3. Toward the end of the Yoldia Epoch the land rose in southwest Sweden, connecting this country with Denmark and cutting the connection of the remains of the Yoldia Sea with the North Sea. A similar emergence in Finland completed the change of this sea into a great landlocked body of water called the Ancylus Lake, from the most common and characteristic mollusk, _Ancylus fluviatilis_. The glaciers had shrunken to a narrow band covering the mountains between Norway and Sweden. The climate, while moderating, was still cold. The Arctic flora retreated northward and was followed in Denmark by woods and even forests of willows, aspens, and poplars, entering from the south and southeast. These were followed by pines, especially in the dryer districts, later by alders, coming from the east across Finland, according to Hoops.[121] The Ancylus Epoch forms our third stage. The settlement at Maglemose probably took place toward its close. 4. The elevation and emergence of land so characteristic of the Ancylus Epoch was followed by a depression of this region, especially in its southern portions. That part of the Ancylus Lake corresponding to the Baltic regained broader and deeper connections with the North Sea than it has at present. Hence the waters of the Baltic contained a larger percentage of salt than now. The marine life, _Littorina littorea_, _Tapes_, and others, testifies to a rise in temperature since the Ancylus Epoch. Oaks had already begun to crowd out the pines, and will be followed after a time by the beeches loving a soil rich in humus, rather than the sandy barrens occupied by the pines. A similar evidence is furnished by other plants, some of which reached a higher latitude than now. The summer temperature was perhaps 2-1/2° Cent. higher than at present, an "optimum temperature" for the plant life of this region. This improvement of climate is most marked in northeastern Europe and seems far less noticeable even in Germany. Our fourth stage is marked by a greatly improved climate and the spread of the shell-heaps. 5. A fifth stage ushers in the full Neolithic period. Between the Littorina stage and the genuine Neolithic culture of lake-dwellings and megaliths there is a considerable gap in our knowledge, a period during which agriculture and domestic animals were brought in and utensils and pottery and general conditions were greatly improved.