This figure represents not inadequately one of the most characteristic plates of the Asterolepis. A very considerable fragment of what seems to be the same plate has been figured by Agassiz from a cast of one of the huge specimens of Professor Asmus ("Old Red," Table 32, Fig. 13); but as no evidence regarding its true place had turned up at the time it was supposed by the naturalist to form part of the opercular covering of the animal. It belonged, however, to a different portion of the head. In almost all the fish that appear at our tables the space which occurs within the arched sweep of the lower jaws is mainly occupied by a complicated osseous mechanism, known to anatomists as the hyoid bone and branchiostegous rays; and which serves both to support the branchial arches and the branchiostegous membrane. Now, in the fish of the Old Red Sandstone, if we except some of the Acanthodians, we find no trace of this piece of mechanism: the arched space is covered over with dermal plates of bone, as a window is filled up with panes. Three plates, resembling very considerably the three divisions of a pointed Gothic window, furnished with a single central mullion, divided atop into two branches, occupied the space in the genera Osteolepis and Diplopterus; and two plates resembling the divisions of a pointed Gothic window, whose single central mullion does not branch atop, filled it up in the genera Holoptychius and Glyptolepis. In the genus Asterolepis this arch-shaped space was occupied, as I have said, by a single plate,—that represented in the wood-cut; and the nail-shaped bone rose on its internal surface along the centre,—the nail-head resting immediately beneath the centre of the arch, and the nail-point bordering on the isthmus below, at which the two shoulder-bones terminated. Now, in all the specimens which I have yet examined, the form and proportions of this plate are such that it can be very nearly inscribed in a semi-circle, of which the length of the nail is the radius. A nail five inches in length must have belonged to a plate ten inches in its longer diameter. I have ascertained further, that this longer diameter was equal to the shorter diameter of the creature's frontal buckler, measured across about two thirds of its entire length from the nape; and that a transverse diameter of ten inches at this point was associated in the buckler with a longitudinal diameter of fourteen inches from the nape to the snout. Thus five inches along the nail represent fourteen inches along the occipital shield. The proportion, however, which the latter bore to the entire body in this genus has still to be determined. The corresponding frontal shield in the Coccosteus was equal to about one-fifth the creature's entire length, and in the Osteolepis and Diplopterus, to nearly one-seventh its length; while the length of the Glyptolepis leptopterus, a fish of the same family as the Asterolepis, was about five and a half times that of its occipital shield. If the Asterolepis was formed in the proportions of the Diplopterus, the ancient individual to which this nail-like bone belonged must have been about eight feet two inches in length; but if moulded, as it more probably was, in the proportions of the Glyptolepis, only six feet five inches. All the Cœlacanths, however, were exceedingly massive in proportion to their length; they were fish built in the square, muscular, thick-set, Dirk-Hatterick and Balfour-of-Burley style; and of the Russian specimens, some of the larger bones must have belonged to individuals of from twice to thrice the length of the Stromness one.
Passing upwards along the strata, step by step, as along a fallen stair, each stratum presenting a nearly perpendicular front, but losing, in the downward slant of the tread, as a carpenter would say, the height attained in the rise, I came, about a quarter of a mile farther to the west, and several hundred feet higher in the formation, upon a fissile dark-colored bed, largely charged with ichthyolites. The fish I found ranged in three layers,—the lower layer consisting almost exclusively of Dipterians, chiefly Osteolepides; the middle layer, of Acanthodians, of the genera Cheiracanthus and Diplacanthus; and the upper layer, of Cephalaspides, mostly of one species, the Coccosteus decipiens. I found exactly the same arrangement in a bed considerably higher in the system, which occurs a full mile farther on,—the Dipterians at the bottom, the Acanthodians in the middle, and the Cephalaspides atop; and was informed by Mr. William Watt, a competent authority in the case, that the arrangement is comparatively a common one in the quarries of Orkney. How account for the phenomenon? How account for the three storeys, and the apportionment of the floors, like those of a great city, each to its own specific class of society? Why should the first floor be occupied by Osteolepides, the second by Cheiracanthi and their congeners, and the third by Coccostei? Was the arrangement an effect of normal differences in the constitutions of the several families, operated upon by some deleterious gas or mineral poison, which, though it eventually destroyed the whole, did not so simultaneously, but consecutively,—the families of weakest constitution first, and the strongest last? Or were they exterminated by some disease, that seized upon the families, not at once, but in succession? Or did they visit the locality serially, as the haddock now visits our coasts in spring, and the herring towards the close of summer; and were then killed off, whether by poison or disease, as they came? These are questions which may never be conclusively answered. It is well, however, to observe, as a curious geological fact, that peculiar arrangement of the fossils by which they are suggested, and to record the various instances in which it occurs. The minerals which I remarked among the schists here as most abundant are a kind of black ironstone, exceedingly tough and hard, occurring in detached masses, and a variety of bright pyrites disseminated among the darker flagstones, either as irregularly-formed, brassy-looking concretions of small size, or spread out on their surfaces in thin leaf-like films, that resemble, in some of the specimens, the icy-foliage with which a severe frost encrusts a window-pane. Still further on I came upon a vein of galena; but a miner's excavation in the solid rock, a little above high-water mark, quite as dark and nearly as narrow as a fox-earth, showed me that it had been known long before, and, as the workings seemed to have been deserted for ages, known to but little purpose. The crystals of ore, small and thinly scattered, are embedded in a matrix of barytes, stromnite, and other kindred minerals, and the thickness of the entire vein is not very considerable. I have since learned, from the "Statistical Account of the Parish of Sandwick," that the workings of the mine penetrate into the rock for about a hundred yards, but that it has been long abandoned, "as a speculation which would not pay."
