64 DISCOVERY REPORTS / 



complicated indeed than in the area farther east — and in that the bottom rises steadily from the middle 

 of the Scotia Sea towards Clarence Island; there does not, however, appear to be any evidence of 

 folding just north of Clarence Island such as is a prominent feature of the bottom, for many miles east 

 and west, a few miles north of the South Orkneys. 



On the eastern side of the Arc the two new profiles of the sea bed begin east of South Georgia and 

 north of the Clerke Rocks and, having crossed the Clerke Rocks-South Sandwich Islands section of 

 the Arc in approximately the same position, continue in an east-south-easterly and a south-easterly 

 direction. The profile shown in Text-fig. 12b commences in 54° 23-3' S, 35° 30' W, crosses the South 

 Sandwich group slightly to the north of Saunders Island and continues across the South Sandwich 

 Trench to 58" 50' S, 20° 05' W. There is a steady rise on the inside of the loop of the Arc to a well- 

 defined ridge at the South Sandwich Islands, and beyond this the bottom shows a marked irregularity 

 before dropping away abruptly into the Trench itself, across which a good line of soundings was 

 obtained. The remaining section (Text-fig. 12c) begins slightly south and east of that just described, 

 crosses the Arc in approximately 55° 15' S, 33° W and, continuing through the South Sandwich 

 Islands via the Douglas Strait, crosses the Trench in approximately 60° 30' S, 25° 15' W and finishes 

 at 61° 55-2' S, 20° 02' W. The soundings between the South Sandwich Islands and the Trench 

 unfortunately were few, owing to a breakdown of the transmitter, and although emergency repairs 

 enabled us to get six extremely valuable soundings across the deepest part of the Trench, there was 

 a further gap of some 60 miles in the line whilst repairs were again being effected. In the profile the 

 bottom is shown as a dotted line for those periods during which the transmitter was out of action. 

 A very good continuous record was obtained in the Douglas Strait on this occasion, though the 

 maximum depth recorded — 321 fm. (587 m.) — was nearly 100 fm. (183 m.) less than the greatest 

 depth determined here during our survey of the South Sandwich group in 1930. Douglas Strait, 

 which has been described by Kemp & Nelson (1931) in their account of our survey operations, lies 

 between Southern Thule and Cook Island and is, geologically, an extremely interesting feature. It is 

 a deep basin, with a maximum depth, so far determined, of 409 fm. (748 m.), and it is cut off at the 

 entrance on either side by a ridge, on which there is an average depth of water of about 14 fm. (26 m.). 

 There can be little doubt that Southern Thule and Cook Island originally were one large island and 

 that this basin is the crater of an extinct volcano, an eruption of which probably separated the island 

 into two. Our record in 1935 was taken on a line across the eastern side of the basin, and agreement 

 with the contours previously determined was good. 



In both the profiles just described it can be seen that the connexion between the Clerke Rocks and 

 the South Sandwich Islands is not very clearly marked, although the deeper water of the western end 

 of the South Sandwich Trench can clearly be seen at the beginning of each section. From this deeper 

 water there is a well-marked rise to the line of the connexion, but of the connecting link itself there is 

 little evidence here other than a rise of some 300-400 m. (164-219 fm.). This, however, when considered 

 in relation to the extension of the Trench in a westerly direction, to a position north of the Clerke 

 Rocks, may be held to constitute a connexion here; especially as there is considerable evidence of 

 folding, such as is commonly found inside the loop on most of the other sectors of the Arc. The approach 

 to the South Sandwich Islands from the west, both in the middle of the Group and at the southern end, 

 is, however, an exception to the irregularity normally found inside the Arc. In each instance the 

 bottom rises steadily towards the connecting ridge, as in the approach to Clarence Island (Text-fig. 12 d), 

 and it is probable that similar conditions prevail over the greater part of the northern side of the ridge 

 between Southern Thule and the South Orkney Islands. 



With the exception of those parts of the loop just mentioned it would appear that the slope of the 

 bottom inside the connecting ridges of the Arc is, in general, steeper than outside. This is most 



