380 CHARLES DARWIN 



there a few years previously ; in some parts, beds of sand and 

 gravel were spread out; in others, the solid rock had been 

 worn into a broad channel, which in one spot was about 40 

 yards in breadth and 8 feet deep. It is self-evident that a 

 person following up the course of a stream, will always 

 ascend at a greater or less inclination: Mr. Gill, therefore, 

 was much astonished, when walking up the bed of this 

 ancient river, to find himself suddenly going down hill. He 

 imagined that the downward slope had a fall of about 40 or 

 50 feet perpendicular. We here have unequivocal evidence 

 that a ridge had been uplifted right across the old bed of a 

 stream. From the moment the river-course was thus arched, 

 the water must necessarily have been thrown back, and a new 

 channel formed. From that moment, also, the neighbouring 

 plain must have lost its fertilizing stream, and become a 

 desert. 



June 2?th. We set out early in the morning, and by mid- 

 day reached the ravine of Paypote, where there is a tiny rill 

 of water, with a little vegetation, and even a few algarroba 

 trees, a kind of mimosa. From having fire-wood, a smelting- 

 furnace had formerly been built here: we found a solitary 

 man in charge of it, whose sole employment was hunting 

 guanacos. At night it froze sharply; but having plenty of 

 wood for our fire, we kept ourselves warm. 



28th. We continued gradually ascending, and the valley 

 now changed into a ravine. During the day we saw several 

 guanacos, and the track of the closely-allied species, the 

 Vicuna: this latter animal is pre-eminently alpine in its 

 habits; it seldom descends much below the limit of perpetual 

 snow, and therefore haunts even a more lofty and sterile 

 situation than the guanaco. The only other animal which we 

 saw in any number was a small fox: I suppose this animal 

 preys on the mice and other small rodents, which, as long as 

 there is the least vegetation, subsist in considerable numbers 

 in very desert places. In Patagonia, even on the borders of 

 the salinas, where a drop of fresh water can never be found, 

 excepting dew, these little animals swarm. Next to lizards, 

 mice appear to be able to support existence on the smallest 

 and driest portions of the earth even on islets in the midst 

 of great oceans. 



