ILLUSTRATIONS (5). MOUNTAIN-CHAIN. 43 



extent the distance which, in the old continent, separates the 

 Pillars of Hercules from the Icy Cape of the Tschuktches, in 

 the north-east of Asia. Where the Andes are divided into 

 several parallel chains, those lying nearest the sea are found 

 to be the seat of the most active volcanoes ; and it has more- 

 over been repeatedly observed that when the phenomenon 

 of an eruption of subterranean fire ceases in one mountain 

 chain, it breaks forth in some other parallel range. The 

 cones of eruption usually follow the direction of the axis 

 of the chain; but in the Mexican table-land, the active vol- 

 canoes are situated on a transverse fissure, running from sea 

 to sea, in a direction from east and west* Wherever the 

 upheaval of mountain masses in the folding of the ancient 

 crust of the earth has opened a communication with the 

 fused interior, volcanic activity continued to be exhibited on 

 the murally upheaved mass by means of the ramification of 

 fissures. That which we call a mountain chain has not been 

 raised to its present elevation, or manifested as it now ap- 

 pears, at one definite period ; for we find that rocks, varying 

 considerably in age, have been superimposed on one another, 

 and have penetrated towards the surface through early formed 

 channels. The diversity observable in rocks is owing to the 

 outpouring and upheaval of rocks of eruption, as well as to 

 the complicated and slow process of metamorphism going on 

 in fissures filled with vapour, and conducive to the conduction 

 of heat. 



The following have for a long time, viz., from 1830 to 

 1848, been regarded as the highest or culminating points of 

 the Cordilleras of the new continent : — 



The Nevado de Sorata, also called Ancohuma or Tusuba} T a 

 (15° 52' south lat.), somewhat to the south of the village of 

 Sorata or Esquibel, in the eastern chain of Bolivia : elevation, 

 25,222 feet. 



The Nevado de Illimani, west of the mission of Yrupana 

 (16° 38 south lat.), also in the eastern chain of Bolivia: ele- 

 vation, 24,000 feet. 



The Chimborazo (1° 27' south lat.), in the province of Quito: 

 elevation, 21,422 feet. 



The Sorata and Illimani were first measured by the dis- 

 tinguished geologist, Pentland, in the years 1827 and 1838; 

 * Humboldt, Essai politique, t. ii. p. 173. 



