Now, in a geological point of view, this angle may be regarded as a vast pyramid, rising perpendicularly from the basis furnished by the primary rocks of the latter county, and presenting newer beds and strata as we ascend, until we reach the apex. The line from south to north in the angle—from Morvheim to Dunnet-head—corresponds to the line of ascent from the top to the bottom of the pyramid. The first bed, reckoning from the base upwards,—the ground tier of the masonry, if I may so speak,—is the great conglomerate. It runs along the line of boundary from sea to sea,—from the Ord of Caithness on the east, to Portskerry on the north; and rises, as it approaches the primary hills of Sutherland, into a lofty mountain chain of bold and serrated outline, which attains its greatest elevation in the hill of Morvheim. This great conglomerate bed, the base of the system, is represented in the Cromarty section, under the Northern Sutor, by a bed two hundred and fifteen feet in thickness. The second tier of masonry in the pyramid, and which also runs in a nearly parallel line from sea to sea, is composed mostly of a coarse red and yellowish sandstone, with here and there beds of pebbles enclosed, and here and there deposits of green earth and red marl. It has its representative in the Cromarty section, in a bed of red and yellow arenaceous stone, one hundred and fourteen feet six inches in thickness. These two inferior beds possess but one character,—they are composed of the same materials, with merely this difference, that the rocks which have been broken into pebbles for the construction of the one, have been ground into sand for the composition of the other. Directly over them, the middle portion of the pyramid is occupied by an enormous deposit of dark-colored bituminous schist, slightly micaceous, calcareous, or semi-calcareous,—here and there interlaced with veins of carbonate of lime,—here and there compact and highly siliceous,—and bearing in many places a mineralogical character difficult to be distinguished from that at one time deemed peculiar to the harder grauwacke schists. The Caithness flagstones, so extensively employed in paving the footways of our larger towns, are furnished by this immense middle tier or belt, and represent its general appearance. From its lowest to its highest beds it is charged with fossil fish and obscure vegetable impressions; and we find it represented in the Cromarty section by alternating bands of sandstones, stratified clays, and bituminous and nodular limestones, which form altogether a bed three hundred and fifty-five feet in thickness; nor does this bed lack its organisms, animal and vegetable, generically identical with those of Caithness. The apex of the pyramid is formed of red mouldering sandstones and mottled marls, which exhibit their uppermost strata high over the eddies of the Pentland Frith, in the huge precipices of Dunnet-head, and which are partially represented in the Cromarty section by an unfossiliferous sandstone bed of unascertained thickness; but which can be traced for about eighty feet from the upper limestones and stratified clays of the middle member, until lost in overlying beds of sand and shingle.
I am particular, at the risk, I am afraid, of being tedious, in thus describing the Geology of this northern county, and of the Cromarty section, which represents and elucidates it. They illustrate more than the formations of two insulated districts: they represent also a vast period of time in the history of the globe. The pyramid, with its three huge bars, its foundations of granitic rock, its base of red conglomerate, its central band of dark-colored schist, and its lighter tinted apex of sandstone, is inscribed from bottom to top, like an Egyptian obelisk, with a historical record. The upper and lower sections treat of tempests and currents—the middle is "written within and without" with wonderful narratives of animal life; and yet the whole, taken together, comprises but an earlier portion of that chronicle of existences and events furnished by the Old Red Sandstone. It is, however, with this earlier portion that my acquaintance is most minute.
My first statement regarding it must be much the reverse of the borrowed one with which this chapter begins. The fossils are remarkably numerous, and in a state of high preservation. I have a hundred solid proofs by which to establish the truth of the assertion, within less than a yard of me. Half my closet walls are covered with the peculiar fossils of the Lower Old Red Sandstone; and certainly a stranger assemblage of forms have rarely been grouped together;—creatures whose very type is lost, fantastic and uncouth, and which puzzle the naturalist to assign them even their class;—boat-like animals, furnished with oars and a rudder;—fish plated over, like the tortoise, above and below, with a strong armor of bone, and furnished with but one solitary rudder-like fin; other fish less equivocal in their form, but with the membranes of their fins thickly covered with scales;—creatures bristling over with thorns; others glistening in an enamelled coat, as if beautifully japanned—the tail, in every instance among the less equivocal shapes, formed not equally, as in existing fish, on each side the central vertebral column, but chiefly on the lower side—the column sending out its diminished vertebræ to the extreme termination of the fin. All the forms testify of a remote antiquity—of a period whose "fashions have passed away." The figures on a Chinese vase or an Egyptian obelisk are scarce more unlike what now exists in nature, than the fossils of the Lower Old Red Sandstone.
