Upper Permian.—What is called in this table the Upper Permian will be seen to attain its chief thickness in the north-west, or on the coast of Cumberland, as at St. Bee’s Head, where it is described by Sir Roderick Murchison as consisting of massive red sandstones with gypsum resting on a thin course of Magnesian Limestone with fossils, which again is connected with the Lower Red Sandstone, resembling the upper one in such a manner that the whole forms a continuous series. No fossil footprints have been found in this Upper as in the Lower Red Sandstone.
Middle Permian—Magnesian Limestone and Marl-slate.—This formation is seen upon the coast of Durham and Yorkshire, between the Wear and the Tees. Among its characteristic fossils are Schizodus Schlotheimi (Fig. 410) and Mytilus septifer (Fig. 412). These shells occur at Hartlepool and Sunderland, where the rock assumes an oolitic and botryoidal character. Some of the beds in this division are ripple-marked. In some parts of the coast of Durham, where the rock is not crystalline, it contains as much as 44 per cent of carbonate of magnesia, mixed with carbonate of lime. In other places—for it is extremely variable in structure—it consists chiefly of carbonate of lime, and has concreted into globular and hemispherical masses, varying from the size of a marble to that of a cannon-ball, and radiating from the centre. Occasionally earthy and pulverulent beds pass into compact limestone or hard granular dolomite. Sometimes the limestone appears in a brecciated form, the fragments which are united together not consisting of foreign rocks but seemingly composed of the breaking-up of the Permian limestone itself, about the time of its consolidation. Some of the angular masses in Tynemouth cliff are two feet in diameter.
The magnesian limestone sometimes becomes very fossiliferous and includes in it delicate bryozoa, one of which, Fenestella retiformis (Fig. 413), is a very variable species, and has received many different names. It sometimes attains a large size, single specimens measuring eight inches in width. The same bryozoan, with several other British species, is also found abundantly in the Permian of Germany.
The total known fauna of the Permian series of Great Britain at present numbers 147 species, of which 77, or more than half, are mollusca. Not one of these is common to rocks newer than the Palæozoic, and the brachiopods are the only group which have furnished species common to the more ancient or Carboniferous rocks. Of these Lingula Crednerii (Fig. 415) is an example. There are 25 Gasteropods and only one cephalopod, Nautilus Freieslebeni, which is also found in the German Zechstein.
Fig. 413: Magnesian Limestone, Humbleton Hill, near Sunderland.[[3]]
Shells of the genera Productus (Fig. 414) and Strophalosia (the latter of allied form with hinge teeth), which do not occur in strata newer than the Permian, are abundant in the ordinary yellow magnesian limestone, as will be seen in the valuable memoirs of Messrs. King and Howse. They are accompanied by certain species of Spirifera (Fig. 416), Lingula Crednerii (Fig. 415), and other brachiopoda of the true primary or palæozoic type. Some of this same tribe of shells, such as Camarophoria, allied to Rhynchonella, Spiriferina, and two species of Lingula, are specifically the same as fossils of the carboniferous rocks. Avicula, Arca, and Schizodus (Fig. 410), and other lamellibranchiate bivalves, are abundant, but spiral univalves are very rare.
Beneath the limestone lies a formation termed the marl-stone, which consists of hard calcareous shales, marl-slate, and thin-bedded limestones. At East Thickley, in Durham, where it is thirty feet thick, this slate has yielded many fine specimens of fossil fish—of the genera Palæoniscus ten species, Pygopterus two species, Coelacanthus two species, and Platysomus two species, which as genera are common to the older Carboniferous formation, but the Permian species are peculiar, and, for the most part, identical with those found in the marl-slate or copper-slate of Thuringia.