Atlantic Ocean, that division of the ocean lying between Europe and Africa on the east and north, and America on the west. Its northern and southern boundaries are not definitely fixed, but are generally considered to extend from the Arctic to the Antarctic Circle. This gives the Atlantic a length of 9000 miles. Its width varies from about 7000 miles, between Greenland and Norway, to 4100 miles, between Florida and the Strait of Gibraltar. The width, between Cape Palmas in Africa and Cape Saint Roque in South America, is 1900 miles. The area exclusive of branches is about 30,000,000 square miles. The important branches of the Atlantic are, on the east, the North Sea, the Baltic Sea, Bay of Biscay, Mediterranean and Gulf of Guinea, and on the west, Gulf of Mexico, Gulf of Saint Lawrence and Hudson Bay. Many geographers consider the Arctic Ocean merely as an extension of the Atlantic, while others consider it as a separate ocean. The coast line of the North Atlantic is irregular, but that of the South Atlantic is more even. The length of the eastern coast is over 32,000 miles; that of the western coast, 55,000 miles. The principal islands along the east coast are the Faroes, the British Isles, the Canaries, the Madeiras and Saint Helena. Those off the coast of America are Greenland, Newfoundland, the West Indies, Trinidad and the Falklands, while the Azores are just a little east and Iceland is just a little west of mid-ocean in the North Atlantic. The bed of the Atlantic is divided, by a ridge extending north and south nearly midway between the continents, into two valleys, each of which is about 500 miles wide. The eastern varies in depth from 14,000 to 15,000 feet, and the western from 13,000 to 16,800. The dividing ridge is comparatively narrow and has a depth of from 9000 to 10,000 feet. North of the Azores the bed of the ocean gradually rises, forming a plateau whose length extends east and west from the Hebrides to Newfoundland. This is sometimes known as the telegraph plateau, because the Atlantic Cable is laid upon it (See CABLE, ATLANTIC). This plateau separates the cold waters of the Arctic Ocean from the warmer waters of the Atlantic. The greatest depths of the North Atlantic have been found east of Newfoundland, where soundings have been obtained as low as 20,000 feet, and north of Porto Rico, where a depth of 27,000 feet has been reached. The South Atlantic has depths varying from 20,000 to 24000 feet. For circulation, see CURRENTS, MARINE; GULF STREAM; also TIDES; WAVES.