MARINE DEPOSITS 225 



seems that the amount of radio-active sub- 

 stances, of manganese nodules, of whales' ear- 

 bones, of sharks' teeth, of cosmic spherules 

 and of zeolitic crystals is greatest where there 

 is every reason to believe that the deposition 

 of material on the sea-floor is at a minimum. 

 The presence of lead (which is supposed to 

 be the ultimate disintegration-product of 

 uranium) in J. Gibson's analysis of manganese 

 nodules from the red clay in the centre of the 

 Pacific is in this connection significant. 



