opening of the jaws exceeded seven feet. Its organs of pad locomotion were four paddles composed of numerous bones, surrounded by rays of true fins; the anterior pair were based upon a firm breast bone, which enabled the animal to give rapidity and precision to its motions. The form tre and arrangement of its vertebræ, which were in some species one hundred and forty in number, were like those of fishes. Some individuals attained a length of forty feet. They were carnivorous, as is shown by their teeth, as well as by the contents of their stomachs which have been found in a few instances preserved.

235. The Plesiosaurus (plesion, near; saurus, reptile,) approached more nearly the true reptiles in structure. Its Fig. 128.

Plesiosaurus.

The

head, which resembled that of a lizard, was very small; its
paddles were relatively longer than those of the Ichthyo-
saurus, and its tail was like that of the crocodile.
most remarkable peculiarity exhibited by this animal was
the inordinate length of its neck. Animals have usually
not more than five cervical vertebræ; the swan has twenty-
four, while the Plesiosaurus had from thirty to forty. The
animal seems to have been fitted for rapid motion. It
attained a large size; a perfect specimen has been obtained
seventeen feet long, and fragments of larger skeletons have
been found. Numerous species of the Ichthyosaurus and
Plesiosaurus have been found in the rocks from the mus-
chelkalk to the chalk.

236. Beds of jet, resembling cannel-coal but harder and more lustrous, are found in the Upper Lias, together with large fragments of bituminized wood of coniferous trees and Cycadeæ.

THE OOLITIC SYSTEM.

237. The Oolite is a marine formation of great extent and thickness, consisting principally of alternations of limestones and clays, embracing vegetable remains, and very numerous corals, shells, fishes and reptiles; insects and mammalia also are found in it. The Oolite derives its name (Oon, an egg; lithos, a stone,) from the fact that some of its beds consist of calcareous globules which resemble the roe of a fish; but this structure is not strictly characteristic of it. This system is developed in Great Britain and on the Continent of Europe, in France and Germany, (called the Jurassic series,) in Russia, India and America. Its subdivisions in England are:

UPPER OOLITE.

f Portland Beds-limestone of an oolitic struc-
ture, abounding with marine shells, ammon-
ites, &c.

Kimmeridge Clay-blue and yellow clay with
septaria, gypsum, marine shells and beds of
lignite or Kimmeridge coal.

MIDDLE OOLITE.

Coral Oolite or Coral Rag

-coarse limestone

full of corals and shells-beds of yellow sands
and calcareous grits.

Oxford Clay-dark blue clay with septaria and

numerous fossils-beds of calcareous sand-
stone.

LOWER OOLITE

Cornbrash-coarse gray limestone separated by beds of clay.

Forest Marble-sand, with thin fissile limestone and coarse shelly oolite.

Great Oolite-oolitic limestone and freestone, with beds of clay, and remains of reptiles, corals, &c.

Stonesfield Slate-oolitic limestone, with re-
mains of land animals, plants, insects, and
mammalia.

Fuller's Earth Beds-marls and clays contain-
ing fuller's earth.
Inferior Oolite-coa

-coarse limestone, ferruginous

sand with shells.

238. The alternations of limestones with clays and shales, displayed by the Oolitic series, give rise to peculiar features of outline in parts of England and France. Three successive ridges are the hard calcareous beds of the Lower, Middle and Upper Oolites, while the intervening plains and vallies consist of clays and shales.

239. The organic remains of the Oolite are numerous and varied, as might be expected from the variety of mineral constitution of the strata.

The corals occur chiefly in the Middle Oolite; the coral rag consists of an extensive coral reef thirty or forty feet thick, composed mostly of a few genera, some of which, as the Caryophyllia, are represented by species in the present seas.

Among the Crinoidea, the Pear Encrinite-Apiocrinites -similar in structure to the Lily Encrinite, grew abundantly, attached to rocks.

The Sea Urchins-Echini-were also numerous.

Of the mollusca, the bivalve acephalous were very abun

tirely made up of their remains. The Trigonia Costata, Fig. 129, abounded in the Oxford Clay. Ammonites and Belemnites were as common as in the Liassic period.

Trigonia Costata.

Crustacea appear in the Oolite with forms closely allied to those of the present day: Figure 130 presents an animal resembling the Lobster, found in the Oolitic clay. Fig. 130.

Fossil Crustacean.

Insects also are found, some of which very closely resembling the common Dragon-fly, are so perfectly preserved that the most delicate markings, and the nerves of the wings are distinctly discernible.

240. Of the vertebrate animals, fishes are found in abundance throughout the series, belonging mostly to the ganoid order. The Ichthyosaurus and Plesiosaurus, so abundant in the Lias, extend through the Oolite; and other saurians of gigantic size are found in these strata-Megalosaurus, Teleosaurus, Steneosaurus and Cetiosaurus. But

the most anomalous saurian of this period, was the Pterodactyle, (Pteron, a wing; dactulos a finger,) an animal, of which Cuvier remarks, "It is undoubtedly the most extraordinary of all the beings of whose former existence a knowledge is granted to us, and that which, if seen alive, would appear most unlike anything that exists in the present world."

The Pterodactyle bore some resemblance to the bat, but its mouth was very unlike that of the bat, having the jaws and teeth of a reptile. It was furnished with powerful membranous wings, enabling it to fly with ease and rapidity, and its feet were not so involved in the membranous expanse of the wings as to prevent walking. Its eyes were very large.

241. The Stonesfield slate

Fig. 131.

Pterodactyle.

furnishes the only specimens of fossil mammalia yet discovered in the secondary rocks. Parts of the skeletons and the

teeth of two genera of the marsupial order of mammiferous

quadrupeds have been found in this rock.