Mr. PouLETT ScROPE OTi the Volcanic District of Naples. 341 



having- been produced by the elevation of flat strata on their edges round a 

 central aperture, by force of elastic gases. Von Buch is the inventor of this 

 last idea, which Dr. Daubeny and some other authors, I believe Humboldt 

 amongst them, support. 



Now the cone of Vesuvius we know to have been created, not in this imagined 

 manner, but by the repeated superposition of one volcanic bed on another, all 

 flowing from a central source ; a process which cannot fail to produce this 

 peculiar form of hill, (as is shown in the mud cones of air-volcanoes, which 

 no one ever thought of attributing to the heaving up of solid strata of clay 

 upon their edges). Again: the crater of Vesuvius, excavated from the entrails 

 of the volcano by the eruption of 1822, shows the internal structure and con- 

 stitution of this cone to be exactly similar to that of Somma, as seen in the 

 Atrio del Cavallo. Their external figure and other features are also perfectly 

 alike, allowing for the difference in size and age ; and it would be therefore 

 irrational to invent for the cone of Somma an unexampled mode of production, 

 entirely different from that by which the same volcano has created, as it were 

 before our eyes, the analogous cone of Vesuvius. The argument, if conceded 

 with respect to Somma, will extend of course to the other regularly conical 

 volcanic mountains in the Canaries or elsewhere, to which this process of 

 formation from elevated strata has been attributed, — the Erhebung's cratere 

 of Von Buch. 



At the same time it is not to be doubted that the continual and often violent 

 earthquake shocks which accompany the eruptions of every habitual volcano, 

 are connected, or rather are occasioned by, elevatory expansions of the solid 

 beds forming the frame-work of the mountain, through the disruptive force of 

 the lava injected from below. The clefts broken in this way across the sides 

 of the cone are no doubt the origin of many of those deep fissure-like gorges 

 (barancos) which furrow the slopes of iEtna, Teneriife, and other volcanic 

 mountains of a large size. All I contend for is, that the parallel and sloping 

 beds, which, with a quaqua-versal dip compose every such mountain, were not 

 deposited horizontally, or otherwise than at a high angle of inclination ; and 

 that the angular elevation they have since sustained, is in general comparatively 

 trifling : — in short, that the conoidal form preserved by an habitual volcanic 

 mountain in every stage of its formation, is owing to the same obvious cause 

 which communicates the similar figure to a simple volcanic hillock, the pro- 

 duce of a single eruption, — viz. the accumulation of erupted matters round a 

 central orifice. 



To return to Ischia. — Unlike that of Vesuvius, though at so short a distance 

 from it, this volcanic vent has produced not a single leucite, and none but 



