3. _First Postglacial Retreat_, _Achenschwänkung_ in the Alpine region. Period of Solutrean industry. A cold dry climate, with dust-storms and wide-spread deposition of 'loess' in western Europe. Flint workers seeking many open stations. Horses and wild asses numerous on the prairies; reindeer and wild cattle very abundant. 2. _Recession of the Ice-Fields of the Fourth Glaciation._ Period of Aurignacian industry. Climate cold and increasingly dry; renewal of the dust-storms and deposits of the 'newer loess.' Flint industry in the caverns, grottos, shelters, and a few open stations. Opening of the Upper Palæolithic period. Arrival of the Crô-Magnon race. 1. _Final Stage of Fourth Glaciation._ Close of the Lower Palæolithic Mousterian culture. Gradual extinction of the Neanderthal race. The arrival of the Crô-Magnon race and the beginning of the Aurignacian industry took place during the period of retreat of the ice-fields of the fourth glaciation. As we pass from the levels of the early Aurignacian industry into those of the middle and upper Aurignacian, we find that the mammal life of Mousterian times continued in its prime all over western Europe, with the addition, one by one, of some new forms from the tundras, such as the musk-ox, and the successive arrival from the mountains and steppes of western Asia of such characteristic forms as the argali sheep and the wild ass, or kiang. [Illustration: FIG. 138. Geographic distribution (horizontal lines) of the reindeer, mammoth, and woolly rhinoceros, the three chief mammals of the tundra fauna, with reference to the retiring ice-fields (dots) of the Fourth Glacial Stage. After Boule and Geikie. (Compare Figs. 95 and 96.)] The extremely cold and moist climate of the fourth glaciation had passed, and a somewhat drier but still extremely cold climatic condition prevailed throughout western Europe. During the early Aurignacian the two northern types of lemming, the banded lemming (_Myodes torquatus_) and the Obi lemming (_Myodes obensis_), were still found along the upper Danube, as in the grottos of Sirgenstein, Ofnet, and Bockstein. From middle Aurignacian on through Solutrean times these denizens of the extreme north disappear from this region of Europe. Further evidence of a dry, cold climate is found in the recurrence of dust-storms and in the great deposits of 'newer loess' beginning in certain parts of Europe at the very close of the Mousterian industry and extending through both middle and late Aurignacian and Solutrean times in all the region of the upper Rhine, along both shores of the Danube, and westward in the valley of the Somme, in northern France. This period is therefore believed to correspond with the _Achen_ retreat of the great glaciers still covering the Alpine region.