At this point the elevation is 47 feet and the shoreline descends 

 almost vertically to a depth of 5 feet below mean low water. The 

 base of the shoreline below water level is undercut approximately 

 4 feet and is thoroughly pitted with small angular cavities (Plate 19), 



Proceeding along bearing 057° for a distance of 1,750 yards the 

 bottom consists of a hard limestone covered by a thin veneer of 

 coarse sand. Occasional solitary corals occur along the track to 

 Buoy 8. In addition there are isolated heads supporting a sparse 

 marine community (Plates 20 and 21 A § B) . In the vicinity of 

 Buoy 9, the bottom changes to a head-sand association. The 

 heads are generally 4 to 5 feet high and up to 10 feet across. 

 Proceeding due east from Buoy 10 the heads increase in abundance 

 to the break-in-slope which occurs at Buoy 12, where the bottom 

 consists entirely of hard, angular corals and algae supporting a 

 variety of soft, sedentary organisms (Plates 21 C § D to 23). 



UPPER MARGINAL (RIM) ESCARPMENT 



The upper marginal escarpment is that area between the break- 

 in-slope at the eastern edge of the outer platform (14 to 16 

 fathoms depth) and the TOTO flanks to 100 fathoms depth. The 

 100 fathom contour is arbitrarily selected due to the depth 

 limitation of the surveying vehicle. The concensus of opinion 

 (Schalk, 1946, Armstrong, 1953, Newell and Rigby, 1953), places 

 the bottom limit around 100 fathoms. Athearn (1963) presented 

 and discussed in detail the bathymetry of the TOTO and stated 

 that the slopes appear to be nearly vertical in the upper 100 

 fathoms with a distinctly less steep slope below. Detailed 

 bathymetric surveys by NAVOCEANO off the sites discussed here 

 show results compatible to those of Athearn ( Ibid .) and places 

 the lower limit of the rim escarpment between 110 and 130 fathoms 

 in depth. 



Four areas of the rim escarpment were studied by proceeding 

 due east from the following locations to a depth of 600 feet: 



24 



