304 LAND SCULPTURE 



that the amount of material annually removed from the land by 

 the sea is only about one cubic kilometre, or less than one- 

 fifteenth the quantity carried away by the subaerial agencies. 



The Sea. — The work of the sea is confined to the coast-line, 

 which it cuts back by the impact of its waves and currents. 

 Speaking broadly, the waves do but little effective work below 

 the limits of low tide, and advance by undermining and cutting 

 down the cliffs which form the coast. The result of the work 

 is to form a platform covered by shallow water, which is called 

 a plain of marine denudation. As observed in actual cases, these 

 platforms are narrow ; for so long as the sea-level remains constant 

 with reference to the land, there is a limit to the effective assault 

 of the waves upon the shore. The water covering the platform 

 is very shallow and only in exceptional cases do the waves have 

 sufficient power to overcome the friction of a wide platform. 

 The material removed from the land, especially the coarser and 

 heavier parts of it, are piled up at the seaward foot of the plat- 

 form and help to extend it in that direction. 



An example of a plain of marine denudation is found on the 

 north coast of Spain, where there is a broad platform between the 

 mountains and the sea, almost perfectly flat. This plain has been 

 uplifted above the sea-level and has been little dissected by the 

 subaerial agents. Narrower platforms, still in process of exten- 

 sion, may be observed on most rocky and precipitous coasts, as 

 those of Scotland, Ireland, and France. Along a slowly sinking 

 coast the platforms may be cut back much farther, for the deep- 

 ening water prevents the loss of wave power by the friction on a 

 shoal bottom. If, on the other hand, the coast rises at intervals, 

 a series of terrace-like platforms will be cut. 



As we shall see in the following section, plains may be produced 

 by the work of the subaerial agencies, and it is often important to 

 distinguish between the plains of submarine and those of subaerial 

 origin. This distinction cannot always be made with certainty, 

 but not unfrequently the plain shows unmistakable signs of the 

 manner in which it was made. In the plain of marine denudation 

 the sediments formed from the waste of the land will be deposited 



