The Encyclopedia Americana (1920)/Abysmal deposits

ABYSMAL DEPOSITS are accumulations at the bottom of the ocean at great depths known as abysmal depths. They consists chiefly of red and gray clays and oozes or combinations of clays with various shells and animals, such as Dictonis, Foraminifera and Radiolarians. These deposits constitute the large part of the deep-sea bottoms. Although there is a vast amount of minute animal life at these abysmal depths this life is confined, so far as is definitely known, to a few species. The deposits are made up of the remains of surface and abysmal animals, the later of which are born, live and die on the bottom of the ocean. Most of the shells of surface animals decompose rapidly at great depths of the ocean, and many of them disintegrate under the pressure of the salt water before they reach the bottom, where they are constantly being added to the deposits, classified according to the depths at which they are found and the local influences under which they have been formed; but only a comparatively few of them can be classed as abysmal. One of these abysmal depths exists in the deep bed of the Gulf of Mexico and along nearly the whole course of the Gulf stream. Very little, if any, of the deposits of these great ocean depths is derived from the shores of the bordering continents; for the geological formations going on there seem to be a thing apart from the debris of all except that of the surface animals that pass over them or live above them. As all the abysmal deposits merge into one another geologists have found great difficulty in determining their character in given areas. The 20 or more species of pelagic Foraminifera constitute over 90 per cent of the vast quantities of carbonate of lime present in the calcareous oozes of the abysmal depths of the oceans. This animal life, thus wonderfully abundant to-day, is present in a like plentifulness in other geological formations and periods. Living as they do at such a great depth below the surface and being subject to a more or less uniform pressure, the shells of those animals are very much alike in appearance and thickness in all the abysmal deposits and zones. See Continental shelf.