216 



COSMOS. 



If the oldest formations of eruptive rock (often perfectly 

 similar to the more recent lavas in its composition), which 

 also in part occupy veins, are to be ascribed to a previous 

 fissure of the deeply-shaken crust of the earth, as I have 

 long been inclined to think, both these fissures and the less 

 simple craters of elevation subsequently produced must be 

 regarded only as volcanic eruptive orifices, not as volcanoes 

 themselves. The principal character of these last consists 

 in a connection of the deep-seated focus with the atmosphere, 

 which is either permanent, or at least renewed from time to 

 time. For this purpose the volcano requires a peculiar frame- 

 works for, as Seneca* says very appropriately, in a letter to 

 Lucilius, "ignis in ipso monte non alimentum habet, sed 

 viam." The volcanic activity exerts, therefore, a formative 

 action by elevating the soil ; and not, as was at one time uni- 

 versally and exclusively supposed, a building action by the 

 accumulation of cinders, and new strata of lava, superposed 

 one upon the other. The resistance experienced in the canal 

 of eruption, by the masses in a stat§ of igneous fluidity when 

 forced in excessive quantities toward the surface, gives rise to 

 the increase in the heaving force. A " vesicular inflation of 

 the soil" is produced, as is indicated by the regular outward 

 declination of the elevated strata. A mine-like explosion, 

 the bursting of the central and highest part of the convex 

 inflation of the soil, gives origin sometimes only to what 

 Leopold von Buch has called a crater of elevation^ that is to 



casion {Cosmos, vol. i., p. 237), and I shall only advert here to an- 

 other passage in Strabo (vi., p. 269), in which hardening lava, called 

 7T7]\ug jitXac, is most distinctly characterized. In the* description of 

 JEtna we find : " The red-hot stream (pvat,) in the act of solidifica- 

 tion converts the surface of the earth into stone to a considerable 

 depth, so that whoever wishes to uncover it must undertake the labor 

 of quarrying. For, as in the craters, the stone is molten and then up- 

 heaved, the fluid streaming from the summit is a black excrementitious 

 mass (7r/;\oc) falling down the mountain, which, afterward hardening, 

 becomes a millstone, and retains the same color that it had before." 



* Cosmos, vol. i., p. 239. 



f Leopold von Buch, On Basaltic Islands and Craters of Elevation, 

 in the Abhandl. der kbnig.Akad. der Wiss. zu Berlin, 1818-1819, s. 51; 

 and Phjsilcalische Beschreibung der canarischen Inseln, 1825, s. 213, 262, 

 284, 313, 323, and 341. This work, which constitutes an era in the 

 profound knowledge of volcanic phenomena, is the fruit of a voyage 

 to Madeira and TenerifFe, from the beginning of April to the end of 

 October, 1815 ; but Naumann indicates with much justice, in his Lehr- 

 bnch der Geognosie, that in the letters written in 1802 by Leopold von 

 Buch, from Auvergne (Gcognostische Beobachtung auf Iieisen durch 

 Deutscliknd und Itodien, bd. ii., s. 282), in reference to the description 



