SOUTH SANDWICH ISLANDS 



CHEMICAL COMPOSITION OF LAVAS FROM THE SOUTH 



SANDWICH ISLANDS 



Four chemical analyses of the lavas are recorded in Table 8, in order of decreasing silica percentage, 

 along with comparable analyses of lavas from the South Shetland Islands, South America, and the 

 West Indies. In the lower part of the table the von Wolff parameters as modified by the author 

 (see p. 59) are given. 



Table 8 



1. Dacite (Dacitoid) lava, Beach Point, Thule Island, South Sandwich Islands. Anal. F. Herdsman. Quoted from 

 G. W. Tyrrell, 'Report on Rock Specimens from Thule Island, South Sandwich Islands', Souih Samhvicli Islands 

 Memoir (1931), p. 192. 



A. ' Trachyandesite ' (Gourdon); Santorinite (Earth and Holmsen), Deception Island, South Shetland Islands. Quoted 

 from E. Gourdon, C.R. Acad. Sci., Paris, clviii, p. igo6 (1914). Also see this Memoir, p. 58. 



B. Dacite, Guaitara Slope, Loma de Ales, Colombia. Quoted from J. P. Iddings, Igneous Rocks, 11, p. 496 (1913). 



2. Hypersthene-andesite lava, Beach Point, Thule Island, South Sandwich Islands. Anal. F. Herdsman. Quoted from 

 G. W. Tyrrell, op. cit. supra, p. 195. 



C. 'Basalt' (Gourdon), Bridgeman Island, South Shetland Islands. Quoted from E. Gourdon, op. cit. supra, p. 1906. 

 Also see this Memoir, p. 59. 



3. ' Olivine-free basalt' (Backstrom), Saunders Island, South Sandwich Islands. Quoted from O. Backstrom, Bull. Geol. 

 Inst. Upsala, xiri, p. 173 (1915). 



D. Olivine-basalt lava. South Soufriere Hill, Montserrat, West Indies. Anal. F. Herdsman. Quoted from A. G. Mac- 

 Gregor, 'The Volcanic History and Petrology of Montserrat. . . ', Philos. Trans., Ser. B, ccxxix, p. 74 (1938). 



4. Olivine-basalt lava. Cook Island, South Sandwich Islands. Anal. F. Herdsman. New analysis. 



E. Olivine-basalt lava. Recent volcano. Penguin Island, King George Island, South Sandwich Islands. Anal. F. Herdsman. 

 New analysis (see this Memoir, p. 59). 



F. Labradorite-basalt, Chateaubelair, St Vincent, West Indies. Quoted from A. Lacroix, 'Les caracteristiques litho- 

 logiques des petites Antilles', Livre Jubilaire, Soc. Geol. Beige, pp. 387-405 (1926). 



There is a wide gap between the dacite (no. i) and the prevalent andesitic and basaltic lavas 

 (nos. 2, 3, 4) of the South Sandwich Islands— a gap which may be filled by future collections, although 

 it seems probable that all of the islands are built mainly of the basic lavas. Comparatively high lime 



