184 FOUNDERS OF OCEANOGRAPHY 



Crustaceans, Polyzoa, Sponges, Tunicata, and other bottom- 

 living animals, and a few plants such as the calcareous 

 Nullipores. I shaU, therefore, classify the submarine deposits 

 under these three primary divisions, which may be defined 

 as follows : — 



Terrigenous (Murray's term restricted), where the deposit 

 is formed chiefly — say at least two-thirds, 66 per cent. — of 

 mineral particles, characteristically quartz, derived from 

 the waste of the land. 



Neritic (Herdman, 1895), where the deposit is largely of 

 organic origin, its calcareous matter being derived from the 

 shells and other hard parts of the animals and plants living 

 on the bottom (benthonic organisms). 



Pelagic (Murray's term unaltered) — or better, planktonic 

 — where the greater part of the deposit (except in the case 

 of " Red Clay ") is formed of the remains of free-floating 

 animals and plants which lived in the sea over the deposit. 

 These pelagic deposits are produced by planktonic organ- 

 isms, and are characteristic of the deep sea, where terri- 

 genous materials do not penetrate, and where benthonic 

 organisms are not present in sufficient quantity to cause 

 neritic deposits. 



The statement in brief form is : — 



Terrigenous, derived from the land ; 

 Neritic, derived from benthonic organisms ; 

 Pelagic, derived from planktonic organisms. 



There are, however, transitional forms of deposit from the 

 one group to another. 



I. Terrigenous. Deposits of varied mineral materials 

 and many textures, but all derived from the waste of the 

 land, and containing on the average about 68 per cent, of 

 silica. The nature of the deposit depends chiefly upon the 

 geological structure of the adjacent land and the agents 

 of denudation and disintegration. There may be large 

 boulders strewn upon the beach or in shallow water de- 

 tached from a cliff or washed out of the Boulder Clay. 



