THE ATLANTIC OCEAN ITS DEPTH AND CONFIGURATION OF ITS BED Previous to the recent scientific exploration of the Atlantic, depths of forty and even fifty thousand feet were occasionally reported, and its basin was regarded as a vast unbroken canal-like abyss, deepest along a middle line be tween the shores of the Old and the New Worlds, and gradually shoaling on either side. This idea, however, has been entirely dispelled by the researches of the Challenger and other scientific expeditions. Instead of a middle line of maximum depth, it is shown that a most remarkable ridge or submarine plateau 'extends from Cape Farewell on the north to Tristan d'Acunha on the south, generally following the outline of the coasts of the New and Old Worlds, thus repeating under water the S-shaped form of the shores of the Atlantic. The course of this great central ridge, which has an average elevation of 1,900 fathoms below the surface, may be roughly marked by a line drawn from Cape Farewell parallel to the coasts of Labrador and Newfoundland to the Azores ; thence sweeping round to St. Paul's Rocks, and following the Equator as far as 12° W. long., where it turns suddenly south by Ascension to Tristan d'Acunha. The first portion of this central ridge is comparatively broad ; south of the Azores it gets narrower, but widens out again south of Ascension, and between the Cape of Good Hope and the La Plata is nearly thirty degrees wide. Two lateral ridges are given off—one in lat. 10° N., connecting with the South American coast at Cape Orange ; another, of less eleva tion, connects with the South African coast near Cape Voltas. Whether the main ridge is prolonged south of Tristan d'Acunha into the Antarctic plateau is as yet uncertain, but most probably it is separated from the South Polar elevations by an area of depression extending along the parallel of lat. S. from the Falkland Islands to the meridian of the Cape.' These submarine ridges divide the Atlantic into four more or less well-defined basins 1 :—(1) The Eastern basin, between the central ridge and the coasts of Europe and Africa, from Ireland to the Cape ; (2) the North-Western basin, be tween the central ridge and the American coasts, from the Grand Banks to Trinidad ; (3) the South-Western basin, between the South American coast and the central ridge ; (4) what may be called the Southern basin, south of lat. and merging indefinitely into the Antarctic basin. As regards depth, the three basins of the Atlantic proper—that is, north of the Cape and Falkland Islands—exceed 2,000 fathoms. The eastern and north-western basins have average depths of 2,500 and 3,000 fathoms respectively. The more considerable
depressions are (a) a nearly circular depression between Cape Verd Islands and the central ridge in the eastern basin ; (b) an elongated depression, somewhat in the shape of a boot, between the Azores, Bermudas, and the West Indies ; (c) a nearly similar oblong trough in the south-western basin occurs between Ascension and Tristan d'Acunha on the east, and Fernando Noronha, Trinidad, and Martin Vaz, on the west. The greatest depth ascertained in the Atlantic, about 80 miles north of St. Thomas, was 3,875 fathoms, or about 4i miles. About 150 miles north of this a sounding of 3,697 fathoms was obtained. Within the same basin the American ship " Gettysburg " obtained two soundings of 3,593 and 3,370 fathoms respectively. So that the deepest part of the Atlantic lies north of the Virgin Islands, along the meridian of 65° W. long.
Special names have been given to the most remarkable submarine elevations in the Atlantic; thus the broad ridge between Ireland and Newfoundland, along which the sub marine telegraph lines are laid, is called the Telegraphic Plateau—while the northern and southern portions of the great central ridge are respectively distinguished as the Dol phin Ridge and Challenger Ridge. The lateral ridges are usually referred to under the general name of connecting ridge. Another peculiar elevation extends from Cape Rocca to Madeira, and includes the well known Josephine Banks. The belt of water along the Norwegian and British coasts is so shallow, that were the level to fall 100 fathoms, the British Islands would be connected by dry land with France, Belgium, Holland, and Denmark, and separated from the Scandinavian peninsula only by a narrow channel [As regards the nature of the bottom of the Atlantic, the belt to about 400 fathoms is generally covered with sand and debris, washed from the beach or brought down by rivers ; from 400 to 2,000 fathoms by the white " globigerina ooze," consisting of the broken and de composed shells of foraminifera. ooze" is found at depths of 2,000 to 2,300 fathoms ; still deeper areas are mostly covered by a "red clay," a silicate of alumina and iron. The pieces of pumice and other• volcanic products which are found scattered extensively over the bed of the Atlantic, may of course be due to submarine eruptions, but the most probable supposition is that they were ejected on land and carried down to the sea, and, becoming "water logged," ultimately sank to the bottom.]