526 Section of the Uspal lata Range. paet n. 



evidently of sedimentary origin, and remarkable from 

 closely approaching in character to an imperfect pitch- 

 stone, and from including extremely thin layers of perfect 

 pitchstone, as well as nodules and irregular fragments 

 (but not resembling extraneous fragments) of this same 

 rock arranged in horizontal lines : I conceive that this 

 bed, which is only a few feet in thickness, must have 

 assumed its present state through metamorphic and 

 concretionary action. Most of these sedimentary strata 

 are much indurated, and no doubt have been partially 

 metamorphosed : many of them are extraordinarily 

 heavy and compact ; others have agate and crystalline 

 carbonate of lime disseminated throughout them. 

 Some of the beds exhibit a singular concretionary ar- 

 rangement, with the curves determined bv the lines of 

 fissure. There are many veins of agate and calcareous 

 spar, and innumerable ones of iron and other metals, 

 which have blackened and curiously affected the strata 

 to considerable distances on both sides. 



Many of these tufaceous beds resemble, with the 

 exception of being more indurated, the upper beds of 

 the great Patagonian Tertiary formation, especially 

 those variously coloured layers high up the river Santa 

 Cruz, and in a remarkable degree the tufaceous forma- 

 tion at the northern end of Chiloe. I was so much 

 struck with this resemblance, that I particularly looked 

 out for silicified wood, and found it under the following 

 extraordinary circumstances. High up on this western 

 flank, 1 at a height estimated at 7,000 feet above the 



1 For the information of any future traveller, I will describe the 

 spot in detail. Proceeding eastward from the Agua del Zorro, and 

 afterwards leaving on the north side of the road a rancho attached 

 to some old gold-mines, you pass through a gully with low but steep 

 rocks on each hand : the road then bends, and the ascent becomes 

 steeper. A few hundred yards farther on, a stone's throw on the 

 south side of the road, the white calcareous stumps may be seen. 

 The spot is about half a mile east of the Agua del Zorro. 



