[Illustration: PALÆOLITHIC CELT OF QUARTZITE FROM NATAL, SOUTH AFRICA. (_Quatrefages._)] In fact the area over which these evidences of man's existence have been found may be best defined by the negative, where they have not been found, as there is every probability that it will eventually be proved that, with a few exceptions, wherever man could have existed during the Quaternary period, there he did exist. The northern portions of Europe which were buried under ice-caps are the only countries where considerable search has failed to discover palæolithic implements, while nearly all Asia, Africa, and America, and vast extents of desert and forests remain unexplored. The next point to observe is, that throughout the whole of the Quaternary period there has been a constant progression of human intelligence upwards. Any theory of human origins which says that man has fallen and not risen is demonstrably false. How do we know this? The time scale of the Quaternary as of other geological periods is determined partly by the superposition of strata, and partly by the changes of fauna. In the case of existing rivers which have excavated their present valleys in the course of ages, it is evident that the highest deposits are the oldest. If the Somme, Seine, or Thames left remains of their terraces and patches of their silts and gravels at heights 100 feet or more above their present level, it is because they began to run at these higher levels, and gradually worked their way downwards, leaving traces of their floods ever lower and lower. In the case of deposits in caves or in still water, or where glacial moraines and _débris_ are superimposed on one another, the case is reversed, and the lowest are the oldest and the highest the most recent. In like manner if the fauna has changed, the remains found in the highest deposits of rivers and lowest, of caves will be the oldest, and will become more modern as we descend in the one case or ascend in the others. This is practically confirmed by the coincidence of innumerable observations. The oldest Quaternary fauna is characterized by a preponderance of three species, the mammoth (Elephas primigenius), the woolly rhinoceros (Rhinoceros tichorinus), and the cave-bear (Ursus spelæus). There are a few survivals from the Pliocene, as the gigantic elephant (Elephas antiquus) and a few anticipations of later phases, as the reindeer, horse, and ox, but the three mentioned are, with palæolithic man, the most characteristic. Then comes a long period when a strange mixture of northern and southern forms occurs. Side by side with the remains of Arctic animals such as the mammoth, the glutton, the musk ox, and the lemming, are found those of African species adapted only for a warm climate, the lion, panther, hyena, and above all the hippopotamus, not distinguishable from the existing species, which could certainly not have lived in rivers that were frozen in winter.