GRADATIONS OF TROPICAL CLIMATE 13 



the want of moisture, the vast region traversed by the mighty 

 Ainazon with its thousand tributary streams, and the gorgeous 

 vegetation of the primitive forest, exhibit no less striking 

 pictures of the fertility which abundant rain, together with 

 lieat, produces in the equatorial lands. 



The slopes of SikJcim and the terraced plateaus of Mexico 

 will show us a gradual change of vegetation as we advance 

 from the sea-borde to the higher mountainous regions, — the 

 frigid, the temperate, and the torrid zones being, as it were, 

 superposed one above the other; and while in the Puna, or 

 liigli table-lands of Peru and Bolivia, we find the rigours of the 

 north transported under the line, the influence of the alter- 

 iiMting dry and rainy seasons appears on a magnificent scale in 

 the vast Llanos of Venezuela and Guiana, to which I shall now 

 introduce the reader. 



