122 THE ANDES OF SOUTHERN PERU 



oped important climatic features not found elsewhere in Peru. 

 The trade winds are greatly modified in direction and effects ; the 

 northward-trending valleys, so deep as to be secluded from the 

 trades, have floors that are nearly if not quite arid; a restricted 

 coastal region enjoys a heavier rainfall; and the snowline is much 

 more strongly canted from west to east than anywhere else in the 

 long belt of mountains from Patagonia to Venezuela. These ex- 

 ceptional features depend, however, upon precisely the same phys- 

 ical laws as the normal climatic features of the Peruvian Andes. 

 They can, therefore, be more easily understood after attention has 

 been given to the larger aspects of the climatic problem of which 

 they form a part. 



The critical relations of trade winds, lofty mountains, and 

 ocean currents that give distinction to Peruvian climate are shown 

 in Figs. 71 to 73. From them and Fig. 74 it is clear that the two 

 sides of the Peruvian mountains are in sharp contrast climatically. 

 The eastern slopes have almost daily rains, even in the dry season, 

 and are clothed with forest. The western leeward slopes are so 

 dry that at 8,000 feet even the most drought-resisting grasses 

 stop — only low shrubs live below this level, and over large areas 

 there is no vegetation whatever. An exception is the Coast 

 Eange, not shown on these small maps, but exhibited in the suc- 

 ceeding diagram. These have moderate rains on their seaward 

 (westerly) slopes during some years and grass and shrubby 

 vegetation grow between the arid coastal terraces below them 

 and the parched desert above. The greatest variety of climate is 

 enjoyed by the mountain zone. Its deeper valleys and basins de- 

 scend to tropical levels ; its higher ranges and peaks are snow-cov- 

 ered. Between are the climates of half the world compressed, it 

 may be, between 6,000 and 15,000 feet of elevation and with ex- 

 tremes only a day's journey apart. 



In the explanation of these contrasts we have to deal with rela- 

 tively simple facts and principles ; but the reader who is interested 

 chiefly in the human aspects of the region should turn to p. 138 

 where the effects of the climate on man are set forth. The 

 ascending trades on the eastern slopes pass successively into 



