The culture of the Crô-Magnons was doubtless influenced by the changing climatic conditions of Magdalenian times, which were quite varied, so that we may trace three parallel lines of development: that of environment, as indicated by the climate and the forms of animal life, that of industry, and that of art.

The entire climatic, life, and industrial cycle of which the Magdalenian marks the conclusion has been presented in Chapter IV (p. 281). After a very long period of cold and somewhat arid climate following the fourth glaciation, it would appear that western Europe in early Magdalenian times again experienced a stage of increasing cold and moisture accompanied by the renewed advance of the glaciers in the Alpine region, in Scandinavia, and in Great Britain. This is known as the Bühl stage in the Alps, in which the snow-line descended 2,700 feet below its present level and the great glaciers thrust down along the southerly borders of Lake Lucerne a series of new moraines distinctly overlying those of the fourth glaciation. Another indication of the lowered temperature and increased moisture in the same geographic region is found in the return of the arctic lemmings from the northern tundras; these migrants have left their remains in several of the large grottos north of the Alps, especially in Schweizersbild and Kesslerloch, composing what is known as the Upper Rodent Layer, with which are associated the implements and art objects of the early Magdalenian culture stage.

We have adopted the minimum estimate of 25,000 years since the fourth glaciation, but Heim[(4)] has estimated that the much more recent prehistoric event of the advance of this minor Bühl glaciation began at least 24,000 years ago, that it extended over a very long period of time, and that the Bühl moraines in Lake Lucerne are at least 16,000 years of age.

The three climatic changes of Magdalenian times are therefore as follows:

First, the Bühl Postglacial Stage in the Alps, which corresponds with what Geikie has named the Fifth Glacial Epoch, or Lower Turbarian, in Scotland; for he believes that a relapse to cold conditions in northern Britain was accompanied by a partial subsidence of the coast lands, that snow-fields again appeared, that considerable glaciers descended the mountain valleys, and even reached the sea. At this time the arctic alpine flora of Scotland also descended to within 150 feet of the sea-level. The result of this renewed or fifth glaciation in western Europe was the advent of the great wave of tundra life and the descent to the plains of all the forms of Alpine life.

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Fig. 180. Correlation of the Postglacial climatic changes with the four stages of Upper Palæolithic culture: the Aurignacian coincident with the final retreat of the fourth glaciation; the Solutrean coincident with the interval preceding the Bühl advance; the Magdalenian coincident with the Bühl and Gschnitz Postglacial advances; and the Azilian coincident with the Daun or third Postglacial advance. (Compare Fig. 14.)

Second, it would appear that in middle Magdalenian times, after the Bühl advance, there occurred a temporary retreat of the ice-fields, and that during this period the full tide of life from the steppes of western Asia and eastern Europe for the first time spread over western Europe, including especially such animals as the jerboa and the saiga antelope, the dwarf pika and steppe hamster. Correlation is very hazardous, but this ice retreat may correspond with the Upper Forestian, or Fifth Interglacial Stage in Scotland, described by Geikie, the stage which he mentions as marked by the elevation of the Scottish coast with the retreat of the sea beyond the present coast-lines; geographic changes which were accompanied by the disappearance of perennial snow and ice, and the return of more genial conditions. The tundra fauna still prevailed; such a typical arctic animal as the musk-ox wandered as far south as Dordogne and the Pyrenees, and became one of the objects of the chase. During what is known as the middle or 'full Magdalenian' the tundra, steppe, alpine, forest, and meadow faunæ spread over the plains and valleys throughout western Europe.

Third, the second Postglacial advance, known as the Gschnitz stage in the Alpine region, appears to have been contemporaneous with the closing period of Magdalenian culture. This was the last great effort of the ice-fields to conquer western Europe, and in the Alpine region the snow-line descended 1,800 feet below the present levels; it marked the closing stage of the long cold climatic period that had favored the presence of the reindeer, the woolly mammoth, and the woolly rhinoceros in western Europe, as well as the close of the 'Reindeer Epoch' of Lartet. Again, in the north of Britain Geikie observes an Upper Turbarian or Sixth Glacial Epoch, accompanied by a partial subsidence of the Scottish coast, and the return of a cold and wet climate; there is evidence of the existence of snow glaciers upon the high mountains only. The Gschnitz stage marks the end of glacial conditions in Europe, the retreat of the tundra and steppe faunæ, and the predominance of the forest and meadow environment and life.