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Ch. XXVIL] 



GKAHAM ISLAND. 



6^ 



removed 



restoration ' of the upper part c 

 the waves : the strong lines represent the part of the volcano 

 which is still under water : in the centre is a great column, 

 or dike, of solid lava, 200 feet in diameter, supposed 

 to fill the space bj which the gaseous fluids rose j and on 

 each side of the dike is a stratified mass of scoriae and frag- 

 mentary lava. The solid nucleus of the reef, where the 

 black rock is now found, withstands the movements of the 

 sea; while the surrounding loose tuffs are cut away to a 

 somewhat lower level. In this 



manner 



more 



the lowest part of the island, or, to speak 

 which scarcely ever rose above the level of the sea when the 

 island existed, has now become the highest point in the reef. 

 No appearances observed, either during the eruption or 

 since the island disappeared, give the least support to the 



Fig. 94. 



Supposed section of Graham Island. (C. Maclaren.*) 



opinion promul 



by some writers, that part of the 



ancient bed of the sea had been lifted up bodily. 



The solid products, says Dr. John Davy, whether they 

 consisted of sand, light cinders, or vesicular lava, differed 



more in form than in com 



The lava contained 



augite; and the specific gravity was 2-07 and 2-70. When 

 the light spongy cinder, which floated on the sea, was reduced 

 to fine powder by trituration, and the greater part of the 

 entangled air got rid of, it was found to be of the specific 



some 



eruption was 2-75 ;t so that the materials equalled ordinary 

 granites in weight and solidity. The only gas evolved in any 



considerable quantity was carbonic acid. J 



Suhmarine eruptions in mid- Atlantic. — In the l^autical 



* Geol. of Fife and the Lothians, 

 p. 41. Edin. 1839. 



t Phil. Trans. 1832, p. 243. 

 i Ibid. p. 249. 



