Hitherto I have dwelt almost exclusively on the fossils of the Lower Old Red Sandstone, and the history of their discovery: I shall now ascend to the organisms of its higher platforms. The system in Scotland, as in the sister kingdom, has its middle and upper groups, and these are in no degree less curious than the inferior group already described, nor do they more resemble the existences of the present time. Does the reader remember the illustration of the pyramid employed in an early chapter—its three parallel bars, and the strange hieroglyphics of the middle bar? Let him now imagine another pyramid, inscribed with the remaining and later history of the system. We read, as before, from the base upwards, but find the broken and half-defaced characters of the second erection descending into the very soil, as in those obelisks of Egypt round which the sands of the desert have been accumulating for ages. Hence a hiatus in our history for future excavators to fill; and it contains many such blanks, every unfossiliferous bar in either pyramid representing a gap in the record. Three distinct formations the group undoubtedly contains—perhaps more; nor will the fact appear strange to the reader who remembers how numerous the formations are that lie over and under it, and that its vast depth of ten thousand feet equals that of the whole secondary system from top to bottom. Eight such formations as the Oolite, or ten such formations as the Chalk, could rest, the one over the other, in the space occupied by a group so enormous. To the evidence of its three distant formations, which is of a very simple character, I shall advert as I go along.
The central or Cornstone division of the system in England is characterized throughout its vast depth by a peculiar family of ichthyolites, which occur in none of the other divisions. I have already had occasion to refer to the Cephalaspis. Four species of this fish have been discovered in the Cornstones of Hereford, Salop, Worcester, Monmouth, and Brecon;[AL] "and as they are always found," says Mr. Murchison, "in the same division of the Old Red System, they have become valuable auxiliaries in enabling the geologist to identify its subdivisions through England and Wales, and also to institute direct comparisons between the different strata of the Old Red Sandstone of England and Scotland." The Cephalaspis is one of the most curious ichthyolites of the system. (See [Plate X.], fig. 1.) Has the reader ever seen a saddler's cutting knife?—a tool with a crescent-shaped blade, and the handle fixed transversely in the centre of its concave side. In general outline the Cephalaspis resembled this tool—the crescent-shaped blade representing the head, the transverse handle the body. We have but to give the handle an angular, instead of a rounded shape, and to press together the pointed horns of the crescent, till they incline towards each other, and the convex, or sharpened edge, is elongated into a semi-ellipse, cut in the line of its shortest diameter, in order to produce the complete form of the Cephalaspis. The head, compared with the body, was of great size—comprising fully one third the creature's entire length. In the centre, and placed closely together, as in many of the flat fish, were the eyes. Some of the specimens show two dorsals, and an anal and caudal fin. The thin and angular body presents a jointed appearance, somewhat like that of a lobster or trilobite. Like the bodies of most of the ichthyolites of the system, it was covered with variously formed scales of bone; the creature's head was cased in strong plates of the same material, the whole upper side lying under one huge buckler—and hence the name Cephalaspis, or buckler-head. In proportion to its strength and size, it seems to have been amply furnished with weapons of defence. Such was the strength and massiveness of its covering, that its remains are found comparatively entire in arenaceous rocks impregnated with iron, in which few other fossils could have survived. Its various species, as they occur in the Welsh and English Cornstones, says Mr. Murchison, seem "not to have been suddenly killed and entombed, but to have been long exposed to submarine agencies, such as the attacks of animals, currents, concretionary action," &c.; and yet, "though much dismembered, the geologist has little difficulty in recognizing even the smallest portions of them." Nor does it seem to have been quite unfurnished with offensive weapons. The sword-fish, with its strong and pointed spear, has been known to perforate the oaken ribs of the firmest built vessels; and, poised and directed by its lesser fins, and impelled by its powerful tail, it may be regarded either as an arrow or javelin flung with tremendous force, or as a knight speeding to the encounter with his lance in rest. Now there are missiles employed in Eastern warfare, which, instead of being pointed like the arrow or javelin, are edged somewhat like the crooked falchion or saddler's cutting-knife, and which are capable of being cast with such force, that they have been known to sever a horse's leg through the bone; and if the sword-fish may be properly compared to an arrow or javelin, the combative powers of the Cephalaspis may be illustrated, it is probable, by a weapon of this kind—the head all around its elliptical margin presenting a sharp edge, like that of a cutting-knife, or falchion. Its impetus, however, must have been comparatively small, for its organs of motion were so: it was a bolt carefully fashioned, but a bolt cast from a feeble bow. But if weak in the assault, it must have been formidable when assailed. "The pointed horns of the crescent," said Agassiz to the writer, "seem to have served a similar purpose with the spear-like wings of the Pterichthys,"—the sole difference consisting in the circumstance, that the spears of the one could be elevated or depressed at pleasure, whereas those of the other were ever fixed in the warlike attitude. And such was the Cephalaspis of the Cornstones—not only the most characteristic, but in England and Wales almost the sole organism of the formation.
[AL] Cephalaspis Lewisii, C. Lloydii, C. Lyellii, and C. rostratus.
