THE VOYAGE OF THE BEAGLE 343 



regions, and thus lose part of that easterly movement which 

 it otherwise would have gained from the earth's rotation. At 

 Mendoza, on the eastern foot of the Andes, the climate is 

 said to be subject to long calms, and to frequent though false 

 appearances of gathering rain-storms: we may imagine that 

 the wind, which coming from the eastward is thus banked up 

 by the line of mountains, would become stagnant and irregu- 

 lar in its movements. 



Having crossed the Peuquenes, we descended into a moun- 

 tainous country, intermediate between the two main ranges, 

 and then took up our quarters for the night. We were now 

 in the republic of Mendoza. The elevation was probably not 

 under 11,000 feet, and the vegetation in consequence exceed- 

 ingly scanty. The root of a small scrubby plant served as 

 fuel, but it made a miserable fire, and the wind was 

 piercingly cold. Being quite tired with my day's work, I 

 made up my bed as quickly as I could, and went to sleep. 

 About midnight I observed the sky became suddenly clouded : 

 I awakened the arrierO to know if there was any danger of 

 bad weather ; but he said that without thunder and lightning 

 there was no risk of a heavy snow-storm. The peril is 

 imminent, and the difficulty of subsequent escape great, to 

 any one overtaken by bad weather between the two ranges. 

 A certain cave offers the only place of refuge: Mr. Cald- 

 cleugh, who crossed on this same day of the month, was 

 detained there for some time by a heavy fall of snow. Casu- 

 chas, or houses of refuge, have not been built in this pass 

 as in that of Uspallata, and, therefore, during the autumn, 

 the Portillo is little frequented. I may here remark that 

 within the main Cordillera rain never falls, for during the 

 summer the sky is cloudless, and in winter snow-storms alone 

 occur. 



At the place where we slept water necessarily boiled, from 

 the diminished pressure of the atmosphere, at a lower tem- 

 perature than it does in a less lofty country; the case being 

 the converse of that of a Papin's digester. Hence the pota- 

 toes, after remaining for some hours in the boiling water, 

 were nearly as hard as ever. The pot was left on the fire 

 all night, and next morning it was boiled again, but yet the 

 potatoes were not cooked. I found out this, by overhearing 



