IV DEPTHS AND DEPOSITS OF THE OCEAN 167 



of pteropods and heteropods and pelagic foraminifera in terri- 

 genous deposits indicates approximately temperate or tropical 

 latitudes ; in the Arctic and Antarctic regions these shells are 

 absent from the deposits. Green muds and sands appear to be 

 limited to regions where there is a wide range of temperature 

 in the surface waters of the ocean, while Red muds are limited 

 to those localities where a large amount of ochreous matter is 

 carried into the sea by rivers, and Volcanic muds and sands are 

 limited to the neighbourhood of volcanic centres, both subaerial 

 and submarine. But the most widely distributed of all the 

 terrigenous types is Blue mud, which occurs in both the Arctic 

 and Antarctic regions, and along the shores of continents and 

 continental islands throughout the world, where not displaced 

 by one or other of the varieties just mentioned. 



Broadly speaking, the terrigenous deposits close to land in 

 shallow water contain more and larger mineral fragments than 

 those farther removed from the land and in deeper water. 

 Where great rivers enter the sea the terrigenous deposits may 

 extend very far seaward, and a Blue mud may occupy the whole 

 of the continental slope, extending perhaps some distance out 

 over the deep bed of the ocean. On the other hand, along 

 high and steep coasts oceanic conditions may approach close to 

 the shore, and a Blue mud may pass into a Green mud or into a 

 Pteropod ooze, and finally into a Globigerina ooze along the 

 continental slope. 



Turning to the pelagic deposits, we find that Pteropod ooze 

 is limited to the tropical and subtropical regions, usually in the 

 neighbourhood of oceanic islands and on the summits and sides 

 of submarine elevations ; it is found in relatively shallow water, 

 and covers a relatively small extent of the ocean-fioor. 



Globigerina ooze is much more widely distributed ; in fact, it 

 covers an area of the entire sea-fioor second only to that occu- 

 pied by Red clay, extending as far north as lat. 72° N. in the 

 Norwegian Sea and as far south as lat. 60° S. in the South 

 Atlantic. A Globigerina ooze from a tropical locality differs 

 greatly from one taken towards the polar regions, for the 

 tropical sample may contain the representatives of more than 

 twenty species of pelagic foraminifera as well as many species 

 of pelagic molluscs, whereas the polar sample would include 

 only one or two species of pelagic foraminifera and no pelagic 

 molluscs. Globigerina ooze is the predominant type of deposit 

 in the North Atlantic, covering all the deeper parts of that 

 ocean except for two areas of Red clay, and it is there found 



