Its 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 reptiles-strange bat-like creatures with disproportionately FIG. 181.-Jurassic Pterosaur, or flying reptile (Pterodactylus crassirostris), Middle Oolite. large heads, and large bone-cased 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 common being Pterodactylus (Fig. 181); others are Dimorphodon and Rhamphorhynchus. The Deinosaurs, which have already been noticed as having appeared in Triassic time, attained a far greater development in the Jurassic period. These huge ostrichlike 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 spines and huge plates of bone on its back, some of them more than 3 feet across. 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 Archaopteryx, found in the lithographic limestone of Solenhofen. Other genera have been obtained in North America. Marsupials, which, so far as yet known, made their appearance in Triassic time, continued to be the only repre FIG. 182. Jurassic Bird (Archæopteryx macroura, about ), Solenhofen Limestone, Middle Jurassic. at least no other types have yet been discovered among FIG. 183.-Jurassic Marsupial (Phascolotherium Bucklandı); (a) Teeth magnified; (6) Jaw, natural size. the fossils. Lower jaws and detached teeth have been obtained from two distinct platforms in England-the Stonesfield Slate and Purbeck beds and have been referred to a number of genera which find their nearest modern representatives in the Australian phalangers and kangaroos and in the American opossums (Phascolotherium, Stereognathus, Spalacotherium, Plagiaulax). The Jurassic system has been arranged in the following subdivisions : Upper fresh-water beds (Purbeck). Middle marine beds Lower fresh-water beds دو دو Limestones and calcareous freestones (Portland Stone). Sandstones and marls (Portland Sand). Dark shales and clays (Kimmeridge Clay). ( Coral rag (limestone with corals), clays, and cal careous grits. Blue and brown clay (Oxford Clay). Calcareous sandstone (Kellaways Rock-Callo- Shelly limestones, clays, and sands (Cornbrash, Shelly limestones (Great or Bath Oolite) Stonesfield Slate. Bajocian (Inferior Oolite) Liassic Fuller's Earth. Marine calcareous freestones and grits (Chelten- Sandy beds and clays (Upper Lias, Toarcian). Thin blue and brown limestones, and dark shales 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; (6) 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 it 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. Tο the south, however, in Provence, it reaches the great thickness of 2300 feet. 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 south-western 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 |