OCEANIC DEPOSITS AND IU)TTOM FAUNA 43 



expedition, thought it was primarily of organ ir origin, being 

 essentially the insoluble residue of the calcareous organisms 

 which form the globigerina ooze. He further suggested that 

 clay, which is generally regarded as essentially the product of 

 the disintegration of older rocks, may in certain rases be of 

 organic origin like chalk. Murray believes that the clayey 

 matter in marine deposits far from land is principally derived 

 from the decomposition of aluminous silicates and rocks spread 

 over the ocean basins by subaerial and submarine eruptions. 



The basis of red clay is hydrated silicate of alumina 

 associated with secondary products, such as manganese-iron 

 nodules and phillipsite. 



There are seventy samples in the Challenger collection 

 from an average depth of 2,730 fathoms. The colour of the 

 deposit varies greatly, but red is the prevailing tint. In the 

 North Atlantic brick-red, and in the South Pacific and Indian 

 Oceans dark chocolate, predominates. Calcareous matter may 

 be entirely absent ; in lesser depths it may be 30 per cent, when 

 the deposit passes gradually into globigerina ooze. Red clay 

 is soft, plastic, and greasy. It can be moulded between the 

 ringers like dough. 



The rate of accumulation of red clay is evidently a 

 minimum, since the calcareous shells falling from the surface 

 are removed either before or shortly after they reach the 

 bottom. In the dredge are found ear-bones of whales and 

 teeth of sharks (many of extinct species), and these are im- 

 pregnated and coated with peroxides of manganese and iron. 



There are also present minute chondritic and metallic 

 spherules which are supposed to have fallen from interstellar 

 space. 



The average composition of red clay is : 



CaCO 3 



Siliceous organisms 



Minerals 



Fine washings 



lOO'OQ 



