It will be seen that our inquiry into the antiquity of man is limited to the last four of the divisions. The most specialized of all animals can not be looked for until the higher Mammalia by which he is surrounded were alive. We can not imagine him in the Eocene age, at a time when animal life was not sufficiently differentiated to present us with any living genera of placental mammals. Nor is there any probability of his having appeared on the earth in the Miocene, because of the absence of higher placental mammals belonging to living species. It is most unlikely that man should have belonged to a fauna in which no other living species of mammal was present. He belongs to a more advanced stage of evolution than the mid-Miocene of Thenay. Up to this time the evolution of the animal kingdom had advanced no further than the Simiadæ in the direction of man; and the apes then haunting the forests of Italy, France, and Germany represent the highest type of those on earth. We may also look at the question from another point of view. If man were upon the earth in the Miocene age, it is incredible that he should not have become something else in the long lapse of ages, and during the changes in the condition of life, by which all the Miocene land Mammalia have been so profoundly affected that they have been either exterminated or have assumed new forms. Nor in the succeeding Pliocene age can we expect to find man upon the earth, because of the very few living species of placental mammals then alive. It is not until we arrive at the succeeding stage, or the Pleistocene, when living species of Mammalia began to abound, that we meet with indisputable traces of the presence of man on the earth. The rudely chipped implements of the River-drift hunter lie scattered through the late Pleistocene river deposits in southern and eastern England in enormous abundance, and as a rule in association with the remains of animals of Arctic and of warm habit, as well as some one or other of the extinct species of reindeer and hippopotamus along with mammoth and woolly rhinoceros.