Postglacial and Recent System. The deposits belonging to this system contain the remains of plants and animals, few of which are not still existing species. The beds consist of more or less incoherent and uneconsolidated materials, which have been formed under very diverse conditions. They are represented by the low-lying alluvial flats that occupy the sites of silted-up lakes, and the bottoms of valleys at moderate elevations above the streams and rivers. Most of the bogs of northern and central Europe belong to the same system, but some had commenced to form towards the close of the glacial period. Many bogs overlie the remains of old forests, and not infrequently trees, occupying the place of growth, occur in the peat at various levels. Two such 'buried forests' have been met with in the bogs over a wide region in north-western Europe. At many places on the coasts of the British Islands and the opposite shores of the Continent peat with buried trees passes out to sea, and has been dredged up from the sea-bottom at considerable distances from the land. The only other formations that need be mentioned are the raised Beaches (q.v.) which are met with at various heights above the present sea-level, and the local moraines and fluvio-glacial gravels of the higher valleys of the Scottish Highlands. Some of these moraines come down to the level of the 45 to 50 feet beach.
The flora and fauna of the period are essentially the same as at present. In the earlier stages of the period, however, the flora of north Germany, Denmark, southern Sweden, &c. was arctic-alpine, and that flora was accompanied by the northern mammals, including the reindeer, &c. Later in the period, as the climate became more genial, the northern flora and fauna disappeared from the low grounds of temperate Europe, and the present plants and animals took their place. Of the more notable mammals of the period in Britain were Megaceros (Irish deer), Bos primigenius, and Bos longifrons. The oldest traces of man met with at this stage belong to the Neolithic phase.
Several geographical and climatic changes appear to have supervened in postglacial and recent times. After the Scandinavian flora and fauna had been succeeded in our area by the present assemblage of plants and animals, the climate appears to have become even more genial than it is in our day. Great forests spread far north into regions where trees do not now grow, and reached elevations on the mountains which they cannot now attain. At the same time many southern types of molluscs migrated into northern seas, some of which have since died out, or still survive in diminished numbers and dwarfed in size. To this genial stage belong the great oaks and other leafy trees in the lower buried forests of the bogs. Eventually the climate changed and became wet and cold. The British area, formerly continental, was insulated and of less extent than now—the sea overflowing the low ground of Scotland up to a height of 45 to 50 feet above its present level. Local glaciers then made their appearance in many mountain-glens, and even descended in some places to the sea. The 'carse-clays' (45–50 feet terrace) belong to this stage. The climate was not so favourable for the growth of great trees, which were now more restricted in their vertical and horizontal range. Over wide areas the forests decayed and became buried by mosses and their allies. The general occurrence throughout north-western Europe of a second well-marked 'buried forest' seems to indicate a return to more genial climatic conditions, giving rise to a second period of great forests, which gradually overspread much of the moory and waste lands. Coincident with this second forest-epoch there appears to have been a gain of land, at least in Scotland, but there is no evidence to show that Britain again became continental. The second forest-epoch was succeeded as the first had been by somewhat cold and wet conditions, under the influence of which the forests decayed, while swamps and morasses increased. At the same time the Scottish area became depressed for some 25 feet or thereabout below its present level. The last physical change of which there is clear evidence is the final retreat of the sea, while the general aspect of the bogs (in which the rate of decay exceeds that of growth) would seem to indicate that we are living under drier conditions than obtained when the second forest-epoch came to a close. See EUROPE, STONE AGE.