The Sea and Its Work 



Putting together what has been said in this 

 chapter with reference to the action of the sea 

 upon the land, it may be concluded that its 

 work on the whole is a work of destruc- 

 tion, yet not exactly like that of rain and 

 rivers. To observe this difference, it must be 

 borne in mind that marine denudation is not 

 equally active at all depths of the sea. The 

 waves, as explained above, indicate only super- 

 ficial agitation, and have no effect on deep water. 

 Most of the destruction wrought by the sea is 

 consequently confined within narrow limits, not 

 extending deeper than a few hundred feet, and 

 being for the most part restricted to the zone 

 of coast below high and low water-marks. At 

 great depths, the abrasion by slow under-currents 

 must be extremely small, for dredgings have 

 shown that, in deep seas, there are no large 

 fragments of rock to assist in the work of demo- 

 lition; and, even if there were, the force of the 

 currents would probably be insufficient to move 

 them. The great business of the sea is therefore 

 confined to eating away the margin of the coast, 

 and planing it down to a depth of perhaps a 

 hundred fathoms. If this action went on for a 

 sufficient time, the entire coast would be nibbled 

 away, and Britain reduced to a great plain below 

 the sea-level. The comparatively smooth sur- 

 face which would be formed in this manner has 

 been called by Prof. Ramsay a plain of marine 

 denudation. Were such a submarine plain to 

 be -upheaved above the suface of the water, it 

 169 



