long swan-like neck enabled it to lie at the bottom and raise its head to the surface to breathe, or, when at the surface, to send down its powerful jaws and catch its prey at the bottom.

Still more extraordinary were the Pterosaurs or flying reptilesstrange bat-like creatures with disproportionately large heads, and large eyes like those of Ichthyosaurus. The outermost finger of each forefoot was prolonged to a great length, and supported a membrane with which the animals could fly. The bones were hollow and filled with air like those of birds. Various forms of these winged lizards are found in the Jurassic rocks, the most typical being

FIG. 181.-Jurassic Pterosaur, or flying reptile (Scaphognathus crassirostris),

Middle Oolite.

Pterodactylus and Scaphognathus (Fig. 181); others are Dimorphodon, Rhamphorhynchus, Rhamphocephalus, and Dorygnathus.

The Deinosaurs, which have already been noticed as having appeared in Triassic time, attained a far greater development in the Jurassic period. These hugest land-reptiles now reached their maximum in size and variety. One of their genera, Megalosaurus, is believed to have been 25 feet long, and to have walked on its massive hind legs along the margins of the shallow waters in search of the smaller animals on which it preyed. Another form, Ceteosaurus, which may have been as much as 50 feet from the snout to the tip of the tail, and stood some 10 feet high, fed on the vegetation that shaded the rivers and lagoons where it lived. Still more gigantic were some deinosaurs, of which the remains have been found in the Jurassic rocks of North America. Brontosaurus, about 50 feet or more in length with a short body, long neck and tail, and small head, had enormous feet, each of which made an imprint measuring about a square yard in area. Stegosaurus, another sluggish deinosaur, was protected by numerous huge plates and spines of bone on its back, some of the latter more than 3 feet long. The largest of all these monsters, and, so far as yet known, the most colossal animal that ever walked on the earth, was the Atlantosaurus, which is believed to have been not much less than 100 feet in length, and 30 feet or more in height.

In another respect, the fauna of the Jurassic period stands out

from those that preceded it; it contained the earliest known birds. These interesting prototypes differed much from modern birds, more particularly in the possession of certain peculiarities of structure that linked them with reptiles. They had teeth in their jaws, and some of them carried long lizard-like tails, each vertebra of which bore a pair of quill-feathers. The best known genus is Archæopteryx (Fig. 182), found in the lithographic limestone of

Solenhofen.

Marsupials, which, so far as yet known, made their appearance in Triassic time, continued to be the only representatives of the mammalia during the Jurassic period, at least no other types have yet been discovered among the fossils. Lower jaws and detached teeth (Fig. 183) have been obtained from two distinct

FIG. 183.-Jurassic Marsupial (Phascolotherium Bucklandi). (a) Teeth magnified; (b) Jaw, natural size.

platforms in England-the Stonesfield Slate and Purbeck bedsand have been referred to a number of genera which find their nearest modern representatives in the Australian bandicoots and in the American opossums (Phascolotherium, Stereognathus, Spalacotherium, Plagiaulax).

The Jurassic system has been arranged in the following subdivisions:

Limestones and calcareous freestones (Portland
Stone); Cerithium portlandicum, Ammonites
giganteus, Trigonia gibbosa.

Sandstones and marls (Portland Sand); Ammon-
ites biplex, Exogyra bruntrutana.
Dark shales and clays (Kimmeridge Clay); Am-
monites decipiens, Exogyra virgula.
Coral rag (limestone with corals), clays, and
calcareous grits; Thamnastræa, Isastrea,
Cidaris florigemma, Ammonites cordatus (Fig.
176).

Blue and brown clay (Oxford Clay); Ammonites
Jason (Fig. 176).

Calcareous sandstone (Kellaways Rock-Callo-
vian); Ammonites calloviensis.

1. The Lias, so called originally by the Somerset quarrymen from its marked arrangement into "layers," extends completely across England from Lyme Regis to Whitby. It can be divided into three distinct sections: (a) A lower group of thin blue limestones and dark shales with limestone nodules, the limestones being largely used for making cement. This is one of the chief platforms for the reptilian remains, entire skeletons of ichthyosaurus, plesiosaurus, etc., having been exhumed at Lyme Regis ; (b) Marlstone or Middle Lias-hard argillaceous or ferruginous limestones which form a low ridge or escarpment rising from the plain of the Lower Lias; in Yorkshire contains a thick series of beds of earthy carbonate of iron, which are extensively mined as a source for the manufacture of iron; (c) Clays and shales surmounted by sandy beds (Upper Lias Sands). The organic remains of the Lias are abundant and well preserved. They are chiefly marine; but that the rocks containing them were deposited near land is indicated by the numerous leaves, branches, and fruits imbedded in them, and by the various insect-remains that have been obtained from them. In Germany, where the Lias is well developed and presents a general resemblance to the English type, it is known as the Lower or Black Jura. It is still better shown in France, where its three stages attain in Lorraine a united thickness of more than 600 feet. To the south, however, in Provence, it reaches the great thickness of 2300

feet.

2. The Bajocian stage, so named from Bayeux in Normandy, where it is well displayed, has long been known in England under the name of Inferior Oolite. It presents two distinct types in this country, being a thoroughly marine formation in the southwestern counties and passing northward into a series of strata which were accumulated in an estuary, and which contain the chief repositories of the Jurassic flora. Among the estuarine beds of Yorkshire a few thin coal-seams occur, which have been worked to some extent. On the continent, this division is characteristically marine; it reaches its greatest development in Provence, where it is 950 feet thick. It runs through the Jura Mountains, where it is made up of more than 300 feet of strata, chiefly limestone. In Germany the strata from the top of the Lias to the base of the Callovian group-that is, the two stages of Bajocian and Bathonian-are classed together as the Middle or Brown Jura, or Dogger.

3. The Bathonian stage is named from Bath, where its subdivisions are admirably exposed. At its base is a local argillaceous band known as Fuller's Earth, because long used for fulling cloth. The chief member of the stage in the south-west of England is the Great or Bath Oolite, a succession of limestones, often oolitic, with clays and sands. The Stonesfield Slate is the name locally given to some thin-bedded limestones and sands forming the lower part of the Great Oolite, and of high geological interest from having supplied among their fossils remains of land-plants, numerous insects, bones of enaliosaurs and deinosaurs, and of small marsupials. The Great Oolite abounds in corals, and contains numerous genera of mollusca, fishes, and reptiles. The Cornbrash (so named from its friable (brashy) character, and from its forming good soil for corn) is one of the most persistent bands in the English Jurassic system, retaining its characters all the way from the south-western counties to near the Humber.

4. The Oxfordian stage, sometimes called the Middle or Oxford Oolite, consists of a lower zone of calcareous sandstone, known as the Kellaways rock or Callovian, from the name of a place in Wiltshire, and of a thick upper stiff blue and brown clay, called, from the locality where it is well developed, the Oxford Clay, and containing numerous ammonites, belemnites, and oysters, but no corals. In Germany, the strata from the base of the Callovian to the top of the Purbeckian group are known as the Malm or White Jura.