Here, then, in this class of animal life, we find that what is defective in the internal structure—if it be a defect—is completely supplied in the outer appendages, whereby the fishes which have the softest bodies are possessed of hard, horny skins, coated with enamel. Their bones are thus all on the surface, sometimes in the form of scales; sometimes assuming the shape of spines and tubercles; now in small, now in large plates; and often disposed in the most singular and grotesque arrangements, as in the genus coccosteus, or the osteolepis, whose entire skull consisted of shining naked bone, and in the cheiracanthus, a creature possessed of fins scaled and enameled all over.
The Swiss naturalist, accordingly, in adopting a new principle of classification, so essential in the case of the fossils of the old red sandstone, has made the scales and external organs the groundwork of his system. The classification of Cuvier and the older naturalists proceeds mainly upon the character and disposition of the fins. Hence the order of the Acanthopterygii, or thorny-finned; and the Malacopterygii, or the soft finned order.—The classification of M. Agassiz, proceeding upon the characters of the scales and plates, has given rise to the following orders, namely, the Placoid, or broad-plated scale; the Ganoid, or the shining-scale; the Ctenoid, or comb-shaped scale; and the Cycloid, or marginated scale. Upon the simple basis of these four orders, he has constructed his system and composed his “Poissons Fossiles,” the standard authority in fossil ichthyology, and elaborate monument of his learning and genius.
The relations, as well as distinguishing peculiarities, of the fishes of the old red, are thus described by Agassiz:—“Of the Placoidian order,” he says, “the genera ctenacanthus, onchus, ctenoptychius, and ptychacanthus, are provided with spinous rays to the dorsal fins, resembling the gigantic ichthyodorulites of the carboniferous and jurassic formations, but differing in their less considerable size; they are distinguished among themselves by the forms and ornaments of their rays. In the order of ganoid fishes, the genera acanthodes, diplacanthus, cheiracanthus, and cheirolepis present themselves at first sight as a separate group; for although covered, like the others, with enameled scales, these are so small, that they impart to the skin the appearance of shagreen. The manner in which the fins are sustained by spinous rays, or the absence of these rays, and the position of the fins themselves, have served as characters in the establishing of these genera. The genera pterichthys, coccosteus, and cephalaspis, form a second group exceedingly curious: the considerable development of the head, its size, large plates which cover it, and which likewise extend over the greater portion of the trunk, and the movable appendages in the form of a wing, placed on the side of the head, give to them the most remarkable appearance. It is these peculiarities, indeed, which caused the class to which these genera belong for a long time to be misunderstood. The large bony and granulated plates of coccosteus, led to their being considered as belonging to trionyx: and it will be sufficient excuse for this error to call to recollection, that the greatest anatomist of our age had sanctioned this approximation. The form of the disc of the head of the cephalaspides, which has the appearance of a large crescent, and their more numerous, but very elevated scales, resembling the transverse articulations of the body, explain how it was possible to see in these fishes the trilobites of a particular genus. Lastly, the winged appendages of the sides of the head of pterichthys, as movable as fins, have easily given rise to the variety of opinions concerning the true affinity of these singular creatures, and has caused them to be taken at one time for gigantic coleoptera, at another for crustacea, or small marine tortoises; so little do the types of the classes appear fixed in certain respects at these remote times. Another singularity of these genera is the association to the bony plates of the head of a vertebral appendage, which is far from having acquired the same solidity; but appears, on the contrary, to have remained fibro-cartilaginous during the whole life of the animal—resembling in this respect the skeleton of the sturgeon.
