INVESTIGATIONS OF STRATIGRAPHY 107 



in suspension than other microfossils such as Foramini- 

 fera, they can be carried along even by bottom currents 

 of low velocity and turbulence. Also, they are less liable 

 to undergo solution during erosion and transportation 

 to different environments than are the forams. By ex- 

 amining mixed faunas of radiolarians in deep-sea cores 

 it has been possible to form a general hypothesis con- 



50Q000 



-20Q000 



^ 100.000 



C.72. 



Tofal T?adiolaria 

 Zyoocircus 



500 1000 



Depfh in the core (cm) 



Fig. 36. Abrupt drop in number of radiolarians 



1500 



cerning erosion by slow bottom currents of small topo- 

 graphical features in the deep ocean. 



Long deep-sea cores taken in areas with a low rate of 

 sedimentation have enabled Riedel to trace the evolu- 

 tion of certain of the groups of Radiolaria from the 

 Recent back to at least the Lower Miocene. These 

 evolutionary trends are being checked in Tertiary 



