This system is throughout highly calcareous, and furnishes, wherever it is developed, valuable materials for architectural and ornamental purposes.
This system is distinguished for the great amount and variety of its organic remains. The vegetable productions were intermediate between those of the coal period and those of the present time. The upper oölite, in the south of England, contains the stumps of trees and other plants, rooted in a black carbonaceous layer, evidently the soil from which they grew. These stumps and prostrate trunks are the remains of coniferous trees of large growth. ([Fig. 30.])
Corals occur in great abundance; also encrinites ([Fig. 31]), mollusks ([Fig. 32]), and cephalopoda.
But this system is specially characterized by the remains of saurian reptiles. The Ichthyosaurus ([Fig. 33], a) was a marine animal, having the general form of a fish, while its head, and especially its teeth, resemble those of the crocodile. It was an air-breathing animal like the cetacea, and was furnished with similar paddles. It was carnivorous, and was undoubtedly the largest and most formidable animal existing in the earlier part of the oölitic period. Its length could not have been less than thirty or forty feet.
The Plesiosaurus ([Fig. 33], b) was also a marine animal, and in ninny respects similar to the Ichthyosaurus; but its general form was more slender, its head was small, and its neck was of great length, the cervical vertebræ exceeding in number those of the swan.
