444 COSMOS. 



and 1850, augite and crystals of hornblende (these nearly 

 nine Parisian lines in length) were contemporaneously formed 

 by exhalations of vapors on fissures.* The hornblende of 

 JEtna, as Sartorius von Waltershausen observes, belongs es- 

 pecially to the older lavas. That remarkable mineral, so 

 widely diffused in Western Asia and at several points of 

 Europe, which Gustav ilose has denominated Uralite, being 

 allied in structure and crystalline form to hornblende and 

 augite, f I here once more gladly point attention to the first 

 occurrence of uralite crystals in the New Continent ; they 

 were recognized by Rose in a piece of trachyte which I ab- 

 stracted from the slope of the Tungurahua, 3200 feet below 

 the summit. 



LEUCITES. 



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 en- 

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

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

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

 the Asiatic portion of the Old. Leopold von Buch discov- 

 ered them round an augite crystal as early as the year 1798, 

 and described in an admirable treatise their frequent forma- 

 tion. J 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 leu- 

 cite raise some chemical difficulties to the explanation of 

 the mode in which the integumental covering is formed. 

 Leucites, partly detached, according to Scacchi, and partly 

 mixed with lava, were extremely abundant in the recent 

 eruptions of Vesuvius in 1822, 1828, 1832, 1845, and 1847. 



OLIVIN. 

 Olivin being very abundant in the old lavas of Vesuvius 



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



f See above, p. 434, note * ; Rose, JReise nach dem UraL, bd. ii., s. 

 369; Bischof, Chem. und Physik. Geologie, bd. ii., s. 528-571. 



% Gilbert's Anna/en der Physik., bd. vi., 1800, s. 53; Bischof, Geolo- 

 ffie, bd. ii., s. 2265-2303. 



The recent lavas of Vesuvius contain neither olivin nor glassy feld- 

 spar ; Roth, Mon. des Vesuvs., s. 139. According to Leopold von Buch, 

 the lava stream of the Peak of Teneriffe of 1704, described by Viera and 



