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CHAPTEE IX. 



THE MEXICAN PLATEAUS, AND THE SLOPES OF SIKKIM. 



Geological Formation of Mexico — The Tierra Caliente— The Ticrra Tempi ada 

 The Ticrra Fria. 



The Sylvan Wonders of Sikkim — Changes of the Forest on ascending — The 

 Torrid Zone of Vegetation — The Temperate Zone — The Coniferous Belt — 

 Limits of Arboreal Vegetation — Animal Life. 



THE prodigious height attained in the torrid zone, not only 

 by single mountains, but by vast tracts of land, and the 

 diminution of temperature, which is the necessary consequence 

 of their elevation above the level of the sea, enable the in- 

 habitants of many tropical countries, without leaving their native 

 land, to view the vegetable forms of every zone, and to pluck 

 nearly every fruit that is found between the equator and the 

 arctic circle. In Asia, Africa, and America, in the islands of 

 the Indian Archipelago, and in the Hawaian group, where the 

 Mauna Loa towers to the height of Mont Blanc, and girdles his 

 foot with palms, while snow rests for a great part of the year 

 upon his summit, we find numerous examples of a rapid transi- 

 tion from the torrid to the temperate or frigid zone, often mthin 

 the range of a single day's journey. 



It would far exceed the limits of a popular work were I to 

 attempt to follow all these gradations of climate throughout 

 the wide extent of the tropics ; but a short description of the 

 Mexican plateaus, and of the slopes of Sikkim, which I have 

 selected as remarkable instances of the wonderful change of 

 vegetation resulting from the progressive elevation of the land, 

 will, I hope, prove not uninteresting to the reader. 



After traversing South America and the Isthmus of Darien, 



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