Washington — Submarine Eruptions of 1831 and 1891. 135 



bling, but on a much smaller scale than, that of Mont Pelee. 

 In a general way, therefore, there is some reason for the belief, 

 though it is now incapable of proof, that the structure of the 

 island was similar to that of Bogoslof as recently described by 

 Jagger,* though with by no means so perfect a spine as that 

 shown in the photographs of Lacroix, Hovey, and Heilprin at 

 Martinique, or in those of Jaggar. The " black rock " reported 

 by Capt. Swinburnef as present in the bank remaining after 

 the disappearance of the island is also evidence in favor of the 

 existence of such a plug. This was 26 fathoms in diameter 

 and projected to within 9 feet of the surface, and was sur- 

 rounded by a bank of blocks and loose sand, sloping steeply 

 down to great depths about 60 fathoms from the central rock. 



According to Davy, carbon dioxide was the only gas evolved 

 in considerable quantity, but other observers report hydrogen 

 sulphide and sulphur dioxide, the odor of which was perceived 

 at Sciacca, so that these may be assumed to have been present. 



With diminishing volcanic activity the erosive action of the 

 waves rapidly destroyed the island. By the end of October 

 nearly all traces of the crater had disappeared, and the island 

 was nearly level with the sea, except for a small hill of scoria 

 which rose to a height of 190 feet on one side. During 

 November destruction was rapid, and by the end of December 

 only a small rock projected above the sea, and this soon disap- 

 peared, leaving a small but dangerous shoal, with a small area 

 only two and a half fathoms deep, as now marked on the 

 British charts. 



An eruption near the site of Graham Island is said to have 

 taken place in 16324 an( ^ another submarine volcano is men- 

 tioned as having been formed in 1801. § Subsequent to the 

 eruption which has been described, another is said to have 

 taken place on the site of that of 1831, beginning on August 

 12, 1863,|| which is reported to have formed an island about 

 three-quarters of a mile in circumference, 200 or more feet 

 high, and with a crater 30-40 yards across. The material of 

 this is stated to have been loose ashes and sand, but none of it 

 seems to have been preserved, and the island soon disappeared. 



Mercalli^f also mentions two other eruptions off the Sicilian 

 coast. That of June 18, 1845, took place in lat. 36° W 56" 

 K and long. 13° 44/ 36" E., near the Madrepore Bank. About 

 9.30 p. m. the English vessel "Victory" felt a violent shock, 



* T. A. Jaggar, Mass. Inst. Tech. Quart., vol. x, p. 31, 1908. 



f Cf. Lyell, op. cit., p. 62. 



% Mercalli, Vulc. Ital., p. 117. 



§ E. Reclus, New Physical Geography, New York, 1886, vol. i, p. 408. 



|| Cf . this Journal (2), vol. xxxvii, 1864, p. 442 ; also Mercalli, Vulc. 

 Ital., p. 120, and Reclus, op. cit., p. 408. There seems to be some uncer- 

 tainty as to the exact location of this eruption. 



IT Mercalli, Vulc. Ital., p. 120. 



