CARBONIFEROUS SYSTEM, the name given to the strata which, in geological order, rest upon the Devonian measures, and are capped by the Permian series. They derive their designation from the amount of carbon contained in them, for to them the great coal-fields of the world belong. In an economic sense, they are the most valuable series of rocks in the earth's crust, forming the great store-house from which is obtained the chief supply of coal, iron, and lime.
The rocks of the system are composed of a vast series of beds of sandstone, lime stone, shale, and coal. In some coal-fields, these are so interstratitied, that it is impos sible to subdivide the strata iu the order of time. In the Edinburgh district, there are nearly 100 coal-seams, omitting all under 6 in. in thickness. Out of the whole depth of the strata, amounting to about 6,300 ft., these seams occupy only 204 feet. The remainder consists of sandstone and shale in the upper half; towards the middle, lime stones appear, and these increase downwards in the number and thickness of the beds, but are still intermixed with seams of coal. The same arrangement exists in the other coalfields of Scotland, as well as in those of the n. of England. In other districts, the limestone is confined to the lower portion of the measures, and separated from the coal. bearing strata, so as to form a natural subdivision of the system into-1. The coal meas• sires, consisting of shale, sandstone, and grit, with occasional seams of coal; and 2. ?his mountain or carboniferous limestone, a calcareous rock, containing marine shells and corals, and devoid of coal. A coarse quartzose sandstone, passing into conglomerate, is occasionally developed to a considerable extent between these two divisions. This is a. local deposit, being almost confined to England, and may be considered as one of the coal sandstones, of coarser texture than usual. Being occasionally used for millstones, it is called millstone grit. It is accompanied with shales containing the usual coal plants, but generally without any true coal seams. Another locally developed series of beds, consisting of indurated shales, sandstones, and grits, occurs below the carboniferous limestone in South Wales and Ireland, and is known as the lower limestone shales. These rest conformably on a series of yellow sandstones, which have been generally referred to the Devonian measures, but which, from their organic contents, as well as from their stratigraphical position, seem to be basement beds of the carboniferous series. The existence and development of these various beds in the United Kingdom will be better understood by an examination of the following table. The maximum thickness of the beds is given in feet when known; the blanks show the absence of the division from the particular coal-field: In the midland countries, the coal measures are the only portion of the C. S. present, and these rest on the Silurian or older rocks. In Devonshire, there occurs au exten sive series of shales and sandstones, with a few beds of earthy anthracite or calm, asso ciated with argillaceous rocks, probably belonging to the lower limestone shales, muck indurated, and traversed by slaty cleavage.
From the great economic value of the contents of the C. S., we are better acquainted with its fossils than with any fauna or flora that flourished before the tertiary epoch. As coal is the result of the mineralization of vegetable matter, the coal measures must necessarily abound in the remains of plants. No less than 294 species have been
described as found in Britain alone. Numerous impressions of plants, as well as traces of structure, are found in the seams of coal themselves; but the more distinct forms are preserved in the interstratified beds of mud and ironstone, often in great number and exquisite beauty. Such remains consist chiefly of impressions of leaves separated from their branches; of casts of trunks, more or less in a broken state; and of roots much compressed, yet occupying their original position iu the clay soil now indurated into shale; with these occur pieces of wood, or remains of trees, in which the vegetable texture is to some extent preserved. The great proportion of the plants seem to have flourished in marshy swamps, and to have accumulated where they grew, like peat, the material after wards converted into coal. Hence a stratum of shale in which are imbedded the roots of sigillaria, calamites, etc., is the invariable floor on which the coal seam rests. The chief coal plants are lepidodendron (q.v.), sigillaria calamites (q.v.), trigonocarpon (q.v.), and ferns (q.v.). The existence of cone-bearing trees during this epoch has bee:• proved from the microscopic examination of prepared sections of fossil woods, in whin. the small discs occur that are characteristic of and peculiar to the conifene.
The animal remains are as numerous and as well preserved as the vegetable. They are found chiefly in the limestone; the greater part, indeed, of this rock, is made up bodily of corals and crinoids. No other such accumulation for extent and variety is known; it has its nearest parallel in the somewhat similar formation now going on in the southern archipelago. The corals and criuoids were specifically as well as indi vidually numerous. The terebratuhe and other allied forms of bivalve shells, though belonging to a comparatively limited number of genera, were very abundant. The more highly developed molluscs were also numerous; they belonged to _a great number of generic types. But the most remarkable group was the fishes. At no time were they more abundant. They belonged to the ganoid and placoid groups of Agassiz. The ganoids, having their entire surface covered with scales, were numerous; some of them inhabited shallow water near the share, and fed on crustaceans and shell-fish, for crush ing which they had a formidable apparatus of conical teeth of a very complicated struc ture. Others were, inhabitants of deep water, and were more powerful and predaceous, and more rapid in their movements. Their jaws were produced into a long snout, like the crocodile of the Ganges, and armed with a double series of enormous teeth, which were sometimes as much as 4 in, long by 2 in. broad, as in megalichthys (q.v.), dimen sions rarely attained even by the largest known reptiles. Associated with these were a great number of sharks belonging to the (q.v.), a family of which we have only a single living representative. They were furnished with a long bony spine to strengthen the dorsal fin, and thus enable them to turn speedily in the water, as they required to do in seizing their prey. These spines are often found fossil. The only remains referred to a higher division of the animal kingdom yet found belong to the saurian archegosaurus (q.v.).