CHAPTER XXII

THE MESOZOIC PERIODS-TRIASSIC

THE great series of red strata referred to in the foregoing chapter as overlying the Carboniferous system in England was called "New Red Sandstone," to distinguish it from the “Old Red Sandstone" which underlies that system. But the progress of geology on the European continent eventually proved that, notwithstanding their general similarity of lithological character, two series of rocks had been comprised under the general title of New Red Sandstone. The older of these, separated from the rest under the name of Permian, was placed at the top of the great succession of Palæozoic formations. The younger division (still sometimes spoken of as New Red Sandstone) was called Trias, and was regarded as the first system in the great Mesozoic or Secondary succession.

Essentially the Permian strata form merely the upper part of the Carboniferous system. Their types of life are fundamentally Palæozoic, but, as we have seen, both the flora and fauna are marked by a decrease in the number and variety of old forms, and by the advent of the precursors of a new order of things. Conifers and cycads now began to replace the early types of lepidodendron and sigillaria; amphibians became more abundant, and saurians now took their place at the head of the animal world.

But when we ascend into the Trias, though in Europe the physical conditions of deposition remained much the same as in Permian time, we meet with a decided contrast in the organic remains. A new and more advanced phase of development presents itself in that richer and more varied assemblage of plant and animal life which characterised Mesozoic or Secondary time.

The word TRIAS has reference to the marked threefold division of the rocks of this system in Germany. In that country, and generally in Western Europe, the rocks consist of bright red sandstones and marls or clays, with beds of gypsum, anhydrite, rock-salt, dolomite, and limestone. These rocks, so closely resembling the Permian series below, had evidently a similar origin. They were in large part deposited in inland seas or salt-lakes, wherein, by evaporation and concentration of the water, the dissolved salts were precipitated upon the bottom, and where, consequently, the conditions must have been extremely unfavourable for the presence of living things. The sites of these inland basins can still be partially traced. They extended at least as far west as the north of Ireland. One or more of them lay across the site of the plains of Central England. Others were dotted over the lowlands of middle Europe. The largest of them occupied an extensive area now traversed by the Rhine. It stretched, on the one hand, from Basel to the plains of Hanover, and, on the other, from the highlands of Saxony and Bohemia across the site of the Vosges Mountains westward to the flank of the Ardennes. The continent must then have been somewhat like the steppes of Southern Russia a region of sandy wastes and salt-lakes, with a warm and dry climate. Probably higher land rose to the north, as in earlier geological times, for traces of its vegetation have been found in Sweden. But southwards lay the more open sea, spreading over part at least of the site of the modern Alps, and thence probably across much of Asia to the Indian and Pacific Oceans.

So long as only the deposits of the salt-basins had been explored, it was but natural that comparatively little should be known of the flora and fauna of the Triassic period. The climate around these lakes was perhaps not a very salubrious one, and hence there may have been only a scanty terrestrial fauna in their immediate vicinity, while the waters of the lakes themselves were unsuited for the support of life. It is not surprising, therefore, that the strata deposited in these tracts are on the whole unfossiliferous; that, indeed, fossils only abound where there are indications that, owing to some temporary depression or breaking down of the barriers, the open sea spread into these basins, and carried with it the organisms whose remains gathered into beds of limestone. But over the tracts that lay under the open sea, a more abundant marine fauna lived and died. It is in the records of that seabottom, rather than in those of the salt-basins, that we must seek for the evidence of the general character of the life over the globe, and for the fossil data with which to compare together the Triassic rocks of distant regions.

There are traces of contemporaneous volcanic action among the Triassic strata. A little group of volcanoes appears to have existed during Triassic time in South Devonshire; but in the region of the Eastern Alps, especially around Predazzo in the Tyrol, evidence of far more extensive eruptions exists.

