Ihc Inner Continental Shelf" profiLo w.is v i ewetl us u two-element 

 sli.ipc by Johnson (1919) and Fisher (L97J), In discussing the origin 

 oF barrier islands, both made extensive use of the planar ramp sector 

 as it extended through or under the shoreface sector. Shepard (1963) 

 presented evidence from borings obtained along the Gulf of Mexico coast 

 that indicated the shoreface of some barrier islands grew upward on the 

 extended ramp as sea level rose. Sheridan, Dill, and Kraft (1974) re- 

 ported that the Delaware barrier island shoreface migrated westward 

 across and above large lagoonal complexes. This westward transgression 

 of the shoreface was on an undulating erosion surface, or ramp, with a 

 gentle slope toward the offshore. 



Field and Duane (1974, 1976) also presented evidence that some 

 barrier islands originated seaward of their present positions, and are 

 presently shifting landward. Using seismic evidence they show that 

 shoreface sectors are structurally different from the ramp sectors and 

 are sometimes superimposed upon a landward extension of the ramp. In a 

 study of the inner shelf near Cape Canaveral, Florida, they found that 

 shallow subbottom strata on the ramp were truncated by a transgressing 

 sea, creating a flat-lying reflector. The shoreface sector now lies 

 above this reflector. No relationship was found between the slope of 

 the reflector and the present nearshore configuration. 



Results of field studies such as Sheridan, Dill, and Kraft (1974) 

 and Field and Duane (1974, 1976) suggest the geometrically different 

 ramp and shoreface are also genetically different. For this reason, 

 the following empirical approach to define the Inner Continental Shelf 

 profile includes separate descriptions of the ramp and shoreface, and 

 a means to couple the two. 



III. MEASUREMENT PROCEDURE 



1 . Inner Continental Shelf Profiles . 



A total of 441 bathymetric profiles from 49 coastal localities was 

 assembled for this study, using National Ocean Survey (NOS) (formerly U.S. 

 Coast and Geodetic Survey) 1200 series hydrographic charts. Nine pro- 

 files from each locality were averaged to obtain a single representative 

 profile (Fig. 1). Localities were chosen according to their location on 

 straight, uninterrupted coasts as distant as possible from inlets, estu- 

 aries, or river entrances, and to nearshore regions (up to 10- to 15- 

 meter (30 to 45 feet) water depths) that displayed relatively smooth 

 bathymetric contours parallel to shore. In all instances, profile loca- 

 tions were selected with a 150° land-free arc for a 500-icilometer (312 

 miles) radius away from the coast. Additionally, locations were selected 

 where bottom materials were unconsolidated as indicated by sediment 

 symbols on the charts. Most of the profiles were obtained from barrier 

 island coastlines. 



At the center of each locality a profile line was drawn on the chart 

 along an azimuth normal to and away from the coast. The latitude and 



