Terrigenous deposits (contain- 

 ing detrital material) 



THE FLOOR OF THE OCEAN — BOSWELL 279 



duced by Sir John Murray, of the Challenger expedition, requires 

 modification only in detail: it may now be summarized thus: 



Shallow-water deposits (be- 1 ~ , 



tween L. W. and 100 fOl^T* 



^Muds 



/ Glauconitic mud 



Diatomaceous muo; 



Deep-sea deposits (belowl Diatomaceous ooze"] 



100 f.) | Globigerina ooze I „ , . , 



„ ,. , . > Pelagic deposits 



Radiolanan ooze 



^Red clay J 



Except for the red clay, the pelagic deposits are almost entirely 

 organic, and they fall into two groups consisting respectively of 

 predominant calcium carbonate or amorphous silica. The cal- 

 careous materials include immense quantities of coccolithophores, 

 which are calcareous algae, the well-known coccoliths being the 

 separated plates of the skeletons; foraminifera, chiefly Globigerina 

 and allied forms; and pteropods. The work of the German Meteor 

 expedition demonstrated that in the Atlantic the coccolithophores 

 are of wide distribution in the ocean, but the Globigerinae lived 

 almost exclusively in temperate or warm water. The solubility of 

 the skeletons of these organisms, which are composed of calcium 

 carbonate, increases with pressure and fall of temperature, that is, 

 with increased depth of water. The siliceous organisms consist 

 of four groups: diatoms, silico-flagellates, radiolaria, and siliceous 

 sponges. The diatom frustules are exceedingly small and enter 

 into deep-sea deposits only where other remains, such as calcareous 

 skeletons, are dissolved away, and where mineral material derived 

 from erosion of the land is slight — as for example in Arctic and 

 Antarctic regions. The occurrence of radiolaria in sea-water is 

 similar to that of other plankton, but the main distribution of radio- 

 larian ooze in the Pacific and Indian Oceans lies in the deeper regions, 

 where the depth and low temperature have assisted in the solution of 

 calcareous remains as they settle down. Recently Dr. E. Neaverson 

 has noted the presence of radiolarian ooze among the samples collected 

 by Discovery II, from the South Atlantic, a first record. Of these 

 deposits, the globigerina ooze and the diatomaceous ooze together 

 occupy a large proportion of the ocean floor, the former 50 million 

 square miles, extending down to a depth of 2,500 fathoms, and the 

 latter 11 million square miles, principally at a less depth and in the 

 colder regions. But there remains a third deposit of even greater 

 extent (52 million square miles) — the red clay, which is confined to 

 the deepest regions, like the radiolarian ooze. It is found mainly in 

 the Atlantic Ocean, though why it should occur there, and the other 

 very deep-water deposit chiefly in the Pacific and Indian Oceans, is at 



