COASTAL PLAINS 



259 



up and widening them. The sand reefs along the southern 

 Atlantic and Gulf coasts have in some places sufficient 

 width and height to accommodate large settlements. In 

 time the sand blowing landward from these reefs, together 



COAST NEAR ATLANTIC CITY 

 Showing marshes, lagoons, and sand reefs. 



with the silt brought by the streams from the mainland, may 

 fill up the water area (lagoon) between the reef and the main- 

 land. The filling of these lagoons, both naturally and arti- 

 ficially, has greatly increased the habitable land of the earth. 



Coastal Plains. A coastal plain is a gradually emerged 

 sea bottom, and so has shallow water extending out for a 



