188 FOUNDERS OF OCEANOGRAPHY 



Red Clay, all these deep-sea oozes are formed mainly of the 

 remains of planktonic animals (such as Foraminifera and 

 Radiolaria) and plants (such as Diatoms and Coccolitho- 

 phorida) which lived in the surface waters over the deposit. 

 The following five distinct kinds of deposit were made known 

 by Murray from the " Challenger " results : Pteropod ooze, 

 Globigerina ooze, Red Clay, Radiolarian ooze, and Diatom 

 ooze, and although typical representatives of each have 

 very distinctive characters and locaUties, they may graduate 

 one into another on their borders. Just as shallow-water 

 coastal terrigenous deposits of gravel and sand may pass 

 into neritic calcareous accumulations of shells or nuUipores, 

 so in deeper water in oceanic areas neritic assemblages of 

 bottom organisms may be gradually replaced by the remains 

 of pelagic molluscs to form a Pteropod ooze, and that in 

 turn at a greater depth of, say, 1,000 fathoms by the dis- 

 appearance of the delicate Pteropod shells becomes a 

 Globigerina ooze, which at depths over 2,500 fathoms is 

 gradually replaced by Red Clay, and that finally in certain 

 abyssal areas acquires the characters of Radiolarian ooze. 



The following short descriptions, summarized in the main 

 from Murray's various writings on the subject, hold good, 

 in general for these oceanic deposits, but do not indicate 

 hard-and-fast boundaries : — 



1. Pteropod Ooze. — A calcareous deposit occupying only 

 about haK a million of square miles and confined to the 

 tropics, generally on submarine ridges, at depths of less 

 than 1,000 fathoms. Its basis is a Globigerina ooze largely 

 mixed with and masked by the large delicate shells of the 

 pelagic mollusca, the Pteropods, and, to a less extent, Hetero- 

 pods. As these thin Pteropod shells expose a large surface 

 to the water as they sink through it, they become dissolved 

 before reaching the bottom at greater depths. The rapidity 

 of solution of the Pteropod shells is probably aided also 

 by the carbonate of lime being in the form of aragonite, 

 while the Globigerina shells are calcite. In the " Challenger " 



