146 



DEPTHS OF THE OCEAN 



Figs. 108 and 109) characteristic of tropical and sub-tropical 

 regions, and the siliceous diatoms characteristic of extra-tropical 

 regions. While the diatom remains are so abundant in the deposits 

 of the Southern Ocean and of the North Pacific as to form a 

 distinct deposit-type (Diatom ooze), the remains of the pelagic 

 calcareous algae are always overshadowed by the abundance of 



^^ 



Fig. no. 

 Eucoronis challengeri, Haeckel. From the surface (magnified). 



the remains of pelagic foraminifera and mollusca in the deposits of 

 the warmer regions of the ocean. These pelagic calcareous algae 

 are so fragile in texture, that it is principally their broken-down 

 parts (coccoliths and rhabdoliths) that occur in the deposits ; in 

 certain favourable localities coccospheres of small size may be 

 fairly numerous, but rhabdospheres are practically unknown in 

 deep-sea deposits, being apparently easily dismembered, and the 

 same remark seems to apply to the large-sized coccospheres. 



