A bench or step that extends along the side of a valley and represents a former level of the valley floor. They are the result of alternating period of erosion and aggradation (silting) within a river valley, brought about by oscillations of sea level relative to land. When sea level is low, the gradient of the river is increased, the water flows more quickly, and cuts away the river bed. During a period of high sea level the gradient is less, 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 aggradation with the fluctuations of Pleistocene climate, and thus to work out the relative dating of artifacts incorporated in the gravels of the terraces. Another type of terrace is cut into bedrock and may have a thin veneer of alluvium, or sedimentary deposits.