242 USPALLATA PASS. [CHAP. iv. 



story which this scene at once unfolded ; though I confess I was at 

 first so much astonished, that I could scarcely believe the plainest 

 evidence. I saw the spot where a cluster of fine trees once waved 

 their branches on the shores of the Atlantic, when that ocean (now 

 driven back 700 miles) came to the foot of the Andes. I saw that they 

 had sprung from a volcanic soil which had been raised above the 

 level of the sea, and that subsequently this dry land, with its upright 

 trees, had been let down into the depths of the ocean. In these depths, 

 the formerly dry land was covered by sedimentary beds, and these 

 again by enormous streams of submarine lava one such mass attaining 

 the thickness of a thousand feet ; and these deluges of molten stone 

 and aqueous deposits five times alternately had been spread out. The 

 ocean which received such thick masses, must have been profoundly 

 deep ; but again the subterranean forces exerted themselves, and I 

 now beheld the bed ot that ocean, torming a chain of mountains more 

 than seven thousand feet in height Nor had those antagonist forces 

 been dormant, which are always at work wearing down the surface 

 of the land : the great piles of strata had been intersected by many 

 wide valleys, and the trees, now changed into silex, were exposed 

 projecting from the volcanic soil, now changed into rock, whence 

 formerly, in a green and budding state, they had raised their lofty 

 heads. Now, all is utterly irreclaimable and desert ; even the lichen 

 cannot adhere to the stony casts of former trees. Vast, and scarcely 

 comprehensible as such changes must ever appear, yet they have all 

 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 fossiliferous strata of Europe and America. 



April ist. 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 crosse d 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 iull, 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 



