TRUE VOLCANOES. 379 



Sounds. Analogies drawn in Europe from the Pyrenees or 

 the Alpine chain, and in South America from the Cordilleras 

 of the Andes, from South Chili to the fifth degree of north 

 latitude in New Granada, supported by fanciful delineations 

 in maps, have propagated, the erroneous opinion that the 

 Mexican mountains, or at least their highest ridge, can be 

 traced along like a wall, under the name of the Sierra Madre, 

 from southeast to northwest. But though the mountainous 

 part of Mexico is a mighty swelling of the land running con- 

 nectedly in the direction above stated between two seas to 

 the height of from 5000 to 7000 feet, yet on the top of this, 

 in the same way as in the Caucasus and in Central Asia, 

 still loftier ranges of mountains, running in partial and very 

 various directions, rise to about 15,000 and 17,800 feet. 

 The arrangement of these partial groups, erupted from fis- 

 sures not parallel to each other, is in its bearings for the most 

 part independent of the ideal axis which may be drawn 

 through the entire swell of the undulating flattened ridge. 

 These remarkable features in the formation of the soil give 

 rise to a deception which is strengthened by the pictorial 

 effect of the beautiful country. The colossal mountains cov- 

 ered with perpetual snow, seem, as it were, to rise out of a 

 plain. The spectator confounds the ridge of the soft swell- 

 ing land, the elevated plain, with the plain of the low lands ; 

 and it is only from the change of climate, the lowering of the 

 temperature, under the same degree of latitude, that he is re- 

 minded of the height to w r hich he has ascended. The fissure 

 of upheaval, frequently before mentioned, of the volcano of 

 Anahuac (running in a direction from east to west between 

 19° and 19^° lat.) intersects* the general axis of the swell- 

 ing land almost at right angles. 



The conformation here described of a considerable portion 

 of the surface of the earth, which only began to be estab- 

 lished by careful measurements since the year 1853, must 

 not be confounded with those swellings of the soil which are 

 met with inclosed between two mountain chains, wdiich bound 

 them, as it were, like walls — as in Bolivia, at the Lake of 

 Titicaca; and in Central Asia, between the Himalaya and 

 Ivuen-liin. The former of these, the South American eleva- 

 tion, which at the same time forms the bottom of a valley, 



* On the axes of the greatest elevations and of the volcanoes in the 

 tropical zone of Mexico, see above, p. 2(54 and .'500. Compare also 

 Essai Pol sur laNouv. J£sj>., t. i., p. 257-2G8, t. ii., p. 173; Views of 

 Nature, p. 37. 



