Remains of fishes are not infrequent in the Carboniferous Limestone. But they present a striking contrast to those of the black shales and ironstones of the Coal-measures. They consist for the most part of teeth or of spines belonging to large predatory sharks. These teeth were placed as a kind of pavement FIG. 155.-Carboniferous Gasteropods. (a) Euomphalus pentangulatus (}); and roof in the mouth, and were used as effective instruments for crushing the hard parts of the animals, on which these larger creatures preyed. If, as is probable, the sharks fed upon the ganoid fishes of the time, they must have required a powerful apparatus of teeth for crushing the hard, bony armour in which these fishes were encased. Of the commoner genera of sharks, which have been named from the forms of their teeth-the only hard parts of their structure that have survived the following may be mentioned: Cochliodus, Orodus, Psammodus, Petalodus. The small ganoids that so abound in the black shales, ironstones, and coal-seams which represent the deposits of the sheltered lagoons of the coal-jungles, are hardly to be found in the thick limestone, whence we may infer that they were inhabitants of the quiet shorewaters, and did not venture out into the open sea, where the sharks found their congenial element. But the occasional occurrence of the teeth and spines of sharks in the Coal-measure shales and coal-seams shows that these monsters now and then made their way into the inland waters, where they would find abundant food. The Carboniferous system in Europe presents at least two well-marked subdivisions. In the lower section the strata are in FIG. 158.-Carboniferous Fishes. (a) Tooth of Rhizodus Hibberti (); (b) Tooth of Orodus ramosus (); (c) Ichthyodorulite or Fin-spine of Pleuracanthus lævissimus (1). large measure marine, for they include the Carboniferous Limestone; in the upper part they consist mainly of sandstones, shales, fire-clays, and coal-seams, constituting what are called the Coalmeasures, or coal-bearing division of the system. The subjoined Table shows the order of succession of the rocks in Britain : Lagoon type. Coal-Measures.-At the top, red and grey sandstones, clays, and thin limestone, resting upon a great thickness of white, grey, and yellow sandstones, clays, shales, and fire-clays, with numerous workable coalseams, and with a lower subdivision of coal-bearing beds, among which there Occur marine fossils (Orthoceras, Posidonomya, etc.) Thickness in South Wales, 12,000 feet; South Lancashire, 8000 feet; Central Scotland, 3000 feet. Marine type, but passing northwards into that of the lagoons. Millstone Grit.-Grits, flagstones, sandstones, and shales, with thin seams of coal and occasional bands containing marine fossils. Thickness 400-1000 feet, increasing in Lancashire to 5500 feet. Carboniferous Limestone.-Consisting typically of massive marine limestones and shales, but passing laterally into sandstones and shales, with thin coal-seams, which indicate alternations of marine and brackish water conditions. Thickness in South Wales, 500 feet, increasing northwards to more than 4000 feet in Derbyshire, and to upwards of 6000 feet in Lancashire, but diminishing northwards into Scotland. The base of the Carboniferous Limestone series passes down conformably into the Upper Old Red Sandstone. The Carboniferous system occupies a number of detached areas on the European continent. Its largest tract extends from the north of France, through Belgium, into Westphalia. The most important coal-fields of Europe belonging to this system are those of Belgium, Westphalia, the north of France, Saarbrücken, St. Etienne in Central France, Bohemia, and the Donetz in Southern Russia. In North America, the Coal-measures of the eastern United States reach a thickness of 4000 feet in Pennsylvania, and contain many valuable seams of coal. They increase in thickness northwards, reaching a maximum of 8000 feet in Nova Scotia. They are underlain by bands of conglomeratic strata, answering to the English Millstone grit, below which comes a group of beds with marine fossils (sub-carboniferous), probably representing the Carboniferous Limestone of Europe. In Australia and New Zealand also thick masses of sedimentary strata contain recognisable Carboniferous organic remains. In New South Wales they include a valuable succession of coal-seams. CHAPTER XXI PERMIAN THE prolonged subsidence during which the Coal-measures were accumulated was at last brought to an end by a series of great terrestrial disturbances, whereby the lagoons and coal-growing swamps were in great measure effaced from the geography of Europe. So abrupt in some regions is the discordance between the Coal-measures and the next series of strata, that geologists have naturally been led to regard this break as one of great chronological importance, serving as the boundary between two distinct systems. Nevertheless, so far as the evidence of fossils goes, there is no such interruption of the Geological Record as might be supposed from this stratigraphical unconformability, many of the Carboniferous types of life having survived the terrestrial disturbances. Again, though the discordance among the strata is, in many parts of Europe, particularly in England, most striking, yet it is by no means universal. On the contrary, some localities (Autun in France, and the Bohemian coal-field, for example) escaped the upheaval and prolonged denudation which elsewhere have produced so marked a hiatus in the chronicle. And in these places a gradual passage can be traced from the strata and fossils of the Coal-measures into those of the next succeeding division of the series, no sharp line being there discoverable, nor any evidence to warrant the separation of the overlying strata as an independent system distinct from the Carboniferous. Hence, by many geologists, the rocks now to be described are regarded as the upper part of the Carboniferous system. To these overlying rocks the name of PERMIAN was given, from the Russian province of Perm, where they are well developed. They consist of red sandstones, marls, conglomerates, and breccias, with limestones and dolomites. In Germany they are often called Dyas, because they are there easily grouped in two great divisions. The coarsest strata-breccias and conglomerates-are composed of rounded and angular fragments of granite, diorite, gneiss, greywacke, sandstone, and other crystalline and older Palæozoic rocks, which must have been upheaved and exposed to denudation before Permian time. The sandstones are usually bright brick-red in colour, owing to the presence of earthy peroxide of iron which serves to cement the particles of sand together. The shales or marls are coloured by the same pigment. So characteristic indeed is the red colour of the rocks that they form part of a great series of strata, originally known as the New Red Sandstone. Generally, greenish or whitish spots and streaks occur in the red beds, marking where the iron-oxide has been reduced and removed by decaying organic matter. Red strata are, as a rule, singularly barren of organic remains, probably because the water from which the iron-peroxide was precipitated must have been unfitted for the support of life. The red Permian rocks are therefore generally unfossiliferous. Among them, however, occur dark shales or "marl-slate," which have yielded numerous remains of fishes. The limestones too are fossiliferous, but they are associated with unfossiliferous dolomite, gypsum, anhydrite, and rock-salt. some places seams of coal also occur. In These various rocks tell distinctly the story of their origin. They could not have been deposited in the open sea, but rather in basins more or less shut off from it, wherein the water was charged with iron and was liable to concentration, with the consequent precipitation of its solutions. The beds of anhydrite, gypsum, and rock-salt are memorials of these processes. The dolomite may at first have been laid down as limestone which afterwards was converted into dolomite by the action of the magnesian salts in the concentrated water. In such intensely saline and bitter solutions, animal life would not be likely to flourish, and hence, no doubt, the poverty of fossils in the Permian series of rocks. But it is observable that where evidence occurs of the cessation of ferruginous, saliferous, and gypseous deposition, fossils not infrequently appear. The brown Marl-Slate, for example, and the thick beds of limestone are sometimes abundantly fossiliferous, and indeed are almost the only bands of rock in the whole series where organic remains occur. They were probably deposited during intervals when the barriers of the inland seas or salt-lakes were broken down, or, at least, when from some cause the waters came to be connected with the open sea, and when a portion of |