OCEANIC DEPOSITS AND BOTTOM FAUNA 43 



expédition, thought it was primarily of organic 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 cases be of 

 organic origin like chalk. Murray believes that the clayey 

 matter in marine deposits far from land is principally derived 

 from the décomposition of aluminoiis silicates and rocks spread 

 over the océan basins by subaerial and submarine éruptions. 



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 

 Océans dark chocolaté, prédominâtes. 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 

 fingers 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 thèse are im- 

 pregnated and coated with peroxides of manganèse and iron. 



There are also présent minute chondritic and metallic 

 spherules which are supposed to hâve fallen from interstellar 

 space. 



The average composition of red clay is : 



CaCOg 



Siliceous organisms 



Minerais 



Fine washings 



loooo 



670 

 2-39 

 5-56 



85-35 



