of the Environs of Naphs, IM 



9. The difference which exists between the nature and the 

 Slate of crystallization of the rocks of the Somma and of those 

 of Vesuvius, confirms the conclusions which result from the 

 study of their relative position. The parallel masses of Somma 

 are chiefly composed of leucite and black augite, while those of 

 Vesuvius consist almost exclusively of crystals of the felspar fa- 

 mily, probably of anorthite, and of green augite (diopside ?). 



10. The lavas of Vesuvius always form narrow thin currents, 

 whose texture bears a certain relation to the inclination of the 

 surface on which they have been solidified. They are vesi- 

 cular and scoriaceous when they have cooled on a surface pre- 

 senting a higher angle than two degrees, and they then always 

 preserve traces of movement. The lavas, on the contrary, 

 are crystalline and compact, when, having attained a certain 

 thickness on a nearly horizontal surface, they have cooled gra- 

 dually. 



Oscillatory Movements of the Surface of the Campania. 



11. The environs of Naples have been subjected to successive 

 depressions and elevations. The temple of Serapis is a cele- 

 brated example of these oscillations ; and the coast of Puzzuoli 

 affords numerous proofs of these oscillatory movements. There, 

 we see, in almost every part of its whole extent, Roman con- 

 structions, covered to a depth of from twenty to twenty-two feet, 

 by sedimentary beds. 



Destruction of Pompeii and Herculaneum, '** 



12. The destruction of these two towns does not seem to 

 have been produced exclusively by a shower of cinders ; the 

 earthy mass which covers them is in a great measure composed 

 of the same elements as the pumice-tuff which forms the sides 

 of the Somma. We find, besides the fragments of pumice, 

 the same blocks of apparently primitive rocks which contain the 

 minerals said to be derived from Vesuvius. It is therefore pro- 

 bable that the eruption of 79, which ejected a prodigious quantity 

 of cinders, produced also the '* eboulement"' of a part of the 

 *« contreforts" of the Somma, and that from it resulted the ex- 



VOL. XX. NO. XXXIX.— JANUAEY 1836. I 



