186 FOUNDERS OF OCEANOGRAPHY 



action of these bacteria. More recently, however, C. B. 

 Lipman has repeated the observations both at Samoa and 

 at Tortugas, and finds that Drew was mistaken in supposing 

 that this precipitation was wholly due to the action of the 

 organism (now known as Pseudomonas calcis). Further 

 investigations on this matter are still (1923) in progress ; 

 but I have mentioned it as an example of the compHcations 

 that may be present in the actions and interactions, mechan- 

 ical, chemical and organic, in connection with such an 

 apparently simple process as the grinding of coral fragments 

 into coral mud. The bearing of these observations upon 

 the formation of oolitic limestones and fine-grained un- 

 fossiliferous limestones must be of pecuUar interest to 

 geologists, and forms a notable instance of the annectent 

 character of oceanography, bringing the metabolism of 

 living organisms in the modern sea into relation with 

 mesozoic and even palaeozoic rocks. 



The seaward limit of the terrigenous deposits is on the 

 average about 200 miles from land, and these deposits cover 

 in all about one-fifth of the area of the ocean. 



II. Neritic. — Amongst the shallow-water deposits there 

 are some which are by no means " terrigenous," as they are 

 not formed of particles derived from the land, but are 

 constituted either wholly or in large part of the hard parts 

 of the bottom (" benthonic ") animals and plants Uving on 

 the spot or close to. The shells of Molluscs, the exo- 

 skeletons of Crustaceans, the tubes of some worms, the spines 

 and plates of Echinoderms, the spicules of sponges, Alcyon- 

 arians and Tunicates, and also some calcareous algae, such 

 as corallines and nullipores, form such neritic deposits of 

 organic origin, but not pelagic like the deep-sea oozes. 

 These neritic deposits are very largely calcareous (up to 

 80 per cent, of carbonate of lime), and would form a highly 

 fossiliferous limestone if consolidated. 



In some places near land, at depths of 10 to 20 

 fathoms, the bottom may be covered with growing 



