OCEANIC DEPOSITS AND BOTTOM FAUNA 41 



Diatom ooze forms a wide zone round the South Polar 

 régions, lying for the most part 

 between the Antarctic Circle and 

 40° S. Lat., where it covers over 

 lof million square miles. There 

 is also a girdle in the North 

 Pacific extending to 40,000 

 square miles. 



The last two sédiments, the 

 (4) Red Clay and (5) Radio- 

 larian Ooze, are sometimes 

 called the abyssal deposits, since 

 they occupy the greatest depths 

 and widest areas of the océan 

 floor. The radiolarian ooze mav, 

 in fact, be regarded as a local 

 variety of the red clay, 



Radiolarian ooze is charac- 

 teristic of deep water in the 

 tropical régions of the Pacific 

 and Indian Océans. While 

 resembling the red clay in many 

 respects, it differs in containing 

 a large number of siliceous re- 

 mains, the shells of radiolaria 

 for the most part, though 

 sponge spicules and diatoms are 

 présent. Nine samples were 

 collected by the Challenger ex- 

 pédition at an average depth of 

 2,894 fathoms, which is deeper 

 than the red clay average, 2,730 

 fathoms. 



The amount of carbonate of 

 lime ranges f rom a trace in 

 Jive cases to 20 per cent, as a maximum, the average being 



<< 00000 



li^ooooo 



