chap. x. in the Valleys of the Co7'dillera. 293 



small proportion of these fragments, and those few well 

 rounded. 



I particularly attended to the appearance of the 

 terraces where the valleys made abrupt and considerable 

 bends, but I could perceive no difference in their struc- 

 ture : they followed the bends with their usual nearly 

 equable inclination. I observed, also, in several 

 valleys, that wherever large blocks of any rock became 

 numerous, either on the surface of the terrace or em- 

 bedded in it, this rock soon appeared higher up in situ : 

 thus I have noticed blocks of porphyry, of andesitic 

 syenite, of porphyry and of syenite, alternately becoming 

 numerous, and in each case succeeded by mountains 

 thus constituted. There is, however, one remarkable 

 exception to this rule ; for along the valley of the 

 Cachapual, M. Gay found numerous large blocks of 

 white granite, which does not occur in the neighbour- 

 hood : I observed these blocks, as well as others of 

 andesitic syenite (not occurring here in situ), near the 

 baths of Cauquenes at a height of between 200 and 300 

 feet above the river, and therefore quite above the 

 terrace or fringe which borders that river ; some miles 

 higher up the valleys there were other blocks at about 

 the same height : I also noticed, at a less height, just 

 above the terrace, blocks of porphyries (apparently not 

 found in the immediately impending mountains), 

 arranged in rude lines, as on a sea-beach. All these 

 blocks were rounded, and though large, not gigantic, 

 like the true erratic boulders of Patagonia and Fuegia 

 M. Gay l states that granite does not occur in situ 

 within a distance of twenty leagues ; I suspect, for 

 several reasons, that it will ultimately be found at a 



1 4 Annales des Scienc. Nat.' (I. series, torn. 28). M. Gay, as I 

 was informed, penetrated the Cordillera by the great oblique valley 

 of Los Cupressos, and not by the most direct line. 



