Qhsetvailons on Volcanoes and titcir Lava, edg 



Those which I denominate extincc volcauocs are such as 

 no longer burn, though surrounded bv the sca^ or placed 

 on the borders of it. They would still burn, were not the 

 inflammable matters by which they were raised, really ex- 

 hausted and consumed. Of this kind i» the volcano of 

 iAgde, in Languedoc. Of this kind also are many of the 

 volcanic islands which have not thrown up lire since time 

 iunnemorial. 



M. Humboldt, in his letters written from Peru, speaks 

 of the volcanoes which he visited, but what he says is nol 

 sulRciently precise to enable us to form a just idea of them. 

 He represents Chimboraco as being composed of porphyry 

 from its bottom to its summit, and adds, that the porphyry 

 is igootoises in thickness; afterwards, he remarks, that it is 

 almost improbable that Chimboraco, as well as Picchincha 

 and Antisana, should be of a volcanic nature : " The place 

 by which we ascended," says he, " is composed of burnt 

 and scorilied rock, niixed with pumice-stone, which re- 

 sembles all the currents of lava in this countrv." 



Here are two characters very different. If' Chinibora(;o 

 be porphyry from the top to the bottom, it is not composed 

 of burnt and scorilied rocks, niixed with pumice-stone; 

 and if itbe ccmiposed of burnt rocks, it cannot be porphyry. 

 This expression, burnt and scorijitd rocks, is not even exact, 

 because it excites the idea of natural rocks, altered in their 

 place by the, and they are certainly lava which have been 

 thrown up by the volcano. But the truth must be, that 

 Chimboraco, and all the otlier volcanoes of Peru, are com« 

 posed of volcanic matters, from their base at the level of 

 the sea to the sununit. 



I havcjust read in the Aiinales du Museum d'Hisioire 

 Naturdle'^y a letter of the same traveller, written from 

 Mexico, on bis reiurn from Peru, where, speaking of the 

 volcanoes of Popayan, Hasto, Quito, and the other~parts of 

 the Andes, he says, " Great masses of this fossil {obsidian) 

 have issued from the craters ; and the sides of tliesc gulphs, 

 uhich we closely examined, consist of porphyrv, theljaseof 

 which holds a mean between obsidian and' pitch-stone 

 (pcchsiein)." M, Humboldt therefore considers obsidian, 

 or black compact glass, as a natural fossil or rock, and not 

 as volcanic glass. 



Father dv- la Torre, who resided at Naples, and has written 

 on Vesuvius, believed also that the interior of its mouth 

 was conipoicd of na'.ural rocks and strata hke e^'ery other 



mountain 



