IV-28 



been cut off from the sea by barrier Islands, Mobile Bay illustrates 

 the initial formation of offshore bars, Matagorda Bay shows the full 

 development of barrier islands, and the marshes around the mouth of 

 the Satilla River represent the ultimate stage in the filling of an 

 estuary. 



The great ice sheet which once covered the estuarine zones of 

 New England, northwest Washington, and southeast Alaska scoured off 

 much of the readily erodable surface material 1n the coastal water- 

 sheds, thus, natural sedimentation has been a relatively minor 

 factor in modifying estuaries in these areas. Narra^ansett Bay and 

 Puget Sound, among many others, still maintain the great depths 

 typical of glacially formed embayments. 



Near the edge of the ice sheet, however, where the scoured-off earth 

 and rock carried along under and 1n the 1ce finally stopped as the 

 glaciers met the sea and melted, small, shallow bays formed in the 

 glacial debris and subsequently developed offshore sand spits and 

 barrier Islands as illustrated by Moriches Bay (Figure IV. 1.15) on 

 the south side of Long Island, which 1s formed of such glacial 

 debris. 



Abundant sediment eroded from the coastal ranges along the Pacific 

 coast of the continental United States has nearly filled several 

 estuaries, and wide tidal flats are common in the few estuaries 

 along these coasts (Figure IV. 1.16). The Columbia, however, 



