254 



PHYSICAL GEOLOGY 



CHANGES IN THE RELATION OF LAND AND SEA 



Sea level is geologically a critical level. It is the level to 

 which the agents of degradation seek to reduce the land. 

 The activities which are dominant on the land above it 

 are different from those dominant in the sea below it. 

 Great and repeated incursions of the sea upon the land, 



FIG. 275. End of Cape Cod. 



alternating with great extensions of the land at the expense 

 of the sea, have been among the most important events in 

 the past history of the continents, for they have changed the 

 dominant processes over vast areas, have modified climates, and 

 have changed the distribution and conditions of plant and 

 animal life. 



