Geological Society. 239 



GEOLOGICAL SOCIETY,, 

 [Continued from p. 150.^ 

 February 2nd, 1859, — Prof. J. Phillips, President, in the Chair. 

 The following communication was read : — 



" On the mode of formation of Volcanic Cones and Craters." 

 By G. Poulett Scrope, Esq., M.P., F.R.S., F.G.S. 



The author commenced by saying that he should not have referred 

 again to this subject, already briefly treated by him in a paper read 

 to the Society in April 1856, had it not been that Baron Humboldt, 

 in the recently published fourth volume of his ' Kosmos,' applies 

 the whole weight of his great authority to the support of the theory 

 of upheaval in contradistinction to eruption as the vera causa of 

 volcanic cones and craters, — a theory which the author, with Sir 

 Charles Lyell, M. Constant Prevost, and many others, believes to 

 be not merely erroneous, but destructive of all clearness of appre- 

 hension as to the character of the subterranean forces, and the part 

 which volcanic action has played in the structural arrangement of 

 the earth's surface. 



He showed, by reference to the works of Spallanzani, Dolomieu, 

 Breislak, &c., that the early observers of volcanic rocks and phe- 

 nomena, together with the unscientific world, looked upon volcanic 

 cones and craters, whether large or small, as the result of volcanic 

 eruptions ; but that of late years a new doctrine had been propa- 

 gated by MM. Humboldt, von Buch, Elie de Beaumont, and 

 Dufrenoy, which denies altogether that volcanic mountains have been 

 formed by the accumulation of erupted matters, and attributes them 

 solely to a sudden " bubble-shaped swelling-up " of pre-existing 

 horizontal strata, — the bubble sometimes bursting at top and then 

 leaving its broken sides tilted up around a hollow (elevation- crater). 

 The author expressed his belief that this notion originated in 

 Baron Humboldt's account of the eruption of JoruUo in 1759, in 

 which (as the author showed in his work on volcanos of 1825) a 

 great error had been committed, — the convexity of the Malpais and 

 its five hills being simply a bulky bed of lava poured out on a flat 

 plain from five ordinary cones of eruption, and the " hornitos" com- 

 mon " fumaroles " coated over with black mud produced from 

 showers of volcanic ashes mixed with rain-water. But the idea of 

 a " bladder-like swelling-up " of horizontal strata into volcanic hills 

 being thus started by M. von Humboldt, it was further extended by 

 M. von Buch ; and hence arose the " elevation-crater" theory. 



The author next proceeded to show the inconsistencies of the 

 advocates of this theory, who disagree among themselves as to the 

 extent to which they apply it, — MM. Humboldt, von Buch, and 

 Dufrenoy asserting both Somma and Vesuvius, the Peak of Tene- 

 riflfe, and all Etna, to be solely due to sudden upheaval, while M. 

 dc Beaumont declares Vesuvius, the Peak, and the upper cone of 

 Etna to be the products of eruption only. Again, while, except M. 

 Dufrenoy, all admit the minor cones and craters of Etna, Vesuvius, 

 Lanzarote, and Central France to be eruptive, all declare the similar 



