Deposit

Deposit, a general term applied in geology to all aqueous rocks, with reference sometimes to their composition, sometimes to their sources or modes of origin, or even to their age. It is applied to the chemical precipitates thrown down from solution, such as stalagmite or rock-salt, and to accumulated remains of plants or animals, such as a bed of lignite or of oyster-shells, as well as to the sediment, whether clay or sand, thrown down from mechanical suspension in water. It might even be applied to the layers of various ores and veinstones lining the two sides or "cheeks" of a vein or "lode," though we know little as to the mode of their deposition. Deposits may be laid down in the sea, in lakes, or in river-beds; as rain-wash at the foot of slopes; or even as loess (q.v.) spread out by wind over wide land areas. A deposit maybe a mere film, as in the mud left on the water-meadows by a river-flood; or continuous, steady, and uniform conditions may produce marine deposits many feet in unbroken thickness. The term is not applicable to intrusive igneous rocks or to eruptive lavas; but even volcanic dust and ashes may, if they fall into water or are spread out at all uniformly over a large surface, be termed deposits.