permanent (a view which Lees opposed vigorously on the grounds 

 that geological structures can be seen that strike out towards the 

 sea and must be supposed to cross the boundary). At that time 

 continental drift was a theory out of favour with geophysicists 

 and the new seismic evidence showed beyond doubt that the 

 Atlantic could contain no sunken continents such as those proposed 

 by geologists to have provided the sediments found in the marginal 

 geosynclines of America and Britain. Likewise, the presence of 

 vesicles in fragments of basalts dredged from the Mid-Atlantic 

 Ridge and the existence of coarse detrital sands dredged by the 

 CHALLENGER from the abyssal plains could no longer be argued 

 as evidence of a one time wholesale emergence of the seafloor, as 

 they had been by Gregory (1929). An alternative explanation of 

 the deep-sea sands was discussed at the Royal Society by Kuenen, 

 and by Shepherd, in terms of transport by turbidity currents. 



-WTErr 



2 65 



// 

 (2-8)/ 



2-95 



33 





28 i J6 ♦ J-3 > 4 • II4--0 



14 , 10 K« cr> 



-■BASAU.V 



OCEANIC 

 CRUST 



WATER 

 \V2-9';" : | BASALT [.SEDIMENTS) 



(325) PEHIDOTITE 



Fig. 2. Diagram to show typical continental and oceanic sectors of the 

 earth's crust. (Hess, in Bullard 1954). 



1955-1959 



By the first International Oceanographic Congress, held in 

 New York in 1959, it was generally agreed that turbidity currents 

 could transport material of shallow water origin down the conti- 

 nental slope and deposit them many hundreds of miles from land 

 in graded beds which formed the abyssal plains. The question of 

 whether these currents eroded or merely kept clear the submarine 

 canyons on the continental margin was not (and still is not) settled, 

 but Laughton (1960) provided very convincing evidence of erosion 

 by rejuvenated turbidity currents at the S.W. corner of the Biscay 

 abyssal plain. There the turbidity currents, already some 400 miles 

 from their source on the continental slope, had gathered speed and 

 flowed down through a gap in the confining hills to spread out 

 again on the Iberia abyssal plain 100 fm. deeper, cutting on their 



30 



