XI.] 



THE SEA AND ITS WORK. 



183 



within narrow limits, not extending deeper than a few 

 hundred feet, and being for the most part restricted to the 

 zone of coast between high and low water-marks. At great 

 depths, the abrasion by slow under-currents must be ex- 

 tremely small, for dredgings have shown that, in deep seas, 

 there are no large fragments of rock to assist in the work 

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

 current 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 



Fig. 49. — Plain of marine denudation. 



below the sea-level. The comparatively smooth surface 

 which would be formed in this manner has been called by 

 Prof Ramsay a plain of marine demidatiou. Were such a 

 submarine plain to be upheaved above the surface of the 

 water, it would immediately be attacked by rain, frost and 

 other atmospheric agents, and would eventually be chiselled, 

 by these means, into a variety of physical features. It is 

 believed that old plains of marine denudation may yet be 

 defected in certain districts. Thus, if Fig. 49 represents a 

 section across a country where the highest points may be 

 connected by a plane, the edge of which is A B;; this plane 

 surface, with a gentle slope seaward, probably coincides with 

 the original plain of marine denudation, or is at least parallel 