Now of this curious ichthyolite we find no trace among the fossils of the Lower Old Red Sandstone. It occurs neither in Orkney nor Cromarty, Caithness nor Gamrie, Nairnshire nor the inferior ichthyolite beds of Moray. Neither in England nor in Scotland is it to be found in the Tilestone formation, or its equivalent. It is common, however, in the Old Red Sandstone of Forfarshire; and it occurs at Balruddery, in the Gray Sandstones which form on both sides the Tay, where the Tilestone formation seems wanting, the apparent base of the system. It is exclusively a medal of the middle empire.
In the last-mentioned locality, in a beautifully wooded dell, known as the Den of Balruddery, the Cephalaspis is found associated with an entire group of other fossils, the recent discovery of Mr. Webster, the proprietor, who, with a zeal through which geological knowledge promises to be materially extended, and at an expense of much labor, has made a collection of all the organisms of the Den yet discovered. These the writer had the pleasure of examining in the company of Mr. Murchison and Dr. Buckland: he was afterwards present when they were examined by Agassiz; and not a single organism of the group could be identified on either occasion, by any member of the party, with those of the lower or upper formations. Even the genera are dissimilar. The fossils of the Lias scarce differ more from those of the Coal Measures, than the fossils of the Middle Old Red Sandstone from the fossils of the formations that rest over and under them. Each formation has its distinct group—a fact so important to the geologist, that he may feel an interest in its further verification through the decision of yet another high authority. The superior Old Red Sandstones of Scotland were first ascertained to be fossiliferous by Professor Fleming, of King's College, Aberdeen,[AM] confessedly one of the first naturalists of the age, and who, to his minute acquaintance with existing forms of being, adds an acquaintance scarcely less minute with those forms of primeval life that no longer exist. He it was who first discovered, in the Upper Old Red Sandstones of Fifeshire, the large scales and plates of that strikingly characteristic ichthyolite of the higher formation, now known as the Holoptychius—of which more anon; and, unquestionably, no one acquainted with his writings, or the character of his mind, can doubt that he examined carefully.
[AM] The Upper Old Red Sandstones of Moray were ascertained to be fossiliferous at nearly the same time by Mr. Martin, of the Anderson Institution, Elgin. There is a mouldering conglomerate precipice termed the Scat-Craig, about four miles to the south of the town, more abundant in remains than perhaps any of the other deposits of the formation yet discovered; and in this precipice Mr. Martin first commenced his labors in the lied Sandstone of the district, and found it a mine of wonders. It is a place of singular interest—a rock of sepulchres; and its teeth, scales, and single bones occur in a state of great entireness; though, ere the deposit was formed, the various ichthyolites whose remains it contains seem to have been broken up, and their fragments scattered. Accumulations of larger and smaller pebbles alternate in the strata; and the bulkier bones and teeth are found invariably among the bulkier pebbles, thus showing that they were operated upon by the same laws of motion which operated on the inorganic contents of the deposit. At a considerably later period the fossils of the upper group were detected in the precipitous and romantic banks of the Findhorn, by Dr. Malcolmson, of Madras, when prosecuting his discoveries of the organisms of the lower formation. He found them, also, though in less abundance, in a splendid section exhibited in the Burn of Lethen, a rivulet of Moray, and yet again in the neighborhood of Altyre. The Rev. Mr. Gordon, of Birnie, and Mr. Robertson, of Inverugie, have been also discoverers in the district. To the geological labors of Mr. Patrick Duff, of Elgin, in the same field, I have already had occasion incidentally to refer. The patient inquiries of this gentleman have been prosecuted for years in all the formations of the province, from the Weald of Linksfield, with its peculiar lacustrine remains—lignites, minute fresh-water shells, and the teeth, spines, and vertebræ of fish and saurians—down to the base of the Old Red Sandstone, with its Coccostei, Dipteri, and Pterichthyes. His acquaintance with the organisms of the Scat-Craig is at once more extensive and minute than that of, perhaps, any other geologist; and his collection of them very valuable, representing, as it does, a formation of much interest, still little known. Mr. Duff is at present engaged on a volume descriptive of the Geology of the province of Moray, a district extensively explored of late years, and abundant in its distinct groups of organisms, but of which general readers have still much to learn; and from no one could they learn more regarding it than from Mr. Duff. It is still only a few months since the Upper Old Red Sandstones of the southern districts of Scotland were found to be fossiliferous; and the writer is chiefly indebted for his acquaintance with their organisms to a tradesman of Berwickshire, Mr. William Stevenson, of Dunse, who, on perusing some of the geological articles which appeared in the Witness newspaper during the course of the last autumn, sent him a parcel of fossils disinterred from out the deep belt of Red Sandstone which leans to the south in that locality, against the grauwacke of the Lammermuirs. Mr. Stevenson had recently discovered them, he stated, near Preston-haugh, about two miles north of Dunse, in a fine section of alternating Sandstone and conglomerate strata that lie unconformably on the grauwacke. They consist of scales and occipital plates of the Holoptychius, with the remains of a bulky, but very imperfectly preserved ichthyodorulite; and the coarse, arenaceous matrices which surround them seem identical with the red gritty Sandstones of the Findhorn and the Scat-Craig,
