One of the three main rock types. Sedimentary rocks were formed by the accumulation of layers of silt, sand, mud, stones, etc. on the bottom of a body of water or on the land by wind. Geologists can tell a lot about what happened in the past by examining these layers, how they are distributed, what is in them, etc.
Rock formed of sediment, and specifically: (1) sandstone and shale, formed of fragments of other rock transported from their sources and deposited in water; and (2) rocks formed by or from secretions of organisms, such as most limestone. Many sedimentary rocks show distinct layering, which is the result of different types of sediment being deposited in succession.