70 THE OCEAN FLOOR 



that this thickness is much less than has been inferred 

 from theoretical calculations based on geochemical 

 data. Thus, in the Pacific depths a sediment thickness 

 of a few hundred meters is the rule, with the figure 

 occasionally rising as high as half a kilometer, compared 

 to the two to three kilometers calculated by Kuenen as 

 average for the thickness of deep-sea sediments. How 

 this startling discrepancy is to be explained remains at 

 present an open question. 



In the North Atlantic Ocean, where Weibull found 

 the greatest sediment thickness, between Madeira and 

 the Atlantic Ridge, measurements by the refraction 

 method made by Ewing and others have given lower 

 figures than the maximum found by Weibull, but on the 

 other hand higher than those from the Pacific depths, 

 namely one-half to one kilometer of unconsolidated 

 sediment. Only in the Puerto Rico Trench, where the 

 greatest known depth in the Atlantic Ocean is situated, 

 has a sediment thickness exceeding nine kilometers been 

 reported by Ewing. In the northeast part of the Atlantic 

 Ocean M. N. Hill and A. S. Laughton have reported a 

 variable thickness of the sediment carpet, from very 

 low in areas of rugged bottom topography to as much 

 as two and a half kilometers over parts of the sea floor 

 with a less rugged structure, the average thickness being 

 about one kilometer. This is higher than the findings 

 of Ewing in the northwest Atlantic, but the difference 

 can be attributed in part to different assumptions con- 



