The Pterodactyle ([Fig. 34]) was a small saurian, of the size, probably, of our largest eagle. The finger-bones, which in the other saurians form the paddles, are in the Pterodactyle very much lengthened, so as to support a membranous expansion, like that of the bat. These wings were of sufficient size to enable it to sustain itself in the air, and to make a rapid and easy flight.
The Iguanodon is a Wealden fossil, remarkable for its great magnitude. It is estimated that its length was seventy feet. It was a lizard, adapted for motion on land, and was herbivorous.
This formation is well developed in England, and, with the exception of the Wealden, on the continent of Europe. It has been supposed that no part of the oölitic series was to be found in this country; but there is a highly arenaceous rock occupying the valley of the James river, in the vicinity of Richmond, Virginia, of considerable extent, and a thousand feet in thickness, containing a bed of coal of forty feet in thickness, which, from its fossils, must be referred to the oölitic series.
6. The Cretaceous Formation.—The lower part of this formation consists of greensand, interstratified with beds of clay. The intermediate portion is a mixture of argillaceous greensand and impure chalk. The upper part is composed of chalk, which is a friable, nearly pure carbonate of lime. The strata of chalk are separated, at intervals of from three to six feet, by layers of flint, either in the form of nodules or of continuous strata.
These characters, by which the cretaceous system is known in England, are but partially recognized elsewhere. Thus, in the Alps, the “Neocomian System,” consisting of crystalline limestones, is the equivalent of the English greensand; while the greensand of this country is the equivalent of the white chalk of England.
The fossils of the cretaceous formation are very different from those of the oölite, and are such as to show that it was deposited in deep seas. Microscopic shells are often so abundant as to constitute a large proportion of the mass. Zoöphytes are very numerous, such as sponges, corals, star-fishes ([Fig. 35], d e), and a few crinoidea (b). Mollusks were also abundant, and cephalopoda, consisting of chamber-shells and belemnites ([Fig. 36]). The belemnite probably resembled the existing cuttle-fish; but the remains consist, in most cases, of a partially hollow calcareous substance (b), which was contained within the animal, and formed its skeleton.