INVESTIGATING THE FLOOR 75 



been held responsible for the transportation of deep-sea 

 sand over several hundred nautical miles from the 

 nearest coast Hne. On the other hand other scientists, 

 both geologists and oceanographers, are skeptical of 

 the hypothesis advanced by Ewing and Bruce C. 

 Heezen that successive cable breaks on the continental 

 slope and in the deep water off the Grand Bank follow- 

 ing an earthquake in 1929 could have been caused by 

 turbidity currents running at a computed velocity of up 

 to 55 knots. ^ To most students of dynamic oceanog- 

 raphy and especially to students of bottom currents so 

 high a velocity for a submarine current appears ex- 

 cessive.* Ewing also asserts that turbidity currents, far 

 from being confined to regions of steep slope, can be 

 sustained along slopes as moderate as 1 : 500. As regards 

 the power of turbidity currents to cause submarine 

 erosion and, more especially, to have eroded the famous 

 submarine canyons along both the Atlantic and Pacific 

 coasts of North America, a specialist on these canyons, 

 Shepard, considers that whereas turbidity currents may 

 be active in sweeping the submarine canyons already 

 eroded free from fresh sediment layers, they cannot be 

 held responsible for the origin of the canyons, since, 

 being already loaded with sediment, their power of 

 erosion is inadequate. - 



* W. Ekman, the great authority on ocean currents, in a 

 letter to the author dated August, 1953, expressed strong 

 skepticism that bottom currents even approaching these veloci- 

 ties can occur in nature. 



