imity of land. In the other, we are presented with evidence of a wide open sea, where the same kinds of deposits and the same forms of marine life extend with little change over vast distances. Obviously, it is not the local type of the northern basin, but the more general and widespread type of Southern Europe that should be taken for the distinctive characteristics of the Cretaceous system. But the northern basin was the first to be systematically explored, and is still the best known, and hence its features have not unnaturally usurped the place of importance which ought properly to be assigned to the other wider area.

Regarding the period as a whole, let us first consider the general character of its distinguishing flora and fauna, and then pass on to trace the history of the period as revealed by the succession of strata. The plants of the Cretaceous system show that the vegetable kingdom had now made a most important advance in organisation. In the lower half of the system the fossil plants yet found are on the whole like those of the Jurassic rocks-that is, they include some of the same genera of ferns, cycads, and conifers which these rocks contained. But already the ancestors of our common trees and flowering plants must have made their appearance, for in the upper half of the system their remains occur in abundance. This earliest dicotyledonous flora numbered among its members species of maple, alder, aralia, poplar, myrica, oak, fig, walnut, beech, plane, sassafras, laurel, cinnamon, ivy, dogwood, magnolia, gum-tree, ilex, buckthorn, cassia, credneria, and others. The modern aspect of this assemblage of plants is in striking contrast to the more antique look of all the older floras. There were likewise species of pine (Pinus), Californian pine (Sequoia), juniper (Juniperus), and other conifers, various cycads, forms of screw-pine (Pandanus), palms (Sabal), and numerous ferns (Gleichenia, Asplenium, etc.) This flora

FIG. 184.-Cretaceous Plants; (a) Quercus rinkiana (3); (b) Cinnamomum sezannense(); (c) Ficus atavina (3); (d) Sassafras recurvata (3); (e) Juglans arctica ().

spread over the land, surrounding the northern Cretaceous basin, and extended northwards even as far as North Greenland, from which nearly 200 species of Cretaceous plants have been obtained. The inference may be deduced that the climate of the globe must then have been much warmer than at present. The luxuriant vegetation disinterred from the Cretaceous rocks of North Greenland includes more than forty kinds of ferns, besides laurels, figs, magnolias, and other plants, which show that, though the winters were no

FIG. 185.-Cretaceous Foraminifera; (a) Textularia baudouiniana (2); (b) Globigerina cretacea (°); (c) Rotalina voltziana (f°).

doubt dark, they must have been extremely mild. There could have been no perpetual frost and snow in these Arctic latitudes in Cretaceous times.

Foraminifera abound in some of the Cretaceous limestones, indeed, in some places they form almost the only constituent of these rocks. They are plentiful in the white chalk of England, France, and Belgium, one of the more frequent genera being Globigerina (Fig. 185) which still lives in enormous numbers in

the Atlantic, and forms at the FIG. 186.--Cretaceous Sponge bottom of that ocean a grey (Ventriculites decurrens, 1⁄2). ooze not unlike chalk (Fig. 33). Sponges lived in great numbers in the Cretaceous sea. Their minute siliceous spicules are abundant in the Chalk, and even entire sponges enveloped in flint are not uncommon (Ventriculites, Fig. 186). Sea-urchins are among the most familiar fossils of the Chalk, and must have lived

FIG. 187. Cretaceous Sea-urchins; (a) Echinoconus conicus, & (= Galerites albo-galerus), under surface and side view; (b) Ananchytes ovatus (2), side view and under surface; (c) Micraster cor-arguinum (1), upper and under surface.

in great numbers on the Cretaceous sea-bottom. Some of their genera are still living, and have been dredged up in recent years from great depths in the ocean. Among the more characteristic Cretaceous types are Ananchytes, Holaster, Micraster, and Echinoconus (Fig. 187). The brachiopods were still represented chiefly by the ancient genera Terebratula and Rhynchonella. Lamellibranchs abounded, especially the genera Ostrea, Exogyra, Inoceramus (Fig. 188), Lima, Pecten, and the various forms of Hippuritids. These last (Hippurites, Radiolites, Caprina, etc., Fig. 189) are specially characteristic, being, so far as we know, con

FIG. 188.-Cretaceous Lamellibranchs; (a) Trigonia aliformis (±); (b) Inoceramus sulcatus (1⁄2); (c) Nucula bivirgata (natural size).

fined to the Cretaceous system; hence their occurrence serves to indicate the Cretaceous age of the rock containing them. They have been imbedded in such numbers in the limestones of the south of Europe as to give the name of hippurite-limestone to these rocks. They are comparatively infrequent in the strata of the northern Cretaceous basin.

Probably the most distinctive feature in the molluscan life of the Cretaceous seas was the extraordinary variety in the development of the cephalopods. This is all the more remarkable from the fact that before the next geological period the great majority of these types appear to have become extinct. The ammonites and belemnites, which played so important a part in the fauna of Mesozoic time, died out about the close of that long succession of periods. At least in Europe, while their remains continue to present