Geology, of all the sciences, addresses itself most powerfully to the imagination, and hence one main cause of the interest which it excites. Ere setting ourselves minutely to examine the peculiarities of these creatures, it would be perhaps well that the reader should attempt realizing the place of their existence, and relatively the time—not of course with regard to dates and eras, for the geologist has none to reckon by, but with respect to formations. They were the denizens of the same portion of the globe which we ourselves inhabit, regarded not as a tract of country, but as a piece of ocean crossed by the same geographical lines of latitude and longitude. Their present place of sepulture in some localities, had there been no denudation, would have been raised high over the tops of our loftiest hills—at least a hundred feet over the conglomerates which form the summit of Morvheim, and more than a thousand feet over the snow-capped Ben Wyvis. Geology has still greater wonders. I have seen belemnites of the Oolite—comparatively a modern formation—which had been dug out of the sides of the Himalaya mountains, seventeen thousand feet over the level of the sea. But let us strive to carry our minds back, not to the place of sepulture of these creatures, high in the rocks,—though that I shall afterwards attempt minutely to describe,—but to the place in which they lived, long ere the sauroid fishes of Burdie House had begun to exist, or the corallines of the mountain limestone had spread out their multitudinous arms in a sea gradually shallowing, and out of which the land had already partially emerged.
A continuous ocean spreads over the space now occupied by the British islands: in the tract covered by the green fields and brown moors of our own country, the bottom, for a hundred yards downwards, is composed of the debris of rolled pebbles and coarse sand intermingled, long since consolidated into the lower member of the Old Red Sandstone; the upper surface is composed of banks of sand, mud, and clay; and the sea, swarming with animal life, flows over all. My present object is to describe the inhabitants of that sea.
Of these, the greater part yet discovered have been named by Agassiz, the highest authority as an ichthyologist in Europe or the world, and in whom the scarcely more celebrated Cuvier recognized a naturalist in every respect worthy to succeed him. The comparative amount of the labors of these two great men in fossil ichthyology, and the amazing acceleration which has taken place within the last few years in the progress of geological science, are illustrated together, and that very strikingly, by the following interesting fact—a fact derived directly from Agassiz himself, and which must be new to the great bulk of my readers. When Cuvier closed his researches in this department, he had named and described, for the guidance of the geologist, ninety-two distinct species of fossil fish; nor was it then known that the entire geological scale, from the Upper Tertiary to the Grauwacke inclusive, contained more. Agassiz commenced his labors; and, in a period of time little exceeding fourteen years, he has raised the number of species from ninety-two to sixteen hundred. And this number, great as it is, is receiving accessions almost every day. In his late visit to Scotland, he found eleven new species, and one new genus, in the collection of Lady Gumming of Altyre, all from the upper beds of that lower member of the Old Red Sandstone represented by the dark-colored schists and inferior sandstones of Caithness. He found forty-two new species more in a single collection in Ireland, furnished by the Mountain Limestone of Armagh.
Some of my humbler readers may possibly be repelled by his names; they are, like all names in science, unfamiliar in their respect to mere English readers, just because they are names not for England alone, but for England and the world. I am assured, however, that they are all composed of very good Greek, and picturesquely descriptive of some peculiarity in the fossils they designate. One of his ichthyolites, with a thorn or spine in each fin, bears the name of Acanthodes, or thorn-like; another with a similar mechanism of spines attached to the upper part of the body, and in which the pectoral or hand-fins are involved, has been designated the Cheiracanthus, or thorn-hand; a third covered with curiously-fretted scales, has been named the Glyptolepis, or carved-scale; and a fourth, roughened over with berry-like tubercles, that rise from strong osseous plates, is known as the Coccosteus, or berry-on-bone. And such has been his principle of nomenclature. The name is a condensed description. But though all his names mean something, they cannot mean a great deal; and as learned words repel unlearned readers, I shall just take the liberty of reminding mine of the humbler class, that there is no legitimate connection between Geology and the dead languages. The existences of the Old Red Sandstone had lived for ages, and had been dead for myriads of ages, ere there was Greek enough in the world to furnish them with names. There is no working-man, if he be a person of intelligence and information, however unlearned, in the vulgar acceptation of the phrase, who may not derive as much pleasure and enlargement of idea from the study of Geology, and acquaint himself as minutely with its truths, as if possessed of all the learning of Bentley.