We are most closely concerned with the changes which took place around the Baltic in Denmark and Scandinavia during this post-glacial retreat of the ice. Here also we find the same disappearance of the tundra and "barren-ground" fauna already noticed in France, and the appearance of a park-flora of forests interspersed with open glades or meadows. But we need not be surprised if we find that the retreat of the great Baltic or Scandinavian ice-sheet does not keep step exactly with that of the Alpine.[120] 1. The last ice-sheet had covered most of Scandinavia except the western half of Denmark and, perhaps, the most southern portion of Sweden. But a broad mass of ice covered most of Schleswig, at least the eastern half of Holstein, and a fairly wide zone of land south of and more or less parallel to the south shore of the Baltic. To the eastward and northward a great sea extended to the Arctic Ocean. This earliest stage marked the farthest advance of the ice just before the final retreat. 2. Slowly and gradually the ice retreated until finally it occupied only the mountains of the backbone of Scandinavia. The region of the Baltic Sea and the Gulf of Bothnia, a large part of Sweden and a good portion of Finland were covered by a great sheet of water, the Yoldia Sea, connected by a broad sound at the present Skager Rack with the North Sea and Atlantic, and still opening widely into the Arctic Ocean northeastward. The submerged regions had been greatly depressed, especially in the north. The clays deposited along the shores of the sea are now raised often to a height of one hundred metres above tide-level. But to the southward the depression was only slightly marked. [Illustration: SUCCESSIVE STAGES AND FORMS OF BALTIC SEA 1. Culmination of last advance of ice. 2. Yoldia Sea during retreat of ice. 3. Yoldia Sea at greatest size. 4. Scandinavia during Ancylus Epoch. (The white represents the ice; dark gray represents the land; light gray the Baltic Sea.)] It is important to our later study to notice that these clays, which are thick and fine-grained, are composed of thin layers of alternating dark material deposited in fall or winter, and lighter, more sandy, brought down by the spring freshets. The temperature of the sea could hardly have been much above freezing-point, as is shown by the presence of arctic forms of mollusks, like _Yoldia arctica_ and _Astarte borealis_. The land-plants of this epoch, the so-called Dryas flora, are dwarf cold tundra forms, now occurring in Spitzbergen, Lapland, and Arctic Russia and Siberia. But certain plants, especially in Sweden, lead us to infer that while the winters were long and severe, the short summers were warm or even hot. This does not surprise us in northern tundra regions. Reindeer still lived in the region. This Yoldia Epoch is our second great post-glacial stage. Man had apparently not yet reached Denmark, though some reindeer hunters probably roamed over Germany.