64 SEA AND LAND 



\\\\.o tlic deeper water, where the currents can no longer stir 

 them, and where they may be bound to the bottom by the 

 organic ooze or shme which aljounds on tlie ocean-floor. In 

 this manner, by tlie endless i)rocession of tide-borne sand, the 

 greater part of tlie continental shelves are formed. 



The work of the tides in conveying the sediments from 

 the shore out toward the margin of these great submerged 

 sand-i)lains, is directly and often effectively opposed by the 

 movement of the sea-waves. These surges, like the incon- 

 ceivably wider tidal oscillations, have little effect upon the 

 bottom of the ocean in its deeper parts. If the abysmal sea- 

 floor were inhabited by a race of philosophical fishes, and 

 they were provided with the most accurate appliances for 

 obser\ation which have been invented by men of science, they 

 would hardly be able to detect the effect of the waves, how- 

 ever high, when they rolled over the surface three miles above 

 the ocean-floor ; at most they would find the water lifted a 

 fraction of an inch as the wave advanced, and lowered by the 

 same amount as it passed by. The trifling currents thus 

 induced would not disturb the finest mud upon the bottom ; 

 but if the imagined aquatic observers carried their studies to 

 higher levels of the sea-floor, they would find an ever-increas- 

 ing dragging action produced by the waves upon the base of 

 the ocean. When they came to the shallows of the conti- 

 nental shelf, they would perceive that the water under each 

 successive wave swung toward the shore with sufficient energy, 

 where; the surges were high, to drag the sand up the declivity. 

 The less the dei)th of the w^ater, the stronger this movement 

 would be, and next the beach, where the water was not more 

 than fifty feet deep, the action would be strong enough to 

 urge coarse sand or even fine pebbles to the margin wdiere 



