212 



PHYSICAL GEOLOGY 



Fig. 200. — Plain of marine denudation, Yorkshire, England. 

 (Photo. J. W. Gregory.) 



it ends abruptly in deep water. The width of such a terrace depends 

 upon the distance that the waves have cut into the land — the wave- 

 cut terrace — and the distance to which the terrace has been built 

 out by the material worn from the cliff and carried out to the edge 

 of the rock terrace by the undertow — the wave-built terrace (Fig. 201). 

 The depth of the water over the outer edge of the " cut and built " 

 terrace depends upon the size of the waves which prevailingly beat 



against the shore. In 



small lakes it is slight, 



while in larger lakes 



it may be twenty or 



more feet in depth. 



The floor of the North 



E. D Sea between Great 



Fig. 201. — Section showing the wave-cut terrace CB, Britain and Europe 



and the wave-built terrace EC, the whole constituting d f he Adantic 



the wave cut and built terrace. 



a few miles west of 

 Ireland is believed by some geologists to be a plain of marine 

 denudation. In eastern Patagonia, southern Australia, and other 

 places the sea beats against cliffs from 200 to 1000 feet high, a fact 

 which implies that marine erosion has cut them back tens or perhaps 

 scores of miles. 



