DEEP-SEARADIUM 127 



sedimentation and ionium precipitation below a water 

 column 7,500 meters high. Obviously it would be futile 

 to attempt to calculate the average rate of sedimenta- 

 tion from radium measurements in the Romanche 

 Deep. It is equally futile to attempt a dating of deep- 

 sea deposits from radium measurements up to one 

 million years back in time, as has recently been at- 

 tempted by J. L. Hough for a core from the south 

 Pacific Ocean, using radium measurements on the same 

 core Urry used to obtain his data. 



It seems necessary to consider here also another way 

 in which radium may become removed from sea water 

 and concentrated on the bottom: through adsorption 

 by peroxide of manganese. That an affinity exists be- 

 tween the two elements, radium and manganese, is well 

 known, manganese deposits from thermal sources on 

 the continents often being rich in radium. Experiments 

 made in Goteborg several years ago proved that braun- 

 stein powder, i.e. peroxide of manganese, shaken with 

 a highly dilute radium solution is effective in removing 

 the radium even in concentrations as low as those exist- 

 ing in sea water. The so-called manganese nodules 

 afford striking examples of this tendency of radium 

 to become adsorbed with manganese peroxide. Meas- 

 uring the radium present in thin concentric layers 

 removed from manganese concretions, the author 

 proved that the radium content falls off rapidly with 

 increasing depth below the nodule surface and becomes 

 too low for accurate measurements at a depth of one 



