There is evidence of a succession of climatic changes in the region of Heidelberg. The Heidelberg jaw with its temperate mammalian fauna occurred at the very base of the Mauer bluff, but higher up the bluff (Fig. 46) on a corresponding level are found the remains of mammals which indicate a marked lowering of temperature and which are referred by some authorities to the period of chilling climate that characterized northern Europe toward the close of Second Interglacial times. The reindeer also occurs in the 'high terrace' gravels of the River Murr, near Steinheim; thus, at Mauer, at Süssenborn, and at Steinheim, we find proof that the reindeer had begun to spread over the colder regions of Europe, and there is some ground for belief that it found its way even as far south as the Pyrenees.
The evidence of the first cold, arid period which for the time greatly affected the climate of western Europe is also found in the layer of so-called 'ancient loess' which lies in the bluff above the 'sands of Mauer.' This loess covers the warm mammalian deposits of the 'sands of Mosbach' as well as the 'high terraces' of many of the ancient river-valleys. Both in Europe and America the climatic sequence of the Second Interglacial Stage from moist to dry appears to have been the same.
Thus, after the recession of the ice-fields of the second glaciation, the climate was at first cold and moist; then followed a long warm stage, favorable to the spread of forests; this was finally succeeded by a period of aridity in which the most ancient 'loess' deposits occurred. In Russia, also, the third glaciation was preceded by an arid and steppe-like climate with high winds favorable to the transportation of 'loess.'
No palæoliths or other proofs of human occupation have been found in this cold, dry period, for there is no evidence in any part of Europe of camping stations in this 'ancient loess' such as we find in the 'loess' which was deposited during the similar arid period toward the close of Third Interglacial and again during Postglacial times. Nor have we any record of the mammalian life in this 'ancient loess' of Europe.
The Third Glaciation[R]
This arid period in northern Europe and in North America was followed by the moist, cool climate of the third glaciation. It is estimated by Penck that the advance of these new ice-fields began 120,000 years ago and that the period of advance and retreat of the glaciers was not less than 20,000 years. In the Alps the snow-line descended 1,250 metres below the present level; consequently this glaciation was more severe than the first but somewhat less severe than the second. In northern Europe the Scandinavian ice-field did not cover so wide an area as during the second glaciation, although Britain and Scandinavia were again deeply buried by ice; the glacial cap and glaciers flowed in a westerly and southwesterly direction across Denmark and the southern portion of the basin of the Baltic into Holland and northern Germany. In the Alps the third glaciation sent vast ice-floes along the valley of the Rhine, into eastern France, and into the valley of the Po, where this glaciation was even more extensive than the second. But the greatest glacier of this time was that of the Isar, a southern tributary of the Danube, which rises in the Bavarian Alps.[(38)]
During the Third Glacial Stage certain of the 'middle terraces' along the Rhine and other rivers flowing from the Alps were formed. In Britain,[(39)] whereas during the second glaciation the ice-fields extended as far south as the Thames, during the third glaciation they did not extend beyond the midlands; yet an arctic climate prevailed over southern England, with tundra conditions and temperature, as indicated by the plant deposits at Hoxne[(40)] in Suffolk. Even before the third glaciation began in Europe a great ice-cap had formed over Labrador, on the eastern coast of North America, and the ice-sheets flowing to the south and southwest extended as far as Illinois, depositing the great Illinoian 'drifts.'
