1897] DISTRIBUTION OF PELAGIC FORAMINIFERA 23 



more abundant than adult ones, still shells as heavy as any in the 

 deposits are occasionally taken in the surface-nets. The young 

 individuals are likewise more abundant at the surface than in the 

 deposit, when compared with the adult shells present ; this is 

 especially the case in deposits from very deep water. This arises, 

 as we shall see, from the more rapid solution of the young shells as 

 they fall through the sea-water to the bottom. 



When examining a deep-sea deposit it is always possible to say, 

 from a study of the pelagic shells of the Foraminifera, whether the 

 sample comes from the tropics, the temperate or the polar regions, 

 but from the examination of these shells alone it would be extremely ^ 

 difficult to say whether the specimen was from the northern or 

 southern hemisphere. 



Off the Agulhas Bank at the Cape of Good Hope, off the east 

 coasts of Australia and Japan, and off the east coasts of North and 

 South America, oceanic currents from different sources meet and 



Fig. 4. — Pulvinulina menardii (d'Orbigiiy), from the tropical deposits. 



mix, and there is a wide range of annual temperature at the sur- 

 face. In these positions large numbers of pelagic Foraminifera (as 

 well as other organisms) appear to be killed by the sudden changes 

 of temperature, and consequently there are indications that the 

 deposits, so far as due to these shells, are accumulating more rapidly 

 in these areas than in other situations. It is a curious fact also 

 that in these regions the deposits of glauconite and phosphatic 

 nodules are more abundant than elsewhere. 



In a certain sense the course of a surface oceanic current can 

 be traced on the bottom by means of these dead pelagic shells ; 

 for instance, the axis of the Gulf Stream is marked out by deposits 

 of Globigerina Ooze from the Strait of Florida to within the Arctic 

 circle. No similar warm current enters the Antarctic region, and 

 consequently no true Globigerina Ooze is found to the south of 

 lat. 50° S. When the Challenger took her first deep-sea sound- 

 ing after leaving Heard Island (in lat. 60° S.) there was much 

 speculation as to what the nature of the deposit would be. I 



V 