I observed scattered over the beach, in the neighborhood of the lead mine, considerable quantities of the hard chalk of England; and, judging there could be no deposits of the hard chalk in this neighborhood, I addressed myself on my way back, to a kelp-burner engaged in wrapping up his fire for the night with a thick covering of weed, to ascertain how it had come there. "Ah, master," he replied, "that chalk is all that remains of a fine large English vessel, that was knocked to pieces here a few years ago. She was ballasted with the chalk; and as it is a light sort of stone, the surf has washed it ashore from that low reef in the middle of the tideway where she struck and broke up. Most of the sailors, poor fellows, lie in the old churchyard, beside the broken ruin yonder. It is a deadly shore this to seafaring-men." I had understood that the kelp-trade was wholly at an end in Orkney; and, remarking that the sea-weed which he employed was chiefly of one kind,—the long brown fronds of tang dried in the sun,—I inquired of him to what purpose the substance was now employed, seeing that barilla and the carbonate of soda had supplanted it in the manufacture of soap and glass, and why he was so particular in selecting his weed. "It's some valuable medicine," he said, "that's made of the kelp now: I forget its name; but it's used for bad sores and cancer; and we must be particular in our weed, for it's not every kind of weed that has the medicine in't. There's most of it, we're told, in the leaves of the tang." "Is the name of the drug," I asked, "iodine?" "Ay, that must be just it," he replied,—"iodine; but it doesn't make such a demand for kelp as the glass and the soap." I afterwards learned that the kelp-burner's character of this strip of coast, as peculiarly fatal to the mariner, was borne out by many a sad casualty, too largely charged with the wild and the horrible to be lightly forgotten. The respected Free Church clergyman of Stromness, Mr. Learmonth, informed me that, ere the Disruption, while yet minister of the parish, there were on one sad occasion eight dead bodies carried of a Sabbath morning to his manse door. Some of the incidents connected with these terrible shipwrecks, as related with much graphic effect by a boatman who carried me across the sound, on an exploratory ramble to the island of Hoy, struck me as of a character considerably beyond the reach of the mere dealer in fiction. The master of one hapless vessel, a young man, had brought his wife and only child with him on the voyage destined to terminate so mournfully; and when the vessel first struck, he had rushed down to the cabin to bring them both on deck, as their only chance of safety. He had, however, unthinkingly shut the cabin-door after him; a second tremendous blow, as not unfrequently happens in such cases, so affected the framework of the sides and deck, that the door was jammed fast in its frame. And long ere it could be cut open,—for no human hand could unfasten it,—the vessel had filled to the beams, and neither the master nor his wife and child were ever seen more. In another ship, wrecked within a cable-length of the beach, the mate, a man of Herculean proportions, and a skilful swimmer, stripped and leaped overboard, not doubting his ability to reach the shore. But he had failed to remark what in such circumstances is too often forgotten, that the element on which he flung himself, beaten into foam against the shallows, was, according to Mr. Bremner's shrewd definition, not water, but a mixture of water and air, specifically lighter than the human body; and so at the shore, though so close at hand, he never arrived, disappearing almost at the vessel's side. "The ground was rough," said my informant, "and the sea ran mountains high; and I can scarce tell you how I shuddered on finding, long ere his corpse was thrown up, his two eyes detached from their sockets, staring from a wreath of sea-weed." There is in this last circumstance, horrible enough surely for the wildest German tale ever written, a unique singularity, which removes it beyond the reach of invention.
