228 DYNAMICAL GEOLOGY. 



of former emerged land. Moreover, the eddying of the wave-and-current 

 flow about islands has made long spits as prolongations of their points 

 or capes. 



7. Actio7i of the oceanic waters over a submerged continent, and during a 

 progressing submergence or emergence. — Were a slowly progressing submer- 

 gence of a continent, or of any large part of one, in progress, the waves and 

 marine currents would work over the loose earth, gravel, and alluvium of 

 the surface, thereby changing them into marine deposits ; the living species 

 of the land and the fresh waters would be destroyed, and marine life would be 

 introduced ; and the general features of the surface would be changed through 

 a wearing off of heights and a filling of 2')reexisting valleys, and not by the 

 excavation of valleys. It might be supposed, at first thought, that the ocean 

 would wash through the valleys with great excavating force, and make deep 

 gorges over the surface. But from the present action on seacoasts, it is 

 learned that with each foot of submergence, the seabeach would be set a 

 little farther inland, so that the whole would successively pass through 

 the conditions of a seashore. The salt waters, in fact, enter the river-valleys 

 of a coast but a short distance, because they are excluded \)j the outflowing 

 stream. During a progressing submergence, therefore, the ocean would have 

 no power of excavating narrow valleys, unless they happened to be open at 

 both ends and of great breadth and depth, so as to allow the oceanic currents 

 to sweep through. 



In a subsequent emergence, the mountains and ridges would be still 

 further degraded, and the valleys filled by their debris. The laws of sea- 

 coast action would again come into play, and the wear of all new headlands 

 and the filling of bays would continue to be the result, so long as the emer- 

 gence was in progress. 



If the continent were to a large extent without mountains, as was the fact 

 in early geological time, the broad flat surface might then lie slightly above 

 or below the tide-level at once, or nearly simultaneously, so that, under a 

 small change of level, the waves might sweep across the whole area and the 

 deposits have a continental extent. Through continental oscillations, caus- 

 ing slight emergences of large areas to alternate with varying submergences, 

 variations in the formations would be produced, differences of depths and 

 differences of currents causing transitions from arenaceous to argillaceous or 

 to pebbly accumulations, or to clear waters fitted for corals and the other life 

 which has contributed to limestone-making. 



Evidence of emergence or elevation is to be looked for in the presence of 

 stratified beds containing marine fossils ; and when no such evidence exists 

 over a country, the proof is defective, so much so, that facts from elevated, 

 beach-like accumulations or terraces of sand or gravel are not \vorthy of 

 much consideration, unless on land fronting the seashore. The sea-border 

 animal life readily moves in when a submergence is in progress ; for each 

 species has its limits in depth and must move or die, and ova float landward 

 with the waves and currents ; hence fossil-bearing, sea-border deposits would 



