IV-17 



chemical compounds, or of speed of motion. Yet they help to explain 

 why lobsters grow in Maine and not along the coast of South Carolina, 

 and they form one basis for regarding the national estuarine system 

 as a unified whole, not as a group of unique coastal systems. 



STRUCTURE OF THE COASTLINE 



The configuration of the coastline itself, even though subject to 

 additional molding by the flow of rivers to the sea, is closely 

 related to the shape and structure of the continental shelf. A 

 wide continental shelf is generally associated with lowland next to 

 the coast, while a narrow shelf is associated with mountainous 

 terrain. These associations throughout the estuarine zone of the 

 United States have produced estuarine systems characteristic of 

 particular regions. 



The northern part of the North American continent was once covered 

 by an ice sheet of continental dimensions, which left its impress on 

 the estuarine zone as far south as New York City on the Atlantic 

 coast and Puget Sound on the Pacific coast. These massive glacial 

 rivers, sometimes over one mile thick, cut their way to the ocean, 

 terminating somewhere in the vicinity of the edge of the continental 

 shelf on both coasts (Figure IV. 1.8). 



The result of their passage 1s the sharply sculptured and generally 

 steep shoreline associated with the New England, Puget Sound, and 

 Southeast Alaska regions. The submarine topography of these regions 



