70 Prof. Bischof on the Natural History of 



These are also formed, like the volcanic islands, in two dif- 

 ferent ways. The Monte Nuovo was formed by the accumu- 

 lation of the loose masses ejected from the volcano, whilst 

 mountains of basalt, trachyte, phonolite, &c. which are so abun- 

 dantly scattered over the surface of the earth, have been formed 

 by the upraising of solid rocks.* 



Vesuvius, or rather its cone, seems also to present an example 

 of an elevation in the historic area. Its formation perhaps does 

 not go farther back than the period of the famous eruption of 79 

 after the Christian area, in which Herculaneiim and Pompeii were 

 destroyed ; for ancient writers never speak of the mountain as 

 consisting of two peaks, which they probably would have done, 

 if the Monte Somma had stood, as at present, distinct from the 

 cone of Vesuvius.^ It is also remarked that the distance men- 

 tioned in ancient writers, as intervening between the foot of 

 Vesuvius and the towns of Pompeii and Stabiae, appears to 

 have been greater than exists at present, unless we measure it 

 from the foot of Monte Somma, so that this affords an addi- 

 tional probability, that the latter mountain was then viewed as 

 a part of the former, and that no separation between them had 

 at that time occurred. We may also be sure from the semicir- 

 <iular figure which the southern escarpment of the Monte Som- 

 ma presents towards Vesuvius, that it constituted a portion of 

 the walls of the original crater; and Visconti, it is said, has 

 proved by actual measurements, that the centre of the circle, 

 of which it is a segment, coincides as nearly as possible with 

 that of the present crater. There seems, therefore, little room 

 to doubt, that the old mouth of the volcano occupied the spot 

 now known by the name of the Attrio del Cavallo, but that it 

 was greatly more extensive than this hollow, as it compre- 

 hended likewise the space now covered by the cone, which was 

 thrown up afterwards in consequence of the renewal of the vol- 

 canic action that had been suspended during so many ages. 



* The late investigations of Buch, Dufrenoy, and Elie Beaumont, shew 

 that the Monte Nuovo is a crater of elevation, therefore not entirely or 

 chiefly composed of loose massos of ejected rocks. — Edit. 



+ Daubeny, a Description of Active and Extinct Volcanos, &c. p. 144. 

 See also Von Buch in PoggendoriF's Ann. t. xsaj^vii. p. 173. 



