222 DISCOVERY REPORTS 



From the bathymetricchart of South Georgia and the Shag Rocks (PlateXLVI)itwill be 

 seen that the coastal shelf of South Georgia has a considerable extent, the average distance 

 of the 500 m. contour from the coast being about 25 miles on the south-west side of the 

 island. This distance varies considerably, there being one point south-west of Cape 

 Disappointment where the 500 m. contour is only about 16 miles from the land and 

 another west-south-west of Annenkov Island where the shelf runs out for nearly 

 60 miles, and then falls away rapidly, the soundings increasing from 500 to 3000 m. in 

 about 15 miles. This sharp drop from the coastal shelf to oceanic depths appears to be 

 a characteristic feature of South Georgia, and, in conjunction with the numerous 

 soundings obtained up to the present, can be a valuable aid to navigation in thick weather 

 for any ship fitted for deep-water echo sounding. 



It has already been stated in the general discussion on the Scotia Arc that in view of 

 its geological structure. South Georgia appears to be one of the weakest links in the 

 chain of islands and submarine ridges constituting the arc, and that some have 

 maintained that an arcuate connexion lying north or south of the island is more 

 probable. The numerous echo soundings round South Georgia do not bear out this 

 theory. On the northern side of the island a small bank has been found about 80 miles 

 north of Cape Crewe which has an average depth of water of about 1800 m., but it is 

 only a few square miles in extent and existing soundings do not show any trace of it 

 to the east or west. On the southern side of the island the concentration of soundings 

 is not so great, but there is sufficient evidence to prove that no submarine ridge parallel 

 to South Georgia exists on this side of the island. 



Influenced, probably, by this theory, those who have drawn bathymetric charts or 

 maps of the Scotia Sea and surrounding areas have hitherto shown the Shag Rocks, 

 which lie about 130 miles east of Willis Island, as an isolated group apparently rising 

 quite sharply from the ocean bed. The depth of water usually shown between the Shag 

 Rocks and South Georgia is 3000-4000 m. In all except Pratje's contour map, where the 

 soundings on which the contours are based are not shown, there appears to be only one 

 sounding to support the theory of an isolated group. This is a sounding of 3380 m. 

 obtained by the ' Antarctic ' in a position slightly north of the direct line between Willis 

 Island and the Shag Rocks. With regard to the geological evidence there is no record of 

 any specimens having been obtained from the Shag Rocks, we therefore have to rely 

 entirely on soundings to prove the connexion with South Georgia. 



In April 1929 the ' William Scoresby ' obtained a Lucas sounding of 232 m. on a rock 

 bottom at St. WS 427, almost exactly half-way between Willis Island and the Shag 

 Rocks, and in March 1930 at St. WS 525 and WS 526, two more wire soundings of 

 159 and 1545 m. respectively on approximately the same line. These soundings indi- 

 cated the probability of a connecting ridge, and between December 1930 and April 193 1 

 the 'Discovery II' was able to obtain four lines of echo soundings in the area. About 

 320 soundings were taken and of these about 50 were in the vicinity of the Shag 

 Rocks and a small outlying rock about 10 miles to the south-west of the main group. 



The four lines of soundings have definitely established the existence of a connecting 



