630 



ORIGIN OF THE CONE OF VESUVIUS. 



[On. XXV. 



matter elected from 



but partly to the injection of lava into dikes, and ' to that 

 force of gaseous expansion, the intensity of which, in the 

 central parts of the cone, is attested by local earthquakes, 



company 



The inclination of 



some of the lavas m 



cases during the rending and dislocation of the cone, but I 

 do not believe, any more than the author just cited, that 



such disturbances have played a conspicuous part in giving 



to volcanic mountains the configuration, whether external 

 or internal, by which they are distinguished. 



from 



tion of its figure given by Strabo, to have been a truncated 

 cone, having a level and even outline as seen from a distance. 

 That it had a crater on its summit, we may infer from a 

 passage in Plutarch, on which Dr. Daubeny has judiciously 



commented 



f The 



crater were evidently entire, except on one side, where there 

 was a single narrow breach. When Spartacus, in the year 

 72, encamped his gladiators in this hollow, Clodius, the 

 praetor, besieged him there, keeping the single outlet carefully 

 guarded, and then let down his soldiers by scaling ladders 

 over the steep precipices which surrounded the crater, at the 

 bottom of which the insurgents were encamped. On the 

 side towards the sea, the walls of this original cavity, which 

 must have been three miles in diameter, have been destroyed, 

 and Brieslak was the first to announce the opinion that this 

 destruction happened during the tremendous eruption which 

 occurred in 79, when the new cone, now called Vesuvius, was 

 thrown up, which stands encircled on three sides by the 

 ruins of the ancient cone, called Monte Somma. 



In the annexed diagram (fig. 67) it will be seen that on 

 the side of Vesuvius opposite to that where a portion of the 

 ancient cone of Somma (a) still remains, is a projection (b) 

 called the Pedamentina, which some have supposed to be 

 part of the circumference of the ancient crater broken down 

 towards the sea, and over the edge of which the lavas of the 



* Geol. Trans. 2nd scries, vol. ii. p. 341. 

 f 2d edit. 1848, p. 216: 



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