132 THE OCEAN FLOOR 



length of only three to four centimeters cut from such a 

 thick core would have been sufficient. It is to be hoped, 

 therefore, that in future expeditions coring devices of 

 the same diameter as those occasionally used on board 

 the "Albatross," that is with an internal diameter of 

 four inches or ten centimeters, will be employed in 

 order to obtain material for more detailed investigations 

 using radiocarbon dating. ^"^ 



Summary. The study of the radioactive elements 

 uranium, ionium, radium, thorium, and radiocarbon 

 which are present in deep-sea sediments and ocean 

 water has proved well worth pursuing further. Geo- 

 chronological studies based on radioactive age deter- 

 minations have proved feasible, although in the case of 

 radium they are complicated by a reshuffling of the 

 sediment. The time span over which such age deter- 

 minations may be extended, even in the most favorable 

 cases, is limited to 300,000 or at the most, 400,000 

 years, that is, about half the length of the Pleistocene. 

 The relatively rapid decay of radiocarbon sets still 

 narrower limits to its use of about 20,000 years. 



