118 THE OCEAN FLOOR 



can be used is therefore much more limited than Pig- 

 got's and Urry's pioneer work led them to anticipate.^ 



The most extensive investigations of this kind so far 

 undertaken have been made in the Oceanographic 

 Institute of Goteborg on cores taken from great depths 

 during the Swedish Deep-Sea Expedition with the 

 "Albatross." •' Out of cores from the central Pacific 

 Ocean, consisting largely of red clay or radiolarian 

 ooze, a considerable number of samples have been 

 measured for radium by the standard method of radon 

 determinations, most of the work being done by Kroll.*' 

 Two of his curves showing radium distribution at vary- 

 ing depths in Pacific sediment cores are here reproduced 

 as Figures 39 and 40. 



It is seen that instead of a simple exponential curve, 

 falling off downward below the near-surface maximum 

 expected (see Figure 39), there are two, four, or even 

 more maxima which are separated by equally sharp 

 minima. Moreover, in certain cores there v/ere found 

 relatively high values of radium content at such great 

 depths below the sediment surface that, considering 

 the slow rate of sedimentation, most of the precipitated 

 ionium from the surface layer ought to have had time to 

 become disintegrated. 



In spite of the fact that these findings are at variance 

 with theory, Kroll, calculating the total amount of 

 radium in a core down to levels where the ionium- 

 supported radium becomes insignificant, has been able 

 to approximate values of the rate of sedimentation on 



