COAL MEASURES

major division of Upper Carboniferous rocks and time in Great Britain (the Upper Carboniferous Period began about 325,000,000 years ago and lasted about 45,000,000 years). The Coal Measures, noted for the great amounts of coal they contain, account for the major portion of England's production of coal. They are the uppermost division of the Upper Carboniferous and consist of a repetitive sequence of marine and nonmarine strata. The marine rocks consist of black carbonaceous shales and some fossiliferous limestones characterized by distinctive cephalopods and beds in which the brachiopod genus Lingula is the dominant form. The largest portion of the Coal Measures, however, consists of nonmarine shales and mudstones in which plant and freshwater invertebrate fossils are found. The productive coal deposits occur in the marine strata and consist largely of soft, bituminous coal; anthracite coals, however, occur in South Wales. Though local variation in the coal seams occurs, great uniformity is evident on a regional scale, and some coal beds can be identified throughout Great Britain and even on the European continent. The upper limits of the Coal Measures have been obscured by deformation of the strata during the Hercynian mountain-building episode and subsequent erosion.