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Geographical Extent.—England, Germany, and Russia are the three main centres of these latest palæozoic strata, and the limestones are the most characteristic parts. The range of magnesian limestone is very limited in England. Commencing at Cullercoats, north of Tynemouth, the lower limestone (zechstein) ranges through a part of Northumberland and across Durham to Coniscliffe on the Tees, being in this course penetrated by many coal pits. Below it is the fish-bed or marl slate, and a coarse yellow pebbly sand (rotheliegende). In the North of Yorkshire the magnesian limestone is poorly developed in patches at Catterick, Crakenhall, &c., but grows prominent near Masham, and then continues uninterruptedly by Knaresborough, Wetherby, Ferrybridge, Doncaster, Tickhill, Barlborough, and Bolsover to Nottingham.

Through the whole of this range it is the lower limestone which prevails and makes the general feature, a low regular continuous terrace; but it is only in the middle part between the river Wharfe and the vicinity of Tickhill that the whole series is visible. As already observed, a few detached parts of magnesian conglomerate (probably coeval with zechstein) occur under the Penine chain near Brough and Ingleton, and along the border of the Salopian coal field, while a more developed section appears in St. Bee's Head, and a mass of the oldest red conglomerate of Malvern may be referred to this period. The magnesian conglomerate of South Wales rests unconformedly upon the coal.

Zechstein is exhibited along the Thuringerwald, in Hesse Cassel, on the southern and eastern sides of the Harz, between the Elster and the Saale, and about Waldeck. In Russia coeval rocks are spread out in the west of the Ural so as to occupy the whole of the ancient kingdom of Perm (whence the name). They consist of limestones, marls, masses of gypsum, rock salt, and repeated alternations of cupriferous strata, and contain a fauna and flora of characters intermediate between