[Illustration: FIG. 94. Europe during the extension of the ice-fields and glaciers of the Fourth Glacial Stage. This is also supposed to have been a period of land depression and of extension of the inland seas of southern Europe. Britain was probably connected with France. The ice-covered areas in western Europe and Britain were far more limited than during the Third Glacial Stage, yet the climate appears to have been more severe than at any previous period. For the snow-level compare Fig. 13. Drawn by C. A. Reeds after Geikie and De Geer.] In the north, Scandinavia and Finland were again enshrouded in ice, and a great _mer de glace_ occupied the basin of the Baltic Sea, sending its terminal moraines into Denmark and Schleswig-Holstein and over the northern provinces of Germany, but this great ice-field did not again become confluent with that of Great Britain.(7) At the commencement of the fourth glaciation large glaciers descended over the Scottish mountain valleys and filled many of them even to the sea; the coast subsided at least 130 feet in this region. In southern Britain along the valley of the Thames there spread an arctic flora, with the polar willow (_Salix polaris_) and the dwarf birch (_Betula glandulosa_); an arctic plant bed has also been discovered in the valley of the Lea. Thus the tundra climate extended from the Scottish lowlands to the south of England, the land being bleak and almost treeless.(8) This, we believe, was also the period of the arctic flora at Hoxne, Suffolk, and of the arctic plant bed in the valley of the Thames. At this time the valley was frequented by the reindeer, the woolly rhinoceros, and the mammoth, whose remains are entombed in the low-level alluvia swept down from the sides of the valley, so that the remains of this arctic fauna may in places actually overlie those of the more deeply buried and far more ancient warm Asiatic fauna of Chellean times. Like the Somme, the Thames(9) was then from 10 to 25 feet below its present level, the bottom having since silted up with alluvial soil. [Illustration: FIG. 95. The two large tundra mammals, the woolly rhinoceros (upper), drawn from the work of Upper Palæolithic artists and from the specimen discovered at Starunia, in Galicia, Austria; and the woolly mammoth (lower). These hardy animals gradually replaced the African-Asiatic pair, Merck's rhinoceros and the straight-tusked elephant. Drawn by Erwin S. Christman. One-sixtieth life size.] This was the period of the deposition of the 'upper drift' over the north German lowlands, the Alps, and northern England, also of the early and late _Wisconsin_, or 'upper drift,' which spreads very widely over the Eastern States, from Wisconsin southward and eastward to the latitude of New York. The gravels and sands of some of the 'lowest terraces' were also deposited. MAMMALIAN LIFE OF MOUSTERIAN TIMES