BELLINGSHAUSEN SEA 233 



were taken over the edge of the continental shelf between Alexander 1st Island and the 

 Biscoe Islands. These soundings show that the shelf extends some 80 miles from the 

 former and about 65-70 miles from the latter. The great breadth of the continental shelf 

 may presumably be taken as evidence of the antiquity of the land masses which lie to the 

 south. From the section (Fig. 4 c), which is based on a line of 32 soundings run on a 

 north-west bearing from Mt Gaudry, Adelaide Island, it will be seen that the edge of the 

 continental shelf is very steep, the depth increasing from 500 to 3000 m. in 15 miles. 

 A very similar slope occurs on the other two lines. 



On these lines regular soundings over 4000 m. were not obtained until we were some 

 200-250 miles from the land, and it seems probable from this evidence and from the 

 extent of the continental shelf that if the same conditions prevail farther to the west, the 

 land must lie a considerable distance to the south of the highest latitudes reached by the 

 'William Scoresby' and 'Discovery II'. 



Approximately 700 echo soundings were taken during the time spent in the Bellings- 

 hausen Sea and on the return trip to Port Lockroy, via the Biscoe Islands and the Pendle- 

 ton Strait. Only about 650 of these soundings are inserted on the chart, as the scale is 

 not sufficiently large to show those taken for navigational purposes when approaching 

 and leaving the Marin Darbel Islands. The majority of the soundings were taken with 

 the deep-water echo machine, and at times with considerable difficulty owing to the 

 noise made by the pack-ice on the hull, which completely drowned the echo in the 

 hydrophone. Another effect of pack-ice which we had anticipated did not, however, 

 occur. It had been thought that the close proximity of pack-ice might cause both the 

 hammer blow and the echo to be reflected from the undersides of the large floes, giving 

 in the first case a false echo and in the other a re-echo of the true depth. We have also 

 tried the effect of taking echo soundings in the vicinity of large icebergs, especially those 

 which would have a draft of several hundred feet, as the under-water portion might be 

 expected to reflect the sound waves from the hammer and cause false echoes. No 

 interference was ever observed, and it seems probable that the water chamber under the 

 hammer is effective in preventing the sound waves from scattering. On the other hand, 

 re-echoes have been obtained on several occasions, but only in waters completely free 

 from ice. One of these was recorded from the Orkney — Clarence Island ridge, where a 

 faint but quite distinguishable re-echo was picked up at exactly double the scale reading 

 of a sounding of 1344 m. These re-echoes were probably obtained on a clean rock 

 bottom, and to this they may be due. 



OTHER SOUNDING WORK 



During the course of our work in the south, opportunity has always been taken, as 

 conditions permitted, to search for various rocks or vigias which have been reported from 

 time to time from the South Atlantic and Southern Oceans. Most of them have been 

 reported, on single occasions only, as isolated rocks in mid-ocean, and we have not been 

 able to find any of those for which we have searched despite care and extensive echo 



