IV DEPTHS AND DEPOSITS OF THE OCEAN 155 



origin is attributed to both forms of magnetic spherules, which 

 are supposed to have been thrown off by meteorites, or falHng 

 stars, in their passage through our atmosphere. 



The secondary products entering into the composition of Secondary 

 deep-sea deposits are (i) clay, (2) manganese nodules, (3) barium P'^°'^"^ts. 



and barium nodules, (4) 

 glauconite, (5) phosphatic 

 concretions, and (6) zeo- 

 lites. 



The clayey matter in Clay. 

 the deposits near land 

 may have been trans- 

 ported by rivers, etc., 

 from the land, but most 

 of the clayey matter 

 present in the deposits 

 far from land is believed 

 to have been derived from 

 the decomposition under the action of water of eruptive and 

 metamorphic rocks and minerals, especially pumice and volcanic 

 glass. The deep-sea clays, some of which are mostly made up 

 of these decomposing volcanic materials, are usually coloured 

 a reddish -brown by the oxides of manganese and iron — 



products of the de- 



124. 



Krithe producta, Brady. From the bottom-deposits 

 (magnified). 



Fig. 125. 



From the bottom-deposits (magnified). 



composition of the 

 same rocks that gave 

 rise to the clayey 

 matter — and a com- 

 paratively small 

 amount of clay may 

 give a clayeycharacter 

 to the deposit. 



The oxides of iron Manganese 



and manganese are "°'^"^^^- 

 widely distributed in 



Cy there dictyon, Brady. , ^ ^ ,. 



marine deposits, and 

 especially in deep-sea deposits. They occur in minute grains, 

 and act as colouring matter in nearly all deep-sea clays, 

 and in certain abyssal regions of the ocean they form con- 

 cretions of larger or smaller size, which are among the most 

 striking characteristics of the oceanic Red clay. Sometimes 

 the oxides cover consolidated masses of tufa, fragments of 

 rocks, portions of the deposit, branches of coral and other 