At my inn I found a pressing invitation awaiting me from the Free Church manse, which I was urged to make my home so long as I remained in that part of the country. A geologist, however, fairly possessed by the enthusiasm without which weak man can accomplish nothing,—whether he be a deer-stalker or mammoth-fancier, or angle for live salmon or dead Pterichthyes,—has a trick of forgetting the right times of dining and taking tea, and of throwing the burden of his bodily requirements on early extempore breakfasts and late suppers; and so reporting myself a man of irregular habits and bad hours, whose movements could not in the least be depended upon, I had to decline the hospitality which would fain have adopted me as its guest, notwithstanding the badness of the character that, in common honesty, I had to certify as my own. Next morning I breakfasted at the manse, and was introduced by Mr. Learmonth to two gentlemen of the place, who had been kindly invited to meet with me, and who, from their acquaintance with the geology of the district enabled me to make the best use of my time, by cutting direct on those cliffs and quarries in the neighborhood in which organic remains had been detected, instead of wearily re-discovering them for myself. There is a small but interesting museum in Stromness, rich in the fossils of the locality; and I began the geologic business of the day by devoting an hour to the examination of its organisms, chiefly ichthyolites. I saw among them several good specimens of the genus Pterichthys, and of what is elsewhere one of the rarer genera of the Dipterians,—the Diplopterus. A well-marked individual of the latter genus had, I found, been misnamed Dipterus by some geological visitor who had recently come the way,—a mistake which, as in both ichthyolites the fins are similarly placed, occasionally occurs, but which may be easily avoided, when the specimens are in a tolerable state of preservation, by taking note of a few well-marked characteristics by which the genera are distinguished. In both Dipterus and Diplopterus the bright enamel of the scales was thickly punctulated by microscopic points,—the exterior terminations of funnel-shaped openings, that communicated between the surface and the cells of the middle table of the scale; but the form of the scales themselves was different,—that of the Dipterus being nearly circular, and that of the Diplopterus, save on the dorsal ridge, rhomboidal. Again, the lateral line of the Diplopterus was a raised line, running as a ridge along the scales; whereas that of the Dipterus was a depressed one, existing as a furrow. Their heads, too, were covered by an entirely dissimilar arrangement of plates. The rounded snout-plate of the Diplopterus was suddenly contracted to nearly one-half its breadth by two semi-circular inflections, which formed the orbits of the eyes; full in the centre, a little above these, a minute, lozenge-shaped plate seemed as if inlaid in the larger one, the analogue, apparently, of the anterior frontal; and over all there expanded a broad plate, the superior frontal, half divided vertically by a line drawn downwards from the nape, which, however, stopped short in the middle; and fretted transversely by two small but deeply-indented rectangular marks, which, crossing from the central to two lateral plates, assumed the semblance of connecting pins. The snout of the Dipterus was less round; it bore no mark of the eye-orbits; and the frontal buckler, broader in proportion to its length than that of the Diplopterus, consisted of many more plates. I may here mention that the frontal buckler of Diplopterus has not yet been figured nor described; whereas that of Dipterus, though unknown as such, has been given to the world as the occipital covering of a supposed Cephalaspian,—the Polyphractus. Polyphractus is, however, in reality a synonym for Dipterus,—the one name being derived from a peculiarity of the animal's fins: the other, from the great number of its occipital plates. There is no science founded on mere observation that can be altogether free, in its earlier stages, from mistakes of this character,—mistakes to which the palæontologist, however skilful, is peculiarly liable. The teeth of the two genera were essentially different. Those of the Dipterus, exclusively palatal, were blunt and squat, and ranged in two rectangular patches;[22] while those of the Diplopterus bristled along its jaws and were slender and sharp. Their tails, too, though both heterocercal, were diverse in their type. In each, an angular strip of gradually-diminishing scales,—a prolongation of the scaly coat which protected the body, and which covered here a prolongation of the vertebral column,—ran on to the extreme termination of the upper lobe; but there was in the Diplopterus a greatly larger development of fin on the superior or dorsal side of the scaly strip than on that of the Dipterus. If the caudal fin of the Osteolepis be divided longitudinally into six equal parts, it will be found that one of these occurs on the upper side of the vertebral prolongation, and five on the under; in the caudal fin of the Diplopterus so divided, rather more than two parts will be found to occur on the upper side, and rather less than four on the under; while in the caudal fin of the Dipterus the development seems to have been restricted to the under side exclusively; at least, in none of the many individuals which I have examined have I found any trace of caudal rays on the upper side. These are minute and somewhat trivial particulars; but the geologist may find them of use; and the non-geologist may be disposed to extend to them some little degree of tolerance, when he considers that they distinguished two largely developed genera of animals, to which the Author of all did not deem it unworthy his wisdom to impart, in the act of creation, certain marked points of resemblance, and other certain points of dissimilarity.