“It would be difficult to find among recent fishes, types presenting any direct analogy with the genera pterichthys, coccosteus, and cephalaspis; it is only from afar that they can be compared to some abnormal genera of our epoch.... The analogy which they offer, on the one hand, in form with the dorsal cord of the embryo of fishes, together with the inferior position of their mouth, which is equally met with in the embryos; and on the other hand, the distant resemblance of these fishes to certain types of reptiles, present the most curious assemblage of characters that can possibly be conceived. A third group of fishes belonging to this formation, comprises those genera whose vertical fins are double on the back and under the tail, and which approach very near to the caudal. These are the genera dipterus, osteolepis, diplopterus, and glyptolepis, which differ from one another by the form of their scales and their dentition. And lastly, it seems necessary to regard as a fourth group of this order, the genera which are characterized by large conical teeth, situated on the margin of the jaws, between which are alternately smaller, and indeed very small ones, in the form of a brush. Such are the genera holoptychius and platygnathus, and the genus recently established by Mr. Owen under the name of dendrodus, and respecting which this learned anatomist has given some exceedingly interesting microscopical details.”
The philosopher here, in these views as to the primitive diversity of the ichthyoid types in the old red sandstone, adduces such illustrations and others not quoted, as subversive of the theory of the successive transformation of species, and of the descent of organized beings now living, from a small number of primitive forms. He asserts the doctrine that the characteristic fossils of each well-marked geological epoch are the representatives of so many distinct creations, and affirms that he has demonstrated by a vast number of species that the presumed identifications are exaggerated approximations of species, resembling one another, but nevertheless specifically distinct. M. Agassiz introduces the same doctrine in his latest great work, the “Iconographie,” wherein he goes the length of saying, that, even when species are, so far as the eye can judge, identical, they may not be so—that there may exist species so nearly allied, as to render it impossible to distinguish them—and reiterates that each geological epoch is characterized by a distinct system of created beings (the results of a new intervention of creative power), including not only different species from those of the preceding system, but also new types. Under his safe guidance we have glanced at the earliest groups and forms of life upon the globe, and have seen the simple structures of the beginning succeeded by higher, if not more perfect or more complex, at least by creatures capable of a wider range of action and enjoyment. The deductions and sweeping inferences of geologists may be often vague and uncertain; but a science, whose direct aim is to decipher the records of the past and compare the successive types of animal life upon the earth, deals with important objects, and leads to salutary trains of thought, keeping continually before the view the Fountain-Head of all being; and adding a new proof to the sublime doctrine, that Man who is privileged so to range through creation and time will himself outlive a term of existence, measurable by a few points of space and a few moments of eternity.
Pamphractus Andersoni.
CHAPTER VI.
TRAP ROCKS.
We do not select the rocks which form the title of this chapter from mere arbitrary choice, or because they are geographically connected with the district under review, but because they are immediately the next in the chronological order of our course. The Sidlaws and Ochils have their position as precisely determined in relation to time as to space, for difficult often as it may be to fix the sequence of events within the historical era, there is generally no lack of evidence by which to ascertain, in the far remoter times, when the several strata and the igneous masses assumed their respective places on the surface of the globe. The proofs here are of a cumulative character, and irresistibly conclusive. The animate and inanimate things of earth, the living and the dead, are both admissible witnesses in the question, and their testimony is alike unexceptionable. The saurian seas had been disturbed upon the upheaval of their beds; these with their organic contents were elevated by the irruption of plutonic matter, and in their altered position gave a bolder contour and additional bulk to the primitive land. New accumulations were forming during the devonian period in the waters still mightily agitated along the lines of disturbance; new races of scale-enameled creatures occupied their depths, and huge crustaceans anchored among their rocky shallows. The interior regions again let loose their giant forces, and these chains of hills rose above the surface, disrupting and heaving into day the various deposits of the old red sandstone. Hence the formation of the one set of rocks preceded, in the order of time, the elevation of the other: not an islet appeared over all these parts while the sedimentary strata were accumulating beneath: plants and trees covered the flanks of the Grampians, algæ and fuci abounded in the waters, and myriads of fishes sported amid their luxuriance; but as yet there was no basin of the Tay, no fertile Carse of Gowrie, no kingdom of Fife stored to repletion with its precious metals of iron, lime, and coal. The Sidlaws and Ochils, therefore, become invested with even a romantic interest, when we thus view them in their geological relations—their age precisely defined—and themselves, flinty and weather-stained, the memorials of the vast convulsions and changes of nature. They mark the outgoing of a period comparatively barren of vegetable life, and the incoming of the exuberant products of the carboniferous epoch.