214 DISCOVERY REPORTS 



sounding. Certain oceanic work, however, such as the search for a reported rock or the 

 detailed examination of a submarine ridge may require soundings to be taken as often as 

 every 5 min., and up to a depth of about 800 m. soundings with the oceanic machine 

 have been taken, in favourable circumstances, at 2 min. intervals. 



THE SCOTIA ARC 



One of the most interesting features of the topography of the bottom in the area of 

 the Falkland Islands Dependencies is the supposition, much discussed by geologists, 

 that the Andes formerly joined Graham Land and the South Shetland Islands to form 

 a mountain arc or loop which extended eastwards into the South Atlantic. It is generally 

 held that if there is such a connexion the probable course must have been from Tierra 

 del Fuego through Staten Island, the Burdwood Bank, the Shag Rocks, South Georgia, 

 the Gierke Rocks, the South Sandwich Islands, the South Orkney Islands, Elephant and 

 Clarence Islands and the South Shetlands. This connexion, if it really exists, is not only 

 of great interest from a geological point of view, but it is also of very great importance in 

 the studies we are making of the hydrological conditions in the area, for if the missing 

 portions of the arc are represented by submarine ridges, they will certainly exert a 

 profound influence on the movements of the water masses in their vicinity. 



Geological writers have generally referred to the supposed arc as the South Antillean 

 Arc. There are, however, no South Antilles, and in view of the grouping of the fragments 

 round the Scotia Sea, it seems preferable, as Mr Wordie has suggested, to speak of the 

 connecting loop as the Scotia Arc. 



The first mention of a possible connexion appears to have been made by Bellings- 

 hausen, of whom Suess writes :^ 



" Second advance : Bellingshausen after a visit to the South Sandwich Islands in 18 19, 

 during which he witnessed a volcanic eruption in Sawadowskij [Zavodovski] , the most 

 northerly of these islands, wrote as follows : — ' The Sandwich Islands and the Traversey 

 Islands appear to form the summits of a mountain ridge which is connected through 

 Clerk's reef with South Georgia, and from there on by the Aurora reef with the Falkland 

 Islands'". 



Since Bellingshausen's time and before Suess' examination of all previous data, 

 several other investigators, notably Barrow, Reiter, Arctowski, Nordenskiold and 

 Gunnar Andersson, had put forward similar theories. 



Suess, after considering all the available evidence, regards it as established^ "that in 

 the interval we have just discussed the Pacific structure advances for the second time 

 into the Atlantic region''. It should be noted, however, that in Suess' opinion South 

 Georgia does not form a continuation of the Burdwood Bank, but that an arcuate con- 

 nexion through the Shag Rocks is more probable, and in his detailed comparisons^ he 

 observes that: 



1 Suess, The Face of the Earth (authorized English Translation), iv, pp. 488, 489 (1909). 

 " Loc. cit., p. 496. ^ Loc. cit., p. 495. 



