The red sandstones seem to have been better adapted to retain the forms which were impressed upon them than to preserve the organic remains which were deposited in them. Hence, while they contain but few fossils, the strata are often covered with ripple marks, with sun cracks, occasioned by contraction while drying, or with depressions produced by rain-drops, and the pits are sometimes so perfect as to show the direction of the wind when the drops fell. (Fig. 28.) The tracks of animals are also well preserved. Some of them were produced by reptiles (Fig. 29, _c_), and some probably by marsupial animals, but most of them by birds (_a_, _b_). President Hitchcock has distinguished the tracks of more than thirty species in the sandstones of the Connecticut valley. Birds, reptiles and marsupial animals, seem to have been first introduced during this period. [Illustration: Fig. 29.] The new red sandstone is well developed in all its members on the continent of Europe. In England, all the members are present, except the Muschelkalk. The Triassic portion of it occurs in North America. It is found in detached portions, probably as parts of a continuous formation, in Nova Scotia, the eastern part of Maine, the Connecticut valley, and from New Jersey southward through Pennsylvania, Maryland, &c., to South Carolina. 5. _The Oölitic System._--The lower portion of this system is the Lias, and consists of a series of fissile, argillaceous limestone, marl, and clays. The _Oölite_ forms the intermediate member of the system, and consists of alternations of clay, arenaceous rock and limestone. Some of the limestones have an oölitic structure, and the whole system takes its name from this circumstance, though this structure is not found in all parts of it, and is often found in other formations. The central part of the oölite, the coral rag, is principally a mass of corals and comminuted shells. The _Wealden_, the highest member of the oölitic system, is an estuary deposit, consisting of calcareous beds, followed by sandstone, and terminated by the Wealden clay. 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. [Illustration: Fig. 30.] [Illustration: Fig. 31.] [Illustration: Fig. 32.]