SOUTH AMERICAN DESERTS. 403 



and condensed the vapours with which the trade winds 

 are charged. Were it not for the accumulations of 

 snow collected upon the mountain tops, it may be very 

 safely assumed that a great deal of the western coast 

 would quickly be converted into uninhabitable desert; 

 for the plains of Peru and Bolivia, which lie to the 

 westward of the Andes, are watered almost exclusively 

 by the streams issuing from their gorges, which are 

 fed by the melting snows. 



By their agency, considerable areas lying between 

 the western spurs of the mountains, are irrigated ; 

 here luxuriant forests spring from the deep and fertile 

 soil, which however are of distinctly malarious char- 

 acter. This occurrence of highly malarious districts, 

 extending along the foot-hills of mountain ranges, 

 seems to be general everywhere in countries where 

 warm sunshine is prevalent. 



Malarial fevers of a serious nature are therefore a 

 thing which a traveller should always anticipate, and 

 be on his guard against, when approaching such 

 localities. 



Once the rivers pass out into the plains however, 

 fertility is mostly restricted to a narrow belt of alluvial 

 land, bordering upon their banks, while the remainder 

 of the country but too often presents an exceedingly 

 barren appearance. 



"The districts between the river valleys," says the Encyclopedia 

 Britannica in its article on Peru, " vary in extent, the largest 

 being upwards of 70 miles across. On their western margin 

 steep cliffs generally rise from the sea, above which is the 

 'Tablazo' or plateau, the whole appearing quite bare of 

 vegetation." * 



* EncycL Brit., gth Edition, Vol. xviii, p. 760 (Article "Peru"). 



