and discontinuous except in the shoal areas where accumulations of more 

 than 12 meters (40 feet) occur. Elsewhere, the sea floor is thinly 

 veneered by Holocene sediments interspersed with outcrops of older 

 sediments . 



The gross morphology of the shelf was probably established by 

 planation during late Tertiary and Pleistocene time. Minor shelf floor 

 features and surficial sediment distribution have been created during 

 the Holocene transgression which began about 15,000 to 20,000 years ago, 

 and by modern shelf processes which have affected the area since the sea 

 level reached its present stand about 3,000 years ago. 



Engineering properties of the shelf floor sediments and subfloor 

 sedimentary units vary considerably from place to place due to differ- 

 ences in lithology and postdepositional history. Foundation problems 

 are most apt to occur in the silt and clay deposits and in deposits of 

 weakly lithified calcareous rock. 



Sand suitable for restoration and nourishment of beaches is scarce; 

 most occurs in Holocene sand deposits. The sandy Cretaceous and Tertiary 

 Coastal Plain sediments underlying the shelf are, for the most part, 

 poorly suited for beach fill; however, suitable material occurs in a few 

 places . 



The boundary between modem and ancient sediment can be perceived 

 in some places by sharp contrasts in lithology which reflect differences 

 in environments of deposition and postdepositional history. However, in 

 many areas lithologic differences are not apparent and the best means of 

 establishing the boundary are by faunal analysis. 



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