SOUNDINGS TAKEN DURING THE DISCOVERY INVESTIGATIONS, 1932-1939 75 



The connexion of the South Orkneys with Clarence Island was presumed before 1932, and we have 

 now presented evidence from soundings which strongly supports the theory of a direct connexion 

 between the South Orkneys and the South Sandwich Group. That the connexion is not likely to lie 

 north of the former islands can be seen from PI. XXIII; here we find more evidence of the folding 

 which, inside the loop of the Arc, appears as a prominent feature of the bottom west of the meridian of 

 40° W. About 30 miles north and west of Laurie Island (the most westerly of the Orkney Group) is 

 found the deepest area yet determined within the Arc; more than twenty soundings greater than 

 5000 m. (2734 fm.) have been obtained here by the ' Discovery II ', the maximum depth being 5548 m. 

 (3034 fm.) in 60° 16' S, 43° 26' W. It is also possible that this deep water extends farther to the west 

 than is at present shown. 



On the southern side of this trench the slopes are comparatively steep ; one line of soundings in the 

 longitude of 44" 30' W gives an average slope of 16°, which is only 4° less than the very steep slope 

 away to deep water immediately north of Coronation Island (the largest of the Orkney Islands) (see 

 p. 66). To the north of the trench the bottom rises quite gradually to an extensive bank of depths less 

 than 2000 m. (1094 fm.), which appears to be roughly circular in shape, with a diameter of about 

 45 miles. To the east this bank cannot extend beyond the limit now shown but it is possible that there 

 may be a slight extension to the west. This, however, cannot be more than 20 miles as there is a well- 

 sounded deeper area, of more than 4000 m. (2187 fm.), between the bank and the nearest depths of 

 less than 2000 m. (1094 fm.) to the west. 



The least depth obtained during our two crossings of this Orkney Bank was 1185 m. (648 tm.) in 

 59° 02-2' S, 44° 33' W. Altogether, nineteen soundings of less than 2000 m. were obtained. 



These facts, together with the new geological evidence, provide almost certain proof that the South 

 Orkney Islands are included in the main line of the Scotia Arc. 



We suggested, in 1932, that the extension of the Arc westwards from the South Orkneys might be 

 found to consist of two parallel submarine ridges, and this assumption now appears to be correct. 

 From the evidence then available we also inferred that the main ridge lay between Coronation Island 

 and Clarence Island. However, the many new soundings now available (especially east and south of 

 the line of connexion) make it almost certain that it is the southern fold which represents the main 

 line of the Arc, and that it connects the South Orkneys direct with the Trinity Peninsula of Graham 

 Land. The northern ridge, which comprises the South Shetland Islands, Elephant Island and Clarence 

 Island lies close to the main connexion, but at its eastern end fades out into deep water at the meridian 

 of 48° W. In the light of our recent work it also appears more likely that the two areas of over 5000 m. 

 (2734 fm.) in depth, which lie between the folds, are part of a continuous trough separating these 

 folds; they are shown thus connected on our present chart. The scale of this chart is small and all our 

 soundings in this area cannot be shown; we have, therefore, reproduced the South Orkney-Clarence 

 Island sector of the Arc on a scale which permits the insertion of all our soundings. This is shown in 

 Text-fig. 15, p. 76. The northern slope in the easternmost of the small 5000 m. trenches shown in this 

 figure is, perhaps, the steepest we have met. In approximately 61" 12' S, 48° W the depth altered 

 abruptly from 105 1 fm. (1922 m.) to 2874 fm. (5256 m.) in a distance of 3-8 miles. This is equivalent to 

 an angle of slope of approximately 40°. The deepest sounding obtained here was 3111 fm. (5689 m.), 

 about 8 miles to the north-west of the depth of 2874 fm. 



Previously we described the South Orkney-Clarence Island sector as the last oceanic link in the 

 chain of the Scotia Arc, but it now becomes evident that we must consider as a whole the soundings 

 between the South Orkneys, the South Shetlands and Trinity Peninsula, together with the soundings 

 north of the South Shetlands. 



Fifty miles north of these islands we again have evidence of folding. Two soundings of more than 



