The regions of the northern Alps bordering the great glaciers of the _Bühl_ and _Gschnitz_ advances, were barren stretches of rock, and the valleys and plateaus now free from ice became tundras, where the swamps alternated with patches of polar willows and stunted fir-trees, while other areas were covered with low, scrubby birches, or reindeer moss and lichens. The return of these hard conditions of life undoubtedly exerted a great influence both upon the physical and mental development of the Crô-Magnon race; it was at the very period when the life conditions in western Europe were most severe that the artistic development of these people began to revive. Forced to return to the shelters and grottos, which certainly were less frequented in Solutrean times, there was time for the development of the imagination and for its expression both in the mobile and parietal arts. There was a less vigorous development of the flint industry, and apparently a degeneration in physique and stature. In Germany and northern Switzerland, on the headwaters of the Rhine and the Danube, the entrance and departure of the northern waves of life are recorded, especially in the grottos of Sirgenstein, Schussenquelle, Andernach, Schmiechenfels, and Propstfels. It would appear that the woolly mammoth and the woolly rhinoceros were not hunted in this region, for their remains are not preserved in any of the grottos or stations mingled with the middle or late Magdalenian cultures. On the other hand, we find the steppe horse, the kiang, the stag, and the reindeer very abundant indeed. The bison is absent, and wild cattle are very rare; so that this region is not typical of the mammalian life of Magdalenian times as found in Dordogne and in the Pyrenees. The migration of the woolly mammoth and woolly rhinoceros along the Pyrenees and westward into the Cantabrian Mountains, and the crossing of the Pyrenees by the reindeer, have already been described. In the mural frescos of Font-de-Gaume, Dordogne, it is noteworthy that the very latest engravings are those of the mammoth superposed on the fine polychromes which belong to the period of middle Magdalenian art. THE DRY STEPPE CLIMATE OF MIDDLE MAGDALENIAN TIMES