SILICIFIED TREES. 85 



the two succeeding days. The geology of the sur- 

 rounding country is very curious. The Uspallata 

 range is separated from the main Cordillera by a 

 long, narrow plain or 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 diffei'ent origin : it consists of various kinds 

 of submarine lava, alternating with volcanic sand- 

 stones 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 for- 

 mations. 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 col- 

 umns. These were petrified trees, eleven being 

 silicified, and from thirty to forty converted into 

 coarsely-crystallized white calcareous spar. They 

 w^ere abruptly broken off, the upright stumps pro- 

 jecting a few feet above the ground. The trunks 

 measured fi-om three to five feet each in circumfer- 

 ence. They stood a little way apart from each 

 other, but the whole formed one group. Mr. Rob- 

 ert 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 aflfinity with the yew. The 

 volcanic sandstone in which the trees were embed- 

 ded, and from the lower part of which they must 

 have sprung, had accumulated in successive thin 

 layers around their trunks ; and the stone yet re- 

 tained the impression of the bark. 



It required little geological practice to interpret 



II. — H 



