“This is not all,” adds M. Fournet: “he who traverses the high plateaux of the country finds at every step deep diggings in the soil, designated pits or scialets, the oldest of which have their sides clothed with a curious vegetation, in which the Aucolin predominates; shelter is found in these pits from the cutting winds which rage so furiously in these elevated regions. Others form a kind of cavern, in which a temperature obtains sufficient to freeze water even in the middle of summer. These cavities form natural glaciers, which we again find upon some of the table-lands of the Jura.
“The cracks and crevasses of the limestone receive the waters produced by falling rain and melted snow; true to the laws of all fluid bodies, they filter through the rocks until they reach the lower and impervious marly beds, where they form sheets of water, which in course of time find some outlet through which they discharge themselves. In this manner subterranean galleries, sometimes of great extent, are formed, in which are assembled all the marvels which crumbling stalactites, stalagmites, placid lakes, and headlong torrents can produce; finally, these waters, forcing their way through the external orifices, give rise to those fine cascades which, with the first gushing torrent, form an actual river.”
The Albien of Alc. D’Orbigny, which Lyell considers to be the equivalent of the Gault, French authors treat as the “glauconie” formation, the name being drawn from a rock composed of chalk with greenish grains of glauconite, or silicate of iron, which is often mixed with the limestone of this formation. The fossils by which it is identified are very varied. Among its numerous types, we find Crustaceans belonging to the genera Arcania and Corystes; many new Mollusca, Buccinum, Solen, Pterodonta, Voluta, Chama, &c.; great numbers of molluscous Brachiopods, forming highly-developed submarine strata; some Echinoderms, unknown up to this period, and especially a great number of Zoophytes; some Foraminifera, and many Polyzoa (Bryozoa). The glauconitic formation consists of two groups of strata: the Gault Clay and the glauconitic chalk, or Upper Greensand and Chloritic Marl.
Upper Cretaceous Period.
During this phase of the terrestrial evolutions, the continents, to judge from the fossilised wood which we meet with in the rocks which now represent it, would be covered with a very rich vegetation, nearly identical, indeed, with that which we have described in the preceding sub-period; according to Adolphe Brongniart, the “age of angiosperms” had fairly set in; the Cretaceous flora displays, he considers, a transitional character from the Secondary to the Tertiary vegetation; that the line between the gymnosperms, or naked-seeded plants, and the angiosperms, having their seeds enclosed in seed-vessels, runs between the Upper and Lower Cretaceous formations. “We can now affirm,” says Lyell, “that these Aix-la-Chapelle plants, called Credneria, flourished before the rich reptilian fauna of the secondary rocks had ceased to exist. The Ichthyosaurus, Pterodactyle, and Mosasaurus were of coeval date with the oak, the walnut, and the fig.”[80]
The terrestrial fauna, consisting of some new Reptiles haunting the banks of rivers, and Birds of the genus Snipe, have certainly only reached us in small numbers. The remains of the marine fauna are, on the contrary, sufficiently numerous and well preserved to give us a great idea of its riches, and to enable us to assign to it a characteristic facies.
The sea of the Upper Cretaceous period bristled with numerous submarine reefs, occupying a vast extent of its bed—reefs formed of Rudistes (Lamarck), and of immense quantities of various kinds of corals which are everywhere associated with them. The Polyps, in short, attain here one of the principal epochs of their existence, and present a remarkable development of forms; the same occurs with the Polyzoa (Bryozoa) and Amorphozoa; while, on the contrary, the reign of the Cephalopods seems to end. Beautiful types of these ancient reefs have been revealed to us, and we discover that they have been formed under the influence of submarine currents, which accumulated masses of these animals at certain points. Nothing is more curious than this assemblage of Rudistes—still standing erect, isolated or in groups—as may be seen, for instance, at the summit of the mountains of the Cornes in the Corbières, upon the banks of the pond of Berre in Provence, and in the environs of Martigues, at La Cadière, at Figuières, and particularly above Beausset, near Toulon.
“It seems,” says Alcide D’Orbigny, “as if the sea had retired in order to show us, still intact, the submarine fauna of this period, such as it was when in life. There are here enormous groups of Hippurites in their places, surrounded by Polyps, Echinoderms, and Molluscs, which lived in union in these animal colonies, analogous to those which still exist in the coral-reefs of the Antilles and Oceania. In order that these groups should have been preserved intact, they must first have been covered suddenly by sediment, which, being removed by the action of the atmosphere, reveals to us, in their most secret details, this Nature of the past.”
In the Jurassic period we have already met with these isles or reefs formed by the accumulation of Coral and other Zoophytes; they even constituted, at that period, an entire formation called the Coral-rag. The same phenomenon, reproduced in the Cretaceous seas, gave rise to similar calcareous formations. We need not repeat what we have said already on this subject when describing the Jurassic period. The coral or madrepore isles of the Jurassic epoch and the reefs of Rudistes and Hippurites of the Cretaceous period have the same origin, and the atolls of Oceania are reproductions in our own day of precisely similar phenomena.
The invertebrate animals which characterise the Cretaceous age are among