134 THE FLOOR OF THE OCEAN 



vated tens of millions of years ago, whereas the valley pattern 

 has the marks of extreme youth. Again, the postulate of a 

 high-level coastal plain as feeder for the underground drainage 

 is still more doubtful in the case of the hundred-mile stretch 

 of canyons and furrows along Georges Bank; for this bank is 

 isolated, out to sea, and not backed by any coastal plain. Per- 

 haps even clearer is the absence of rock structure and topography 

 that could give the required head to spring-sapping streams off 

 the canyoned shore-belts of India, California, and the west 

 coast of Africa. 



There is a fifth difficulty. The development of a subaerial 

 box-head valley depends on the removal of rock fallen from 

 the walls, as these undergo spring-sapping. We saw that the 

 removal is by solution and by transportation downstream by 

 running water. Now, Professor Johnson expressly excludes the 

 possibility of adequate bottom currents of the kind, and is 

 therefore forced to rely on solution as the one essential for 

 furrowing the continental slope. Yet, if the submarine spring 

 be capable of dissolving rock, its water must be relatively fresh, 

 and, because of its lower density, must rise in the heavier sea 

 water and so lose contact with any rock. The spring water 

 could not wash away or dissolve away the detritus fallen from 

 the valley wall at the point of emergence of the spring. 



A final and likewise telling objection: the spring-sapping 

 hypothesis postulates important solution of one of the least 

 soluble materials known to geology — clay. With that premise, 

 neither geologist nor geochemist is likely to be satisfied. 



In summary, it seems clear that the spring-sapping explana- 

 tion of the submarine valleys cannot be retained. 



4. Professor W. H. Bucher, also preferring submarine 

 erosion to subaerial erosion, attributes canyon and furrow pri- 

 marily to cutting by the reflux currents associated with power- 

 ful earthquake waves in the ocean. 11 Like wind wave and true 



