Page:EB1911 - Volume 21.djvu/194

Rh potassium and magnesium salts, including carnallite, kieserite and polyhalite, which are exploited at Stassfurt and are the only important potassium deposits known. Permian rocks of the Rothliegende type are scattered over a wide area in France, where the lower beds are usually conformable with the Coal Measures. In the upper beds occur the bituminous or “Boghead” shale of Autun. In Russia strata of this age cover an enormous area, in the Ural region, in the governments of Perm, Kasan, Kostroma, and in Armenia. The Russian Permian shows no sharp division into two series; the two types of deposit tend to be more mixed and include in addition some deposits of the more open sea. The general sequence begins with the Artinsk beds, sandy and marly or conglomeratic beds in closing connexion with the Carboniferous, overlain by the Kungur limestones and dolomites; these are followed by red fresh-water sandstones, over which comes an important series of copper-bearing sandstones and conglomerates. Above this, in Kostroma, Vyatka and Kasan there is a calcareous and dolomitic series, the so-called "Russian Zechstein" with marine fossils; the uppermost beds are red marls, with few fresh-water fossils, the Tartarian beds.

The character of the fossils in the Permian of the Mediterranean and south-east Europe-well exemplified in the deposits of Sicily—together with their more generally calcareous nature, indicate a more open sea and more stable marine conditions than obtained farther north. This sea is traceable across south-east Russia into the middle of Asia, through Turkestan and Persia, into the Salt Range of India, where the Productus limestone may be taken as representative of the normal marine plan of Permian times. Southwards, however, of the Nerbudda River another and quite distinct continental assemblage of deposits holds the ground, viz. the lower portion of the great fresh-water Gondwana system. The coarse Talchir conglomerates at the base are succeeded by the sandstones and shales of the Karharbari group, with numerous coal seams, and these in turn are followed by the Damuda series (upwards of 10,000 ft.) of similar rocks, with ironstones and very valuable coal seams. All these strata are characterized by the presence of the Glossopteris flora. A similar succession of beds has been recorded in north-west Afghanistan. In close relationship with the lower members of the Indian Gondwana series, both as regards fossil contents and lithological characters, are the lower Karoo beds of South Africa (Dwyka conglomerate, Ecca shales and mudstones, Beaufort beds and Kimberley shales), also the coal-bearing beds of the Transvaal; the Permo-carboniferous rocks of Australia (including the rich coal measures of Newcastle, the Greta coal measures and marine beds, upper and lower, of New South Wales; those of Tasmania, the Bowen River beds of Queensland, and the Bacchus Marsh glacial beds of Victoria), and similar rocks in New Zealand (Maitai formation, south island; Dun Mountain limestone and Rimutaka beds of the north island) and South America. In North America Permian rocks occur in the east in Pennsylvania, West Virginia, Maryland and Ohio ("Upper Barren Measures"), and in Prince Edward Island, New Brunswick, where they succeed the Carboniferous rocks very regularly. West of the Mississippi, in Texas (7000 ft, including the Wichita beds, Clear Fork and Double Mountain beds), Kansas and Nebraska, the Permian is more extensive and on the whole is more readily separable from the Carboniferous. Here the lower beds are marine and contain many limestones and dolomite's, the higher beds are mainly red sandstones and marls with gypsum; in Texas it is of interest to note the occurrence of copper-stained strata. These upper "Red Beds" are' often not clearly distinguishable from the Trias.

Life of the Permian Period.—The records of the plants and animals of this period are comparatively meagre. The plants show that a gradual change from the Carboniferous types was in progress. Two floral regions are clearly indicated, a northern and a southern. In the latter, which may be regarded as conterminous with the continent of Gondwana, the Lepidodendrons, Sigillarias, Calamites, &c., of the Coal Measures gave place to a distinct flora, named from the prevalence of Glossopteris, the Glossopteris (tongue-fern) flora. Traces of this southern flora have been found in northern Russia. Gangamopteris, Callipteris, Taeniopteris, Schizopteris, Walchia, Voltzia, Ullmannia, Saportea, Baiera are characteristic Permian genera. Among the larger animals amphibians occupied a prominent position, their footprints being very common in the sandstones; the include numerous Labyrinthodonts, Archegosaurus, Stereorachis, Branchiosaurus. At this time the true reptiles began to leave their remains in the rocks; many highly interesting forms are known—Palaeohatteria, Proterosaurus, Stereosternum; others having certain mammalian characteristics include Pareiosaurus, Cynognathus, Dicynodon. Among the fishes may be mentioned Platysomus, Palaeoniscus, Amblypterus, Pleuracanthus. Turning to the invertebrates, undoubtedly the most interesting feature is gradual introduction into the Cephalopoda of the ammonite-like forms such as Medlicottia, Waagenoceras, Popanoceras, in place of the more simple lobed goniatites of the Carboniferous. Brachiopods (Productus horridus, Bakevellia tumidla), Bryozoa and corals were by no means scarce in the more open Permian seas. Schizodus Schlotheimii, Strophalosia Goldfussi, Myophoria, Leimyalind, Bellerophon are characteristic Permian molluscs. The last of the trilobites appears in the Permian of North America.

The evidence so far obtained indicates that in Permian times much of the land in the northern hemisphere was near the general sea-level, and that conditions of considerable aridity prevailed which involved the repeated isolation and evaporation of marine lagoons and land-locked seas. South of this region in Europe and Asia there extended an open "Mediterranean" sea the "Tethys" of E. Suess; while over an enormous area in the southern hemisphere a great land area was spread, "Gondwana land," the land of the Glossopteris flora. At many points in this vast tract, as we have seen, coarse conglomeratic deposits, Talchir, Dwyka, Bacchus Marsh, &c., indicate profound glacial conditions, which some have thought were present also in Britain, Germany and elsewhere in the north. Moderate earth movements were taking place in North America, where the Appalachian and Ouachita mountains were in course of elevation, and in Europe this was a time of great volcanic activity. In the Saal region volcanic rocks in the lower Rothliegende have been penetrated for 1100 ft without reaching the bottom, and elsewhere in central Europe great sheets of contemporaneous quartz porphyry, granite porphyry, melaphyre and porphyrite are abundant with their corresponding tuffs. Melaphyres and tuffs appear in the Vosges, which in the south of France are enormous masses of melaphyre and quartz porphyry. Basic lavas and tuffs—diabase, pierite, olivine basalt and andesite tuffs—were erupted from many small vents in Ayrshire and the Nith basin, and basic lavas occur also in Devonshire. Volcanic rocks occur also in New Zealand, Sumatra and the Transvaal.

Table of Permian Strata, showing approximate correlations.