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



appearances whose causes cannot be ascertained, or even investi- 

 gated without such a distinction. 



That from the middle of such an elevation-crater, whose ac- 

 tion was only for a short period of time, a new cone should arise, 

 generally of trachyte, which becomes a permanent volcano, and 

 spreads its eruptive phenomena over a wide circle around it, is 

 strikingly and pre-eminently exemplified by the Peak of Tene- 

 riffe. 



But, as in many other volcanos, melted substances which flow 

 in the form of streams of lava, are raised to the edge of the vol- 

 canic crater; it has been supposed to be a fundamental truth, 

 that a mountain of this description must have been produced by 

 means of such a rising up, and the subsequent hardening of the 

 flowing lava ; that thus, Vesuvius, even Etna, and many simi- 

 lar mountains, have gradually been raised from a low level to 

 their present height ; and the certainty that volcanic cones must 

 have attained their present elevation by this process, has led 

 some geologists to suppose and assert a similar gradual increase 

 of height in the case of the enclosures of craters of elevation ; al- 

 though streams of lava never occur in elevation craters. Our 



o 



journey has afforded us complete proof, that a volcanic cone can 

 never be produced by the continued building up of streams of 

 lava^ that its height can be increased only by the sudden eleva- 

 tion of solid masses, and that the whole cones of Etna, Vesuvius, 

 Volcano, and Stromboli, owe their first elevation to a sudden 

 projection above the surface. 



We have to thank the unceasing activity in observing of M. 

 Elie de Beaumont, for the chief proof of this important fact, 

 a proof which I may term truly striking, inasmuch as it direct- 

 ly seizes hold of the subject, and leaves so few difficulties un- 

 explained. He has ascertained by the careful measurement of 

 about thirty streams round Etna, and of a great many on 

 Vesuvius, that a stream having an inclination of 0^ or more can- 

 not possibly form a continuous mass; it falls so rapidly that it 

 can acquire only an inconsiderable thickness — not amounting 

 to more than a few feet. It is only when the inclination is 

 not more than 3% that the mass can spread, and can accu- 

 mulate to a considerable height. Now as the last third of 

 Etna rises with an inclination of W to 3^% it is clear, that 



