368 PERCY SLADEN TRUST EXPEDITION. 



the Pacific Ocean. Next in importance come Diatom Ooze and Red Clay, which are 

 nearly equally extensive, followed by the terrigenous deposits, and finally Radiolarian 

 Ooze and Pteropod Ooze are the least extensive. 



The various types of deposits may be briefly characterized and their distribution 

 within the Indian Ocean indicated : — 



Globigerina Ooze is so named from the predominance of the dead shells of Porami- 

 nifera which lived in the surface waters of the ocean, the genus Globigerina being the 

 most characteristic. These dead shells accumulate in the moderate depths of the ocean 

 in tropical and subtropical regions, but are evidently removed in solution from all the 

 deepest parts in depths exceeding about 3000 fathoms, as will be more fully treated of 

 when dealing with the percentage of calcium carbonate in tbe deposits. Globigerina 

 Ooze is by far the most extensive deposit in the Indian Ocean, forming a continuous 

 area from lat. 50° S. to 18° N., interrupted here and there by other kinds of deposits, 

 and with small isolated areas in the Red Sea, in the Bay of Bengal, and in the far south. 

 In the Bay of Bengal and the Arabian Sea this type of deposit extends farther north 

 and approaches nearer the land than was previously supposed. Thi'ee small isolated 

 areas have been found by the ' Valdivia ' (1898-99) and the ' Gauss ' (1901-03) in 1939, 

 1743, and 2025 fathoms respectively, within the Diatom Ooze area of the far south, each 

 based on one sounding only, but these deposits differ considerably from the typical 

 Globigerina Oozes of the tropical regions of the Indian Ocean. 



Ttero-pod Ooze differs from Globigerina Ooze only in the greater number of the shells 

 of pelagic molluscs (Pteropods and Heteropods). Up to 1891 no typical Pteropod Ooze 

 liad been found in the Indian Ocean, but several small areas are now known in the 

 Bed Sea, off the coast of Africa, in the Timor Sea, and off the coasts of Sumatra and 

 Nicobar Islands. Mr. Gardiner met with this type of deposit off Mauritius in 

 818 fathoms, and oif the Chagos Archipelago in 223 to 575 fathoms. 



Hed Clay is the most characteristic, and probably the most widely distributed, of all 

 deep-sea deposits over the floor of the entire ocean, covering nearly one-half of the floor 

 of the Pacific, though in the Atlantic and Indian Oceans it occupies a less area than 

 Globigerina Ooze. This type occurs in the deepest parts of the central regions of the 

 great ocean-basins, and usually contains few or no remains of calcareous organisms. 

 Deposition of materials derived from land and from the surface waters is at a minimum 

 in the Red Clay areas, the clayey matter and secondary formations, like manganese 

 nodules and zeolilic minerals, being derived from the decomposition of basic volcanic 

 matter, the principal source being floating pumice. Red Clay is represented by a large 

 central area occupying the eastern half of the Indian Ocean between the Equator and 

 lat. 30° S. and between long. 73° and 120° E., with three outlying smaller areas, viz. : — 

 (1) one to the south of the Great Australian Bight in lat. 35° to 45° S. and long. 123° 

 to 138° E. ; (2) one to the south-east of Madagascar in lat. 22° to 27° S. and long. 50° 

 to 60° E. ; and (3) one in the Arabian Sea in lat. 7° to 12° N. and long. 62° to 72° E. 



Madiolurian Ooze is distinguished from Red Clay by the abundance of the skeletons 

 of Radiolaria, and is typically found in very deep water in tropical and subtropical 

 n^gions. It occurs in the Indim Ocean in two areas to the south of the Equator, the 