From the Museum, accompanied by one of the gentlemen to whom Mr. Learmonth had introduced me at breakfast, and who obligingly undertook to act as my guide on the occasion, I set out to visit a remarkable stack on the sea-coast, about four miles north and west of Stromness. We scaled together the steep granitic hill immediately over the town, and then cut on the stack, straight as the bird flies, across a trackless common, bare and stony, and miserably pared by the flaughter spade. The landed proprietors in this part of the mainland are very numerous, and their properties small; and there are vast breadths of undivided common that encircle their little estates, as the Atlantic encircles the Orkneys. But the state in which I found the unappropriated parts of the district had in no degree the effect of making me an opponent of appropriation or the landholders. Our country, had it been left as a whole to all its people, as the Communist desiderates, would ere now be of exceedingly little value to any portion of them. The soil of the Orkney commons has been so repeatedly pared off and carried away for fuel, that there are now wide tracts on which there is no more soil to pare, and which present, for the original covering of peaty mould, a continuous surface of pale boulder-clay, here and there mottled by detached tufts of scraggy heath, and here and there roughened by projections of the underlying rock. All is unredeemable barrenness. On the other hand, wherever a bit of private property appears, though in the immediate neighborhood of these ruined wastes, the surface is swarded over, and the soil is the better, not the worse, for the services which it has rendered to man in the past. Whatever the Chartist and the Leveller may think of the matter, it is, I find, virtually on behalf of the many that the soil has been appropriated by the few. After passing from off the tract of moor which overlies the granitic axis of the district, to a tract equally moory which spreads over the gray flagstones, I marked, more especially in the hollows and ravines, where minute springs ooze from the rock, vast quantities of bog-iron embedded in the soil, and presenting greatly the appearance of the scoria of a smith's forge. The apparent scoria here is simply a reproduction of the iron of the underlying flagstones, transferred, through the agency of water, to that stratum of vegetable mould and boulder-clay which represents the recent period.
I found the stack which I had been brought to see forming the picturesque centre of a bold tract of rock scenery. It stands out from the land as a tall insulated tower, about two hundred feet in height, sorely worn at its base by the breakers that ceaselessly fret against its sides, but considerably broader atop, where it bears a flat cover of sward on the same level with the tops of the precipices which in the lapse of ages have receded from around it. Like the sward-crested hammock left by a party of laborers, to mark the depth to which they have cut in removing a bank or digging a pond, it remains to indicate how the attrition of the surf has told upon the iron-bound coast; demonstrating that lines of precipices hard as iron, and of giddy elevation, are in full retreat before the dogged perseverance of an assailant that, though baffled in each single attack, ever returns to the charge, and gains by an aggregation of infinitesimals,—the result of the whole. From the edge of a steep promontory that commands an inflection of the coast, and of the wall of rock which sweeps round it, I watched for a few seconds the sea,—greatly heightened at the time by the setting in of the flood-tide,—as it broke, surge after surge, against the base of the tall dark precipices; and marked how it accomplished its work of disintegration. The flagstone deposit here abounds in vertical cracks and flaws; and in the line of each of the many fissures which these form the waves have opened up a cave; so that for hundreds of yards together the precipices seem as if founded on arch-divided piers, and remind one of those ancient prints or drawings of Old London Bridge in which a range of tall sombre buildings is represented as rising high over a line of arches; or of rows of lofty houses in those cities of southern Europe in which the dwellings fronting the streets are perforated beneath by lines of squat piazzas, and present above a dingy and windowless breadth of wall. In course of time the piers attenuate and give way; the undermined precipices topple down, parting from the solid mass behind in those vertical lines by which they are traversed at nearly right angles with their line of stratification; the perpendicular front which they had covered comes to be presented, in consequence, to the sea; its faults and cracks gradually widen into caves, as those of the fallen front had gradually widened at an earlier period; in the lapse of centuries, it too, resigning its place, topples over headlong, an undermined mass; the surge dashes white and furious where the dense rock had rested before; and thus, in its slow but irresistible march, the sea gains upon the land. In the peculiar disposition and character of the prevailing strata of Orkney, as certainly as in the power of the tides which sweep athwart its coasts, and the wide extent of sea which, stretching around it, gives the waves scope to gather bulk and momentum, may be found the secret of the extraordinary height to which the surf sometimes rises against its walls of rock. During the fiercer tempests, masses of foam shoot upwards against the precipices, like inverted cataracts, fully two hundred feet over the ordinary tide-level, and, washing away the looser soil from their summits, leaves in its place patches of slaty gravel, resembling that of a common sea-beach. Rocks less perpendicular, however great the violence of the wind and sea, would fail to project upwards bodies of surf to a height so extraordinary. But the low angle at which the strata lie, and the rectangularity maintained in relation to their line of bed by the fissures which traverse them, give to the Orkney precipices,—remarkable for their perpendicularity and their mural aspect,—exactly the angle against which the waves, as broken masses of foam, beat up to their greatest possible altitude. On a tract of iron-bound coast that skirts the entrance of the Cromarty Frith I have seen the surf rise, during violent gales from the north-west especially, against one rectangular rock, known as the White Rock, fully an hundred feet; while against scarcely any of the other precipices, more sloping, though equally exposed, did it rise more than half that height.