1835.] ACROSS THE RIO VACAS. 331 



occurred within a period, recent when compared with the 

 history of the Cordillera : and the Cordillera itself is 

 absolutely modern as compared with many of the fossil- 

 iferous strata of Europe and America, 



April 1st. — We crossed the Uspallata range, and at night 

 slept at the custom-house — the only inhabited spot on the 

 plain. Shortly before leaving the mountains, there was a 

 very extraordinary view ; red, purple, green, and quite 

 white sedimentary rocks, alternating with black lavas, were 

 broken up and thrown into all kinds of disorder by masses 

 of porphyry of every shade of colour, from dark brown 

 to the brightest lilac. It was the first view I ever saw, 

 which really resembled those pretty sections which geologists 

 make of the inside of the earth. 



The next day we crossed the plain, and followed the 

 course of the same great mountain stream which flows 

 by Luxan. Here it was a furious torrent, quite impassable, 

 and appeared larger than in the low country, as was the 

 case with the rivulet of Villa Vicencio. On the evening 

 of the succeeding day, we reached the Rio de las Vacas, 

 which is considered the worst stream in the Cordillera 

 to cross. As all these rivers have a rapid and short 

 course, and are formed by the melting of the snow, 

 the hour of the day makes a considerable difference in 

 their volume. In the evening the stream is muddy and 

 full, but about daybreak it becomes clearer and much 

 less impetuous. This we found to be the case with the 

 Rio Vacas, and in the morning we crossed it with little 

 difficulty. 



The scenery thus far was very uninteresting, compared 

 with that of the Portillo pass. Little can be seen beyond 

 the bare walls of the one grand, flat-bottomed valley, which 

 the road follows up to the highest crest. The valley and 

 the huge rocky mountains are extremely barren : during 

 the two previous nights the poor mules had absolutely 

 nothing to eat, for excepting a few low resinous bushes, 

 scarcely a plant can be seen. In the course of this day 

 we crossed some of the worst passes in the Cordillera, 

 but their danger has been much exaggerated. I was told 

 that if I attempted to pass on foot, my head would turn 

 giddy, and that there was no room to dismount ; but 1 

 did not see a place where an^ one might not have walked 

 over backwards, or got oflf his mule on either side. One 

 of the bad passes, called las Animas (the Souls), I had 