The flora of the Triassic period has been preserved chiefly in the dark shales and thin coal-seams formed in some of the inland

FIG. 164. Triassic Plants. (a) Horse-tail Reed (Equisetum columnare, ); (b) Conifer (Voltzia heterophylla, ); (c) Cycad (Pterophyllum Blasii, 1).

basins. So far as known to us it consisted chiefly of ferns, equisetums or horse-tails, conifers, and cycads. Among the ferns a few Carboniferous genera still survived, but some of the most characteristic forms were tree-ferns. The oldest known true horsetails are met with in the Trias (Fig. 164, a). The most abundant conifer is the cypress-like Voltzia (Fig. 164, 6). Cycads, already a feature in the vegetation of the Permian system, now increase in number and variety. During the Mesozoic ages they continued to be the most characteristic members of the terrestrial flora, insomuch that this division of geological time is sometimes spoken of as the "Age of Cycads." Some of the more common cycads in the Triassic rocks are Pterophyllum, Zamites, and Podozamites (Fig. 164, c).

The red gypseous and saliferous strata, for the reason already

FIG. 165. Triassic

given, are on the whole unfossiliferous. Here and there, footprints of amphibians, preserved on the sandstones, give us a glimpse of the higher forms of life that moved about on the margin of the salt-lakes. The beds of limestone, which represent intervals when, for a time, the sea overspread the lakes, contain sometimes abundant fossils. But they are numerous in individuals rather than in species or genera, as if the conditions for life in those waters were still somewhat unfavourable. On the other hand, the limestones laid down in the opener sea are crowded with a varied fauna. One of the most typical fossils of the Trias is the crinoid Encrinus liliiformis (Fig. 165), one of the most familiar fossils of the limestones (Muschelkalk) which in Germany form the central division of the system. Among the lamellibranchs, Myophoria, Avicula, Pecten, Cardium, Pullastra, Daonella, and Monotis are characteristic genera (Fig. 166), some species such as Avicula contorta, Pecten valoniensis, and Cardium rhaticum being eminently useful in tracing the upper parts of the Trias (Rhætic) all over the most distinctive features of the Triassic fauna is its development of cephalopod life. In the limestones of the middle subdivision in Germany, a few species of cephalopods occur, the two prevalent forms being species of Nautilus and the ammonite Ceratites (Fig. 167). But when we turn to the Trias of the Eastern Alps, which represents the deposits of the more open sea, we meet with a remarkable abundance and variety of cephalopods, and with a striking admixture of ancient and more modern types. For example, the venerable genus Orthoceras, which occurs even down in the Cambrian rocks, is found also here as a survival from Palæozoic time. But new types now appeared. In particular, the tribe of Ammonites, so preeminently typical of the molluscan life of the Mesozoic seas, is represented by numerous genera and species (Arcestes, Trachyceras, Pinacoceras, Phylloceras, besides Ceratites above referred to). Among the fishes of the Trias, the genera Acrodus, Ceratodus, Gyrolepis, Hybodus, and Pholidophorus may be mentioned. Labyrinthodonts still haunted the lagoons and sandy shores (Mastodonsaurus, Trematosaurus); but they no longer remained the most important members of the animal world. Various early types of

Crinoid (Encrinus Europe from Italy to Scandinavia.

lizards now took their places in the ranks of creation (Hyperodapedon, Telerpeton, Fig. 168). A strange order of Triassic reptiles was characterised by the jaws having the form of a beak, somewhat

FIG. 166. Triassic Lamellibranchs. (a) Avicula contorta (natural size); (b) Pecten valoniensis(); (c) Cardium rhæticum (natural size); (d) Myophoria vulgaris ().

like that of a turtle; Dicynodon, one of these forms, carried two huge tusks in the upper jaw. A remarkable and long-extinct order of reptiles, that of the Deinosaurs, made its first appearance in

FIG. 167. Triassic Cephalopods. (a) Nautilus bidorsatus (f); (b) Ceratites
nodosus (reduced).

Triassic time. These creatures were marked by peculiarities of structure that linked them both with true reptiles and with birds, while in size they sometimes resembled elephants and rhinoceroses. They seem to have walked mainly on their hind feet, the three-toed or