TRUE VOLCANOES. 239 



voured to bring together, in a separate atlas, a number of out- 

 lines of the Cordilleras of Quito and Mexico, sketched from my 

 own drawings. As basalt occurs sometimes in conical domes, 

 somewhat rounded at the summit, sometimes in the form ol 

 closely-arranged twin-mountains of unequal elevation, and 

 sometimes in that of a long horizontal ridge bounded at 

 each extremity by a more elevated dome, so we principally 

 distinguish in trachyte the majestic dome-form 97 (Chim- 

 borazo, 21,422 feet), not to be confounded with the form 

 of the unopened but less massive bell-shaped mountains. The 

 conical form is most perfectly 98 exhibited in Cotopaxi (18,877 

 feet), and next to this in Popocatepetl 99 (17,727 feet), as seen 

 on the beautiful shores of the lake of Tezcuco, or from the 

 summit of the .ancient Mexican step-pyramid of Cholula; 

 and in the volcano of Orizaba 100 (17,374 feet, according to 

 Ferrer 17,879 feet). A strongly truncated conical form 1 is 

 exhibited by the Nevado de Cayambe-Urcu (19,365 feet), 

 which is intersected by the equator, and by the volcano of 

 Tolima (18,129 feet), visible above the primaeval forest at 

 the foot of the Paramo de Quindiu, near the little town of 

 Ibague. 2 To the astonishment of geognosists an elongated 

 ridge is formed by the volcano of Pichincha (15,891 feet), at 

 the less elevated extremity of which the broad, still ignited 

 crater 3 is situated. 



Fallings of the walls of craters, induced by great natural 

 phenomena, or their rupture by mine-like explosion from 



9 ' Humboldt, Umrisse von Vullcanen der Cordilleren von Quito und 

 Mexico, ein Beitrag zur Pliysiognomik der Natur, Tafel iv (Kleinere 

 Schriften, Bd. i, s. 133205). 



98 Umrisse von Vulkanen, Tafel vi. 



99 Op. tit. sup. Tafel viii (Kleinere Schriftin, Bd. i, s. 463467). 

 On the topographical position of Popocatepetl (smoking mountain, in 

 the Aztec language), near the (recumbent) White woman, Iztaccihuatl, 

 and its geographical relation to the western lake of Tezcuco and the 

 pyramid of Cholula situated to the eastward, see ray Atlas Geographique 

 et Physique de la Nouvelle Espagve, pi. 3. 



00 Umrisse von Vulkanen, Tafel ix; the Star-mountain, in the Aztec 

 language Citlaltepetl ; Kleinere Schriften, Bd. i, s. 467 470, and my 

 Atlas Geogr. et Phys. de la Nouvelle Espagne, pi. 17. 



1 Umrisse von Vulkanen, Tafel ii. 



2 Humboldt, Vues dts Cordilleres et Monumens des peuples indigenes de 

 lAmerique (fol.), pl.lxii. 



3 Umrisse von Vidkanen. Tafel i and x (Kleinere Schriften, Bd. L 

 a. 1-99). 



