550 Volcanic Island betweeji Pantellaria and Sciacca. 



agitated in the interior ; and is farther opposed to the state- 

 ments of Captain Senhouse and Mr. Osborne. 



The isolation of the volcanic action is also demonstrated 

 by the fact, that the temperature of the sea, within ten or twelve 

 yards of the crater, was only 1 ° higher than the average ; and 

 to the leeward, in the direction of the current, it was not at 

 all affected, though a mirage played on the island. (Captain 

 Swinburne; Report to Admiral Sir H. Hotham.) 



There was, at a subsequent period of the eruption, on the 

 south-west side of the island, adjoining the principal crater, a 

 terrific ebullition and agitation of the sea, apparently seated 

 in another canal of communication ; attended by the emission 

 of a dense white steam, and a temperature increased to 190° 

 Fahr. [Letter of Mr, Osborne) ; and the information has, I 

 believe, since reached the Admiralty, that this crater is now 

 elevated above the level of the waters. De Buch has already 

 pointed out, that the internal action which manifests itself 

 at the surface of the soil or sea by a crater of elevation, may 

 constitute at the same time a permanent volcanic crater be- 

 neath ; the eruptions of which may take place sometimes by 

 the centre of the crater of elevation, sometimes by neigh- 

 bouring points. 



Though it is difficult, from the meagre details hitherto 

 obtained, to form any correct opinion of the mineralogical 

 character of the upraised mass, yet there is nothing in those 

 details to warrant the supposition that there is no stability or 

 permanence in the composition of the island. The pulverised 

 remains of coal deprived of its bitumen, the hard scorias, 

 dense and sonorous (phonolites?), the amorphous rocks 

 with metallic lustre and ironstone clay, would appear to asso- 

 ciate the eruption with the rocks of the carboniferous series ; 

 an opinion which receives additional probability from the 

 ejection of unchanged pieces of limestone : as we see, between 

 Pettycur and Bruntisland in Fifeshire, beds of limestone and 

 of non-bituminous coal elevated by rocks of plutonic origin, 

 and argillaceous and argillo-calcareous rocks changed into 

 leucostines and spilites. If this is the case, a farther and 

 more accurate investigation of the mineralogy of Graham 

 Island will be of as much utility to the study of changes pro- 

 duced by volcanic action, as the forms and characters of the 

 upraised formations have been in pointing out their geolo- 

 gical age and associations. 



