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.