476 COSMOS. 



though not in large quantities, in the trachytes of the vol- 

 canoes of Cotopaxi, Rucu-Pichincha, Tungurahua and Anti- 

 sana, along with augite and oligoclase, but scarcely ever along 

 with these two minerals on the slope of the Chimborazo up 

 to a height of more than 19,000 feet. Among the many speci- 

 mens which I brought from Chimborazo, hornblende is recog- 

 nized only in two, and even then in small quantity. In the 

 eruptions of Vesuvius in the years 1822 and 1850, augite 

 and crystals of hornblende (these nearly 9 Parisian lines in 

 length) were contemporaneously formed by exhalations of 

 vapours on fissures. 95 The hornblende of Etna, as Sar borius von 

 Waltershausen observes, belongs especially to the older lavas. 

 That remarkable mineral, so widely diffused in Western A sia 

 and at several points of Europe, which Gustav Rose has de- 

 nominated Uralite, being allied in structure and crystalline 

 form to hornblende and augite, 96 I here once more gladly 

 point attention to the first occurrence of uralite crystals in 

 the New Continent ; they were recognised by Rose in a 

 piece of trachyte which I abstracted from the slope of the 

 Tungurahua, 3200 feet below the summit. 



LEUCITE. 



Leucites, which in Europe belong exclusively to Vesuvius, 

 the Rocca Monfina, the Albanian Mountains near Rome, the 

 Kaiserstuhl in the Breisgau, and the Eifel (in the western 

 environs of the Lachar Lake in blocks, and not in the con- 

 tiguous rock, as in the Burgberge near Rieden), have never 

 yet been found in volcanic rocks of the New Continent, or 

 the Asiatic portion of the old. Leopold von Buch discovered 

 them round an augite-crystal as early as the year 1798, and 

 described in an admirable treatise their frequent forma- 

 tion. 97 The augite-crystal round which, according to this 

 great geologist, the leucite is formed, is seldom wanting, but 

 appears to me to be sometimes replaced by a small grain or 

 morsel of trachyte. The unequal degrees of fusibility, be- 

 tween the grain of trachyte and the surrounding mass of 



95 Roth, Monographic des Vesuvs. s. 267, 382. 



96 See above, note 82 ; Rose, Reise nach dein Ural., Bd. ii, s. 369 ; 

 Bischof, Ckem. und PhysiTc. Geologic, Bd. ii, s. 528571. 



'# Gilbert's Annalen der PhysiTc., Bd. vi, 1800, B. 53; Bischof; 

 Geologic, Bd. ii, s. 22652303. 



