Alluvium

Alluvium, a term originally applied to those deposits which were supposed to have been formed subsequently to the Flood, while Diluvium (q.v.) included the strata produced by it. In modern geological classification, these two terms have ceased to be used in this sense. By alluvium is now meant any earthy material deposited by the ordinary operation of water in motion. Hence it includes the mud, silt, sand, and gravel brought down by streams and rivers, and spread over lower lands, where it frequently forms flats and terraces. Some geologists extend the term to those wide accumulations of silt and mud which are formed in the upper reaches of estuaries, and laid bare at low tide. These are spoken of as marine alluvium. See DELTA, DENUDATION.