122 THE FLOOR OF THE OCEAN 



Table V 



DIMENSIONS OF THE CANYONS OFF THE MIDDLE ATLANTIC STATES 



For Comparison 



Colorado 



River. . . . 

 Snake 



River. . . . 



1 : 530 (mean 

 gradient) 



1 : 400 (mean 

 gradient) 



*In each case the actual dimension is greater. 



percentages as well as in feet per mile. Again the mean slope 

 is seen to be less steep than the slope at the head of the canyon. 

 A similar relation is characteristic of subaerial river valleys. 



The side slopes of submarine canyons are variable but com- 

 paratively steep. Along the upper and deeper parts of these 

 valleys, as mapped by Smith and Veatch, the side slopes range 

 from i in 3 to i in 6 and average about 15 degrees from the 

 horizontal. Such gradients suggest angles of rest for the soft 

 sediments of the terrace.* 



The whole topographic pattern is on a scale nowhere 



* The contour-lines of the maps under discussion are generalizations from a 

 limited number of soundings, and therefore cannot represent the submarine relief 

 with exactitude. Departure from the reality is doubtless most serious where the depth 

 of water exceeds 6000 feet. Evidendy many more soundings over the continental 

 slope are desirable, but it seems already clear that ultimate correction of the contour- 

 ing will not in principle change the canyon-furrow-ridge pattern. 



