CAUSES OF STEEILITY. I99 



miles. Extensive sea-beaches, at an elevation of over half 

 a mile, indicate long cessations in the action of the eleva- 

 tory forces, while the waves of the Pacific were beating 

 against and wearing down the rising wall of the Andes. 

 This great desert, extending from the sea to the foot of the 

 Coi'dilleras, stretches with a varying breadth of ten to 

 twenty leagues, from three degrees south of the equatorial 

 line to the northern portions of Chili, over the whole of the 

 Peruvian coast. The absence of rain upon this coast, and 

 its consequently arid aspect, are due to the proximity of 

 the lofty wall of the Andes, which eifectually arrests all 

 storm-clouds from the east, while the prevailing southerly 

 trade-winds drive all the vapors of the Pacific from the 

 coast. As has been often observed, had the physical con- 

 formation of South America been changed, the Andes be- 

 ing jDlaced along the Atlantic coast, the greater j^ortion 

 of the continent would have been swept by winds, de- 

 prived of all their moisture ; and, instead of South Ameri- 

 ca, with its teeming valley of the Amazons, we would have 

 had another Africa with its Libyan desert. But now the 

 Cordilleras, standing close to the Pacific shore, with their 

 cool heights acting as a " great condenser," wring every 

 drop of moisture from the clouds borne upon the equatorial 

 trade-winds fi-om the Atlantic, and throw down their 

 waters in torrential rains all along the eastern slope of 

 the Andes. South America owes what it is — a continent 

 of vegetation — to this mountain- wall along its western 

 border. As one looks up to the whitened summit of those 

 Cordilleras, lifted all along to the line of perpetual snow, 

 he is sometimes led to ask why they were raised so high. 

 The long desert coast-line returns an answer. They are 

 the great wall, lifted by a wise Creator to guard a conti- 

 nent and water the rich garden of the Amazons. As in 

 all of Nature's work we find a beautiful proportion and 

 harmony, we can conceive, before climbing that mountain- 



