12. 
Cores from Northwest Atlantic mid-ocean canyon, Cores taken 
in and nearby Northwest Atlantic mid-ocean canyon have given more evi- 
dence of the important role the turbidity currents play in the topographic 
evolution of the deep-sea basins (Ewing, Heezen, Ericson, Northrop, 
Dorman, 1953). 
In one of two cores from the canyon bed the upper 123-cm. sec- 
tion is composed of clay and silty clay in part as graded layers. This 
overlies 2 1/2 meters of well-sorted fine sand, In the other canyon bed 
core only 2 meters of core were recovered, consisting mostly of graded 
beds of silt size. There is clear evidence that about 2 meters of sand 
were lost from the bottom of the core. 
A third core from the nearly flat western bank, 90 m. (50 fms. ) 
above the canyon bed, contains numerous graded layers which show that 
fully three-quarters of the 4.6 meters total thickness was deposited by 
turbidity currents. Fine sand makes up only 3 per cent of the total 
thickness. It is inferred that the sediment deposited on the canyon banks 
was carried in the highest part of the turbidity currents. 
Evidence in cores for turbidity currents in the cable break area. 
In ''The American Journal of Science", December 1952, Heezen and Ewing 
concluded that the breaking of all submarine telegraph cables in sequence 
from north to south following the Grand Banks earthquake of 1929 could 
be explained satisfactorily only by supposing that a turbidity current 
generated in the epicentral area flowed southward, breaking the cables 
as it reached them. 
