*i40 Mr. PouLETT ScROPE on the Volcanic District of Naples. 



wind mostly set that way during the twenty days continuance of the eruption, 

 did they fall to the depth of a quarter of an inch. The crater produced by 

 the eruption of 79 ought then to have been greater than that of 1822 in the 

 proportion of the greater mass of projected fragments ; and the apparent size 

 of the crater of Somma, which measures about three miles in diameter, is cer- 

 tainly rather within than beyond what would be anticipated from this consi- 

 deration. 



In this view then, previous to the eruption of 79, Somma, or rather Vesu- 

 vius, (for it had then but one appellation,) was a regularly conical mountain 

 with perhaps a flattish or but slightly depressed surface at the top ; and the 

 scanty notices we have received of its figure from Strabo and other writers of 

 that period, correspond with this supposition. The eruptions that occurred 

 after this epoch must have thrown up a parasitic cone in the centre of the 

 great crater ; and if we suppose the walls that circumscribed this cavity to 

 have been considerably lower towards the sea than on the opposite side, it is 

 obvious that in course of time the lava produced by the central cone, must 

 have filled up the crater so far as to pour over its edge, and thence descend 

 towards the sea. That portion of the circumference of the ancient crater 

 which was in this manner over-flooded and concealed from view, is yet marked 

 out most clearly by a terrace-like projection called the Pedamentina, which 

 encircles the base of the recent cone of Vesuvius on the south side, and exactly 

 continues the circular sweep of the remaining walls of the crater which still 

 exist on the north ; the axis of the present cone being precisely the centre of 

 this circle. There is nothing incredible in the idea of the entire massive cone 

 of Vesuvius having been formed since the year 79. We are acquainted with 

 the dates of above fifty very considerable eruptions since that epoch ; and less 

 than the fourth of that number, were they as productive of volcanic matter as 

 the eruption which broke out from the flank of vEtna, and overwhelmed Ca- 

 tania with its lava in 1669, would have sufficed to build up the actual cone of 

 Vesuvius*. 



I have dwelt the longer on these facts in the history of Somma, as attested 

 by its structure, because 1 observe that the mode of creation of this very sim- 

 ple volcanic mountain, which indeed may be taken as a type of such forma- 

 tions, is not yet generally well understood ; and that writers of high authority 

 still continue to speak, — sometimes, of its craters being owing to the falling-in 

 of the sides of the mountain, instead of to their being blown into the air 

 through the violence of its explosions ; — sometimes, of the whole mountain 



* That the cone of Vesuvius was formed since the year 79 A. D., was the opinion of Brieslak, 

 who, I believe, was the first to announce ik See his Forages dans la Campanie, vol. i. p. 133. 



