254 COSMOS. 



twice as high as Etna, and five times and a half as high aa 

 Vesuvius. The scale of volcanoes that I have suggested, start- 

 ing from the lowly Maars (mine-craters without a raised 

 framework, which have cast forth olivine bombs surrounded 

 by half-fused fragments of slate) and ascending to the still 

 burning Bahama 22,354 feet in height, has shown us that 

 there is no necessary connexion between the maximum oi 

 elevation, the smaller amount of the volcanic activity and 

 the nature of the visible species of rock. Observations con- 

 fined to single countries may readily lead us to erroneous 

 conclusions. For example, in the part of Mexico which 

 lies in the torrid zone, all the snow-covered mountains, 

 that is to say the culminating points of the whole country, 

 are certainly volcanoes ; and this is also usually the case 

 in the Cordilleras of Quito, if the dome-shaped trachytic 

 mountains, not opened at the summit (Chimborazo and 

 Corazon), are to be associated with volcanoes ; on the other 

 hand, in the eastern chain of the Bolivian Andes, the 

 highest mountains are entirely non- volcanic. The Uevados 

 of Sorata (21,292 feet), and Illimani (21, 153 feet) consist of 

 grauwacke schists, which are penetrated by porphyritic 

 masses, 48 in which (as a proof of this penetration), fragments 

 of schist are enclosed. In the eastern Cordillera of Quito, 

 south of the parallel of 1 35' the high summits (Condorasto, 

 Cuvillan. and the Collanes) lying opposite to the trachytes, 

 and also entering the region of perpetual snow, are also 

 mica-slate and firestone. According to our present know- 

 ledge of the mineralogical nature of the most elevated parts 



48 These penetrating porpliyritic masses show themselves in peculiar 

 vastness, near the Illimani, in Cenipampa (15,949 feet) and Totora- 

 pampa (13,709 feet); and a quartzose porphyry containing mica, and 

 enclosing garnets and at the same time angular fragments of silicious 

 schist forms the superior dome of the celebrated argentiferous Cerro de 

 Potosi (Pentland in MSS. of 1832). The Illimani, which Pentland 

 estimated first at 7315 (23,973 feet), and afterward sat 6445 (21, 139 feet) 

 metres, has also been, since 1847, the object of a careful measurement 

 by the engineer Pissis, who, on the occasion of his great trigonometrical 

 survey of the Llanura de "Bolivia, found the Illimani to be on the ave- 

 rage 6509 metres (21,349 feet) in height, by three triangles between 

 Calamarca and La Paz : this only differs about 64 metres (210 feet) from 

 Pentland' s last determination. See Investigadones Sobre la Altitud de 

 los Andes, in the Anales de Chile, 1852, p. 217 and 221. 



