First, a continental period, towards the close of which the forest of Cromer flourished (p. 214): when the land was at least 500 feet above its present level, perhaps much higher, and its extent probably greater than that given in the map, fig. 41.
Secondly, a period of submergence, by which the land north of the Thames and Bristol Channel, and that of Ireland, was gradually reduced to such an archipelago as is pictured in map, fig. 40; and finally to such a general prevalence of sea as is seen in map, fig. 39. This was the period of great submergence and of floating ice, when the Scandinavian flora, which occupied the lower grounds during the first continental period, may have obtained exclusive possession of the only lands not covered with perpetual snow.
Thirdly, a second continental period when the bed of the glacial sea, with its marine shells and erratic blocks, was laid dry, and when the quantity of land equalled that of the first period, and therefore probably exceeded that represented in the map, p. 279. During this period there were glaciers in the higher mountains of Scotland and Wales, and the Welsh glaciers, as we have seen, pushed before them and cleared out the marine drift with which some valleys had been filled during the period of submergence. The parallel roads of Glen Roy are referable to some part of the same era.
As a reason for presuming that the land which in map, fig. 41, p. 279, is only represented as 600 feet above its present level, was during part of this period much higher, Professor Ramsay has suggested that, as the previous depression far exceeded a hundred fathoms (amounting in Wales to 1,400 feet, as shown by marine shells, and to 2,300, by stratified drift), it is not improbable that the upward movement was on a corresponding scale.
In passing from the period of chief submergence to this second continental condition of things, we may conceive a gradual change first from that of map 39 to map 40, then
