ON ITS EXTEEIOK. VOLCANOES. 431 



in Phrygia, and Kajadschyk and Donanlar in Mysia, in 

 which glassy felspar, much oligoclase, some hornblende, 

 and brown mica are intermixed." 



Third Division. "The ground-mass of this dioritic 

 trachyte contains many small crystals of oligoclase with 

 black hornblende and brown magnesia-mica. To this 

 division belong the trachytes of ^gina ( 598 ), of the 

 Kozelnik valley near Schemnitz ( 599 ), of Nagyag in 

 Transylvania, of Montabaur in the Duchy of Nassau, of 

 Stenzelberg and of the Wolkenburg in the Siebengebirge 

 near Bonn, of Puy de Chaumont near Clermont in 

 Auvergne, and of Liorant in the Cantal; Kasbegk in 

 the Caucasus, the Mexican volcanoes of Toluca ( 60 ) and 

 Orizaba, the volcano of Purace, and, although it is 

 very uncertain whether these latter are trachytes, the 

 magnificent columns of Pisoje ( 601 ) near Popayan. Von 

 Buch's ( domites ' also belong to this division. In the 

 white fine-grained ground-mass of the trachytes of the 

 Puy de Dome there are glassy crystals which have 

 always been taken for felspar, but which are most dis- 

 tinctly streaked in the plane of cleavage, and are really 

 oligoclase; hornblende and some mica are found with 

 them. According to the volcanic specimens for which 

 the royal collection is indebted to Herr Mollhausen, the 

 draftsman and topographer of Lieutenant Whipple's 

 exploring expedition, we should also regard, as belonging 

 to this third division, or to the dioritic Toluca trachytes, 

 those of Mount Taylor, between Santa Fe del Nuevo 

 Mexico and Albuquerque, as well as those of Cieneguilla 

 on the western slope of the Rocky Mountains, where, 

 according to the fine observations of Jules Marcou, 

 black lava-streams are seen to have flowed over the 



