OCEANIC DEPOSITS AND BOTTOM FAUNA 41 



Diatom oo/e forms a wide zone round the South Polar 

 regions, lying for the most part 

 between the Antarctic Circle and 

 40 S. Lat., where it covers over 

 loj million square miles. There 

 is also a girdle in the Nortli 

 Pacific extending to 40,000 

 square miles. 



The last two sediments, 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 ocean 

 floor. The radiolarian ooze may, 

 in fact, be regarded as a local 

 variety of the red clay. 



Radiolarian ooze is charac- 

 teristic of deep water in the 

 tropical regions of the Pacific 

 and Indian Oceans. 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 

 present. Nine samples were 

 collected by the Challenger ex- 

 pedition 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 from a trace in 

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



