OCEANIC DEPOSITS AND BOTTOM FAUNA 39 



by pliosphatic material. When (he cemented particles are 

 purely mineral, the phosphatic material acts simply as a 

 cement, but when there are remains of calcareous organisms 

 in the concretions the calcium carbonate of the shell is pseudo- 

 morphosed into calcium phosphate. 



Manganese nodules are not especially abundant in 

 globigerina ooze. 



The oxides of iron and manganese are widely distributed 

 in marine deposits. They occur in minute grains, and act as 

 colouring matter in all deep-sea clays. The commonest form 

 is more or less rounded nodules of varying size, so that in one 

 area they look like marbles, in another like potatoes or cricket- 

 balls. Generally the nodules are concretions formed round a 

 nucleus which may be a shark's tooth or whale's ear-bone, or 

 a piece of pumice or fragment of volcanic glass. 



The manganese of the nodules is chiefly derived from the 

 decomposition of the more basic volcanic rocks and minerals 

 with which the nodules are nearly always associated 'in deep- 

 sea deposits. The manganese and iron of these rocks and 

 minerals are at first transformed into carbonates and then into 

 oxides, which, on depositing from solution in the watery ooze, 

 take a concretionary form around various nuclei. 



Among the other foreign bodies present in globigerina 

 ooze note must be made of glaciated stones. These glaciated 

 fragments were found by the Challenger west of the Azores 

 (to 35 N. Lat.). If the position of these fragments be compared 

 with a map showing the distribution of icebergs, it will be seen 

 that they are all within, or just beyond, the limits of the iceberg 

 regions. They are therefore due to floating ice. 



Globigerina ooze has a very wide distribution on the ocean 

 floor. Its total area is over 49^ million square miles, coming- 

 second only to the red clay. Its maximum development is in 

 the Atlantic (22^ million square miles), occupying by far the 

 larger portion of the sea floor of this ocean from the Arctic 

 Circle to 60 S. Lat. 



\n the Indian Qcean it occupies about I2j million square 



