MARINE DEPOSITS 211 



great bulk of the red clays consists of what 

 are called " fine washings," largely made 

 up of clayey matter, intimately mixed with 

 oxides of iron and manganese and the 

 smallest comminuted fragments of the other 

 constituents found in the same deposits. 

 Red clay covers an area estimated at 

 about fifty millions of square miles. In the 

 Pacific Ocean it attains its maximum develop- 

 ment, but it is also present in the Indian and 

 Atlantic Oceans. In the Atlantic the red 

 days are usually of a lighter shade of red than 

 in the Indian and Pacific, where they very 

 frequently assume a dark chocolate-brown 

 colour due to the large proportion of grains of 

 manganese peroxide. 



10. Radiolarian Ooze, — This type is merely 

 a variety of red clay, in which the skeletons 

 of radiolaria and the frustules of the large 

 diatom, Coscinodiscus rex, fallen from the 

 surface waters, become so abundant as to form 

 an appreciable proportion of the deposit. 

 Otherwise the mineral particles (pumice and 

 volcanic glass more or less completely trans- 

 formed into palagonite, associated with man- 

 ganese peroxide in grains and nodules) and 

 other constituents are similar to those in the 

 red clays. It will be seen from the map that 

 this type of deposit is limited to those regions 

 of the ocean where the surface conditions are 



