CLIMATE OF PERU. 297 



east to west, finds free play only on the Montana and the Amazonian slopes. Here 

 it reveals itself in the moisture-charged clouds which it brings from the Atlantic, 

 and which precipitate such an abundant rainfall on the upland valleys. Beyond 

 the mountain barriers, over which it throws a snowy mantle, it penetrates to the 

 plateau through breaches in the outer rampart, and thus reaches the eastern slopes 

 of the successive ranges of Cordilleras, all of which receive their share of mois- 

 ture in the form of snow or rain. But the intervening valleys remain dry, and 

 travellers crossing the Puna meet by the wayside the carcasses of pack-animals 

 mummified in the dry cold air without showing any symptoms of decomposition. 



After surmounting the Western Cordillera the trade wind ascends into the 

 higher atmospheric regions, returning to the surface of the ocean at distances of 

 from 120 to 600 miles from the seaboard, according to the seasons and the nature 

 of the coastlands. Thus the intermediate spaces are again withdrawn from the 

 influence of the regular winds, and here the aerial currents set in diverse 

 directions. The light winds come especially from the high seas, either as return 

 currents of the trade winds striking the ocean far seawards, or as southern 

 breezes following the Humboldt current northwards. These cold breezes from 

 the polar seas are attracted landwards by the relatively high temperature of 

 the littoral plains and deserts. 



But the eastern rain-bearing clouds are intercepted by the crests of the 

 Cordillera, while the marine breezes have too restricted a range to take up 

 moisture to the point of saturation ; thus it happens that the Peruvian coastlands 

 receive very little rain, and certain districts, especially those that have earned the 

 title of " deserts," near Tumbez, south of Piura and Sechura, on the plains of lea 

 and the pampa of Tunga, come altogether within the rainless zone. When 

 Boussingault visited the northern coasts of Peru in 1832, no rain was said to have 

 fallen at Chocope for eighty-eight years. 



Nevertheless, the cordillera is low enough in these regions, which corresjDond 

 to the axis of the Amazons valley, to allow occasional passage through their gaps 

 to the moisture-laden trade winds. On such occasions the wilderness bursts into 

 verdure, and is brought by the inhabitants under temporary cultivation. But 

 twenty or thirty years pass in the Peruvian deserts without a single shower, and 

 the brazen firmament is unrelieved b}?- the endless forms of shifting clouds which 

 form the glory of the skies in most other regions of the globe. 



Haz}^ masses of vapour, however, are seen in the distance hanging over the 

 Ceja of the Sierra, and at sunset these vapours reflect the flashes of lightning 

 from storms too far off for their thunder to be heard. After a tempest in 1803 

 sixty-four years passed before the rattle of thunder was again heard by the 

 citizens of Lima. But towards the end of 1877 a fierce thunderstorm burst 

 over the place, accompanied by such a deluge of rain that it was feared it might 

 be completely washed away. A certain coincidence is said to have often been 

 observed between such downpours and the underground disturbances. 



Despite the lack of rain, the beds of the coast streams are not always waterless ; 

 in the region about their source they are fed by the snows of the cordillera, while 



