M. Von Buch on Volcanos and Craters of Elevation. 195 



1500 feet higher. In the whole plain of Naples the horizontal 

 strata of tufFa rise only at one point to the height of 1419 feet, 

 near Camaldoli of Pouzzoli, and there only for a very limited 

 space. Their usual height in the plain never exceeds 800 feet 

 above the sea, and that is not half the height to which they 

 are elevated on the Somma. At the volcano, therefore, they 

 are no longer in their original position, but have actually been 

 elevated round an axis, which is the axis of the crater itself. 



It is not generally stated, that the strata of white pumice-tufFa 

 surround not only the side of the mountain towards the Apen- 

 nines, or towards S. Anastasia, Somma, and Ottajano ; but also 

 all the part towards the sea ; and it may escape many observers, 

 that the Hermit's Hill, which is cut through by the path^ be- 

 longs to the general covering of the plain of Naples, and not at 

 all to the rocks of Vesuvius. It is easy to be convinced of this 

 being the fact, by examining the direct connection which subsists 

 between the mass composing the little eminence, and the lower 

 strata at the base of the mountain. It is equally certain, that 

 similar strata appear in the ravines above Torre del Greco, and 

 that the products which occur at the foot of the hill of Camal- 

 doli of Annunziata, are to be included under the same head. As 

 Professor Link and myself descended on the 21st of October 

 1834, from the Lava which had burst out on the 8th August 

 to Bosco trc Case, we saw also, on that side, considerable strata 

 of white tuffa, almost directly above Pompeii. Hence it seemed 

 evident, that it must have been from such strata that the. frag- 

 ments of pumice which cover Pompeii were separated, and 

 which, hitherto so inexplicable, there lie mixed with Vesuvi^n 

 leucitophyre. Leucitic rocks are not found in connection with 

 pumice. The latter is a product of the conversion of trachyte 

 into obsidian. But both these are substances which never oc- 

 cur in Vesuvius ; and the volcano has never been known to 

 throw out the smallest fragment of pumice. Hence the pu- 

 mice of Pompeii remained an enigma. If, however, as is now 

 nearly certain, it has been torn from such strata, similar to those 

 existing above Bosco tre Case, it becomes extremely probable 

 that Vesuvius, when it rose from the middle of the crater of 

 Somma as a permanent volcano, projected around on the side 

 towards the sea, not only the upper portion of the surrounding 



