Fig. 130.—Fossil Palms restored.
But if the vegetation of the Cretaceous period exhibits sensible signs of approximation to that of our present era, we cannot say the same of the animal creation. The time has not yet come when Mammals analogous to those of our epoch gave animation to the forests, plains, and shores of the ancient world; even the Marsupial Mammals, which made their appearance in the Liassic and Oolitic formations, no longer exist, so far as is known, and no others of the class have taken their place. No climbing Opossum, with its young ones, appears among the leaves of the Zamites. The earth appears to be still tenanted by Reptiles, which alone break the solitudes of the woods and the silence of the valleys. The Reptiles, which seem to have swarmed in the seas of the Jurassic period, partook of the crocodilian organisation, and those of this period seem to bear more resemblance to the Lizards of our day. In this period the remains of certain forms indicate that they stood on higher legs; they no longer creep on the earth, and this is apparently the only approximation which seems to connect them more closely with higher forms.
It is not without surprise that we advert to the immense development, the extraordinary dimensions which the Saurian family attained at this epoch. These animals which, in our days, rarely exceed a yard or so in length, attained in the Cretaceous period as much as twenty. The marine lizard, which we notice under the name of Mosasaurus, was then the scourge of the seas, playing the part of the Ichthyosauri of the Jurassic period; for, from the age of the Lias to that of the Chalk, the Ichthyosauri, the Plesiosauri, and the Teleosauri were, judging from their organisation, the tyrants of the waters. They appear to have become extinct at the close of the Cretaceous period, and to give place to the Mosasaurus, to whom fell the formidable task of keeping within proper limits the exuberant production of the various tribes of Fishes and Crustaceans which inhabited the seas. This creature was first discovered in the celebrated rocks of St. Peter’s Mount at Maestricht, on the banks of the Meuse. The skull alone was about four feet in length, while the entire skeleton of Iguanodon Mantelli, discovered by Dr. Mantell in the Wealden strata, has since been met with in the Hastings beds of Tilgate Forest, measuring, as Professor Owen estimates, between fifty and sixty feet in length. These enormous Saurians disappear in their turn, to be replaced in the seas of the Tertiary epoch by the Cetaceans; and henceforth animal life begins to assume, more and more, the appearance it presents in the actually existing creation.
Seeing the great extent of the seas of the Cretaceous period, Fishes were necessarily numerous. The pike, salmon, and dory tribes, analogous to those of our days, lived in the seas of this period; they fled before the sharks and voracious dog-fishes, which now appeared in great numbers, after just showing themselves in the Oolitic period.
The sea was still full of Polyps, Sea-urchins, Crustaceans of various kinds, and many genera of Mollusca different from those of the Jurassic period; alongside of gigantic Lizards are whole piles of animalculæ—those Foraminifera whose remains are scattered in infinite profusion in the Chalk, over an enormous area and of immense thickness. The calcareous remains of these little beings, incalculable in number, have indeed covered, in all probability, a great part of the terrestrial surface. It will give a sufficient idea of the importance of the Cretaceous period in connection with these organisms to state that, in the rocks of the period, 268 genera of animals, hitherto unknown, and more than 5,000 species of special living beings have been found; the thickness of the rocks formed during the period being enormous. Where is the geologist who will venture to estimate the time occupied in creating and destroying the animated masses of which this formation is at once both the cemetery and the monument? For the purposes of description it will be convenient to divide the Cretaceous series into lower and upper, according to their relative ages and their peculiar fossils.
The Lower Cretaceous Period.
| English equivalents. | French classification. | |
| Lower Greensand, upper part. | Étage | Aptien st. |
| Lower Greensand, lower part. | „ | Néocomien supérieur. |
| Weald clay and Hastings sands. | „ | Néocomien inférieur. |
The Lower Wealden or Hastings Sand consists of sand, sandstone, and calciferous grit, clay, and shale, the argillaceous strata predominating. This part of the Wealden consists, in descending order, of:—
| Feet. | |
| Tunbridge Wells sand—Sandstone and loam | 150 |
| Wadhurst clay—Blue and brown shale and clay, with a little calc grit | 100 |
| Ashdown sands—Hard sand, with beds of calc grit | 160 |
| Ashburnham sands—Mottled, white, and red clay and sandstone | 330 |
The Hastings sand has a hard bed of white sand in its upper part, whose steep natural cliffs produce the picturesque scenery of the “High rocks” of Hastings in Sussex.