234 COSMOS. 



Rocks which arc .Tierely broken through by the volcanic ac- 

 tion are often inclosed in the igneous products. Thus I have 

 Ibund angular fragments of feldspathic syenite imbedded in the 

 black augitic lava of the volcano of Jorullo, in Mexico ; but 

 the masses of dolomite and granular limestone, which contain 

 magnificent clusters of crystalline fossils (vesuvian and garnets, 

 covered with mejonite, nepheline, and sodalite), are not the 

 ejected products of Vesuvius, these belonging rather to very 

 generally distributed formations, viz., strata of tufa, which arc 

 more ancient than the elevation of the Somma and of Vesu 

 vius, and are probably the products of a deep-seated and con 

 cealed submarine volcanic action.* We find five metals among 

 the products of existing volcanoes, iron, copper, lead, arsenic, 

 and selenium, discovered by Stromeyer in the crater of Volca- 

 no, t The vapors that rise from the fuinarolles cause the sub- 

 limation of the chlorids of iron, copper, lead, and ammonium ; 

 iron glance} and chlorid of sodium (the latter often in large 

 quantities) fill the cavities of recent lava streams and the fis- 

 sures of the margin of the crater. 



The mineral composition of lava differs according to the na 

 ture of the crystalline rock of which the volcano is formed, the 

 height of the point where the eruption occurs, whether at the 

 foot of the mountain or in the neighborhood of the crater, and 

 the condition of temperature of the interior. Vitreous volcanic 

 formations, obsidian, pearl-stone, and pumice, are entirely want- 

 ing in some volcanoes, while in the case of others they only 

 proceed from the crater, or, at any rate, from very considera- 

 ble heights. These important and involved relations can only 

 be explained by very accurate crystallographic and chemical 

 investigations. My fellow-traveler in Siberia, Gustav Rose, 

 and subsequently Hermann Abich, have already been able, 

 by their fortunate and ingenious researches, to throw much 

 light on the structural relations of the various kinds of vol- 

 canic rocks. 



* Leop. von Buch, in Poggeud., Annaten, bd. xxxvii., s. 179. 



\ [The little island of Volcano is separated from Lipari by a narrow 

 channel. It appears to have exhibited strong signs of volcanic activ- 

 ity long before'lhe Christian era, and still emits gaseous exhalations. 

 Btromeyer detected the presence of selenium in a mixture of sal ammo- 

 uiac and sulphur. Another product, supposed to be peculiar to this 

 volcano, is boracic acid, which lines the sides of the cavities in beauti- 

 ful white silky crystals. Daubeney, op. cit., p. 257.] 2V. 



t Regarding the chemical origin of iron glance in volcanic masses, seo 

 Mitacherlich, in Poggend., Annalen, bd. xv., s. 630 ; and on the liber* 

 tion of hydrochloric acid in the crater, see Gay-Lussac, in the Annah\ 

 to Chimique et de Physique, t. xxii., p. 423. 



