78 DISCOVERY REPORTS 



circumnavigated and deptlis approaching the Antarctic continent were determined, in March 1939, 

 in the meridian of Greenwich, when it was also possible to make a rough survey of the ice barrier and 

 coastline between this meridian and that of 4° E. Additions were also made to our previous work 

 around South Georgia. The lines of soundings in the Ross Sea in 1936, and between 1936 and 1939 

 across the Discovery Bank (in approximately 42° S, 1° E) cannot, perhaps, be classed strictly as 

 hydrographic surveys; reference to this work is made in a later section. 



For the purpose of this report it is not necessary to describe the various surveys in their full detail. 

 A short account of the work in each of the more important regions will, perhaps, suffice to give some 

 idea of the value of echo sounding at these times. 



SOUTH ORKNEYS SURVEY 



A very complete account of the running survey of 1933 and of the preliminary work leading up to it 

 has been given by Marr (1935). The 'Discovery' made a short visit to Signy Island in 1927, and in 

 193 1 the 'Discovery II' made some observations on the west and north sides of Coronation Island. 

 The principal survey was undertaken by the latter ship in a period of 28 days beginning on 2 January 

 1933, during which about 2250 soundings were made, mostly with the Pattern 751 'listening' type 

 shallow-water set. Later on the ' Discovery II ' made two further short visits in April 1934 and 

 February 1937. On this last occasion (which was subsequent to the publication of Marr's report) the 

 south coasts of the islands were free from ice and in the nine days available much was done towards 

 the completion of the survey. Continuous soundings were taken with both recorders, and records 

 representing some 41 hours of steaming (or, approximately, 240 miles) were obtained. The various 

 tracks of the ship during this period of continuous sounding are shown in Text-fig. 3 c, p. 46. Each 

 record has a number, and reference to Appendix II of this report will provide fuller details. 



For further details of the South Orkney surveys reference should be made to Marr. All that need 

 be said here is that the shelf surrounding these islands (where the majority of soundings were taken 

 with the shallow-water set) offers an interesting comparison with that of other islands comprising the 

 Scotia Arc. At South Georgia, for instance, depths on the western side of the island are comparatively 

 shallow over a fairly wide coastal shelf and the bottom is certainly more regular than on the eastern 

 side. Here there are a number of fjords and glaciers, and depths of considerably more than 250 m. 

 (137 fm.) are often found. The coastal shelf is narrower and much more irregular, with a greater 

 mean depth. 



Of the various islands comprising the South Sandwich Group only one, Leskov Island, rises 

 sharply from moderate depths. At the remainder there is generally a narrow but shallow coastal shelf, 

 although in certain places where there are signs of comparatively recent volcanic activity, moderately 

 deep water is found close to land. The submarine crater in Douglas Strait, to which we have already 

 made reference, is, perhaps, the most interesting example of these exceptions. 



The coastal shelf around the South Orkneys is, perhaps, the most outstanding example of the 

 varying features of these shelves in the whole Arc. The islands themselves are rugged in character 

 and it might well be expected that considerable variations in depth would occur in the various straits 

 and harbours, and off the coasts. With only a few exceptions such conditions are not found. In general 

 the coastal shelf, straits and harbours are shallow, although two small deeper areas exist south-east of 

 Signy Island and north of Larsen Island; the latter has a maximum depth, so far determined, of 

 348 fm. (636 m.) in a position approximately i mile north-east of Melsom Rocks (see British Admiralty 

 Chart No. 1775 — in Marr, 1935). On the northern side of the islands the coastal shelf, at depths of 

 less than 250 m. (137 fm.), extends at the most for some 3 or 4 miles and the slopes away to deep water 

 are considerable. 



