426 COSMOS. 



nitz ;* of Nagyag, in Transylvania ; of JMontabaur, in the 

 Duchy of Nassau ; of the Stenzelberg and the Wolkenburg, 

 in the Siebengebirge, near Bonn ; of the Puy de Chaumont, 

 near Clermont, in Auvergne ; and of the Liorant, in Cantal ; 

 also the Kasbegk, in the Caucasus ; the Mexican volcanoes 

 of Tolucaf and Orizaba ; the volcano of Purace, and the 

 splendid columns of Pisoje, J near Popayan, though whether 

 the latter are trachytes is very uncertain. The domites of 

 Leopold von Buch belong likewise to this third division. In 

 the white fine-grained fundamental mass of the trachytes of 

 the Puy de Dome are found glassy crystals, which were con- 

 stantly taken for feldspar, but which are always streaked on 

 the most distinct cleavage surface, and are oligoclase ; horn- 

 blende and some mica are also present. Judging from the 

 volcanic specimens for which the royal collection is indebted 

 to Herr Mollhausen, the draughtsman and topographist of 

 Lieutenant Whipple's exploring expedition, the third division, 

 or that of the dioritic Toluca trachytes, also includes those 

 of Mount Taylor, between Santa Fe del Nuevo Mexico and 

 Albuquerque, as well as those of Cieneguilla, on the»westem 

 slope of the Rocky Mountains, where, according to the able 

 observations of Jules Marcou, black lava streams overflow the 

 Jura formation." The same mixture of oligoclase and horn- 

 blende which I saw in the Azteck highlands, in Anahuac 

 proper, but not in^the Cordilleras of South America, are 

 also found far to the west of the Rocky Mountains and of 

 Zuni, near the Mohave River, a tributary of the Rio Colorado 

 (see Marcou, Resume of a geological reconnaissance from the 



* See the admirable geological map of the district of Schemnitz by 

 Bergrath, Johann von Peltko, 1852, and the Abhandlungen der k. k. 

 geolocfischen Reichsanstalt, bd. ii., 1855, abth. i., s. 3. ' 



t Cosmos, see above, p. 375-6. 



X The basaltic columns of Pisoje, the feldspathic part of which has 

 been analyzed by Francis (Poggend., Annal., bd. Hi., 1841, s. 471), near 

 the banks of the Cauca, in the plain of Amolanga (not far from the 

 Pueblos of Sta. Barbara and Marmato), consist of a somewhat modi- 

 fied oligoclase in large beautiful crystals, and small crystals of horn- 

 blende. Nearly allied to this mixture are the quartz, containing dio- 

 ritic porphyry of Marmato, brought home by Degenhardt, the feld- 

 spathic part of which was named by Abich andesine — the rqck, desti- 

 tute of quartz, of Cucurusape, near Marmato, in Boussingault's collec- 

 tion (Charles Ste.-Cl. Deville, Etudes de Lithologie, p. 29); the rock 

 which I found twelve geographical miles eastward of Chimborazo, be- 

 low the ruins of old Riobamba (Humboldt, Kleinere Schriften^ bd. i., 

 s. IGl) ; and, lastly, the rock of the Esterel Mountains, in the de- 

 partment of the Var (Elie de Beaumont, Explic. de la Carte Gcol. de 

 France, t. i., p. 473). 



