Volcafios and Earthquakes. 71 



This view likewise tends, as it seems, to reconcile the accounts 

 which ancient writers have given of the structure of the moun- 

 tain, antecedently to the period before mentioned.* 



As for the mode of action of the vapours, it is indifferent 

 whether they have to contend with loose and unconnected, or 

 with melting masses, only that the former are propelled into 

 tlic air like cannon balls,-|- and falling into a parabolic curve, 

 accumulate and 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 vapour cannot 

 escape through the uplifted mass. This mass is supported by 

 the elastic force of the vapour, cools gradually, and then re- 

 mains, as it were, wedged in between the strata it has broken 

 through. But according to Von Buch^sj: observations on Palma 

 and Gran Canaria, it may happen, that the vapour bursts 

 forth from the centre of the mass it has raised, and thus ex- 

 poses 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 eruption, by which true volcanos open a 

 communication with the atmosphere. 



Further, this philosopher has pointed out,|| that volcanic 

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



'•■ See the Historical Notices given by Daubeny, loco cit. p. 1 45 and fol- 

 lowing. 



t V. Humb. (Reise v. i. p. 226) calculates from the time the stones thrown 

 out during the lateral eruption of the Peak of Tenerijf'e, on the 9th June 1708, 

 took in falling (which according to Colofjan was from twelve to fifteen se- 

 conds, reckoning from the moment they reached their greatest height), that 

 they were projected to a height of more than 3000 feet. In some similar 

 observations made by Von Humboldt during the eniptions of Vesutlm in 

 1805, he satisfied himself that such observations are capable of a great de- 

 gree of exactitude. Similar calculations made by other observers, give still 

 greater heights. The maximum height of such projections was observed 

 at Cotopaxl by La Condamine (Voyage ji I'Equateur), Ho saw proi)elled 

 laterally, a block of about 1000 square feet, to a distance of nearly I4 geo- 

 graphical miles. 



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



II Poggcndoi-ii''s Anual. t. xxxvii. p. 170, &c. 



