The TRIESTE depth was determined to be 35, 800 feet 

 following calibration tests of the Bourdon tube- type hydrau- 

 lic pressure gauges by the Eastern Standards Laboratories, 

 U. S. Naval Weapons Plant, Washington 2 5, D. C. Addi- 

 tional calculations of the depth attained were made and 

 offered to the author by Dr. John A. Knauss, Scripps Insti- 

 tution of Oceanography, Dr. John Lyman, National Science 

 Foundation, and Dr. Ernest R. Anderson of the Navy 

 Electronics Laboratory. These calculated values varied 

 from 34, 931 to 35, 805 feet depending upon the calibration 

 data used. The "best value" for the depth may be a few 

 hundred feet less than the figure 35, 800 used throughout 

 this report. Further investigation of the temperature 

 corrections to the pressure gauges may resolve the differ- 

 ence. 



DIVE NO. 76 



Dive No. 76 was made primarily to acquire sound- 

 velocity measurements. The ultimate depth reached for 

 these measurements was 18, 900 feet. The bottom was 

 obviously bedrock covered by only a thin mantle of whitish 

 sediment (fig. 10). The greater portion of the exposed 

 black bedrock was clearly rounded and appeared encrusted, 

 as if by accretion. Some individual small rocks, also 

 rounded and no more than 2 to 3 inches in diameter were 

 strewn about the sediment cover. The sea floor beneath 

 the mantle of sediments appeared to be a solidified mater- 

 ial with long ridges of outcroppings. The ridges formed 

 at the boundary where a minor drop in the downslope pro- 

 file existed. 



The bedrock was exposed for long sections at this 

 nominal break in the slope. The slope gradient was esti- 

 mated to be 2 to 3 degrees. From a viewing vantage point 

 60 feet from the bottom, a distinct ridge of exposed rock 

 extended for more than 100 feet; it apparently ran parallel 

 to the axis of the trench. Isolated clumps of rocks were 

 for the most part flat, about 1 foot in diameter. They 

 protruded out of the bottom about 3 inches. Smaller frag- 

 ments, about 0. 2 5 inch thick and only 2 to 3 inches in 

 diameter were also distributed at random on the sea floor. 



A few worm tubes protruded out of the sediment. 

 These tubes were approximately 0. 2 5 inch in diameter and 

 2 inches high. Within the thin sediment mantle, several 

 conical hummocks of sediment with a distinct aperture in 



26 



