58 



DISCOVERY REPORTS 



igneous series in Admiralty Bay, King George Island. The present study of dredged stones from 

 Bransfield Strait has brought out the fact that somewhere in the surrounding region there must be 

 a basement series of greywackes, mudstones and slates, which has undergone severe cataclastic meta- 

 morphism. There is good evidence from contact-metamorphic effects that the plutonic masses of 

 the South Shetlands, the Palmer Archipelago and Graham Land, have broken through this sedimentary 

 basement ((i), pp. 75-7), and also through the older series of andesite lavas. Hence the metamorphosed 

 sedimentary basement must be at least of early Mesozoic age, and quite possibly Palaeozoic. 



CHEMICAL CHARACTERS 



For a discussion of the chemistry of the igneous series of the South Shetland Islands there are 

 available twelve previously published analyses and two others made for the present investigation 

 and here published for the first time. Seven of the twelve published analyses were given by E. Gourdon 



I. 



2. 



3- 

 A. 



4- 

 5- 

 6. 



7- 

 8. 



Trachyandesite, Deception Island. E. Gourdon, C.R. Acad. Sci., Pan's, clviii, 1914, p. 1906. 



Tridymite-santorinite, Deception Island. Barth and Holmsen ({4), p. 14). 



Trachyandesite, Deception Island. Gourdon, op. cit. 



Average of nos. i, 2, and 3. 



Andesite,* Deception Island. Gourdon, op. cit. 



Bandaite,f pillow-lava. Deception Island. Barth and Holmsen ((4), p. 11). 



Andesine-basalt, Deception Island. Barth and Holmsen {{4), p. 11). 



Basalt (' Labradorite' — Gourdon), Deception Island. Gourdon, op. cit. 



Doleritic basalt, block (in tuff or agglomerate.') Deception Island. Gourdon, op. cit. 



* The alkalis in this analysis are given as recorded in Gourdon 's first paper of 1914, i.e. NajO, 6-25; K„0, 1-20. In Washing- 

 ton's Tables (U.S.G.S. Prof. Paper 99, 1917, p. 466) the alkalis are given as Na^O, 6-67; K2O, 0-78, and as the summation 

 remains the same it seems clear that 0-42 per cent has been transferred from KjO to Na,0. This may have been a correc- 

 tion of the original analysis when it was transmitted to Washington by Gourdon, but it has been thought best to leave the 

 original figures intact, especially as they are repeated in Gourdon's later work published in Deuxieme Expedition Antarctique 

 Franfaise (1908-1910), commande par le Dr Charcot: Mineralogie, Geologic, Paris, 1917, p. 7. The earlier figures for the alkalis 

 are also more accordant with the serial characters of the Deception Island suite than the later. 



•f- Correct summation, 100-14, given in the table. Barth and Holmsen give 100-08. 



