DEEP-SEA RADIUM 125 



and arrived at the conclusion that in the central and 

 western region of the equatorial Pacific Ocean, from 

 which most of the cores he has studied were raised, a 

 general increase in the rate of sedimentation probably 

 occurred about 100,000 years ago, possibly as the re- 

 sult of an increase in submarine volcanic activity. Such 

 an increase is likely to have given rise to a locally in- 

 creased intensity of bottom currents, which in turn 

 brought about a horizontal transportation of sediment. 



That other postdepositional changes in the sediment 

 stratification could have been operative in causing a 

 redistribution of radioactive layers appears to be borne 

 out by the remarkable curve showing the radium dis- 

 tribution in the upper eight meters of core 238, raised 

 from the great depth of 7,500 meters in the Romanche 

 Deep. This being a long core raised by means of the 

 excellent Kullenberg piston-corer, its uppermost part 

 is likely to be missing, which may explain the absence 

 of a superficial layer rich in radium. The surprisingly 

 high radium content of 69 to 58 units of the twelfth 

 decimal place (the highest ever found in any core from 

 the open ocean) occurs at a depth of between 128 and 

 139 centimeters below the top of the core. Measure- 

 ments of both uranium (marked by crosses below the 

 curve) and ionium prove that this abnormally high 

 concentration of radium is ionium and not uranium 

 supported. 



The most plausible explanation of this distribution 

 of ionium-supported radium is suggested by a con- 



