120 



THE FLOOR OF THE OCEAN 



FIGURE 66. MAP OF THE NORFOLK CANYON AND VICINITY. OUTSIDE THE 

 IOO-FATHOM ISOBATH THE CONTOUR-INTERVAL IS 25 FATHOMS. 



that none of the canyons of Georges Bank has any obvious or 

 probable relation to rivers of the continent — a fact to be empha- 

 sized when we consider the origin of all this submerged 

 topography. 



Table V gives some of the significant data regarding the 

 five canyons mapped by Dr. Veatch. The unit of length is the 

 statute mile. For comparison some dimensions are stated for 

 two major land canyons of our Far West. Note particularly 

 the enormous difference in the longitudinal gradients for sub- 

 aerial and submarine canyons. 



That contrast is even more striking when the mean slopes 

 of the groups of submarine canyons in different parts of the 

 world are compared with the mean slopes of the Colorado and 

 Snake River valleys. In Table VI the averages are expressed in 



