COMMENTS ON THE GEOLOGIC fflSTORY OF THE SEA 

 ISLANDS OF THE SOUTHEASTERN UNITED STATES 1) 



by 



John M. Zeigler 

 Woods Hole Oceanographic Institution 



Sea islands off Georgia and South Carolina are of several kinds: 



1. Marsh islands - formed by upgrowth of marsh. 



2. Beach ridge islands - formed when rising sea level 



floods low places around groups 

 of beach ridges. 



3. Compound islands - which are composed both of beach 



ridges, and marshes surrounding 

 a central core of bedded sediments 

 more related to the mainland than 

 to marine built features. 



Cores of the compound islands represent fragments of mainland divides 

 which extended seaward between rivers. They became isolated when streams 

 cut a valley parallel to the coast across the divides during lowered sea level 

 ol the Wisconsin glacial epoch. It is a hypothesis that this valley was local- 

 ized by erosion of a less -resistant, probably limey, member of coastal plain 

 sediments . 



1) published in Geographical Review, 1959. (accompanied by time lapse film 

 of Atlantic Coast of U. S.) 



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