112 THE FLOOR OF THE OCEAN 



world-wide. Its explanation, when made clear beyond per- 

 adventure, is certain to establish new, fundamental principles 

 of earth science and to engage the attention of all those inter- 

 ested in the grander processes of Nature. Let us look more 

 closely at the facts and then at the different hypotheses so far 

 offered to account for the submerged relief. 



The essential facts, won even by preliminary exploration in 

 regions so unfamiliar, are numerous and not easily held in full 

 memory during the attempt to picture the mysterious furrow- 

 ing of the continental slopes. Perhaps this difficulty will be 

 eased if the writer baldly states what seems to be the best 

 among the various explanations for valley and ridge, so that 

 this explanation will be in mind from the start. 



According to the preferred theory, the continental slopes 

 were originally unfurrowed and comparatively smooth. Their 

 present ruggedness is due to erosion, down-cutting, by under- 

 flows of heavy water that used to rush down the continental 

 slopes, much as gushes of rain-water gully hillsides on the land. 

 The water of these bottom currents was heavy because laden 

 with mud and sand in suspension, the mud and sand being 

 made of rock particles which are two to three times as dense 

 as clean sea water. The mud and sand were brought into sus- 

 pension during the tumult of storm waves that broke on the 

 shallows of the continental shelf, and during the run of the 

 turbulent tides across the shelf. The water thus made denser, 

 heavier per unit of volume, than the clean water of the ocean, 

 crept slowly down the gently inclined continental shelf and 

 then rushed down the much steeper continental slope. The 

 velocity of these underflows was so great that deep canyons and 

 furrows were cut in the original sediments of the continental 

 slope, and as many ridges were left between the new valleys. 



Such submarine cutting of trenches may be possible at the 

 present time, especially where the zone of intense wave-action 



