390 KEACTION OF THE INTERIOR OF THE EARTH 



gies derived from Europe, from the chains of the 

 Pyrenees or the Alps, and from South America from 

 the Cordilleras of the Andes from the south of Chili to 

 the fifth degree of north latitude in New Granada, sup- 

 ported by fanciful representations in maps, have propa- 

 gated the erroneous opinion that the Mexican high 

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

 as a wall-like rampart, from south-east to north-west 

 under the name of a " Sierra Madre." In reality, how- 

 ever, the mountainous part of Mexico is a broad mighty 

 intumescence, which does indeed hold its way continu- 

 ously at a height of from 5300 to 7400 feet, in the 

 assigned direction, between the two seas ; but upon 

 which, as in the Caucasus and in Central Asia, loftier 

 volcanic mountain-systems following partial and very 

 different directions rise to above 15,000 and 17,800 feet. 

 The directions of these partial groups, which have broken 

 forth over fissures which are also not parallel with each 

 other, are for the most part independent of the ideal 

 axis which can be drawn through the middle of the 

 whole swelling wave of the flattened ridge. These 

 remarkable relations in the form of the ground, occa- 

 sion an illusion which heightens the picturesque effect of 

 this beautiful land. The giant mountains clothed with 

 perpetual snow appear to rise as from a plain. The 

 surface of the softly swelling undulation, or the " high 

 plain," is scarcely distinguished from the plains of the 

 lowlands; and it is only the climate, the diminished 

 temperature under the same parallel of latitude, which 

 reminds us that we have ascended. The often-men- 

 tioned elevation-fissure of the volcanoes of Anahuac 

 (running east and west between the parallels of 19 



