194 FOUNDERS OF OCEANOGRAPHY 



of living organisms. It is made up of fragments of fish- 

 bones, mollusc shells, corals, spicules of sponges, alcyonaria 

 and tunicates, shells of foraminifera, remains of calcareous 

 algae, and indeed of all the calcareous structures secreted 

 by marine organisms. 



These calcareous remains may be divided into two 

 classes, viz., (1) Those that have been secreted by organisms 

 which Uve habitually in the surface waters of the ocean, 

 such as Pteropods and Heteropods, pelagic Foraminifera, 

 such as Globigerina, Pulvinulina, Orbulina, and other allied 

 genera, and calcareous algse, such as the Coccospheres and 

 Rhabdospheres. The remains of all these pelagic (plank- 

 tonic) organisms are especially abundant in the deposits 

 far from land. Near the land their presence is masked 

 by terrigenous detrital matters. In great depths they 

 disappear, being dissolved by the action of sea- water either 

 while faUing through it or soon after they reach the bottom. 

 In depths of 1,000 fathoms, far from land, they may make 

 up fully 95 per cent, of the deposit. (2) Those organisms 

 (the Benthos) that hve on the bottom of the ocean, viz., 

 corals, moUuscs, Foraminifera (very different species from 

 those of pelagic habit) and calcareous algae, are poorly repre- 

 sented in the great depths, but in shallow water their 

 remains may make up nearly the whole of the deposits 

 (Neritic) now in process of formation. This is especially 

 the case around coral islands. 



It is well known that carbonate of hme is very sparingly 

 secreted in the cold water either of the polar regions or of 

 the deep sea, while it is very abundantly secreted in warm 

 seas where there is a nearly uniform temperature throughout 

 the year. In warmer water the Hme is, in some cases, 

 secreted in the form of aragonite (though calcite is also 

 present), while in the colder water it appears more frequently 

 in the form of calcite. In this connection it may be pointed 

 out that in the deposits now forming on the floor of the 

 ocean, the remains of organisms may be found which during 



