for the Indo-Atlantic Antarctic Basin stretches from near the South Sandwich Islands towards Kerguelen with depths exceeding 2500 fathoms and reaching in places 3100. The Cape Trough runs northward from this basin. It was long believed on the strength of a sounding of “4000 fathoms, no bottom” reported by Sir James Ross in 68° 22′ S., 12° 49′ W., that the Indo-Atlantic Basin was of enormous depth, but W. S. Bruce, in the “Scotia,” showed in 1904 that the real depth at that point is only 2660 fathoms.
In the Indian Ocean the Kerguelen Rise stretches broadly southward, east of the island which gives it a name, to the Antarctic Shelf with the greatest depths upon it usually less than 2000 fathoms, and it stretches northward beyond New Amsterdam to 30° S. This rise is separated from the Crozet Rise by a depression extending to 2675 fathoms, through which the Kerguelen Trough (which lies north of Kerguelen) is brought into free communication with the Indo-Atlantic Antarctic Basin. The greater part of the Indian Ocean is occupied by the great Indian Basin, which covers 35,000,000 sq. km. (13,500,000 sq. m.) and extends from the Chagos Islands eastward to Australia and south-eastward to Tasmania. The Australian Shelf rises steeply as a rule from depths of 2500 to 3000 fathoms. A broad depression with depths of from 3300 to 3500 fathoms lies to the east of the Cocos Islands and extends into the angle between the Malay Archipelago and Australia. On the north this depression sinks into the long and narrow Sunda Trench south of Java, and here in 10° 15′ S., 108° 5′ E., the German surveying-ship “Planet” obtained a sounding of 3828 fathoms in 1906. The Sunda Trench is distinguished by the wave-like configuration of its floor, and this wave-like character is continued to the westward of Sumatra with islands rising from the higher portions. The western part of the Indian Ocean has been shown by the surveys of H.M.S. “Sealark” and the German surveying-ship “Planet” to have a somewhat complicated configuration, the island groups and banks of atolls which occur there rising abruptly as a rule from depths of about 2000 fathoms or more. Between the Seychelles and Sokotra (0°-9° N.) there are great stretches of the ocean floor forming an almost level expanse at a depth of 2800 fathoms. The Arabian Gulf and Gulf of Aden are also very uniform with depths of about 1900 fathoms, while the floor of the Bay of Bengal rises very gradually northwards and is 1000 fathoms deep close up to the Ganges Shelf.
The Pacific Ocean consists mainly of one enormous basin bounded on the west by New Zealand and the Tonga, Marshall and Marianne ridges, on the north by the festoons of islands marking off the North Pacific fringing seas, on the east by the coast of North America and the great Easter Island Rise and on the south by the Antarctic Shelf. The total area of this basin is about 80,000,000 sq. km. (30,000,000 sq. m.), its surface being almost twice that of Asia. Half of this basin lies deeper than 2750 fathoms, and the greater part of it belongs to the northern hemisphere. From the floor of this vast and profound depression numerous isolated volcanic cones rise with abrupt slopes, and even between the islands of the Hawaiian group there are depths of more than 2000 fathoms. The Society Islands and Tahiti crown a rise coming within 1500 fathoms of the surface, two similar rises form the foundation of the Paumotu group Where Agassiz found soundings of 2187 fathoms between Marokau and Hao. This greatest of ocean basins contains also the largest and deepest trenches. The Tuscarora Deep of the Japan Trench (4655 fathoms in 44° 55′ N., 152° 26′ E.) was famed for many years as the deepest depression of the earth's crust. This great trench is continued along the Luchu Islands where the cable-steamer “Stephan” sounded in 4080 fathoms, and through the Bonin Trench (with a maximum of 3595 fathoms) to the famous Marianne Trench in which the U.S.S. “Nero” in 1899 found 5269 fathoms in 12° 43′ N., 145° 49′ E., the greatest depth yet measured. The northern part of the Marianne Trench leads to a wave-like configuration of the ocean floor, the depth to the east of Saipan being over 4300 fathoms, followed by a rise to 1089 fathoms and then a descent to 3167 fathoms. The trenches of Yap (4122 fathoms) and Palau (Pelew) (4450 fathoms) are not immediately connected with that of Marianne. To the east of the Philippines a sounding of 3490 fathoms is found close to the Strait of St Bernardino and north-east of Talaut there is a trench with 4648 fathoms. To the north-east the Japan Trench adjoins the Aleutian Trench, where a depth of 4038 fathoms has been found south-west of Attu. Trenches of great size also occur south of the equator. The Tonga and Kermadec trenches, both deeper than 4000 fathoms, stretch from the Samoa Islands southwards toward New Zealand for a distance of 1600 nautical miles. The deepest sounding obtained in the Tonga Trench is 5022 fathoms in 23° 39.4′ S., 175° 4′ W., and in the Kermadec Trench, 5155 fathoms, 30° 27.7′ S., 176° 39′ W. The steep western sides of these trenches often show an angle of slope of 7°.
