AQUEOUS AGENCIES. 



51 



submarine banks also the low islands about the mouths 

 of estuaries and harbors, such as Sandy Hook and Coney 

 Island about New York 

 Harbor, and the long 

 sand-spits off the shores 

 of shallow seas, as, for 

 example, the shores of 

 North Carolina (Fig. 

 26), and nearly the 

 whole southern Atlan- 

 tic coast. The debris 

 brought down by the 

 rivers to the estuaries 

 is carried by the re- 

 treating tide seaward 

 and dropped near shore. 

 On the sea-margin bank 

 thus formed, the waves 

 beat up long, narrow 

 sand - spits, separated 

 only by tidal inlets. 

 This is the condition on 

 the North Carolina 

 coast. These barriers 

 to the retreating tide 

 then cause the estuaries to fill up, until they are separated 

 from the mainland only by narrow tidal channels. Thus 

 are probably formed the sea-islands on the South Carolina 

 coast. Finally, the tidal channels may be filled up, the 

 islands added to the land, and the coast-line transferred 

 seaward. 



Along nearly all coasts we find a line of small islands. 

 These are of two kinds. The one consists of high, rocky 

 islands, off bold coasts, as in Norway, Greenland, etc.; 

 the other of low, sandy islands, off level coasts, as on the 

 southeastern coast of the United States. Those of one 



FIG. 26. North Carolina coast. 



