SOUTH ORKNEY ISLANDS TO CLARENCE ISLAND 227 



smaller but well-marked ridge where the soundings average about 3000 m. This in turn 

 is succeeded by a deeper trench with soundings over 5600 m. Comparison with the 

 Deutschland soundings shows that they also found a double ridge, their minimum 

 soundings being 1050 and 1012 m., with a deep trench of over 5000 m., lying to the 

 south. These deep soundings following a ridge show a great similarity to the conditions 

 prevailing in the neighbourhood of the South Sandwich Islands, and it seems possible 

 that the Deep extends round outside this sector of the arc. 



About half-way between the Discover^' II line of soundings and Southern Thule the 

 British Admiralty chart^ shows three soundings under 2000 m. Two of these, 1079 and 

 1 158 m., were obtained by the ' Scotia ' between 1902 and 1904, the other of 1862 m. was 

 taken by the 'Deutschland' on her journey south to the Weddell Sea in 191 1. These 

 depths compare very closely with those taken to the westward, and may be regarded 

 as evidence in favour of a connecting ridge. 



Between the line of Deutschland soundings in 37° W and the South Orkneys there 

 are also only a few soundings. These were taken by the ' Scotia' between 1902 and 1904 

 and show that the 500 m. contour extends to a point 75 miles east of the islands. The 

 extension of the coastal shelf so far to the east is strong evidence in favour of a Southern 

 Thule — South Orkney ridge. It is hoped to obtain more soundings in this area in 

 the near future. 



SOUTH ORKNEY ISLANDS TO CLARENCE ISLAND 

 (Plate XLV, Chart 2) 



Although geologically the South Orkneys do not appear to support the theory of an 

 arc owing to the apparent lack of any true Andean type of rock, it has been shown by 

 soundings that to the east there is a strong probability of a connexion between them and 

 the South Sandwich Group. On the western side of the South Orkneys the probable 

 existence of a submarine ridge was brought to our notice by two soundings obtained in 

 the 'Discovery' while working St. 169 in February 1927. Here a Lucas sounding of 

 2514 m. was obtained in a position 60° 48' 50" S, 51° 00' 20" W. After the station a deep 

 net was towed, but it fouled the bottom after a few miles and a second sounding gave 

 a depth of 1849 m. in a position approximately 5 miles to the west of the other. This 

 station was worked alongside a very large tabular berg, which, from our observations, 

 appeared to be aground. 



From this date until the season 1930-1 no more soundings were obtained from this 

 area, but in this season the complete absence of pack-ice from these waters enabled us to 

 obtain numerous echo soundings. These have been considerably amplified during the 

 season 1931-2, and there can be no doubt that a submarine ridge with a depth of water 

 of under 2000 m . connects the South Orkneys and Clarence Island . The average sounding 

 is from 1600 to 1700 m., and it appears fairly certain that a double ridge is to be found 

 over practically the whole distance. The secondary' ridge, which lies to the north of the 



1 British Admiralty Chart, 2202 b. 



