354 USPALLATA PASS 



basin, like those so often mentioned in Chile, but higher, being- 

 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, 

 alternating 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 

 o-enerally characteristic of those formations. I was gratified in 

 a very extraordinary 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- crystallised 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 }et 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 

 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 



