332 



USPALLATA PASS. [chap. xv. 



six thousand feet above the sea. This range has nearly the 

 same geographical position with respect to the Cordillera, which 

 the gigantic Portillo line has, but it is of a totally different 

 origin : it consists of various kinds of submarine lava, alternat- 

 ing with volcanic sandstones and other remarkable sedimentary 

 deposits; the whole having a very close resemblance to some 

 of the tertiary beds on the shores of the Pacific. From this 

 resemblance I expected to find silicified wood, which is generally 

 characteristic of those formations. I was gratified in a very ex- 

 traordinary manner. In the central part of the range, at an 

 elevation of about seven thousand feet, I observed on a bare slope 

 some snow-white projecting columns. These were petrified 

 trees, eleven being silicified, and from thirty to forty converted 

 into coarsely-crystallized white calcareous spar. They were 

 abruptly broken off, the upright stumps projecting a few feet 

 above the ground. The trunks measured from three to five feet 

 each in circumference. They stood a little way apart from each 

 other, but the whole formed one group. Mr. Robert Brown has 

 been kind enough to examine the wood : he says it belongs to the 

 fir tribe, partaking of the character of the Araucarian family, 

 but with some curious points of affinity with the yew. The 

 volcanic sandstone in which the trees were embedded, and from 

 the lower part of which they must have sprung, had accumulated 

 in successive thin layers around their trunks ; and the stone yet 

 retained the impression of the bark. 



It required little geological practice to interpret the marvel- 

 lous 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 sub- 

 sequently 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 sedimen tary 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 



