1859.] SCROPE CONES AND CEATEES. 539 



M. de Buch, who supposes the entire cone of Yesuvius to have been 

 bodily upheaved at that time, should not have perceived that all the 

 phenomena reported by Pliny the younger to have been witnessed 

 on that occasion, and all such of its undoubted results as are to be 

 seen at the present day, are of the very opposite character to those 

 which would accompany or follow the upheaval of flexible strata in 

 a hollow protuberance. The loud and long-continued explosions, 

 the lofty ^' pine" of vapour that rose from the mountain, the dense 

 cloud of ashes that darkened the air, the fountain of stones and 

 lapilli ejected for many days, in such prodigious abundance as 

 entirely to bury three populous cities under from 15 to 150 

 feet of accumulated dejections, are all phenomena indicative of 

 violent eruption^ not at all of upheaval. It seems clear that the 

 southern half of the old crater's periphery was on this occasion blown 

 into the air, and it is to the ejections of this eruption that are owing, 

 in all probability, the thick beds of loose tuff, or pumice-ash, which 

 mantle round the outer slopes of Somma, and indeed rise to a con- 

 siderable height upon them, in some places having evidently filled 

 up vast hollows or ravines that previously existed there. There 

 is no reason to believe these tuffs to be marine alluvia, as M. 

 Dufrenoy terms them. They are undistinguishable in character 

 from and continuous with those that cover Herculaneum and Stabiae, 

 as Sir William Hamilton long since observed. Even at the distance 

 of Naples there is reason to believe that the ejected ashes of this 

 eruption fell to the thickness of several feet. In a section behind 

 the Studii in that town, I observed a deposit of stratified pumice 

 and lapilli, from 6 to 10 feet thick, overlying made ground in which 

 were numerous tombs and other remains of the Greek and Roman 

 eras, which deposit was probably formed at the period of the erup- 

 tion of 79 *. 



The vast abundance of fragmentary matter ejected from the vol- 

 cano on that occasion must (as I remarked in the paper read to the 

 Society in March 1827) have left a proportionate cavity in the moun- 

 tain ; and considering that the analogous, but very minor explosions 

 of 1822, which completely gutted the cone of Yesuvius, leaving a 

 crater a mile in diameter, only covered the base of the mountain 

 with a depth of ashes averaging a foot,while at Naples it was but half 

 an inch, it is reasonable to suppose that the crater produced by the 

 eruption of 79 must have been greater than that of 1822, in the pro- 

 portion of the greater mass of ejected fragments ; and the size of that 

 of Somma, which measures about three miles in diameter, is rather 

 within than beyond what we might anticipate from this considera- 

 tion to have been formed by the eruption of 79. 



The idea, indeed, of the foundering of the summit of a volcanic 

 mountain, by the subsidence into some vast empty gulf below of 

 what was but a hollow crust or roof, is opposed to the characteristic 

 phenomena of volcanic eruptions, which are inconsistent with the 

 existence of any such internal void immediately beneath such a 

 mountain. They seem to attest, on the contrary, an overflowing 

 * See plate to Greol. Trans, ser. 2. vol. ii. part iii. p. 341. 



