Permian System. In Britain this series of strata rests unconformably upon the Carboniferous rocks. It consists of the following groups:
UPPER RED SANDSTONES, clays and gypsum (50 to 100 feet thick in east of England; west of Pennine chain, 600 feet thick).
MAGNESIAN LIMESTONE (500 to 600 feet) = Zechstein of Germany.
MARL SLATE (about 60 feet) = Kupferschiefer.
LOWER RED AND MOTTLED SANDSTONES, with conglomerates and breccias (3000 feet in Cumberland; in the east of England not over 250 feet) = Rothliegende of Germany.
The Lower Red Sandstones are greatly developed in Staffordshire, Cheshire, and Lancashire, and the Vale of Eden in Westmorland and Cumberland. Small areas also occur in the valleys of the Nith and Annan and in Ayrshire; and similar areas appear in the districts of Down, Tyrone, and Annagh in Ireland. The breccias met with in this group often contain erratics, and have the general aspect of glacial accumulations; and Sir A. Ramsay thought they probably indicate the occurrence of a glacial episode in the Permian period. In the Scottish area the rocks contain sheets of lava-form rocks and tuffs, associated with which are many small filled-up volcanic vents or necks. The most important member of the overlying groups is the Magnesian limestone, which is the chief repository of Permian fossils. Many of its beds assume curious concretionary forms, as is well seen on the coast of Durham.
In Germany the Permian consists of an upper and lower group—hence the system is often termed Dyas—the Zechstein and Kupferschiefer forming the upper, and the Rothliegende the lower group. Volcanic rocks are associated with the latter. The Kupferschiefer has long been famous for its ores of copper and other metals, and fossil fishes; while associated with the Zechstein are beds of anhydrite, gypsum, rock-salt, and bituminous shales. In Russia the system occupies an area of more than 15,000 sq. m. between Moscow and the Urals. It is well developed in the government of Perm, from which it derives its name. While the German Dyas presents the same general features as the Permian of Durham and the east of England, the Russian development resembles the Permians of the Midlands and north-west of England—limestone being quite a subordinate formation, and often wanting. Although there is commonly an unconformity between the Permian and the Carboniferous, yet in some places, as at Autun in the heart of France, a conformable passage is traced from the coal-measures into the Permian. The same is the case in North America, where in the western part of that continent no hard and fast line can be drawn between the two systems—the Carboniferous graduating upwards into the Permian.
Life of the Period.—The Permian strata as a whole are not rich in fossils—the red sandstones which form so large a portion of the system being for the most part barren. As contrasted with the flora of the Carboniferous period that of the Permian is poor and meagre. But that poverty may be only apparent—the conditions for its preservation not having been so favourable as during Carboniferous times. It may be considered as an impoverished continuation of the Carboniferous flora. The most common plants are ferns—both herbaceous and arborescent—many of the genera being Carboniferous, while others, such as Callipteris, are not known as Carboniferous forms. Conifers were likewise numerous, especially the yew-like Walchia and the cone-bearing Ullmannia. Traces of what some suppose to have been cycads (Næggerathia) are met with in Permian strata. Finally, it may be noted that many characteristic Palæozoic types died out in Permian times, such as the Lepidodendroids, Sigillarioids, and Calamites. The animal life of the period is somewhat better represented; but it too appears impoverished when contrasted with that which flourished in the preceding Carboniferous period. We note that rugose corals, so abundant in the older Palæozoic rocks, are very sparingly met with in Permian strata; even tabulate forms are feebly represented. Polyzoa are fairly numerous in the Magnesian limestone. Amongst brachiopods the more abundant types are survivals from the Carboniferous, as Producta, Spirifera, Strophalosia. Lamellibranchs are somewhat more numerous than brachiopods, common forms being Schizodus, Bakevellia, Gervillia, &c. Gasteropods (Murchisonia, Pleurotomaria) are feebly represented, and the same is the case with the cephalopods (Nautilus, Orthoceras, Cyrtoceras). It is worthy of note that the trilobites are represented by one form (Phillipsia)—the last appearance of that eminently Palæozoic order. Among the fishes the principal genera are Palæoniscus and Platysomus. Amphibians seem to have abounded; they are all labyrinthodonts (Archegosaurus, Branchiosaurus, Pelosaurus). At this horizon true reptiles (Proterosaurus) make their earliest appearance.
In most parts of Europe where Permian strata are developed they rest unconformably on Carboniferous and other rocks, from which it is evident that towards the close of Carboniferous times considerable earth-movements took place. These caused the sea to disappear from wide regions in Europe, and resulted eventually in the isolation of certain areas, which thus became inland seas or salt lakes. In these latter mottled sandstones, dolomitic limestones, rock-salt, and gypsum were accumulated, so that the conditions were not favourable to life. One or more such inland seas covered large areas of what is now central England, and extended into southern Scotland and the north of Ireland. Similar large inland seas existed in middle and eastern Europe. The strata accumulated in such basins show plentiful footprints and other indications of shallow-water conditions, such as worm-tracks, sun-cracks, rain-pittings, and ripple-marks—evidence which indicates that the level of the lakes was often abnormally lowered during dry seasons, leaving wide tracts exposed over which crawled annelids, amphibians, and reptiles. Volcanic action was rife in Scotland and Germany, and it has been suggested that the abundant and well-preserved fish remains which occur in the Kupferschiefer may have been poisoned by the sudden influx of mineral springs connected with the volcanic disturbances of the time. Some of the inland seas may have had occasional connection with the open sea for longer or shorter periods, as, for example, during the formation of the thicker fossiliferous limestones. But, taken as a whole, the general character of the strata is that of accumulations formed in inland seas. The climate of the period, so far as one can judge from the aspect of flora and fauna, was probably mild and genial. Nevertheless the occurrence of coarse breccias, with their scratched stones and erratics, in the Permian of Britain and the Continent, and the similar appearances met with in strata, which are believed to be of the same age, in India, Australia, and South Africa seem hard to explain without the agency of floating ice.