TRUE VOLCANOES. 427 



Arkansas to California, July, 1854, p. 46-48. See also two 

 important French treatises Resume explicatif tfune Carte 

 Geologique des Etats-Unis, 1855, p. 113-116, and Exquisse 

 cfune Classification des Chaines de Montagues de VAmerique du 

 Nord, 1855 ; Sierra de S. Francisco et Mount Taylor, p. 23). 

 Among the trachytes of Java, for specimens of which I am 

 indebted to my friend Dr. Junghuhn, we have likewise rec- 

 ognized those of the third division in three volcanic districts ; 

 namely, Burung-agung, Tyinas, and Gurung Parang (in the 

 Batugangi district). 



Fourth Division. " The leading mass contains augite with 

 oligoclase the Peak of Teneriflfe,* the Mexican volcanoes 

 Popocatepetl! and Colima, the South American volcanoes 



* The feldspar in the trachytes of Teneriffe was first recognized in 

 1842 by Charles Deville, who visited the Canary Islands in the autumn 

 of that year; see that distinguished geologist's Voyage Geologique aux 

 Antilles et aux lies de Teneriffe et de Fogo, 1848, p. 14, 74, and 169 ; 

 also Analyse du Feldspath de Teneriffe, in the Comptes rendus de VAcad. 

 des Sciences, t. xix., 1844, p. 46. "The labors of Messrs. GustavEose 

 and H. Abich," he says, " have contributed in no small degree, both crys- 

 tallographically and chemically, to throw light on the numerous varie- 

 ties of minerals which were comprised under the vague denomination 

 of feldspar. I have succeeded in submitting to analysis carefully iso- 

 lated crystals whose density in different specimens was very uniformly 

 2-593, 2-594, and 2-586. 'This is the first time that the oligoclase 

 feldspar has been indicated in volcanic regions, with the exception, 

 perhaps, of some of the great masses of the Cordillera of the Andes. 

 It was not detected, at least with any certainty, except in the ancient 

 eruptive rocks (Plutonic, granite, syenite, syenitic porphyry ....;) 

 but in the trachytes of the Peak of Teneriffe it plays a part analogous 

 to that of the Labrador in the doleritic masses of ./Etna." Compare 

 also Rammelsberg, in the Zeitschr. der Deutschen Geol. Gesellschaft, bd. 

 v., 1853, s. 691, and the 4th Supplement of his Handworterbuchs der 

 Chem. Mineralogie, s. 245. 



f The first determination of height of the great volcano of Mexico, 

 Popocatepetl, is, so far as I am aware, the trigonometrical measure- 

 ment already mentioned (see above, p. 43, note f), executed by me on 

 the 24th of January, 1804, in the Llano de Tetimba. The summit 

 was found to be 1536 toises above the Llano, and as the latter lies bar- 

 ometrically 1234 toises above the coast of Vera Cruz, we obtain 2770 

 toises, or 17,728 English feet, as the absolute height of the volcano. 

 The barometrical measurements which have succeeded my trigono- 

 metrical calculation lead me to conjecture that the volcano is still 

 higher than I have made it in the Essai sur la Geographie des Plantes, 

 1807, p. 148, and in the Essai Politique sur la Nouvelle Espagne, t. i., 

 1825, p. 185. William Glennie, who first reached the margin of the 

 crater on the 20th of April, 1827, found it, according to his own cal- 

 culation (Gazeta del Sol, published in Mexico, No. 1432), 17,884 feet, 

 equal to 2796 toises ; but, as corrected by the mining director, Burkart, 

 who has acquired so high a reputation in the department of American 

 hypsometry, and who compared the calculation in Vera Cmz with baro- 



