186 



MARINE BOTTOM SAMPLES OF LAST CRUISE OF CARNEGIE 



clay which completely separated one part from the 

 remainder. Apparently the accretion of manganese ox- 

 ide had gone on, keeping the same configuration, after 

 the coating of clay had been deposited. These features 

 are apparent in the accompanying photographs. The 

 sawdust obtained from sectioning this nodule contained 

 12.0 X 10"12 grams of radium per gram. 



Various mechanisms have been suggested to account 

 for this high concentration of radium on the ocean bot- 

 tom, some of which seem to have lost sight of the fact 



that the significant chemistry involved is the chemistry 

 of uranium and not that of radium per se. 



It has been suggested that the concentration is brought 

 about by the numerous minute living organisms in the sea. 

 These extract, more or less selectively, the salts of 

 uranium and radium from the sea water, incorporate 

 them in their skeletons, and when they die their remains 

 take the radioactive material to the bottom along with 

 them. In opposition to this reasoning are the calcula- 

 tions of Bischof that an oyster requires the lime from 



Table 1. Radium in ocean-bottom sediments collected by Challenger and Albatross (Joly) 



Latitude 



Longitude 



Depth, 

 meters 



Type of sediment 



Radium 

 X 10-12 per g 



Princess Alice 11 (Pettersson) 



Latitude 



Longitude 



Depth, 

 meters 



Type of sediment 



Radium 

 X 10-12 per g 



