CONTINENTAL TERRACES AND SUBMARINE VALLEYS 123 



Table VI 



AVERAGE LONGITUDINAL GRADIENTS OF SUBMARINE CANYONS, BY GROUPS 



matched on the lands, where, however, there are small-scale 

 analogies. Among these are the gullied slopes of many railway 

 cuts. Illustrations are found where the initially smooth sides 

 of the cuttings have exposed weak material, and that so long 

 ago that gushes of rain-water have had time to gully the artifi- 

 cial slopes. Particularly fine examples are to be seen along 

 hundreds of miles of railway traversing the southern Appalach- 

 ians. Another analogy, with more generous dimensions, is the 

 system of rain gullies eroded out of the soft Californian forma- 

 tions shown in Figures 68 and 69. At the railway cut an occa- 

 sional gully is more deeply incised than the average gully, and 

 also heads far back of the break of slope at the limit of higher 

 ground alongside the cutting. Such an exceptional gully cor- 

 responds to the typical submarine canyon. 



As yet, soundings in belts other than those around the 

 United States have not been detailed enough to show how 

 general is the furrowing of continental flanks the world over. 

 On the other hand, the more easily discovered canyons are 



