IV DEPTHS AND DEPOSITS OF THE OCEAN 145 



origin, derived from (i) the decomposition of terrestrial and 



submarine rocks, (2) extra- 

 terrestrial sources, (3) pro- 

 ducts synthesized at the 

 bottom of the sea. 



Organic remains belong- Materials of 

 ing to the vegetable kingdom "^g^™'^ ongi"- 

 are on the whole compara- 

 tively rare on the sea-floor, 

 when compared with those 

 belonging to the animal 

 kingdom ; still, in the neigh- 

 bourhood of land, vegetable 

 matter, branches of trees, piant remains 

 leaves, fruits, etc., may be 

 carried into deep water 

 through the agency of large 

 rivers, storms, off- shore 

 winds, etc., along with the 

 shallow water. Similarly 



in marine 

 deposits. 



Fig. 108. 

 Discosphara thomsoni, Ostenfeld. 



From the surface 



remains of sea-weeds 

 in coral-reef re- 

 gions, the re- 

 mains of algae 

 which lived on 

 the reefs, such 

 as LithotJiani- 

 niuin and Coral- 

 Una, occur in 

 the deposits in 

 the vicinity. But 

 the most con- 

 stant compon- 

 ents of vegetable 

 origin are the 

 remains of algse, 

 which secreted 

 either calcium 

 carbonate or 

 silica from the 

 surface waters 

 of the ocean to 

 form their hard 

 parts, viz. the calcareous coccospheres and rhabdospheres (see 



Fig. 109. 



Rhabdosphcera claviger, Murray and Blackman. 



From the surface ( " "/* " ). 



