; that the more ancient type characterized, throughout, the semi-cartilaginous order of fishes, just as the more modern type characterizes the osseous fishes; and that the upper line of the Magnesian Limestone marks the period at which the order became extinct. Conjecture lacks footing in grappling with a revolution so extensive and so wonderful. Shall I venture to throw out a suggestion on the subject, in connection with another suggestion which has emanated from one of the first of living geologists? Fish, of all existing creatures, seem the most capable of sustaining high degrees of heat, and are to be found in some of the hot springs of Continental Europe, where it is supposed scarce any other animal could live. Now, all the fish of the ancient type are thickly covered by a defensive armor of bone, arranged in plates, bars, or scales, or all the three modes together, as in the Osteolepis and one half its contemporaries. The one-sided tail is united invariably to a strong cuirass. And it has been suggested by Dr. Buckland, that this strong cuirass may have formed a sort of defence against the injurious effects of a highly heated surrounding medium. The suggestion is, of course, based purely on hypothesis. It may be stated, in direct connection with it, however, that in the Lias—the first richly fossiliferous formation overlying that in which the change occurred—we find, for the first time in the geological system, decided indications of a change of seasons. The foot-prints of winter are left impressed amid the lignites of the Cromarty Lias. In a specimen now before me, the alternations of summer heat and winter cold are as distinctly marked in the annual rings as in the pines or larches of our present forests; whereas in the earlier lignites, contemporary with ichthyolites of the ancient type, either no annual rings appear, or the markings, if present, are both faint and unfrequent. Just ere winter began to take its place among the seasons, the fish fitted for living in a highly heated medium disappeared: they were created to inhabit a thermal ocean, and died away as it cooled down. Fish of a similar type may now inhabit the seas of Venus, or even of Jupiter, which, from its enormous bulk, though greatly more distant from the sun than our earth, may still powerfully retain the internal heat.
I still pursued my inquiries, and received a valuable auxiliary in a gentleman from India, Dr. John Malcolmson, of Madras—a member of the London Geological Society, and a man of high scientific attainments and great general knowledge. Above all, I found him to possess, in a remarkable degree, that spirit of research, almost amounting to a passion, which invariably marks the superior man. He had spent month after month under the burning sun of India, amid fever marshes and tiger jungles, acquainting himself with the unexplored geological field which, only a few years ago, that vast continent presented, and in collecting fossils hitherto unnamed and undescribed. He had pursued his inquiries, too, along the coasts of the Red Sea, and far upwards on the banks of the Nile; and now, in returning for a time to his own country, he had brought with him the determination of knowing it thoroughly as a man of science and a geologist. I had the pleasure of first introducing him to the ichthyolites of the Lower Old Red Sandstone, by bringing him to my first-discovered bed, and laying open, by a blow of the hammer, a beautiful Osteolepis. He was much interested in the fossils of my little collection, and at once decided that the formation which contained them could be no representative of the Coal Measures. After ranging over the various beds on both sides the rectilinear ridge, and acquainting himself thoroughly with their organisms, he set out to explore the Lower Old Red Sandstones of Moray and Banff, hitherto deemed peculiarly barren, but whose character too much resembled that of the rocks which he had now ascertained to be so abundant in fossils, not to be held worthy of further examination. He explored the banks of the Spey, and found the ichthyolite beds extensively developed at Dipple, in the middle of an Old Red Sandstone district. He pursued his researches, and traced the formation in ravines and the beds of rivers, from the village of Buckie to near the field of Culloden; he found it exposed in the banks of the Nairn, in the ravines above Cawdor Castle, on the eastern side of the hill of Rait, at Clune, Lethen-bar, and in the vale of Rothes—and in every instance low in the Old Reel Sandstone. The formation hitherto deemed so barren in remains proved one of the richest of them all, if not in tribes and families, at least in individual fossils; and the reader may form some idea of the extent in which it has already been proved fossiliferous, when he remembers that the tract includes as its extremes Orkney, Gamrie, and the north-eastern gorge of the great Caledonian Valley. The ichthyolites were discovered in the latter locality in the quarry of Inches, three miles beyond Inverness, by Mr. George Anderson, the gentleman to whose geological attainments, as one of the authors of the Guide Book, I have lately had occasion to refer.