THE VOYAGE OF THE BEAGLE 351 



berless dwarf cacti, armed with formidable spines, and called 

 by the inhabitants " little lions." There were, also, a few 

 low bushes. Although the plain is nearly three thousand feet 

 above the sea, the sun was very powerful ; and the heat, as 

 well as the clouds of impalpable dust, rendered the travelling 

 extremely irksome. Our course during the day lay nearly 

 parallel to the Cordillera, but gradually approaching them. 

 Before sunset we entered one of the wide valleys, or rather 

 bays, which open on the plain: this soon narrowed into a 

 ravine, where a little higher up the house of Villa Vicencio 

 is situated. As we had ridden all day without a drop of 

 water, both our mules and selves were very thirsty, and we 

 looked out anxiously for the stream which flows down this 

 valley. It was curious to observe how gradually the water 

 made its appearance : on the plain the course was quite dry ; 

 by degrees it became a little damper; then puddles of water 

 appeared ; these soon became connected ; and at Villa Vicen- 

 cio there was a nice little rivulet. 



30th. The solitary hovel which bears the imposing name 

 of Villa Vicencio, has been mentioned by every traveller who 

 has crossed the Andes. I stayed here and at some neigh- 

 bouring mines during the two succeeding days. The geology 

 of the surrounding country is very curious. The Uspallata 

 range is separated from the main Cordillera by a long nar- 

 row 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 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 generally 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-crystallized white calcareous spar. They were ab- 



