to wedge out and be supplanted by the sediment stratum below the yellow 

 reflector. The uppermost prominent and continuous reflector of the sub- 

 bottom section, whether overlying sediments characteristically associated 

 with the yellow or blue reflectors, is interpreted to be associated with 

 a single geologic event and to be a continuous surface within study limits. 

 Figure 12, a surface and isopach map of overlying sediment thickness, 

 follows this surface throughout. 



Few shoals are crossed by the Fort Pierce- Canaveral Bight reconnais- 

 sance lines; thus the sediment overlying the isopach reflector (which is 

 relatively flat) remains generally thin except under the shoreface where 

 it thickens greatly shoreward. Thomas Shoal, which lies on this section 

 of the shelf, was not covered by the survey and is thus not assessable 

 in this study as a source of beach sand. However, analogy with similar 

 offshore shoals in the grid area suggests that Thomas Shoal may contain 

 suitable fill material. The only shoal crossed by a reconnaissance line 

 is centered about 2,000 yards northeast of Sebastian Inlet. 



(3) Fort Pierce to Palm Beach - In the reconnaissance area south 

 of Fort Pierce Inlet, the blue reflector can be followed with reasonable 

 confidence southward to the vicinity of Palm Beach. As far as can be 

 determined, this reflector is continuous with the "bedrock" reflector 

 traced from Palm Beach southward to Key Biscayne by Duane and Meisburger 

 (1969) . 



Figure 13 is a surface and isopach map of sediment thickness over the 

 blue horizon between Fort Pierce and Palm Beach. As in the Fort Pierce 

 grid, the blue reflector has a nearly level seaward dipping surface over 

 which sediment accretions are thickest under shoal ridges and hills. 



South of Jupiter Inlet, the shoals, ridges, and hills characteristic 

 of the shelf to the north are no longer apparent, and the blue surface is 

 apparently covered only nearshore where a thick wedge of sand overlaps 

 the inner part of the shelf. 



26 



