HYDROGRAPHY OF THE MARINE WATERS 9 



continuation of this state boundary, there are 10,450 square miles of con- 

 tinental shelf .^ 



The more modern sounding techniques have not been continued on the 

 shelf south of the North Carolina-Virginia line. To the north such sounding 

 clearly outlines numerous canyons indenting the continental slope and it is 

 probable that such canyons are present to the south as well. Knowledge 

 accumulated by the experience of fishermen and others, which has acquainted 

 us with the shelf off New England, for example, is very limited off North 

 Carolina, but it is probably a safe generalization to say that inshore the 

 bottom tends to be sandy and that a combination of mud and rock exists in 

 deeper waters. Much of the rock south of Hatteras is in the form of coral 

 patches (see section below on Nature of the Bottom). 



The contours of the shoals of the continental shelf are well mapped. Three 

 prominent ones, Diamond Shoal off Hatteras, Cape Lookout Shoals, and 

 Frying Pan Shoals off Cape Fear, are extensions of the cuspate shoreline and 

 project seaward almost half way across the shelf. 



The shelf waters off North Carolina are directly affected by the Florida 

 Current of the Gulf Stream System, a deep-sea current that overlaps the 

 loo-fathom contour, by the coastal waters from the north and south, and by 

 brackish water from the inlets. This complex interaction will be mentioned 

 frequently in this chapter, and a comprehension of it, especially as discussed 

 below in the section on Temperatures Offshore, is probably the most im- 

 portant item to be considered in trying to evaluate the State's offshore fisheries 

 potentialities. 



Circulation in the Sounds 



Factors that interact to produce the circulation in the sounds include: 



1. Wind. 



2. River discharge. 



3. Evaporation and rainfall over the sound waters. 



4. Tide. 



5. Corioli's force, which tends to deflect currents to the right in the 

 northern hemisphere but has little effect in shallow waters such as these 

 sounds. 



Finally, to arrive at the probable resultant effects, all these must be con- 

 sidered in terms of the coastal physiography. 



Chiefly as the result of oyster investigations planned with the knowledge 

 that currents are important in the ecology of this species, many investigators 

 have made current observations in North Carolina coastal waters, but the 

 scattered nature of these observations and the fact that the many interacting 



3. These continental shelf measurements are from planimeter readings by the author. --iitr* .*'^- 



