In geology the system of Primary rocks overlying the Devonian. It takes its name from the extensive coal-beds which it contains. In the system there are two well-marked sub-divisions-the lower section consisting of carboniferous limestone, and the upper, of the coal-bearing division of the system known as the coal-measures. These comprise sandstones, dark shales, and seams of coal. The flora of the Carboniferous period consisted almost entirely of flowerless plants, such as ferns; and among the fauna, fossils of true air-breathing animals and various insects are found. The system is very largely developed in the the United States. (See Coal.)