38 A TEXTBOOK OF OCEANOGRAPHY 



depending on the nature of the inorganic substances mixed up 

 with the foraminifera. The prevailing colour is milky-white 

 or rose-coloured far from land, and dirty white, blue, or grey, 

 near land. In the Challenger lists there are 118 samples of 

 this ooze, the bulk (84) being between 1,500 and 2,500 fathoms. 

 There are only 5 samples below 1,000 fathoms and 16 from 

 over 2,500 fathoms. 



The carbonate of lime varies from 30 per cent, in 2,575 

 fathoms to 97 per cent, in 425 fathoms. The average is 

 64^ per cent. The amount of carbonate of lime diminishes as 

 the depth increases. Although the organic substance in 

 globigerina ooze is not large, this deposit does yield abundance 

 of food for the Benthos. 



Such creatures as echinoderms and annelids are nourished 

 by the ooze which they pass through their alimentary canals. 



The average composition of the Challenger globigerina 



ooze is : 



Per Cent. 



CaCO 3 64-47 



Siliceous organisms ... ... ... 1-64 



Minerals 3-33 



Fine washings ... ... ... 30*56 



lOO'OO 



The siliceous organisms are mainly radiolaria ; then follow 

 sponge spicules and diatom frustules. 



Of minerals which have been formed in situ, the globi- 

 gerina ooze contains glauconite, phosphate concretions, and 

 manganese nodules. The glauconite (see under Green Sands 

 above), though not abundant, is widely distributed, and occurs 

 as a nucleus of what was originally an enveloping calcareous 

 chamber. 



The phosphatic concretions are rare in globigerina ooze. 

 They are of very localised occurrence, and are, in the last 

 resort, of biological origin. They vary greatly in size and 

 form, and are made up of heterogenous fragments (grains of 

 glauconite or other minerals or remains of organisms) cemented 



