Banks,

Banks, in Navigation, are shelving elevations in the sea or the bed of a river, rising to or near the surface, composed of sand, mud, or gravel. When tolerably smooth at the top, they constitute shallows, shoals, and flats; but when rocky, they become reefs, ridges, keys, &c. A good chart always defines them, indicating whether they are sands or rocky. Some sandbanks shift their position by reason of currents, &c., and are specially troublesome.