SOUNDINGS TAKEN DURING THE DISCOVERY INVESTIGATIONS, 1932-1939 79 



On the southern side of the South Orkneys, however, we find a coastal shelf considerably wider 

 than is usual around the islands in the Arc. The shelf, as determined by the 250 m. (137 fm.) contour, 

 extends for some 15 or 20 miles south of the islands, but it is the extension beyond here of depths 

 between 250 m. (137 fm.) and 500 m. (273 fm.) which is, perhaps, one of the most interesting features 

 in these parts. The 500 m. contour extends south to the latitude of 62° S and, as will be seen from 

 our bathymetric chart (PI. XXIII) of the Scotia Arc, a wide area is thus included. Furthermore, there 

 is a very gentle slope from here to the 1000 m. (547 fm.) contour, and it is only then that a moderate 

 slope to the greater depths occurs. 



The extent of the coastal shelf in relation to the South Shetland Islands, to the survey of which we 

 shall shortly refer, is again different to those already mentioned. To the north of the islands there is 

 a comparatively wide shelf where depths do not exceed 250 m. (137 fm.), but over almost the whole 

 length of the Bransfield Strait moderately deep water is found close to the south of nearly all the 

 islands. In the southern part of the straits which separate the various islands, and in Admiralty and 

 King George Bays, it will be seen (PI. XXIV) that depths of more than 250 m. (137 fm.) extend in 

 a northerly direction for some distance. In two instances the 500 m. (273 fm.) depth contour enters 

 the Strait and the slopes here are among the steepest we have met. Nearly all the islands appear to 

 be steep -to both on the southern side and in the various straits. Admiralty Bay resembles a fjord and 

 moderately deep water extends almost to its head, but King George Bay is in general much more 

 shallow. The shelf on the northern side of the group is generally flat, and the slopes away to deep 



water are gentle. 



SOUTH SHETLANDS SURVEY 



In 1927 the 'Discovery' carried out some preliminary work on the survey of the South Shetlands, 

 but the number of soundings taken was small. Between December 1930 and March 193 1 the 

 ' Discovery II ' was working in this area and considerable progress was made with a running survey of 

 Livingston and Snow Islands. A total of 1432 soundings was taken around the western end 

 of the South Shetlands and in the Bransfield Strait, to which reference has already been made 

 in our earlier report (Herdman, 1932). In December 1934 and January 1935 further work by 

 the same ship completed the survey of the islands, with the exception of the eastern half of King 

 George Island. Continuous soundings were taken whenever possible with the 'Acadia' recorder, and 

 the records obtained totalled 140 hours of steaming. The speed of the ship varied considerably 

 with the ever-changing conditions of this survey, but it can safely be said that during this time 

 we recorded soundings continuously over not less than 600 miles of the sea bed. In addition to these 

 soundings the 'listening' type shallow-water set was used when entering or leaving a harbour or 

 anchorage, and as a relief to the deep-water set when it became necessary to clean the hammer or 

 make a small repair. Every effort was made to do this in depths at which the shallow machine could 

 provide an alternative, but breakdowns did not always occur at perhaps the most convenient times. 

 Some 1600 soundings were taken with the shallow-water set during the thirty-one days occupied on 



the survey. 



The remaining work on King George Island was begun in December 1936 and, as before, continued 

 for a month. The weather was bad throughout and it was not possible to finish the survey, although 

 all that remained uncharted was a few miles of the north coast of the island. The part that remains 

 unsurveyed, however, would be difficult of access by ship, even in the best weather. In fact, it may be 

 said that a running survey along the northern coasts of the South Shetlands requires almost perfect 

 weather, and even with this it would be extremely difficult. The shallow-water echo-sounding set 

 was now fully automatic and continuous soundings were thus obtained from both shallow- and deep- 

 water instruments. The records totalled 120 hours of steaming and represent, very approximately, 



