Volcanoes in the diffeimt regions of the Earth. 237 



to speak, an individual character, which remains always the 

 same through long periods. The neighbouring mountains 

 most commonly afford entirely different products, lavas of 

 leucite and felspar, obsidian and pumice, and basaltic masses 

 containing olivine. They belong to the most recent forma- 

 tions of the globe, and traverse nearly all the strata of the 

 secondary mountains. Their eruptions and their torrents of la- 

 va are of a more recent origin than our valleys. Their life, if 

 we may be permitted to make use of such an expression, de- 

 pends upon the mode and duration of their communication with 

 the interior of the earth. They frequently remain quiet for 

 ages, suddenly kindle again, and end with being solfaterras, ex- 

 haling aqueous vapours, gases and acids. Sometimes, as in the 

 Peak of Teneriffe, their summit has already become a laborato- 

 ry of regenerated sulphur ; while from their sides there yet flow 

 great torrents of lava, basaltic and lithoid in their lower parts, 

 vitreous, in the form of obsidian and pumice, in their upper 

 part, where the pressure is less. 



Independently of these volcanoes provided with permanent 

 craters, there is another species of volcanic phenomena, which is 

 more rarely observed, but which is peculiarly calculated to throw 

 light on geology, because it recalls the primitive world, or, in 

 other words, the most ancient revolutions of our globe. Moun- 

 tains of trachyte, opening of a sudden, vomit forth lava and 

 ashes, and again shut perhaps for ever. This is what took place in 

 the gigantic Antisana, in the Chain of the Andes, and at Mount 

 Epomeus in the island of Ischia, in 1302. An eruption of this 

 kind sometimes takes place in the plains ; for example, on the 

 plain of Quito ; in Iceland, at a distance from Hecla ; in Eu- 

 beus, in the fields of Lelantee. Many islands, suddenly ele- 

 vated from the bottom of the sea, belong to these transitory 

 phenomena. In these cases, the communication with the inte- 

 rior of the earth is not permanent ; the action ceases as soon as 

 the aperture of the canal of communication is closed anew. 

 Veins of basalt, greenstone, and porphyry, which in the different 

 zones of the earth traverse almost all the formations, masses 

 of syenite, augite, porphyry and amygdaloid, which characte- 

 rize the newest strata of the transition, and the oldest strata of 

 the secondary rocks, have probably been formed in this manner. 



