The New Student's Reference Work/Alluvium

Allu'vium', the name given to the masses of sand, earth and gravel brought down by currents of water and spread over plains, forming what is called alluvial land. Thus the Ganges, the Nile, the Amazon and the Mississippi have formed their deltas. It is estimated that the Mississippi every year carries down enough sediment to cover 268 square miles of land with a layer of earth one foot deep. The so-called bottom lands are those formed by alluvial deposits. Along rivers it is sometimes formed into terraces by the rising of floods to different heights.