The south-western part of the Pacific Ocean has a very rich and diversified submarine relief, abounding in small basins separated by ridges and rises. There are no depths, however, much exceeding 2500 fathoms amongst these depressions. The south-eastern part of the Pacific is mainly occupied by the Easter Island Rise with depths rarely so great as 2000 fathoms; but close to the continent of South America the Atacama Trench is a typical example of the deepest form of depression culminating with 4175 fathoms in 25° 42′ S., 71° 31.5′ W. The Pacific Antarctic Basin occupies the vast region south of 50° S. right up to the Antarctic Shelf, with depths ranging down to 2500-3000 fathoms, and communicating with the main Pacific Basin to the east of New Zealand.
The greatest of the intercontinental seas, the Arctic, comes nearest to oceanic conditions in the extent and depth of its depressions. The soundings of Nansen and Sverdrup on the “Fram” expedition indicate that northward from the Siberian Shelf the great North Polar Basin has an area of about 4,000,000 sq. km. (1,500,000 sq. m.) with depths down to 2200 fathoms. A rise between Spitsbergen and Greenland separates the Norwegian Trough (greatest depth 2005 fathoms in 68° 21′ N., 2° 5′ W.) which in turn is divided from the Atlantic by the Wyville Thomson Ridge which runs between the Faeroe and Shetland islands and is covered by only 314 fathoms of water at the deepest point. The ridge across Denmark Strait west of Iceland nowhere exceeds 300 fathoms in depth, so that the deeper water of the North Polar Basin is effectively separated from that of the Atlantic. A third small basin occupies Baffin Bay and contains a maximum depth of 1050 fathoms. Depths of from 100 to 300 fathoms are not uncommon amongst the channels of the Arctic Archipelago north of North America, and Bering Strait, through which the surface water of the Arctic Sea meets that of the Pacific, is only 28 fathoms deep.
The Central American Sea communicates with the Atlantic through the channels between the Antilles, none of which is quite 1000 fathoms deep, and it sinks to a depth of 2843 fathoms in the Caribbean Basin, 3428 fathoms in the Cayman Trench and 2080 fathoms in the Gulf of Mexico.
The Austral-Asiatic or Malay Sea is occupied by a great shelf in the region west of Borneo and north of Java, while in the east there are eight abruptly sunk basins of widely different size. The China Sea on the north has a maximum depth of 2715 fathoms off the Philippines, the Sulu Basin reaches 2550 fathoms, and the Celebes Basin 2795 fathoms. Some of the channels between the islands are of very great depth, Macassar Strait exceeding 1000 fathoms, the Molucca Passage exceeding 2000 fathoms, and the Halmahera Trough sinking as deep as 2575 fathoms. The deepest of all is the Banda Basin, a large area of which lies below 2500 fathoms and reaches 3557 fathoms in the Kei Trench. A depth of 2789 fathoms also occurs north of Flores. The borders of the Malay Sea are everywhere shallower on the side of the Indian Ocean than on that of the Pacific, and consequently water from the Pacific preponderates in the depths.
The Mediterranean Sea, the best-known member of the intercontinental class, is separated from the Atlantic Ocean by a ridge running from Cape Spartel to Cape Trafalgar on which
