OCEANIC DEPOSITS. The materials form ing the floor of the ocean may be classed as terrig 'mous deposits, which have been derived from the waste of the adjacent land, and as pelagic or abysmal aveumulations, which are found in the open ocean beyond the influence of the land. The terrigenous deposit:, eomprising gravel. sand, and clay, are limited in their distribution to the continental shores, seldom occurring at a dis tance of more than 200 miles from the land. As a rule the coarser materials occur in the shallow marginal water., while the tine sands and muds are found in the deeper portions, where they have been carried by the drifts and currents. In the free ocean the character of the bottom shows little variation over great areas. When the depth is comparatively slight the deposits con sist of the shells of minute organisms that live at or near the surface, of volcanic (Inst, bones and teeth of fish, and chemical precipitates. The
most widespread and characteristic material in the tropical and temperate regions is globigerina ooze, an accumulation of the fossil calcareous casts of foraminifera. In the colder waters, such as those of the South Atlantic and the Southern Ocean. the principal organisms are of siliceous character, and their remains compose the diatom ooze that is so characteristic of those regions. When the floor lies at a depth of 2500 fathoms or nu,re, only the most refractory materials can resist the solvent action of the water, and the deposits take the form of a red or brownish clay composed of the insoluble portions of shells, mixed with meteoric and volcanic dust. These deposits cover great areas in the middle portion of the Atlantic and the northern part of the Pacific ocean. See OCEAN ; DEEP-SEA EXPLORA TION ; OOZE, etc.