SOUTH SHETLAND ISLANDS 



63 



from the Ruminahui volcano (Table 4, col. K). Some spilites as, for example, those of Oregon 

 (Table 4, col. L), are also quite similar. The basalt (' Labradorite ' — Gourdon) of Deception Island 

 (Table 4, col. 7) differs from the andesine-basalt only in its positive O. Comparable analyses are those 

 of a hornblende-soda-andesite-basalt, an inclusion in dacite lava from the San Franciscan volcanic 

 field of Arizona (Table 4, col. M), and a hypersthene-augite-andesite from the Czerhat Mountains of 

 Hungary (Table 4, col. N). These rocks, however, are only isolated examples of the type, for in both 

 the Arizona and Hungarian fields the great majority of the andesites otherwise comparable to the 

 Deception Island rocks have a much higher k ratio. 



Table 4. Andesitic basalts of Deception Island and comparable analyses 



6. 

 K. 



7- 

 M. 



N. 



Andesine-basalt, Deception Island (Table i, col. 6). 



Basalt, Panang Hondon, Ruminahui volcano, Ecuador. A. Young, op. cit. supra, p. 243. Quoted from Washington's 



Tables, op. cit. supra, p. 538. 



Spilite, Poorman Mine, Oregon. J. Gilluly, ' Keratophyres of Eastern Oregon and the Spilite Problem', Amer. J. Set. 



XXIX, 1935, p. 235. 



Basalt ('Labradorite' — Gourdon), Deception Island (Table i, col. 7). 



Hornblende-soda-andesite-basalt, inclusion in hornblende-soda-dacite, Bill Williams Mt, San Franciscan Volcanic 



Field, Arizona. H. H. Robinson, ' The San Franciscan Volcanic Field, Arizona', U.S.G.S. Prof. Paper 76, 1913, p. 147. 



Hypersthene-augite-andesite, Czerhat Mountains, Hungary. A. Vendl, 'Ober die Pyroxenandesite des Czerhat- 



gebirges (Ungarn)', Min. u. Petr. Mitt, xlii, 1932, p. 516. 



The Deception Island series has been treated at some length because, chemically at least, it appears 

 to be almost unique among andesitic series, especially in its richness in soda. As a series, only that 

 of the Aegean volcano Santorin approaches it in chemical character, although sporadic examples of 

 similar rocks occur in andesitic regions of the normal type, and especially among the volcanoes of 

 Ecuador. 



It is not necessary to deal with the King George Island and Bridgeman Island series in such detail, 

 for it consists of perfectly normal andesites and basalts conforming closely in their minerals and 

 chemistry with the great circum-Pacific granodiorite-andesite region, and other similar regions (western 



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