62 



GEAHAM ISLAND. 



[Ch. XXVII. 



Ct 



commencement 



(1832), there was 



depth of 150 feet where the island ha;d been: but 



a 



this 



account was quite erroneous ; for in the early part of that 

 year Captain Swinburne found a shoal and discoloured water 

 there, and towards the end of 1833 a dangerous reef existed 

 of an oval figure, about |- of a mile in extent. In the centre 

 was a black rock, of the diameter of about 26 fathoms, from 

 9 to 11 feet under water; and round this rock are banks of 

 black volcanic stones and loose sand. At the distance of 

 60 fathoms from this central mass, the depth increased 

 rapidly. There was also a second shoal at the distance 

 of 450 feet SW. of the great reef, with 15 feet water over 

 it, also composed of rock, surrounded by deep sea. We can 



middle 



b 



is solid lava, which rose up in the principal crater, and that 



m 



SW 



From 



whole of the facts above detailed, it appears 



was formed by a 



more 



that a hill 800 feet 

 submarine volcanic vent, of which the upper part (only about 

 200 feet high) emerged above the waters, so as to form 

 an island. This cone must have been equal in size to 

 one of the largest of the lateral volcanos on the flanks of 



Mexico 



& 



mountain 



1759. In the centre of the new volcano a large cavity was 

 kept open hj gaseous discharges, which threw ont scorise ; 

 and fluid lava probably rose up in this cavity. It is not 

 uncommon for. small subsidiary craters to open near the 

 summit of a cone, and one of these may have been formed in 

 the case of Graham Island ; a vent perhaps, connected with 

 the main channel of discharge which gave passage in that 

 direction to elastic fluids, scoria?, and melted lava. It does 

 not appear that, either from this duct, or from the principal 

 vent, there was any overflowing of lava; but 

 may have flowed from the flanks or base of the coi 

 occurrence on land), and may have spread in a 

 over the bottom of the spp. 



melted 



The dotted lines in the annexed figure are an imaginary 



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