Area of southern Britain The Ice Age

Beyond the ice margins, that is in the area of southern Britain characterized by an east-west trend in structure and relief, periglacial activity was the only Pleistocene effect. But periglacial processes were not confined to this region, for they spread back and forth across the country as the ice-sheets waxed and waned.

Glacial diversions of drainage may be found in any of the glaciated areas. In the highlands they may have been due to ice becoming so congested in narrow valleys that it spilled over the divides and ground out an escape route which was later followed by the post-glacial rivers. Alternatively, in both highlands and lowlands, proglacial lakes dammed between the ice front and escarpments or ranges of hills, may have risen in level and overflowed at the lowest available cols, the violent escape of meltwater ripping these out into typical overflow channels. Glacial diversion or superimposition provides the explanation of most of the anomalies between Britain's structure and drainage.

The Ice Age was a period of oscillating sea-level, as water was alternately abstracted from the oceans to form the ice-sheets and returned to the oceans as the ice-sheets melted. Interglacial sealevels were high and glacial sea-levels low, but they were not equally high nor equally low. The lack of uniformity between the high interglacial sea-levels may have been due to the continued tendency for intermittent negative movements of base-level to occur, or to differences in the extent to which the ice caps thawed out in different interglacials, or to a combination of both factors. Whatever the exact truth, the general effects on the coastal regions of Great Britain may be seen in the frequent occurrence of raised beaches, buried channels and submerged forests, and the possibility of sea-level having reoccupied the same level more than once makes it especially difficult to assign particular features to particular periods.

Neither may warping be excluded from the recent physical history of Great Britain. The Highlands of Scotland appear to have been domed gently upwards, as they were relieved of the weight of the ice cap and restored to isostatic equilibrium: the evidence is provided by the up-warped '100-foot' and '25-foot' raised beaches, both of them no older than the last glaciation. This is a small-scale repetition of the 1,000 ft or more of up-warping which has occurred since the melting of the ice cap in Scandinavia. Warping of a different type has affected the extreme east of England, principally the counties of Norfolk, Suffolk and Essex, for these are sufficiently near to the downsinking southern North Sea to have shared in its subsidence, though to a much smaller degree than the Netherlands.

The themes, then, of the recent physical development of Britain have been emergence and glaciation and these have accentuated the differences between the different structural and relief zones of Britain.

Two major regions are commonly recognized in Britain, highland and lowland, with the dividing line formed by the base of the Coal Measures. Like all great generalizations this creates difficulties, especially in the diversity of landforms placed in the highlands. Probably the only really satisfactory solution is to avoid classification and to treat all areas individually, but on a broad scale a case may be made for a threefold division into what may be termed highlands, uplands, and lowlands.