OCEANIC DEPOSITS AND BOTTOM FAUNA 39 



by phosphatic material. When the cemented particles are 

 purely minerai, the phosphatic material acts simply as a 

 cernent, but when there are remains of calcareous organisms 

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

 morphosed into calcium phosphate. 



Manganèse nodules are not especially abundant in 

 globigerina ooze. 



The oxides of iron and manganèse are widely distributed 

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

 colouring matter in ail 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 concrétions formed round a 

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

 a pièce of pumice or fragment of volcanic glass. 



The manganèse of the nodules is chiefly derived from the 

 décomposition of the more basic volcanic rocks and minerais 

 with which the nodules are nearly always associated in deep- 

 sea deposits. The manganèse and iron of thèse rocks and 

 minerais 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 présent in globigerina 

 ooze note must be made of glaciated stones. Thèse glaciated 

 fragments were found by the Challenger west of the Azores 

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

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

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

 régions. They are therefore due to floating ice. 



Globigerina ooze has a very wide distribution on the océan 

 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 océan from the Arctic 

 Circle to 60° S. Lat. 



^^ thç Indian Océan it occupies about 12^ million square 



