Coral mud and sand occur similarly around the oceanic coral islands and off those coasts and islands fringed by coral reefs. Coral mud and sand cover about 2,557,000 square miles-1,417,000 in the Pacific, 760,000 in the Atlantic, and 380, 000 in the Indian ocean.
Of pelagic deposits there are five types, four of organic origin, receiving their designations from the distinctive presence of the remains of calcareous or siliceous organisms, the fifth and most extensive being of inorganic origin.
Globigerina ooze is so called from the presence of the dead shells of pelagic Foraminifera, those belonging to the genus Globigerina predominating, which live in the surface and sub-surface waters of the ocean, being especially abundant in tropical regions, and the shells of which after death fall to the bottom and there accumulate in moderate depths. The depth at which Globigerina ooze is found varies from less than 500 to over 2,500 fathoms, the average depth being about 2,000 fathoms. Globigerina ooze covers about 49,520,000 square miles-17,940,000 in the Atlantic, 11,300,000 in the Pacific, 10,560,000 in the Southern, and 9,720,000 in the Indian ocean.
Pteropod ooze resembles Globigerina ooze in all respects, except that there is a greater abundance of the dead shells of pelagic mollusca, such as pteropods and heteropods; it is usually found in lesser depths than the Globigerina ooze. Pteropod ooze covers about 400,000 square miles in the Atlantic.
Diatom ooze is distinguished by the presence of numerous remains of siliceous organisms, principally Diatoms, though fragments of siliceous sponge spicules and Radiolaria and Forarninif era are rarely absent. It is found in the Antarctic and Southern oceans and also in the north west Pacific. Diatom ooze covers about 10.880,000 square miles-10,000,000 in the
Southern, 840,000 in the Antarctic, and 40,000 in the Pacific.
Radiolarian ooze in like manner con tains a varying proportion of siliceous remains, in this case principally Radio laria and their fragments. Calcareous organisms and mineral particles are nearly always present in both these oozes, being usually more numerous and the mineral particles larger in the diatom ooze than in the radiolarian ooze, which latter generally occurs in greater depths than the former. Radiolarian ooze covers about 2,290,000 square miles-1,161,000 in the Pacific, and 1,129,000 in the Indian ocean.
Red clay occupies nearly the whole of the deeper abysses of the ocean, occurring in its most characteristic form in the central regions of the Pacific, far re moved from continental land. It is of a reddish or chocolate color, due to the presence of the oxides of manganese and iron. Mineral particles of secondary ori gin, arising from the decomposition of volcanic debris, are associated with the red clay, and in some regions of the central Pacific isolated crystals and spheroidal groups of phillipsite of secon dary origin formed in situ make up a considerable quantity of the deposit. The presence of the remains of vertebrates, some of them belonging to extinct species lying alongside others belonging to exist ing species, as well as the formation of manganese nodules and zeolitic crystals in situ, and the presence of metallic and chondritic spherules of cosmic origin, ap pear to indicate that the red clay accu mulates at a very slow rate. Red clay covers about 51,500,000 square miles 37,230,000 in the Pacific, 5,800,000 in the Atlantic, 4,350,000 in the Southern, and 4,120,000 in the Indian ocean.