446 COSMOS. 



chyles called La reventazon del Volcan de Anzango* contain 

 no olivin. It was only in the great brown-black lava stream, 

 with a crisp, scoriaceous surface raised like a cauliflower, 

 whose track we followed in order to reach the crater of the 

 volcano of Jorullo, that we met with small grains of olivin 

 imbedded.! The prevailing scarcity of olivin in the modern 

 lavas and the greater part of the trachytes seem less striking 

 when we recollect that, essential as olivin appears to be for 

 basalt in general, yet (according to Krug von Nidda and Sar- 

 torius von Waltershausen) in Iceland and in the German 

 Rhone Mountains the basalt destitute of olivin is not dis- 

 tinguishable from that which abounds in it. The former it 

 has been the custom from the earliest times to call trap and 

 wacke, the latter we have in modern times denominated Ane- 

 masitei Olivins, which sometimes occur as large as a man's 

 head in the basalts of Rentieres, in the Auvergne, attain 

 also in the Unkler quarries, which were the object of my 

 first youthful researches, to the size of six inches in diameter. 

 The beautiful hypersthene rock ofElfdalen, in Sweden, much 

 employed for ornamental purposes, a granulated mixture 

 of hypersthene and Labrador! te, which Berzelius has described 

 as syenite, likewise contains olivin, || as does also (though 

 more rarely) the phonolite of the Pic de Griou, in the Can- 

 tal.^[ While, according to Stromeyer, nickel is a very con- 

 stant accompaniment of olivin, Rumler has, on the other hand, 

 discovered arsenic in it,** a metal which has been found in 

 the most recent times widely diffused in so many mineral 



* Humboldt, KkinereSchriften, s.202; and Cbs;os,see above, p. 222. 



t Humboldt, Kl. Schr., vol. i., p. 344. I have also found a great 

 deal of olivin in the tezontle (cellular lava, or basaltic amygdaloid ? in 

 Mexican, tetzontli, ". e., stone-hair, from tetl, stone, and tzontli, hair) 

 6elonging to the Cerro de Axusco, in Mexico^- 



J Sartorius vou Waltershausen, Physisch-geographische Skizze von 

 Island, s. 64. 



[ It is there cut into vases, sometimes of a considerable size, and 

 other ornamental objects. From the high polish it takes, and the 

 contrast of its colors, it is one of the most beautiful stones in exist- 

 ence. Tr.] 



|| Berzelius, Sechster JaJiresbericht, 1827, p. 392 : Gustav Kose. in 

 Poggend., Ann., vol. xxxiv., 1835. p. 14. 



^f Jenzsch, Phonolit/ie, 1856, p. 37 : and Senft, in his important work, 

 Classification der Felsarten, 1857. p. 187. According to Scacchi. olivin 

 occurs also, along with mica and augite. in the lime blocks of the Som- 

 ma. I call these remarkable masses erupted blocks, not lava?, for the 

 Somma appears never to have ejected the latter. 



** Poggend., ArmaL, bd. xlix., 1840, s. 591, and bd. Ixxxiv., s. 302; 

 Daubre'e, in the Annaks des Mines, 4me Serie, t xix., 1851, p. 669. 