Now, a few years since, I had the pleasure of introducing Professor Fleming to the Organisms of the Lower Old Red Sandstone, as they occur in the neighborhood of Cromarty; and, notwithstanding his extensive acquaintance with the upper fossils of the system, he found himself, among the lower, in an entirely new field. His knowledge of the one group served but to show him how very different it was from the other. With the organisms of the lower he minutely acquainted himself; he collected specimens from Gamrie, Caithness, and Cromarty, and studied their peculiarities; and yet, on being introduced last year to the discoveries of Mr. Webster at Balruddery, he found his acquaintance with both the upper and lower groups stand him in but the same stead that his first acquired knowledge of the upper group had stood him a few years before. He agreed with Agassiz in pronouncing the group at Balruddery essentially a new group. Add to this evidence the well weighed testimony of Mr. Murchison regarding the three formations which the Old Red Sandstone contains in England, where the entire system is found continuous, the Cornstone overlying the Tilestone, and the Quartzose conglomerate the Cornstone; take into account the fact that, there, each formation has its characteristic fossil, identical with some characteristic fossil of the corresponding formation of Scotland—that the Tilestones of the one, and the lower group of the other, have their Dipterus in common—that the Cornstones of the one, and the middle group of the other, have their Cephalaspis in common—that the Quartzose conglomerate of the one, and the upper group of the other, have their Holoptychius in common; and then say whether the proofs of distinct succeeding formations can be more surely established. If, however, the reader still entertain a doubt, let him consult the singularly instructive section of the entire system, from the Carboniferous Limestone to the Upper Silurian, given by Mr. Murchison, in his Silurian System, (Part II., Plate XXXI., fig. 1,) and he will find the doubt vanish. But to return to the fossils of the Cornstone group.
The characteristic fossil of this deposit, the Cephalaspis, occurs in considerable abundance in Forfarshire, and in a much more entire state than in the Cornstones of England and Wales. The rocks to which it belongs are also developed, though more sparingly, in the northern extremity of Fife, in a line parallel to the southern shores of the Tay. But of all the localities yet known, the Den of Balruddery is that in which the peculiar organisms of the formation may be studied with best effect. The oryctology of the Cornstones of England seems restricted to four species of the Cephalaspis. In Fife, all the organisms of the formation yet discovered are exclusively vegetable—darkened impressions of stems like those of the inferior ichthyolite beds, confusedly mixed with what seem slender and pointed leaflets drawn in black, and numerous circular forms, which have been deemed the remains of the seed-vessels of some unknown sub-aerial plant. "These last occur," says Professor Fleming, the original discoverer, "in the form of circular flat patches, not equalling an inch in diameter, and composed of numerous smaller contiguous circular pieces;" the tout ensemble resembling "what might be expected to result from a compressed berry, such as the bramble or the rasp." In Forfarshire, the remains of the Cephalaspis are found associated with impressions of a different character, though equally obscure—impressions of polished surfaces carved into seeming scales; but in Balruddery alone are the vegetable impressions of the one locality, and the scaly impressions of the other, together with the characteristic ichthyolites of England and Forfarshire, found associated with numerous fossils besides, many of them obscure, but all of them of interest, and all of them new to Geology.
One of the strangest organisms of the formation is a fossil lobster, of such huge proportions, that one of the average sized lobsters, common in our markets, might stretch its entire length across the continuous tail-flap in which the creature terminated. And it is a marked characteristic of the fossil, that the terminal flap should be continuous; in all the existing varieties with which I am acquainted, it is divided into angular sections. The claws nearly resembled those of the common lobster; their outline is similar; there is the same hawk-bill curvature outside, and the inner sides of the pincers are armed with similar teeth-like tubercles. The immense shield which covered the upper part of the creature's body is more angular than in the existing varieties, and resembles, both in form and size, one of those lozenge-shaped shields worn by knights of the middle ages on gala days, rather for ornament than use, and on which the herald still inscribes the armorial bearing of ladies who bear title in their own right. As shown in some of the larger specimens, the length of this gigantic crustacean must have exceeded four feet. Its shelly armor was delicately fretted with the forms of circular or elliptical scales. On all the many plates of which it was composed we see these described by gracefully waved lines, and rising apparently from under one another, row beyond row. They were, however, as much the mere semblance of scales as those relieved by the sculptor on the corslet of a warrior's effigy on a Gothic tomb—mere sculpturings on the surface of the shell. This peculiarity may be regarded as throwing light on the hitherto doubtful impressions of the sandstone of Forfarshire—impressions, as has been said, of smooth surfaces carved into seeming scales. They occur as impressions merely, the sandstone retaining no more of the original substance of the organism than the impressed wax does of the substance of the seal; and the workmen in the quarries in which they occur, finding form without body, and struck by the resemblance which the delicately waved scales bear to the sculptured markings on the wings of cherubs—of all subjects of the chisel the most common—fancifully termed them Seraphim. They have turned out, as was anticipated, to be the detached plates of some such crustacean as the lobster of Balruddery.