THE SCOTIA ARC 217 



Shag Rocks and South Georgia the soundings indicate a connexion which is single for the 

 greater part of its length, a double ridge being as yet demonstrated for a few miles only 

 at the point where the section Fig. 2 b runs across. From South Georgia to the South 

 Sandwich Islands the section (Fig. 2 a) shows little evidence of a connexion, but, as will 

 be shown later, the influence of the South Sandwich Deep begins to be noticeable not far 

 from the Gierke Rocks. In the South Sandwich Group itself we have the most pronounced 

 example of ridging in the whole arc. Here there are two comparatively shallow sub- 

 marine ridges, with an average depth of water of about 2000 m., separated by a very 

 narrow deep with soundings of over 8000 m. It is of great interest to note that the 

 existence of this deep was forecast many years previously by Suess^ as follows: 

 " Immediately to the east of the South Sandwich islands no soundings have been made. 

 We might, perhaps, expect to find a foredeep there similar to that which occurs outside 

 a part of the Antilles". 



The discovery of the South Sandwich Deep by the ' Meteor', in 1926, when running 

 their fifth profile eastwards along the 55th parallel of south latitude, confirmed this 

 theory of Suess. Although their line of soundings only crossed the Deep at its extreme 

 northern end, their conjecture that it extends right down the eastern side of the South 

 Sandwich Group has proved correct, at any rate in part. In November 1930, while the 

 ' Discovery II ' was on passage from Cape Town to South Georgia via the ice-edge, we 

 were able to confirm the Meteor's observations. We were unable, however, to obtain as 

 deep an echo sounding as the 'Meteor' at this point, although we took a number of 

 soundings over a considerable area. The Meteor's deepest echo sounding in this area is 

 now given in their latest report ^ as 8264 m., the original echo distance of 8060 m. given 

 in an earlier publication => having apparently been corrected, using a velocity of sound in 

 sea water of 15 17 m. per second. The deepest sounding obtained by the ' Discovery IT 

 in this area was 7977 m., and the velocity of sound in sea water used for the correction of 

 the depth was 1515-7 m. per second. The table of velocities of sound (see p. 236) used in 

 the correction of all the echo soundings taken by the 'Discovery 11' in the South 

 Sandwich Deep and adjacent w^aters was compiled in accordance with the instructions 

 contained in the Admiralty tables of the velocity of sound in sea water. The hydrological 

 observations necessary for this work were made at St. 471 in 54° 57' S, 27° 59*' W, 

 when water samples and temperatures were obtained to a depth of 7250 m. Actually 

 this table varied very little from Table 23 in the Admiralty handbook as far as the 

 latter went; its great value was in providing velocities of sound below 5000 m. without 

 having to resort to extrapolation, which might have introduced errors. 



In the latter half of February 193 1, two more lines of echo soundings were taken by 

 the ' Discovery 11' in the area of the South Sandwich Deep. The first crossed the line 

 of the islands in about 57° S, approximately midway between the Candlemas Islands and 

 Saunders Island. These islands lie about 45 miles apart, the greatest distance between 



' Suess, loc. cit., supra, p. 496. 



2 ^y„. Ergebn. Deutsch. Atlant. Exped. 'Meteor', i, pp. 183-4. 



3 Spiess, Das Meteorfahric, p. 336, Berlin. 



