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



Somma, but also a considerable mass of the upper strata of 

 tuffa, in order to open a place for its own beds ; and then by 

 these appearances, Strabo"'s description will be confirmed as per- 

 fectly consonant with truth, and will be recognised as a most 

 important document in the history of volcanos in general. 



The Neapolitan puraice-tuffa is not a direct product of vol- 

 canic eruption, but is a tertiary formation as much as the lime- 

 stone of Syracuse and Palermo. It has been formed in the sea 

 and distributed by the sea with regularity over the surface. 

 This has not been doubted since the time of Hamilton ; but it 

 is too often forgotten when separate eruptive phenomena of the 

 Neapolitan district are described, and when the origin of the 

 tuffa is ascribed to such particular eruptions. But there is al- 

 most no district that is connected by this tuffa, in which marine 

 productions do not occur in the strata; and these occur of 

 such beauty and perfection, and with such completely preserved 

 shells, that we might think it impossible that they had ever been 

 at any period, exposed to the violent movements of volcanic ac- 

 tion. The Neapolitan collections, especially those of the Aca- 

 demy, of Monticelli, and of Dr Leopold Pilla, contain excellent 

 specimens of this description from various localities ; and others 

 from many different places, we find figured but indifferently in 

 Hamilton's work. Among the last there is in Plate xlv. a large 

 beautiful oyster included in the tuffa, from a quarry at Baiae, 

 Dr Pilla has a similar oyster contained in the tuffa of Posilipo, 

 from where the new road is cut through the hill. Hamilton 

 has figured a whole collection of a Cerithium, probably the Ce- 

 rithium vulgatum, found in a quarry at the summit of Posi- 

 lipo, and similar to the species which occurs so frequently in 

 Ischia, and at the Faro of Messina. The 47th plate is en- 

 tirely a representation of such a Cerithium conglomerate, which 

 was found in the Fossa Grande, under the Hermit's Hill, near 

 the Somma, and which is so well known as a rich locality for 

 minerals. Fig. 6. of Plate xlii. of Hamilton's work represents a 

 group of shells of a Pectunculus, from a tuffa quarry under 

 Capo di Monte ; and Monticelli has a similar pectunculus from 

 the Somma in his collection. Dr Pilla has discovered a small 

 Echinoneus, in considerable quantity, in the tuffa above the vil- 

 lage of Somma. which is very similar to the Echinoneus sub- 



