I30 THE FLOOR OF THE OCEAN 



seems quite beyond possibility. Geologists know full well the 

 stubbornness of the earth's crust in resisting forces of deforma- 

 tion, especially where the deformed region has a span of only 

 a few scores of miles. In this case any distortion of the strong 

 crust would have to be to a high degree irreversible. 



Second, we note that, to account for the world-wide dis- 

 tribution of the canyons, the double movement of the crust 

 would have been assumed to affect the borders of every con- 

 tinent (except Antarctica, off which canyons have not been 

 reported), and that contemporaneously or nearly so. No ex- 

 perienced geologist could credit crustal displacement defined 

 by so delicate conditions of time as well as of space. 



Third, the hypothesis lacks support because no reason for 

 either uplift or later subsidence has ever been proposed. Until 

 this question is properly answered, the imagined up-and-down 

 swinging of the crust will remain a matter of pure conjecture. 



Fourth, the idea can be tested in still another way. If tem- 

 porary emergence of the continental slope permitted rain-made 

 furrowing, master rivers that head far within the original 

 shoreline should have dug comparable furrows in their own 

 delta deposits and other weak formations of the coastal belt. 

 Yet no river of the eastern United States, though flowing long 

 distances across weak sediments, has done that. They, like the 

 Mississippi, have trenched themselves in their lower courses as 

 much as 300 feet, but this limit is precisely the depth expected 

 on a sounder theory of the furrowing. As we shall see, this 

 theory is based on the assumption of moderate swings of sea- 

 level up and down, the earth's crust remaining undisturbed. 



Without further elaboration it seems clear that the attempt 

 to account for the submarine valleys by assuming a mighty, 

 vertical oscillation of each continental terrace is a failure. If 

 Dana had been acquainted with the wealth of data secured by 



