Hitherto we have been dealing with climatic changes which can be recognized with more or less certainty over most of the polar and temperate regions of the world, but we have now to describe a stage which appears to have been peculiar to Europe and possibly Asia—the Forest period. By 3000 B.C., or towards the close of the Neolithic period, considerable elevation had again taken place over the central latitudes of western Europe (the northern parts of Norway and Sweden were still several hundred feet below their present level). The southern part of the British Isles, which had remained slightly elevated since the last Glacial period, had now emerged to a height of nearly ninety feet above its present level; the area of Ireland had increased appreciably and part of the North Sea was land. The geographical changes were not great, but they were sufficient to turn the scale in the direction of a continental climate in the British Isles. The more or less complete closing of the Straits of Dover, and the consequent bar to the free circulation of the Gulf Drift, must have had an appreciable effect on the climate in the direction of continentality. At the same time the low level of northern Norway, and possibly the persistence of warm conditions in the Arctic basin, more and more attracted depressions to the northernmost track, so that the British Isles especially, and to a lesser extent Holland, Germany, southern Scandinavia and Russia, came more persistently under the influence of anticyclonic conditions. The rainfall of these countries diminished, and the surface of the bogs dried sufficiently to enable forests to grow in the western countries; in Germany heath-plants took the place of bog-plants, while in Russia steppe conditions supervened. The normal meteorological conditions at this time in fact resembled those of the memorable drought of 1921, which was characterized by low pressure and stormy conditions in the Arctic Ocean and a belt of high pressure and persistently fine weather across central Europe. During this phase the winters may have been severe, but the summers were warmer than the present, for in the peat-bogs of Ireland and Scotland are the remains of trees larger than any now found in the neighbourhood. The Irish bogs dried so completely that they were extensively inhabited; corded oak roads have been found at this horizon, while in 1883 a two-story log house, surrounded by an enclosure, was found in Drumkelin Bog, Co. Donegal; it was twelve feet square and nine feet in height, and a roadway led to it across the bog. Both house and roadway were entirely constructed of oak. With the hut were found a stone chisel and a flint arrowhead. Beneath the floor were fourteen feet of bog, and above the floor twenty-six feet. This time was also one of relatively little wind movement, for stools occur even in exposed positions on the mountain slopes of western Ireland, where trees will only grow now in sheltered positions near sea-level.