ROCK SPECIMENS 197 



plutonic types which occur most frequently in the cores of fold-mountain ranges such 

 as the Andes in association with andesite lavas. This fact is worth emphasizing because 

 andesites are frequently thought of as the volcanic representatives of the diorites only. 



CONCLUSIONS. 



The geology of the South Sandwich Islands, and its bearing on the disputed question 

 of the tectonics of the " South Antillean Arc" of Suess, is discussed on p. 154 of this 

 Report. The writer has also recently discussed the question in his paper on the petro- 

 graphy and geology of South Georgia/ in which he states that : " If Suess's homology of 

 the Southern Antillean loop with that of the Caribbean Antilles were complete, the 

 Andean type of volcano erupting andesitic lavas, and batholithic masses of the typical 

 Cordilleran andendiorites and granodiorites in the cores of the mountain chains, should 

 be present. They are, however, entirely wanting, with the possible exception of the 

 South Sandwich Islands, about which the geological information is very scanty". The 

 typical Andean lavas described in this Report therefore go far to support Suess's view of 

 the tectonic relations of the " Southern Antilles". The writer has also pointed out {op. 

 cit. supra, p. 53) that the South Sandwich Islands, according to O. Pratje's map,^ are 

 situated on an arcuate ridge which, to the east, is followed by a profound but narrow 

 deep, and that, in its turn, by another narrow submarine ridge, both of which run 

 parallel to the arc of the South Sandwich Islands. Hence in all probability we have here 

 two parallel arcs of folding separated by a deep. These facts, which are supported by the 

 statement in this Report (p. 154) that the echo soundings taken during the Expedition 

 show conclusively that most of the submerged portions of the South Antillean Arc can 

 still be traced in the relief of the sea bottom, therefore seem to indicate an enormous 

 protrusion of circum-Pacific tectonic structures, accompanied by circum-Pacific lava 

 types, for 1500 miles into the heart of the alien tectonic region of the Southern Atlantic 

 Ocean, conditions which are found nowhere else in the whole vast extent of the Atlantic 

 Ocean except in the Caribbean region. 



^ 'Quest' Expedition Report, British Museum {Nat. Hist.), chapter in (1930). See especially pp. 51-4. 

 - O. Pratje, " Beitrag zur Bodengestaltung des Siidatlantischen Ozeans ", Cenlr. f. Min. Abt. B, pp. 129- 

 52, Map, p. 132(1928). 



