280 



The Realm of Nature 



CHAP. 



in the south. On the rainless short slope in the centre 

 nitrate of soda forms extensive deposits. 



359. Eastern Mountains and Low Plains. The long 

 slope of South America from the base of the Andes forms 

 one vast low plain stretching from north to south, the portion 

 of which, at a less elevation than 600 feet, is equal to two- 

 fifths of the continent. It is broken into three divisions 

 by two very gentle ridges stretching eastward from the 

 Andes. The northern and smaller swells up into the 

 High Plain of Guiana, which is cut into lines of heights, 

 known as the Sierra Parima, the Sierra Pacarai, cul- 

 minating in Roraima ( 312), and the Sierra Acaray. 

 The larger or High Plain of Brazil fills the whole eastern 

 outcurve. It is an upheaval of very ancient rock, which 

 has been cut by the valleys of numerous great rivers into a 

 medley of mountain masses, few of which exceed 3000 feet 

 in height. The Sea Range, under many names, runs along 

 the coast from 10 S. to 30 S., forming the steep seaward 

 slope of the High Plain. The eastern mountains contain 



FIG. 57. Section across South America on parallel of 18 S. Vertical scale 

 300 times the horizontal. Sea-level marked O. 



deposits of gold and of diamonds, and are covered in many 

 parts by fertile soil. Fig. 57 gives an idea of the form of 

 the slopes of South America on the parallel of 18 S. 



360. Orinoco Basin. The northern division of the Low 

 Plain is known as the Llano, and forms the basin of. the 

 Orinoco River, which is kept supplied with water by tribu- 



