M. Von Buch on Volcanos and Craters of Elevation, 199 



ject. When, on the 11th October 1834, the distinguished 

 French geologists Elie de Beaumont and Dufrenoy, and my- 

 self, made the circuit of the crater, and descended into its in- 

 terior, we saw, with the greatest distinctness, on the declivities, 

 the terminations of the strata, whose component rock could 

 hardly be distinguished from the ordinary tufFa of Posihpo. 

 The inclination of the strata is to the exterior all around, as 

 may be easily observed. In the interior of the crater, and on 

 its bottom there are black slags in large masses ; and on the 

 outer surface the external covering is formed by large scattered 

 porous blocks of altered trachyte and other similar fragments. 

 Had the internal walls of the mountain been formed of ejected 

 masses, they would not be white, fine-grained, and compact, 

 but would only resemble shapeless conglomerates, composed of 

 extremely large and earthy fragments, to which they have no 

 similarity whatever. 



Not long afterwards, we ascended the crater of Astruni, 

 one of the largest, and probably also the most beautiful, of all 

 the craters in the Phlegrean fields. The rock, which makes its 

 appearance on the interior declivities, is by.no means black and 

 slaggy, as we might expect it to be in such a crater 5 on the 

 contrary, it is rather striking from its great whiteness. Slags 

 lie in it as at Posilipo. It is composed of the strata of tufFa, 

 which are inclined round the axis to the exterior, and which are 

 well seen in Hamilton's representation, plate 20. This crater is 

 not level at the bottom, like Monte Nuovo, but presents in its 

 centre several hills, which rise to a height of 200 feet, and unite to 

 form a dome-shaped whole. These hills are composed oHrachyte. 

 The rock is not a lava, for we can nowhere observe the slight- 

 est trace of a stream. The mass also is every where continuous 

 and compact, being composed of large rocky portions, which are 

 separated only by clefts into large blocks. The trachyte con- 

 sists of a grey, coarsely splintery, much shattered basis, in which 

 are imbedded numerous and often considerable crystals of glassy 

 felspar, and in smaller quantity, black, small crystals, resembling 

 augite. The whole rock is like what we would expect to find 

 in a hill in the Siebcngehirge. How beautifully does not this 

 phenomenon explain the whole cause or history of the volcanic 

 operations ! In Mo9ite Nuovo we have a mountain with a era- 



