March, 1835. passage of cordillera. 



399 



state of atmospheric dryness. The latter quaUty was shown 

 by the manner in which woodwork shrunk (as I soon found 

 by the trouble my geological hammer gave me) ; by articles 

 of food, such as bread and sugar, becoming extremely hard ; 

 and by the preservation of the skin and parts of the flesh of 

 the beasts, which perish on the road. To the same cause we 

 must attribute the singular facihty with which electricity is 

 excited. My flannel-waistcoat, when rubbed in the dark, 

 appeared as if it had been v/ashed with phosphorus ; — every 

 hair on a dog's back crackled ; — even the linen sheets, and 

 leathern straps of the saddle, when handled, emitted sparks. 



March 23d. — The descent on the eastern side of the Cor- 

 dillera is much, shorter or steeper than on the Pacific side ; 

 in other words, the mountains rise more abruptly from the 

 plains, than from the alpine country of Chile. A level and 

 brilliantly white sea of clouds was extended beneath our feet, 

 and thus shut out the view of the equally level Pampas. 

 We soon entered the band of clouds, and did not again 

 emerge from it that day. About noon, finding pasture for 

 the animals and bushes for firewood, in a part of the valley 

 called Los Arenales, we stopped for the night. This was 

 near the uppermost limit of bushes, and the elevation, I 

 suppose, was between seven and eight thousand feet. 



I was very much struck with the marked difference between 

 the vegetation of these eastern valleys and that of the oppo- 

 site side : yet the climate, as well as the kind of soil, is nearly 

 identical, and the difference of longitude very trifling. The 

 same remark holds good with the quadrupeds, and in a lesser 

 degree with the birds and insects. We must except certain 

 species which habitually or occasionally frequent elevated 

 mountains ; and in the case of the birds, certain kinds, which 

 have a range as far south as the Strait of Magellan. This 

 fact is in perfect accordance with the geological history of 

 the Andes ; for these mountains have existed as a great 

 barrier, since a period so remote that whole races of animals 

 must subsequently have perished from the face of the earth. 

 Therefore, unless we suppose the same species to have been 



