THE OCEAN AND ITS WORK 



231 



Fig. 225. — Map showing the conditions 

 which sometimes give rise to the belief that a 

 coast has sunk. If the bar is cut through by 

 the waves, salt water will invade the fresh water 

 marsh and kill any trees which may be growing 

 on it, and salt-water peat may in time cover 

 the fresh-water peat. (After D. W. Johnson.) 



increase the height of the tides. A 

 recent study of the evidence for and 

 against subsidence of the Atlantic 

 coast indicates that a subsidence of 

 one foot during the last century is 

 impossible. 



In other parts of the world 

 submergence and elevation 

 are certainly taking place. 

 In Sweden careful measure- 

 ments show that certain por- 

 tions are rising and others 

 sinking. 



Cycle of Shore Erosion. — 

 If one takes into account the 

 combined effects of erosion 

 and accumulation on coasts, 

 it will be seen that all coasts tend to become simple. A coast 

 recently formed by the advance of the sea (submergence of the 

 land), as has been seen (p. 226), has many irregularities, with 

 promontories corresponding to the hills and bays to the depressions. 

 At first the effect of the waves is to render the coast even rougher 

 than it originally was, by the formation of stacks and rocky islets. 

 The effect of difference in hardness is, however, of short duration. 

 A hard stratum may be isolated for a time, but it is an unstable 

 situation, and the islet or point thus formed is destined after a 

 short delay to disappear; marine erosion is incapable of penetrating 

 several miles inland by the excavation of a softer stratum. In 

 these earlier stages of marine erosion (Fig. 226 A, B)> the coast 

 may also for a time be made more irregular by the formation of 

 sand spits, or incomplete bars, but their further development tends, 

 as has been seen, to the formation of a smoother coast by cutting 

 off the indentations which are thus converted into lagoons and 

 later into marshes. In this early stage, which may be compared to 

 the stage of youth in the evolution of land surfaces, the wave-cut 

 terrace is narrow, and much of the shore drift is carried into deep 

 water, out of reach of the littoral currents. The coast of Maine is 

 in general in the youthful stage. The east coast of Scotland is 

 also in early youth, while the Baltic coast of Germany is typical of 

 later youth. 



