The rocks of the Upper Carboniferous or Pennsylvanian include the great coal fields of eastern North America. (For the origin of coal fields, see Cowl.). They are sandstones or conglomerates, gifts, shales, clays, limestones and seams of coal. The total thickness of the Nova Scotia coal measures is 7,000 feet, and 76 distinct seams of coal are known. In Penn sylvania the coal measures have a total thick ness of 4,000 feet. In Michigan the coal meas ures are about 300 feet thick; in the eastern interior (Illinois-Indiana) field 600 to 1,000 feet, and in the western interior field the thick ness varies widely, reaching a maximum in Arkansas.
The Upper Carboniferous rocks cover wide areas in Utah, Colorado and Arizona ; they also occur in the Black Hills in South Dakota, and in California, and British Columbia. They are generally limestones or sandstones and contain no coal beds. The distinction between Upper and Lower Carboniferous is not as sharp as in the Mississippi Valley. The total thickness of the whole Carboniferous series in Nevada and Utah is about 13,000 feet.
Carboniferous in other Continents.— In western Europe the Lower Carboniferous limestones reach from Ireland to Central Ger many, with a maximum thickness in England of 6,000 feet, and are overlaid by coal measures. In Asia the Chinese coal measures are of Upper Carboniferous Age, and are underlaid by Lower Carboniferous limestone. In South America the Lower Carboniferous is mostly made up of sandstones, and the upper of limestones, with very few coal seams.
Life of the The plant life of the Carboniferous Period showed some advances from the Devonian. The ferns were most abundant, some being like tall trees, others as small as the maidenhair fern of to-day. The
most conspicuous growths in the Carboniferous forests were the Lycopods or club-mosses, now represented by insignificant forms, but then growing sometimes 75 feet or more high, with trunks three feet in diameter, and spreading branches (Lepidodendron). Other Lycopods (Sigillaria) had short, thick trunks with few if any branches. Still another group, the horse tail rushes, were of far greater importance in Carboniferous times than now. Of these the calansites, with their tall, slender stems, must have been one of the commonest plant forms of the Carboniferous forest. No plant with con spicuous flowers existed.
Of animal corals were abundant; and the Foraminifera, especially the genus Fang lina, became of importance. The extinct blas toids were abundant, and the Carboniferous is the period in which the crinoids, or sea-lilies, reached their highest development. Sea urchins were more plentiful than in the De vonian, but the trilobites were slowly dying out Scorpions were fairly abundant, and the first true spiders appeared. The brachiopods were less abundant than in the Devonian. Bivalve mollusks were numerous, among them being the first land shell. Of the fishes, the sharks were remarkably developed. Amphibians, which probably existed in Devonian, increased greatly in time, but belonged to an order now extinct, and were of moderate size, no species being over eight feet long. Consult Chamberlin and Salisbury, (Geology' (VoL New York 1907); Cleland, H.. F. (Geology, Physical and Historical' (New York 1916); Dana, (Manual of Geology'. (New York 1895) ; Geikie, (Text Book of Geology' (London 1903) Report of the United States Geological Sur vey' (1900-01, part III). See COAL ; CLAY ; GEOLOGY.