XV 
SI LI ClFI ED TREES 
355 
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 of that 
ocean, forming 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 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. 
