།、、ཙངང conglomerate; this is succeeded by coarse red and yellow sandstones alternating with green and red marls; upon this lie very thick beds of calcareous, micaceous and bituminous schists, loaded with fossil fishes, and containing impressions of plants. The middle group, corresponding to the Cornstone of England, consists of a bluish gray sandstone and beds of friable stratified clay, while the contemporaneous English beds are principally red and green marls. The upper part of the formation presents beds of sandstone alternating with limestone barren of fossils, and containing masses of exceedingly hard chert. 200. The subdivisions of the Devonian System, in Scotland and England are local, but serve as standards of comparison for the rocks of the same system in other parts of the world. They have been investigated as developed in Ireland, Belgium, and Russia; and are known to exist in South America and Australia. In North America, their essential characteristics, mineral and organic, have been shown to be identical with those of the Scottish series; they are developed in the States of Pennsylvania and New York, and west of the Alleghanies, in some places from one thousand to fifteen hundred feet thick. 201. The organic remains of this period are very peculiar, consisting of corals, molluscous and radiated animals, not differing widely from those of the Silurian system; but the vertebrate animals are here represented by a large number of species of singular fishes, in many instances so well preserved as to exhibit their outlines distinctly. These fossil fishes are sometimes denominated ichthyolites, (ichthus a fish; lithos a stone,) and although traces of them are discerned in the Silurian rocks, their abundance and perfect pe class no preservation in the Devonian system have rendered them. Fig. 98. exception of the sturgeon, shark, and bony pike, the vertebral column terminates at the point, from which the caudal fin is given off equally above and below, constituting a homocercal tail, as exhibited in figure 99. All the fishes of the Paleozoic period had unequally bilobate or heterocercal tails. Fig. 99. 202. The Cephalaspis was a fish, whose most striking feature was an enormous shield forming the head; hence the name (kephale, head; aspis, shield.) This crescentshaped buckler gave the animal the appearance of a trilobite, and the first discovered specimens were supposed to be crustaceous. The body was comparatively small, elon gated, terminating in a heterocercal tail. It was furnished with fins; the dorsal fins are usually conspicuous. The body and head were covered with bony, enamelled scales. This fish seems not to have attained a large size; specimens are about seven inches in length. Fig. 100. 203. Another equally singular genus was the Pterichthys-the winged fish (Pteron, a wing; ichthus, a fish,) characterized by its two wing-like lateral appendages, which were its weapons of defense, and may have assisted in locomotion. Its body was protected by strong, bony, enamelled plates; its head was small, body flat, and its tail thickly covered with scales. It did not exceed a foot in Cephalaspis Lyellii. length. Fig. 101. Pterichthys Cornutus. Fig. 102. Coccosteus. 204. The Coccosteus resembles the Pterichthys in general structure and covering, but was destitute of wing-like appendages. It derives its name from the berry-like tubercles which stud its enamelled bony plates (kokkos a berry; osteon, a bone.) Its head was large, covered with several plates, and attached to the body by small articulating surfaces. The upper part of the body was covered with one plate and the lower part with four. The tail was much longer than the body and furnished with two fins. Many other genera belonging to this period have been described, among which may be named the Holoptychius, whose bony plates are more numerous and smaller; and the Osteolepis, in which the bony plates become scales and the figure of the animal approximates that of existing fishes. Some of these attained a large size. 205. The brachiopodous genera of shells, Terebratula, Orthis, Spirifer &c., except the Pentamerus, of the Silurian period are extended into that of the Old Red Sandstone. The corals Cyathophyllum and Favosites also are common to the two periods. The Favosites consisted of a congeries of diverging ascending tubes divided by lamellæ and communicating with each other by lateral openings. Figure 104 presents a polished section magnified to show the interior Fig. 103. Favosites Polymorpha. Fig. 104. structure. The rocks of New York and Ohio abound in specimens of this genus. The trilobites of the previous period reappear in the Devonian, in several species of which the Brontes grew to the length of four feet, and closely resembled the lobster, having similar tuberculated claws. 206. The plants of the Devonian period appear to have been mostly marine fucoids, which are so numerous in some of the straty, that the slate beds owe their fissile character to the layers of carbonated sea weeds. Ferns and plants allied to the Lepidodendra of the carboniferous period occur; and Mr. Miller has recently proved that Dicotyledonous gymnospermous plants with true woody fibre existed at that time.* 207. The igneous rocks associated with these strata, are principally varieties of the trap, which have invaded and distorted many of the beds. At the close of the Devonian period, the true granitic eruptions appear to have ceased. THE CARBONIFEROUS SYSTEM. 208. The Carboniferous system consists of a widely extended series of fossiliferous limestones, alternating with sandstones and dark bituminous shales, containing beds of coal. The subdivisions of the system in England are represented in the following table. The COAL MEASURES, 3000 feet thick. CARBONIFEROUS SYSTEM. Sandstone, Shale, and Coal, alternating with beds of clay and ironstone. plants in profusion. Land Limestone, with fresh-water and marine shells. *Footprints of the Creator, p. 222. |