Thus the Neanderthal races were entering the Mousterian stage of culture during the close of the Third Interglacial Stage and during the early period of the advance of the ice-fields from the great centres in Scandinavia and the Alps. As these ice-fields slowly approached each other from the north and from the south a very great period of time must have elapsed during which all the south Asiatic mammals abandoned western Europe or became extinct, with the exception of the lions and hyænas, which became well fitted to the very severe climate that prevailed over Europe during the fourth glaciation, and even during the long Postglacial Stage which ensued. The large carnivora readily become thoroughly adapted to cold climates, as they subsist on animal life wherever it may be found; tigers of the same stock as those of India have been found as far north as the river Lena, in latitude 52° 25', where the climate is colder than that of Petrograd or of Stockholm, while the lion throve in the cold atmosphere of the upper Atlas range. Thus the cave-lion (_Felis leo spelæa_) and the cave-hyæna (_H. crocuta spelæa_) doubtless evolved an undercoating of fur as well as an overcoating of long hair, like the tundra mammals. In size the lion of this period in France often equalled and sometimes surpassed its existing relatives, the African and west Asiatic lion; it frequently figures in the art of the Upper Palæolithic artists and survived in western Europe to the very close of Upper Palæolithic times. THE FOURTH GLACIATION Penck(4) has estimated that the first maximum of the fourth glaciation in the Alps was reached 40,000 years ago, and that after the recession period the second maximum ended not less than 20,000 years ago. This would extend the Mousterian industry over a very long period of time, for there can be no doubt that the Mousterian culture was practically contemporaneous with the fourth glaciation, even if a briefer period of time should be allotted to this great natural event. The fourth glaciation, like the first, is believed to have been contemporaneous in Europe and North America,(5) a fact which is of especial importance to American anthropologists in connection with the question of the date of arrival of primitive man in America. In both countries the glaciation reached an early maximum, which was followed by a period of recession of the ice-fields, a time during which a somewhat more temperate climate prevailed, but this in turn gave way to a second advance of as great severity as the first.[AE]