VULCANICITY. 159 



the production of crystalline rock from a fused mass are con- 

 ceivable even in a sphere which is regarded as destitute of 

 both air and water. 



The genetic connection of the classes of volcanic phenom- 

 ena here referred to is indicated by the numerous traces of 

 the simultaneousness of the simpler and weaker with stronger 

 and more complex effects, and the accompanying transitions 

 of the one into the other. The arrangement of the mate- 

 rials in the representation selected by me is justified by such 

 a consideration. The increased magnetic activity of our 

 planet, the seat of which, however, is not to be sought in 

 the fused mass of the interior (even though, according to 

 Lenz and Riess, iron in the fused state may be capable of 

 conducting an electrical or galvanic current), produces evolu- 

 tion of light in the magnetic poles of the earth, or at least 

 usually in their vicinity. We concluded the first section of 

 the volume on telluric phenomena with the luminosity of the 

 earth. This phenomenon of a luminous vibration of the 

 ether by magnetic forces is immediately followed by that class 

 of volcanic agencies which, in their essential nature, act pure- 

 ly dynamically, exactly like the magnetic force — causing 

 movement and vibrations in the solid ground, but neither 

 producing nor changing any thing of a material nature. 

 Secondary and unessential phenomena (the ascent of flames 

 during the earthquake, and eruptions of water and evolu- 

 tions of gas* following it) remind one of the action of ther- 

 mal springs and salses. Eruptions of flame, visible at a dis- 

 tance of many miles, and masses of rock, torn from their 

 deep seats and hurled about,f are presented by the salses, 

 which thus, as it were, prepare us for the magnificent phe- 

 nomena of the true volcanoes; which again, between their 

 distant epochs of eruption, like the salses, only exhale aque- 

 ous vapor and gases from their fissures : so remarkable and 

 instructive are the analogies which are presented in various 

 stages by the gradations of Vulcanism. 



* Cosmos, vol. i., p. 217. 



f Cosmos, vol. i.. p. 225. Compare Bertrand-Geslin, " Sur les roches 

 lancees par le J r olcan de bone du Monte Zibio pres du bourg de Sassiiolo," 

 in Humboldt, Voyage aux Regions Equinoxiales du Nouveau Continent 

 (Relation Historique), t. iii., p. 566. 



