TRUE VOLCANOES. 4G5 



have found so diffused on the Asiatic side of the Ural 

 (Ibid. s. 544). 



Fifth division. " A mixture of labradorite 81 and augite,* 3 

 a doleritic trachyte : Etna, Stromboli ; and, according to 

 the admirable works on the trachytes of the Antilles by 

 Charles Saint e-Claire Deville, the Soufriere de la Guadeloupe, 

 as well as the three great cirques which surround the Pic de 

 Salazu, on Bourbon." 



Sixth division. "The ground-mass, often of a grey 

 colour, in which crystals of leucite and augite lie imbedded, 

 with very little olivine : Vesuvius and Sornma ; also the 

 extinct volcanoes of Yultur, Kocca Monfina, the Albanian 

 hills and Borghetto. In the older mass (for example, in the 

 wall and paving-stones of Pompeii) the crystals of leucite are 

 more considerable in size and more numerous than the augite. 



average of 777 m ., or 2549 English feet, more than my barometrical 

 measurement. To have corresponded with this, the boiling point, 

 should have been found about 2.25 cent, higher, if the summit of 

 Chimborazo bad actually been reached. Poggendorffs Annalen, Bd. c, 

 1857, s. 479. 



bl That the trachytic rocks of Etna contain labradorite was demon 

 strated by Gustav Rose in 1833, when he exhibited to his friends the rich 

 Sicilian collections of Friedrich Hoffmann in the Berlin Mineralogical 

 cabinet. In his treatise on the minerals known by the names of green- 

 stone and green-stone porphyry (Poggend. Annal., Bd. xxxiv, 1835, 

 p. 29), Gustav Rose mentions the lavas of Etna, which contain augite 

 and labradorite (compare Abich in his interesting treatise on the whole 

 felspathic-family, (Poggend. Annul., 1840, Bd. 1, s. 347). Leopold von 

 Buch describes the rock of Etna as analogous to the dolerite of the 

 basalt-formation (Poggend. Annal., Bd. xxxvii, 1836, s. 188). 



82 Sartorius von Waltershausen, who has for many years carefully 

 investigated the trachytes of Etna, makes the following important 

 observations : " the hornblende there belongs especially to the older 

 masses, the green-stone veins in the Val del Bove, as well as the 

 white and red trachytes, which form the ground mass of Etna in 

 the Serra Giannicola. Black hornblende and bright yellowish-green 

 augite are there found side by side. The more recent lava-streams 

 from 1669 (especially those of 1787, 1809, 1811, 1819, 1832, 1838, 

 and 1842), show angiie, but no hornblende. The latter seems to be 

 generated only after a longer period of cooling'' (Waltershausen, Ueber 

 die vulkainscken Getteine ron SiciUen und Island, 1853, s. Ill 114). 

 Ill the augitiferous trachytes of the fourth division in the chain of the 

 Andes, along with the abundant augites, I have indeed sometimes found 

 none, but sometimes, as at Cotopaxi (at an elevation of 14,068 feet) and 

 at Rucu-Pichincha, at a height of 15,304 feet, distinct black hornblende- 

 crystals in small quantities. 



VOL. V. 2 H 



