Washington — Submarine Eruptions of 1831 and 1891. 143 



Although the eruption of Foerstner Volcano ceased in 

 October, 1891, there appears to have been another submarine 

 eruption in December of the same year, which took place 

 south of Pantelleria and is said to have formed a small island 

 about 500 meters in diameter.* Foerstner also mentions the 

 formation of a small island " in the waters of Pantelleria " in 

 July, 1881, observed by Captain Swinburne, but he cites no 

 authority and there would seem to be some error in the date. 

 This is not mentioned by Fuchsf in his list of volcanic erup- 

 tions of 1881, nor by Mercalli. 



Petrography. 



The petrographical characters of the bombs have been briefly 

 described by Butler,^ and in greater detail by Foerstner.g 

 The material examined by me was obtained in 1897 from Mr. 

 Francis H. Butler, of London, a cousin of the author of the 

 papers cited above, who collected with him on Pantelleria. 

 Mr. Butler wrote me as follows in a letter dated 21st Novem- 

 ber, 1907, by which it appears that there can be no doubt as to 

 the authenticity of my specimen : 



" My specimens of the Pantelleria rocks were collected by 

 myself early in November, 1891. The submarine lava was 

 floated to the sea among the fishing boats N.E. {sic) of Pan- 

 telleria during an eruption in, I think, October, 1891 



The vesicular submarine lava from which my specimen came 

 was obtained by some fishermen. Many of the masses of lava 

 floated to the surface exploded, and all, after awhile, that were 

 not saved by the fishermen became waterlogged and sank. I 

 was present at the purchase of the big mass of submarine lava 

 from which your specimen came : the greater part of the block 

 was presented to Prof. Judd for the Poyal College of Science." 



According to Gr. W. Butler the bombs show a brownish out- 

 side layer, about one inch thick, due to the vesiculation of 

 brown glass, which contains phenocrysts of triclinic feldspar, 

 olivine, magnetite, and probably augite. Beneath this is a 

 darker layer about one-half an inch thick, which is mostly 

 glass with the same minerals. The greater part of the bomb 

 is coarsely spongy, perfectly black with a pitchstone-like luster, 

 and more highly crystalline in thin section, composed of about 

 one-third triclinic feldspar, olivine, and augite, and the rest a 

 black groundmass, opaque in thin section. 



My specimen probably came from the interior, as may be 

 inferred from this description and from the small amount of 



*H. Foerstner, Tsch. Min. Petr. Mitth., vol. xii, p. 510, 1891. 

 fC. W. C. Fuchs, Tsch. Min. Petr. Mitth., vol. v, pp. 97-101, 1883. 

 X G. W. Butler, op. cit., p. 251. 

 £ H. Foerstner, op. cit. , p. 513-518. 



