126 



THE OCEAN FLOOR 



sideration of the topography of the Romanche Deep. 

 At a distance of only 10 nautical miles from the great 

 depth out of which the core was obtained the Mid- 

 Atlantic Ridge rises sharply to a level of only 2,600 

 meters below the water surface, i. e. a difference in level 

 of nearly 5,000 meters, or an average slope of about 



m 2 ^ 



Fig. 41. Radium distribution in the Romanche Deep 



25:100. The conditions are thus favorable for a sub- 

 marine landshde, technically called a slump. It seems 

 reasonable, therefore, to assume that a relatively short 

 time ago — short compared to the half-value period of 

 ionium — a slump carried sediment down from the 

 slope, covering with more than one meter of in- 

 active sediment the former surface layer of the bottom 

 of the great deep, which had earlier been exposed to 



