TRUE VOLCANOES. 405 



whole earth, we ought rather to say the circumference of the 

 largest of those portions oi it which penetrate between con- 

 tinents) it remains for us now to describe the tract of country 

 which extends from Rio Gila to Norton's and Kotzebue's 

 Sounds. Analogies drawn in Euro] e 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 lati- 

 tude in New Grenada, supported by tanciful delineations in 

 maps, have propagated the erroneous opinion that the Mexi- 

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

 along like a wail, under the name of the Sierra Madre, from 

 south-east to north- west. But though the mountainous 

 part of Mexico is a mighty swelling of the land running 

 connectedly 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 irom fissures 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 undu- 

 lating 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 covered with perpetual snow seem as it 

 were, to rise out of a plain. The spectator confounds the 

 ridge of the soft swelling 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 reminded of the height to 

 which 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.) inter- 

 sects 10 the general axis of the swelling land almost at right 

 angles. 



Marchand, confounds the whole with a part, and consequently leads 

 to misapprehension. 



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

 the tropical zone of Mexico, see above pp. 279 and 319. Compare 

 also Essai Pol. sur la Nouv.-Etp. t. i, pp. 257268, t. ii, p. 173 ; Vieic* 

 of Nature, p. 37. 



