GLOBIGERINA OOZE 451 



(Fig. loi), in the northern hemisphere and most of the tropical 

 seas ; Globigerina dutcrtrci, for the higher southern latitudes ; and, 

 further, Orhidina universa (Fig. 102) and Ilastigerina pclagica. 

 The foraminifera of this ooze all inhahit the upper 200 meters of 

 the ocean, leading a planktonic existence (Chapter XX\'TTI). It is 

 only on the death of these organisms that their shells sink to the bot- 

 tom and become incorporated in contemporaneous sediments of other 

 origin, or, if this is rare or absent, to accumulate as extensive, more 

 or less pure deposits of shells. The ooze is never absolutely com- 

 posed of foraminiferal shells, for the shells of other planktonic or- 

 ganisms also enter into the composition. Among these are the 

 shells of pelagic molluscs, such as the pteropods and heteropods, 

 both often of considerable size; ostracods {Crithe proditcta, Cy~ 

 there diet yon) ; minute planktonic algae, Coccolithophores or coc- 



FiG. 103. Piilviir.illiia. A multicham- Fig. 104. Coccolithophora. (After 

 bered foraminiferal shell (after A. Agassiz.) x 600. 



Murray) much enlarged. 



eoliths (Fig. 104) and rhabdoliths. These pelagic admixtures are 

 further supplemented by those of sea-bottom or benthonic origin, 

 among which bottom-living Foraminifera may constitute as high as 

 3 per cent, of the mass. Furthermore there are clastic lime and 

 other fragments ; spines of echinoderms, shells of molluscs ; worm 

 tubes ; deep-sea corals ; Bryozoa, etc. In all, these never make up 

 more than 25% of the mass, and, according to Murray and Re- 

 nard, on the average only 9%. From the amount of pelagic cal- 

 careous organisms in these deposits, Murray and Renard have cal- 

 culated that there are at least sixteen tons of floating carbonate of 

 lime in one square mile of water surface, distributed through the 

 upper 100 fathoms of the sea. The clastic material is often less 

 than 1% and averages 3.3% in the 118 samples obtained by the 

 Challenger expedition. In depth the Globigerina ooze is most abun- 

 dant between 2,500 and 4,500 meters, its mean depth being 3,660 



