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 FIG. 165.-Triassic Crinoid (Encrinus are characteristic genera (Fig. 166), some liliiformis, ). species such as Avicula contorta, Pecten valoniensis, and Cardium rhæticum being eminently useful in tracing the upper parts of the Trias (Rhætic) all over Europe from Italy to Scandinavia. One of the most distinctive features of the Triassic fauna is its development of cephalopod life. In the limestones of the middle subdivision of 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 pre-eminently typical of the molluscan life of the Mesozoic seas, is represented by numerous genera and species (Arcestes, Trachyceras, Pina

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

coceras, Phylloceras, besides Ceratites above referred to).

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

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 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 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

FIG. 168. Triassic Lizard (Telerpeton elginense, ).

FIG. 169. Triassic Crocodile (Scutes of Stagonolepis elginensis, ).

in Triassic time. These creatures were marked by peculiarities of structure that linked them both with true reptiles and with birds, while in size they resembled elephants and rhinoceroses. They seem to have walked mainly on their hind feet, the three-toed or five-toed bird-like imprints of which are numerous on some beds of sandstone. They are characteristically Mesozoic types of life. Another not less typically Mesozoic form, that of the Plesiosaurs, likewise began in Triassic time; but it will be more particularly alluded to in the following chapter. The earliest known crocodiles have been found in Triassic rocks; some of the

a

scutes or scales of one of these animals are shown in Fig. 169. But the most important advance in the fauna of the globe during the Triassic period was the first appearance of mammalian life. Detached teeth and lower jaws have been met in the uppermost parts of the Triassic system which have been identified as possessing structures like those of some of the marsupial animals of Australia (Microlestes, Fig. 170). It is in

C

FIG. 170.-Triassic teresting to know that the earliest repreMarsupial (Micro- sentatives of the great class of the mamlestes Moorei); (a) malia belonged to one of its lowest diviLower molar tooth, sions. They were small creatures, probably

outer side (1);(b)

Ditto (nat.size); (c) resembling the Myrmecobius or Banded Ditto, front side (1). Ant-eater of New South Wales.

The Triassic strata of the inland basins (England, Germany, France, etc.) have been subdivided into the following groups :

Rhætic.

Keuper or Upper
Trias.

Muschelkalk or
Middle Trias.

Bunter or Lower
Trias.

Red, green, and grey marls, black shales, sandstones, bone-beds, and in Germany sometimes thin seams of coal. Characteristic fossils are Cardium rhæticum, Avicula contorta, Pecten valoniensis, Pullastra arenicola, Acrodus, Ceratodus, Hybodus, Saurians, Microlestes.

Red, grey, and green marls, with beds of rocksalt and gypsum.

Red sandstones and marls (England); grey sandstones and dark marls and clays, with thin seams of earthy coal (Germany).

Limestones and dolomites, with bands of anhydrite, gypsum, and rock-salt. The limestones are the great repository of the fossils. This subdivision is absent, or only feebly represented in England.

Mottled red and green sandstones, marls, and sometimes pebble-beds.

The salt-beds of Cheshire have long been worked for commercial purposes. The lower bed is sometimes more than 100 feet thick; but the salt deposits of Germany are much more important. Thus at Sperenberg, 20 miles south of Berlin, a boring was put down through about 290 feet of gypsum, and then through upwards of 5000 feet of rock-salt, without reaching the bottom of the deposit.

The alternation of bands of rock-salt with thin layers of anhydrite or of gypsum no doubt marks successive N.B. periods of desiccation and inflow; in other words, each seam of the sulphate of lime (which is the least soluble salt, and is therefore thrown down first) seems to indicate a renewed supply of salt water from outside, probably from the open sea, while the overlying rock-salt shows the continued evaporation during which the water became a concentrated solution, and deposited the thicker layer of sodium chloride. Sometimes the concentration continued until still more soluble salts, such as chlorides of potassium and magnesium, were also eliminated. These phenomena are well displayed at the great salt-mines of Stassfurt, on the north flank of the Harz Mountains. The lowest rock there found is a mass of pure, solid, crystalline rock-salt of still unknown thickness, but which has been pierced for about 1000 feet. This rock is separated into layers, averaging about 3 inches in thickness, by partings of anhydrite + inch thick or less. If each of these "year rings," as the German miners call them, represented the deposit formed during the dry season of a single year, then the mass of 1000 feet would have taken more than 3000 years for its formation. But there do not appear to be any good grounds for believing that each band marks one year's accumulation. Above the rock-salt lie valuable deposits of the more soluble