In the days of Cuvier the Tertiary formations were considered as a mere chaos of superficial deposits, having no distinct relations to each other. It was reserved for the English geologists, with Sir Charles Lyell at their head, to throw light upon this obscure page of the earth’s history; from the study of fossils, science has not only re-animated the animals, it has re-constructed the theatre of their existence. We see the British Islands now a straggling archipelago, and then the mouth of a vast river, of which the continent is lost; for, says Professor Ramsay, “We are not of necessity to consider Great Britain as having always been an island; it is an accident that it is an island now, and it has been an island many times before.” In the Tertiary epoch we see it surrounded, then, by shallow seas swarming with numerous forms of animal life; islands covered with bushy Palms; banks on which Turtles basked in the sun; vast basins of fresh or brackish water, in which the tide made itself felt, and which abounded with various species of sharks; rivers in which Crocodiles increased and multiplied; woods which sheltered numerous Mammals and some Serpents of large size; fresh-water lakes which received the spoils of numerous shells. Dry land had increased immensely. Groups of ancient isles we have seen united and become continents, with lakes, bays, and perhaps inland seas. Gigantic Elephants, vastly larger than any now existing, close the epoch, and probably usher in the succeeding one; for we are not to suppose any sudden break to distinguish one period from another in Nature, although it is convenient to arrange them so for the purposes of description. If we may judge from their remains, these animals must have existed in great numbers, for it is stated that on the coast of Norfolk alone the fishermen, in trawling for oysters, dredged up between 1820 and 1833, no less than 2,000 molar teeth of Elephants. If we consider how slowly these animals multiply, these quarries of ivory, as we may call them, must have required many centuries for their production and accumulation.
Fig. 179.—a, Tooth of Machairodus, imperfect below, natural size; b, outline of cast of tooth, perfect, half natural size; c, tooth of Megalosaurus, natural size.
The same lakes and rivers were at this time occupied, also, by the Hippopotamus, as large and as formidably armed as that now inhabiting the African solitudes; also the two-horned Rhinoceros; and three species of Bos, one of which was hairy and bore a mane. Some Deer of gigantic size, as compared with living species, bounded over the plains. In the same savannahs lived the Reindeer, the Stag, a Horse of small size, the Ass, the Bear, and the Roe, for Mammals had succeeded the Ichthyosauri of a former age. Nevertheless, the epoch had its tyrants also. A Lion, as large as the largest of the Lions of Africa, hunted its prey in the British jungles. Another animal of the feline race, the Machairodus ([Fig. 179]), was probably the most ferocious and destructive of Carnivora; bands of Hyænas and a terrible Bear, surpassing in size that of the Rocky Mountains, had established themselves in the caverns; two species of Beaver made their appearance on the scene.
The finding of the remains of most of these animals in caverns was perhaps among the most interesting discoveries of geology. The discovery was first made in the celebrated Kirkdale Cave in Yorkshire, which has been described by Dr. Buckland; and afterwards at Kent’s Hole, near Torquay. This latter pleasant Devonshire town is built in a creek, shut out from exposure on all sides except the south. In this creek, hollowed out of the rocks, is the great fissure or cavern known as Kent’s Hole; like that of Kirkdale, it has been under water, from whence, after a longer or shorter interval, it emerged, but remained entirely closed till the moment when chance led to its discovery. The principal cavern is 600 feet in length, with many crevices or fissures of smaller extent traversing the rock in various directions. A bed of hard stalagmite of very ancient formation, which has been again covered with a thin layer of soil, forms the floor of the cavern, which is a red sandy clay. From this bed of red loam or clay was disinterred a mass of fossil bones belonging to extinct species of Bear, Lion, Rhinoceros, Reindeer, Beaver, and Hyæna.
Such an assemblage gave rise to all sorts of conjectures. It was generally thought that the dwelling of some beasts of prey had been discovered, which had dragged the carcases of elephants, deer, and others into these caves, to devour them at leisure. Others asked if, in some cases, instinct did not impel sick animals, or animals broken down by old age, to seek such places for the purpose of dying in quiet; while others, again, suggested that these bones might have been engulfed pell-mell in the hole during some ancient inundation. However that may be, the remains discovered in these caves show that all these Mammals existed at the close of the Tertiary epoch, and that they all lived in England. What were the causes which led to their extinction?
It was the opinion of Cuvier and the early geologists that the ancient species were destroyed in some great and sudden catastrophe, from which none made their escape. But recent geologists trace their extinction to slow, successive, and determinative action due to local causes, the chief one being the gradual lowering of the temperature. We have seen that at the beginning of the Tertiary epoch, in the older Eocene age, palms, cocoa-nuts, and acacias, resembling those now met with in countries more favoured by the sun, grew in our island. The Miocene flora presents indications of a climate still warm, but less tropical; and the Pliocene period, which follows, contains remains which announce an approach to our present climate. In following the vegetable productions of the Tertiary epoch, the botanist meets with the floras of Africa, South America, and Australia, and finally settles in the flora of temperate Europe. Many circumstances demonstrate this decreasing temperature, until we arrive at what geologists call the glacial period—one of the winters of the ancient world.
But before entering on the evidences which exist of the glacial era we shall glance at the picture presented by the animals of the period; the vegetable products we need not dwell on—it is, in fact, that of our own era, the flora of temperate regions in our own epoch. The same remark would apply to the animals, but for some signal exceptions. In this epoch Man appears, and some of the Mammals of the last epoch, but of larger dimensions, have long disappeared. The more remarkable of these extinct animals we shall describe, as we have those belonging to anterior ages. They are not numerous; those of our hemisphere being the Mammoth, Elephas primigenius; the Bear, Ursus spelæus; gigantic Lion, Felis spelæa; Hyæna, Hyæna spelæa; Ox, Bison priscus, Bos primigenius; the gigantic Stag, Cervus megaceros; to which we may add the Dinornis and Epiornis, among birds. In America there existed in the Quaternary epoch some Edentates of colossal dimensions and of very peculiar structure, these were Megatherium, Megalonyx, and Mylodon; we shall pass these animals in review, beginning with those of our own hemisphere.