The Trias of Europe has been so thoroughly studied and throws so much light upon American problems, that it will be profitable to depart from the usual order of treatment and take up first the development in that continent. As in the Permian, the Triassic rocks of Europe are found in two contrasted fades, the continental and the oceanic; the former extending, with interruptions, from Ireland, across England, France, central and southern Germany, to Poland, and consisting chiefly of red sandstones and red marls and clays, with conglomerates and some limestones. From this it follows that the rocks in the mountains which bordered the Triassic basins and plains had been profoundly decomposed, as in the southern Appalachians of to-day, where the crystalline rocks are changed into a red clay for depths of 100 feet or more, and the quartz grains are covered with a red film. As we have learned (Chapter IV (Destructive Processes - The Atmosphere)) the red laterites of warm regions may be derived from very many different kinds of parent-rock, igneous rocks, crystalline schists, limestones, and dolomites. "This makes intelligible the close agreement of the continental Triassic rocks over great areas of the earth's surface.
It is not at all necessary that the mountain ranges which surrounded the Triassic basins and plains should have been built up of the same rocks, which, as a matter of fact, was probably never the case. ... It seems to be undoubted that the continental Triassic sediments were deposited in basins, or on low plains, and that their material was derived from plateaus and mountains. It may likewise be inferred from the size and rounded shape of the conglomerate pebbles that running water transported the material from the highlands to the basins." (E. Philippi).
In Germany, where the plainly marked threefold division of the strata has given its name to the system, the lower series, or Bunter Sandstein, varies from 650 to 1800 feet in thickness and is chiefly made up of red sandstones and sandy shales. In northern and central Germany it is so intimately connected with the Upper Permian that any line of separation between them appears to be arbitrary, but in the west and southwest there is an overlap of the Bunter upon older rocks. Around the margins of the Triassic basins are coarse conglomerates, with finer materials toward the centres. Occasional and temporary lakes, or playas, were formed in the basins, and floods rushing from the mountains spread sheets of sand and gravel far out over the plains, while cross-bedded sands were piled up by the winds over extensive areas. Locally, the playas formed deposits of salt and gypsum, and clastic beds marked by sun-cracks, rain-prints, and tracks of animals. All of these features point unmistakably to an arid climate, though one that was probably less extremely dry than that of the Upper Permian. The mountain ranges appear to have been sufficiently high to cause abundant precipitation upon them; such a juxtaposition of rainy mountains and arid plains has nothing unusual about it.
The Middle Trias, or Muschelkalk, is marked by successive incursions of the sea, the first of which came at the end of the Bunter epoch and eventually extended over a great part of the area occupied by the Bunter Sandstein, leaving deposits with a maximum thickness but little exceeding 1100 feet. The fossils show that this was an inland sea, connected with the ocean, but having a fauna which consists of comparatively few species, though these are sometimes individually very abundant. The relation of these fossils to those of the contemporary part of the oceanic Trias is much like the relation between the modern faunas of the Black Sea and the Mediterranean. In the middle of theMuschelkalk the connection with the ocean was shut off and the German sea converted into a salt lake, as is demonstrated by the deposits of gypsum and salt, but the marine conditions were soon reestablished.
An elevation of the land caused the withdrawal of the Middle Triassic sea and the resumption of the conditions of continental sedimentation, resulting in the formation of the Keuper (maximum thickness 2000 feet). The lower parts of the Keuper contain some marine beds and, locally, thin beds of coal, but most of it consists of sandy and clayey beds, which change rapidly from point to point, and are, on the whole, of finer materials than those of the Bunter. The basins had been largely filled with sediment and the mountains had been lowered by denudation, so that the coarser materials could no longer be transported. The middle Keuper was a time of extensive salt lakes, in which large bodies of gypsum and some salt were precipitated. The latest stage of the Keuper, the Rhcetic, witnessed a renewed transgression of the sea.
Trias of continental origin occurs in other European countries. In Great Britain the Triassic is almost all continental, the Middle Triassic marine invasion not extending so far to the northwest, but the Rhaetic transgression did, and beds of this stage form a thin, though persistent band at the top of the Keuper. The Triassic beds cover a large part of the central plains of England, extending to northeastern Ireland, and small areas occur on the east coast of Scotland. In France Trias of the German type, including the Muschelkalk, extended into the eastern and southern parts of the country to the Pyrenees and along eastern and southern Spain. Triassic rocks also occur around the margins of the central Plateau of France. In the south of Sweden is a considerable area of Triassic rocks: the Keuper is coal-bearing and is overlaid by marine Rhaetic beds. In northeastern Russia is a great extent of beds belonging to the Tataric stage, which has been mentioned in connection with the Permian, but which may be in part Triassic.
In the Alps are two well-distinguished regions; in the western part conditions were not unlike those of Germany, while the eastern part displays a great development of the oceanic limestones. The western Alpine Trias is much folded and metamorphosed and becomes very thick on the Italian side of the mountains, and is conspicuous in the northern Apennines. On the east, the Palaeozoic rocks of the Alps extended as a long island, or chain of islands, from the Engadine into southern Austria. "North of this old insular tract the Triassic strata are on the whole somewhat sandy. . . . On the south side the deposition of limestone and dolomite went on more continuously, though interfered with occasionally by submarine volcanic eruptions." (A. Geikie.) Almost the whole Triassic succession, except the lowest members, is represented here by great limestones and dolomites, many of the latter probably of coral-reef origin.