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On the Nomenclature, Origin, and Distribution of Deep-Sea Deposits 1


    II. Globigerina Ooze.—We designate by this name all those truly pelagic deposits containing over 40 per cent, of carbonate of lime, which consists principally of the dead shells of pelagic Foraminifera—Globigerina, Orbulina, Pulvinulina, Pullenia, Sphœroidina, &c. In some localities this deposit contains 95 per cent, of carbonate of lime. The colour is milky white, yellow, brown, or rose, the varieties of colour depending principally on the relative abundance in the deposit of the oxides of iron and manganese. This ooze is fine grained; in the tropics some of the Foraminifera shells are macroscopic. When dried it is pulverulent. Analyses show that the sediment contains, in addition to carbonate of lime, phosphate and sulphate of lime, carbonate of magnesia, oxides of iron and manganese, and argillaceous matters. The residue is of a reddish brown tinge. Lapilli, pumice, and glassy fragments, often altered into palagonite, seem always to be present, and are frequently very abundant. The mineral particles are generally angular, and rarely exceed 0.08 mm. in diameter; monoclinic and triclinic feldspars, augite, olivine, hornblende, and magnetite are the most frequent. When quartz is present, it is in the form of minute, rounded, probably wind-borne grains, often partially covered with oxide of iron. More rarely we have white and black mica, bronzite, actinolite, chromite, glauconite, and cosmic dust. Silliceous organisms are probably never absent, sometimes forming 20 per cent, of the deposit, at other times only recognisable after careful microscopic examination. In some regions the frustules of Diatoms predominate, in others the skeletons of Radiolarians.

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