352 



HKEZEN AN'n LAUGHTON 



[chap. 14 



When in 1061 and 1962 a shot spacing of 2-3 min (roughly one shot each 

 one-half mile) was first used this previous view was completely repudiated. 

 Sub-bottom horizons completely uncorrelatable in earher studies could ho fol- 

 lowed through complex sub-])ottom topograjihy. The contrast between oceanic 

 rises and the abyssal plains mentioned above was substantiated. The new 

 seismic-profiler records, however, add much new information on the total 

 sediment thickness in the ocean floor. This work has been carried out under the 



6tO 



im 



618 



617 



BERMUDA RISE 



SOHM 

 ABYSSAL PLAIN 



Fig. 29. Comparison of seismic -reflection records from the Bermuda Rise and the adjacent 

 Sohm Abyssal Plain. Records from Bermuda Rise show strong discrete sub-bottom 

 echoes, while those from the Sohm Abyssal Plain show a great many reflections which 

 are extremely difficult to correlate. 



supervision of Maurice Ewing and John Ewing of the Lamont Geological 

 Observatory by scientists aboard the Research Vessel Vema. 



The sediment thickness on the oceanic rises is sur])risingly very similar to 

 that beneath the abyssal i)lains, generally ranging from 1 to 2 km. The sediment 

 thickness in the abyssal hills is generally too small to measure and the sediment 

 thickness on the mid-oceanic ridge is generally extremely variable, being 



