CARBONIFEROUS, the name applied to the last period of the Paleozoic era, and to the system of rocks formed during that period. The Carboniferous has been variously subdi vided, the following being the current usage of the United States Geological Survey: Permian.
Pennsylvanian (coal measures, Upper Car boniferous).
Mississippian (sub-Carboniferous or Lower Carboni ferons ) .
Many geologists divide the Carboniferous into Lower and Upper, but give the Permian the rank of a period. Mississippian and Penn sylvanian are terms derived geographically in the United States, and are not used abroad. A few American geologists consider that they too are of the rank of periods, and would discard the old term Carboniferous altogether. Permian is derived from the province of Perm, in Russia, and Carboniferous from carbon (coal) in the rocks of the system.
Palaogeoqraphy of the Carboniferous in North The Mississippian opened with shallow epicontinental seas widespread over central United States, as at the close of the Devonian (q.v.). In the east the Pocono and Mauch Chunk formations are largely terrestrial, being a great series of delta and coastal plain deposits built up at the west edge of a land mass, Old Appalachia, which was persistent through several of the preceding periods, on the site of the present Piedmont, Coastal Plain, and farther east into the present Atlantic Ocean. In the seas of the great interior the sediments of the epoch are largely limestone. At the close of the Mississippian there was widespread emer gence east of the Rocky Mountains, with fold ing in the Ouachitas and also in Europe. This emergence was accompanied by widespread erosion, and the Pennsylvanian rocks rest un conformably on the Mississippian and older beds. Throughout Pennsylvanian times most of eastern United States was low and swampy with luxuriant vegetation, which accumulated and was buried to form coal. Occasional submer gences occurred and marine beds are inter calated with coal seams. The marine beds are more abundant in central than in eastern United States; and in the Rocky Mountains and Great Basin the sea persisted practically through the epoch, and the rocks are almost wholly marine.
During the Permian the region east of the Mississippi River was land, and humid during the early part of the epoch, as shown by coal beds. West of the Mississippi River, the land gradually emerged during late Pennsylvanian and early Permian and the climate grew arid. Great salt lakes were extensive and beds of salt and gypsum are abundant. At the same time there were similar deserts in Germany, in which the great German salt deposits were formed. Strangely enough, other continents, even within the torrid zone, were undergoing glaciation at the same time, particularly Africa, Australia and India. These extreme conditions, together with the great period of folding that formed the Appalachian Mountains, wrought a pro found change in types of plants and animals, and brought to a close not only the Carbon iferous Period, but the Paleozoic Era as well.
As the rocks laid down in Carboniferous time furnish by far the greater part of the world's supply of coal, they have been very carefully studied in many different places and accurately mapped, so that more is known of the Carboniferous rocks than those of any other Paleozoic system.
The Lower Carboniferous or Mississippian series, in Nova Scotia and New Brunswick, is made up of thick beds of sandstone and lime stone overlaid by limestones containing masses of gypsum. The total thickness of the series is 6,000 feet. In Pennsylvania the Lower Car boniferous series has a total maximum thick ness of 4,000 feet of sandstone and shale. Farther west the Lower Carboniferous is rep resented largely by limestones with a maximum thickness of over 1,200 feet in southern Illinois. In southwestern Virginia are limestones, sand stones and shales of Lower Carboniferous Age, 2,000 feet thick, and containing a few workable beds of coal In the Rocky Mountains the Lower Carboniferous rocks are, with few ex ceptions, limestones.