Some Brachiopods are attached to stones, like oysters; in others the larger valve is perforated, and a sinewy kind of foot, passing through the aperture, serves as a holdfast to the animal.
Most of these helpless creatures did not survive the Carboniferous period, but the Terebratulæ, which still have their representatives in the modern seas, existed even then, so that their genealogical tree may justly boast of a very high antiquity.
The fishes, of which the oldest known specimen has been found in the Upper Silurian group (Lower Ludlow), become more frequent in the next following Devonian epoch, where they appear in a variety of wonderful forms, widely different from those of the present day. While in nearly all the existing fishes the scales are flexible, and generally either of a more or less circular form (cycloid), as in the salmon, herring, roach, &c., or provided with comb-like teeth, projecting from the posterior margin (ctenoid), as in the sole or perch, the fishes of the Devonian, Permian, and Carboniferous periods were decked with hard bony scales, either covered with a brilliant enamel, as in our sturgeons (ganoid), and arranged in regular rows, the posterior edges of each slightly overlapping the anterior ones of the next, or irregular in their shape, and separately imbedded in the skin (placoid), as in the sharks and rays of the present day. With rare exceptions their skeleton was cartilaginous; but the less perfect ossification of their bones was amply compensated by the solid texture of their enamelled coat of mail, which afforded them a better protection against enemies and injuries from without than is possessed by any bony-skeletoned fish of our days. They were, in fact, comparatively as well prepared for a hostile encounter as an ancient knight in armour, or as one of our modern iron-plated war ships. One of the most remarkable of these mail-clad Ganoids was the Pterichthys Milleri of the Old Red Sandstone of Scotland. In most of our fishes the pectoral fins are but weakly developed; here they constitute real arms, moved by strong muscles, and resembling the paddle of the turtle.
PTERICHTHYS MILLERI—RESTORED. (OLD RED SANDSTONE OF SCOTLAND.)
Besides the enormous masses of vegetable matter which distinguish the Carboniferous period, the stone beds of that formation likewise contain a vast number of animal remains. From the reptiles and fishes down to the corals and sponges, many new families, genera, and species crowd upon the scene, while many of the previously flourishing races have either entirely disappeared, or are evidently declining. Thus the Trilobites, formerly so numerous, are reduced to a few species in the Carboniferous period, and vanish towards its close.
In 1847 the oldest known reptiles were found in the coal field of Saarbrück, in the centre of spheroidal concretions of clay iron-stone, which not only faithfully preserved the skulls, teeth, and the greater portions of the skeletons of these ancient lizards, but even a large part of their skin, consisting of long, narrow, wedge-shaped, tile-like, and horny scales, arranged in rows. What a lesson for human pride! The pyramid of the Pharaoh Cheops, reared by the labour of thousands of slaves, has been unable to preserve his remains from spoliation even for the short space of a few thousand years, and here a vile reptile has been safely imbedded in a sarcophagus of iron ore during the vast period of many geological formations.
Still more recently (1854) other wonders have been brought to light in the clay iron-stone of Saarbrück. The wing of a grasshopper, with all its nerves as distinctly marked as if the creature had been hopping about but yesterday, some white ants or termites (now confined to the warmer regions of the globe), a beetle, and several cockroaches, give us some idea of the insects that lived at the time when our coal-beds were forming. Another highly interesting circumstance, relating to the fossils of that distant period, is that in several of them the patterns of their colouring have been preserved. Thus Terebratula hastata often retains the marks of the original coloured stripes which ornamented the living shell. In Aviculopecten sublobatus dark stripes alternate with a light ground, and wavy blotches are displayed in Pleurotomaria carinata. From these facts Professor Forbes inferred that the depth of the seas in which the Mountain Limestone was formed did not exceed fifty fathoms, as in the existing seas the Testacea, which have shells and well-defined patterns, rarely inhabit a greater depth.
The Magnesian Limestone or Permian group is remarkable chiefly for the vast number of fishes that have been found in some of its members, such as the marl slate of Durham and the Kupferschiefer, or copper slate, of Thuringia. From the curved form of their impressions, as if they had been spasmodically contracted, the fossil fish of the latter locality are supposed to have perished by a sudden death before they sank down into the mud in which they were entombed. Probably the copper which impregnates the stratum in which they occur is connected with this phenomenon. Mighty volcanic eruptions corrupted the water with poisonous metallic salts, and destroyed in a short time whole legions of its finny inhabitants.
