COAST, the edge of the land in contact with the sea. The term (from Lat. costa, a rib, side) is sometimes applied to the bank of a lake or wide river, and sometimes to a coastal zone (cf. Gold Coast, Coromandel Coast). If the coast-line runs parallel to a mountain range, such as near the Central Andes, it has usually a more regular form than when, as in the rias coast of south-west Ireland, it enters between the crustal folds. A recently elevated coast is usually regular, while a recently depressed coast shows the irregularities which were present upon the surface before sub mergence. Waves and sea-currents are the chief agents in coast sculpture. A coast of homogeneous rock exposed to steady erosion will present a regular outline, but if exposed to differential action it will be most embayed where the action is greatest. A coast con sisting of rocks of unequal hardness will be marked, when the wave and current action remains similar throughout, by headlands, "stacks" and "needles" of hard rocks, and bays or gulfs of softer or more loosely aggregated rocks, e.g., the southern shore-lines of the Isle of Wight and of south-western Wales. Subsequently the coast becomes "mature" and its outline undergoes little change as it gains on the land, for the hard rock being now more exposed is worn away faster than the softer rock which lies protected in the bays and re-entrants.