Natural History of Volcanos and Earthquakes. 273 



produce a mountain, whilst the latter remain at the height to 

 which they are borne up by the elastic fluids. 



In elevations of the latter description, the vapor cannot escape 

 through the uplifted mass. This mass is supported by the elas- 

 tic force of the vapor, cools gradually, and then remains, as it 

 were, wedged in between the strata it has broken through. But 

 according to Von Buch's* observations on Palma, and Gr-an Ca- 

 naria, it may happen, that the vapor bursts forth from the centre 

 of the mass it has raised, and thus exposes its interior. Such a 

 crater would thus be the effect of the elevation of the island, 

 for which reason he gives it the name of crater of elevation, 

 (Erhebungs Krater,) to distinguish it from the craters of erup- 

 tion, by which true volcanos open a communication with the at- 

 mosphere. 



Further, this philosopher has pointed out,f that volcanic cones 

 cannot be generated by the building up of streams of lava. He 

 infers this from observations made by Elie de Beaumont, and 

 which have been already alluded to. This philosopher meas- 

 ured the mean inclination of about thirty lava streams of Etna, 

 and of a great many of Vesuvius^ and found that a stream hav- 

 ing an inclination of 6°, or even more, forms no continuous 

 mass. Such a stream inclines too much to be able to attain 

 more than a thickness of a few feet. When its inclination is 

 only 3^ or less, the mass may be spread, and accumulated to a 

 considerable height. | 



Lastly, we have to notice the upraisings which are the conse- 

 quences of earthquakes, and often extend to large islands and 

 whole tracts of country. Elevations of small compass, accom- 

 panied by partial depression, which is no doubt merely a conse- 

 quence of the elevations, were observed before,-^ and during|| the 

 famous earthquake of Lisbon. Small elevations also took place 

 during that in Calahria.% The commissioners who were em- 

 ployed to make observations of the earthquakes in the county of 

 Pignerol, relate, that the very day (2d April, 1808) when one 



* Abhandlungen der Berliner Acad, loco cit. p. 58. 

 t PoggendorfF's Annal. t. xxxvii. p. 170, &c. 



X Vied Memoire of Elie de Beaumont, in vol. xx. p. 376, &c. Edin. New Phil. 

 Journ. ; and Description Geologiqiie de la France, t. iv. 



§ Palassou Mem. pour, servir k THistoire Nat. des Pyren. p. 260. 



I| Piiilos. Trans, t. xlix. p. 417. W Jour, de Phys. Ixii. 1806. p. 264. 



Vol. XXXVI, No. 2— April-July, 1839. 35 



