104 THE OCEAN FLOOR 



accumulation below the equatorial divergence, where 

 at a certain substage of the Pleistocene glaciation it 

 should have reached 860 milligrams of SiOo per square 

 centimeter in 1,000 years. However, a microscopic 

 examination of the cores proves that many siliceous 

 remains are strongly corroded, which makes it probable 

 that a great part of the biogenetic silica is present in 

 colloidal form. 



4. Similar analyses deal with the distribution of 

 organic matter (marine humus), with phosphorus, 

 with the carbon-nitrogen relationship, and with the 

 presence of peroxide of manganese, both in dispersed 

 form and as nodules and micronodules. 



A great number of excellent diagrams make clear 

 the main relationships found; these relationships en- 

 able Arrhenius to establish correlations among the 

 different cores he has examined and to define the limits 

 between the Pleistocene and Pliocene parts of the cores. 

 These conclusions he supports by similar distribution 

 studies of forams, diatoms, and radiolarians in the 

 cores. 



Special attention has been given to the reworking of 

 sediments by mud-eating organisms and to recrystal- 

 lization and chemical redistribution after deposition. 

 Studies of thin sections of carefully washed Foramini- 

 fera revealed the fact that planktonic forams which are 

 not recrystallized are more easily attacked than are 

 recrystallized shells and benthonic forams, which ap- 

 pear to be remarkably resistant to dissolution. 



