310 PORTILLO PASS. [cn.\r. xv. 



first it appears rather surprising, that the trade-wind along the 

 northern parts of Chile and on the coast of Peru, should blow in so 

 very southerly a direction as it does ; but when we reflect that the 

 Cordillera, running in a north and south line, intercepts, like a 

 great wall, the entire depth of the lower atmospheric current, we 

 can easily see that the trade-wind must be drawn northward, fol- 

 lowing the line of mountains, towards the equatorial 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 : 

 wo may imagine that the wind, which coming from the eastward is 

 thus banked up by the line of mountains, would become stagnant 

 and irregular in its movements. 



Having crossed the Peuquenes, we descended into a mountainous 

 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 exceedingly 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. Caldcleugh, who crossed on this same day 

 of the month, was detained there for some time by a heavy fall of 

 snow. Casuchas, 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 temperature than 

 it does in a less lofty country ; the case being the converse of that 

 of a Papin's digester. Hence the potatoes, after remaining for some 

 hours in the boiling water, were nearly as hard as ever. The pot 



