A layer of soil, organic material, or rock particles which are no longer in the place where they were formed geologically but which have been redeposited away from their source. The agents of redeposition can be weathering, erosion, decay, soil-forming processes, and man himself. The material is carried by, suspended in, or dropped by air, water, or ice; or a mass that is accumulated by any other natural agent and that forms in layers on the earth's surface such as sand, gravel, silt, mud, fill, or loess. Thus an archaeological site is a complicated sequence of various sediments and soils. The study of such sequences is called stratigraphy.