COAST RECORDS OF THE RISE OR FALL OF LAND 251 



some places as high as forty-seven feet, to the accompaniment of 

 a terrific earthquake and sea wave. Above the terrace which 



**. *** 



FIG. 280. Diagrams to show how excessive sinking upon the sea floor will cause 

 the shore to migrate landward as it is uplifted. 



marks the beach line of 1899 there is a higher terrace of similar 

 form now overgrown with trees, but none the less clearly to be rec- 

 ognized as a shore line of the past century 

 which preceded in the long sequence the 

 uplift of 1899. 



As was noted in our study of earth- 

 quakes, the recent instrumental records of 

 distant earthquakes tell us that the move- 

 ments upon the sea floor are many times 

 larger than those upon the continents, and 

 that while the mountainous coasts are gen- 

 erally rising, the deeps of the sea are sink- 

 ing. The effect of this over-balance of 

 sinking, or resultant shrinking of the earth's 

 shell, may be to compress the mountain 

 district and so cause the shore line to move 

 landward at the same time that it moves 

 upward (Fig. 280). 



The sunk or embayed coast. When 

 now, upon the other hand, a section of the 

 coast line sinks with reference to the sea, 

 the water invades all the near-shore val- FIG. 281. A drowned river 

 leys, thus " drowning " them and yielding mouth or estuarv u P n a 

 the " drowned river mouth " or estuary. 



If the relief of the shore was slight, as it generally is upon a 

 coastal plain, slight depression only will produce broad estuaries, 



