Notice of Active and Extinct Volcanos. 263 



It is believed that within the crater of the ancient Somma, 

 Spartacus the general of the Roman insurgents took refuge, 

 when pursued. 



" Vesuvius was the spot pitched upon for their first enterprise. 

 Being besieged there by Clodius Glaber, they descended through 

 the defiles of this mountain by means of vine twigs, and reached 

 its very bottom, where they surprised by a sudden assault the 

 camp of the general, who anticipated nothing of the kind. 



" Plutarch, who evidently refers to the same event, notices it 

 in a manner, which perhaps will enable us to ascertain what the 

 real structure of the mountain at that time must have been. After 

 describing the first successes of Spartacus and his army, he says : 

 "Clodius the Praetor was sent against them with a party of three 

 thousand men, who besieged them in a mountain (meaning evi- 

 dently Vesuvius) having but one narrow and difficult passage, 

 which Clodius kept guarded ; all the rest was encompassed with 

 broken and slippery precipices, but upon the top grew a great 

 many wild vines ; they cut down as many of these boughs as they 

 had need of, and twisted them into ladders, long enough to reach 

 from thence to the bottom, by which, without any danger, all got 

 down except one, who stayed behind to throw them their arms, 

 after which he saved himself with the rest." 



The direction of the strata of Monte Somma, is such as 

 corresponds with the supposition that it was anciently a cra- 

 ter, and notwithstanding some difficulties as to the dykes of 

 this mountain, the passage is instructive as to the formation 

 of volcanic mountains ; we shall quote it. 



" Every mountain of this description, he maintains, has been 

 originally produced by a series of operations succeeding each 

 other in the following order. When once the violence of the 

 volcanic operations has arrived to such a pitch as to create a 

 rupture of the strata of the earth, the elastic vapours, hitherto 

 pent up, throw out portions of the liquid lava, through which 

 they force their way, just as takes place when a mass of melted 

 metal happens to fall into a vessel containing water. These por- 

 tions, projected into the air, descend again either in the form of 

 scoriae or sand, and collect into an aggregate, which when ag- 

 glutinated together will form tuff. But the projection of these 

 fragments is soon followed by the overflow of the melted lava it- 

 self, which by degrees reaches the brim, spreads over the tuff, 

 and forms a regular bed encircling the original aperture. The 

 repetition of these successive operations causes that alternation 

 of beds of lava and tuff which compose the substance of most 

 volcanic mountain's, and it will be at once perceived, that thedi- 



