Section A (Figure 7a) is characterized by a step-like bathymetric 

 profile consisting of a series of linear plateaus (flats) each lower than 

 its immediate shoreward neighbor. Separating the flats are irregular 

 rocky ridges and slopes. In Section B (Figure 7b) the step-like character 

 of the profile is replaced by a relatively thick mass of fine gray sand 

 forming a gentle seaward slope over the central part of this portion of 

 the shelf surface. 



Immediately seaward of the low water line and terminating at -10 to 

 -18 feet MLW is the shoreface slope evident in both Section A and B. This 

 narrow zone seaward from the low tide shoreline is continuously influenced 

 by the effects of waves, currents, and littoral sediment supply. At the 

 seaward boundary of the shoreface slope the profile flattens and gives way 

 to what is here referred to as the inner flat, a broad platform extending 

 between depths of around -10 to -30 feet MLW. The surface of this flat is 

 characterized by linear swales and ridges of low relief. The inner flat 

 is essentially an exposed, partially lithified, deposit of algal .plates, 

 mollusk fragments, foraminifers, corals and unidentified calcareous 

 material. A considerable portion of the unidentified fragments may be 

 debris from Sabellariid reefs (Kirtley and Tanner, 1968). South of Port 

 Everglades {26°06' N) the main part of the inner flat lies at around -16 

 to -25 feet MLW with some depths to 30 feet. Northward, this feature 

 becomes narrower, shoaler and less conspicuous. ^^ 



Succeeding the inner flat in Section A is a second plateau at a 

 characteristic depth of -35 to -45 feet MLW. This plateau is separated 

 from the inner flat by a rocky, irregular slope with 10 to 15 feet relief 

 which is locally interrupted by a linear flat at around -30 feet MLW. 

 The second plateau is level, and the surface for the most part is un- 

 consolidated sediment. Its width ranges from 250 to 700 yards, but it 

 is generally of the order of 350 yards and is terminated by a rocky reef- 

 like ridge having irregular crest elevations of about 40 feet. South of 

 25°48' N, this reef line lies along the outer edge' of the si'.elf and is 

 succeeded by the major slope leading to the Miami Terrace. 



North of 25°48' N the second reef is fronted by a third plateau with 

 depths of -60 to -70 feet MLW. Like the second plateau this feature is a 

 relatively level sediment-floored depression 250 to 400 yards wide. The 

 surface of this plateau has a pronounced landward dip, particularly in the 

 southern part of the region. Seaward of the third flat is a prominent 

 reef-like ridge with 10- to 15-foot relief which is periodically inter- 

 rupted by narrow passages and by very broad interruptions at around 26''00' 

 N and just north of 26°30' N. The reef crests typically at approximately 

 -50 feet MLW, but is quite irregular. Throughout Section A the shoreline 

 is not quite parallel to the reef, consequently the shore trends progress- 

 ively toward the reef from south to north, and the reef lies 3,500 yards 

 seaward of Miami Beach but only about 1,500 yards seaward of Boca Raton. 

 North of Boca Raton (26°20' N) the reef parallels the shoreline at a 

 distance of about 1,500 yards. 



15 



