River terraces

These are a result of alternating periods of erosion and silting up a river valley, brought about by rises and falls of sea level. When sea level is low (eg during the height of an Ice Age) the river has to cut away the river bed to reach the sea and therefore the water flows more quickly. During a period of high sea level the river does not have to cut down, the river flows sluggishly, and gravel is deposited on the valley floor. A second period of erosion will carry away most of this gravel, except at the edge of the valley where a residual platform, or terrace, may remain. It is often possible to correlate cycles of erosion and silting with the fluctuations of Pleistocene climate, and thus to work out the relative dating of artefacts incorporated in the gravel of the terraces.