183.;.] GEOLOGY OF THE COEDILLERA. 307 



rock. On the quartz, there rest beds of a conglomerate several 

 thousand feet in thickness, which have been upheaved by the red 

 granite, and dip at an angle of 45 towards the Peuqiaenes line. I 

 was astonished to lind that this conglomerate was partly composed 

 of pebbles, derived from the rocks, with their fossil shells, of the 

 Peuquenes range; and partly of red potash-granite, like that of 

 the Portillo. Hence we must conclude, that both the Peuquenes 

 and Portillo ranges were partially upheaved and exposed to wear 

 and tear, when the conglomerate was forming ; but as the beds of 

 the conglomerate have been thrown off at an angle of 45 by the 

 red Portillo granite (with the underlying sandstone baked by it), 

 we may feel sure, that the greater part of the injection and upheaval 

 of the already partially formed Portillo line, took place after the 

 accumulation of the conglomerate, and long after the elevation of 

 the Peuquenes ridge. So that the Portillo, the loftiest line in this 

 part of the Cordillera, is not so old as the less lofty line of the 

 Peuquenes. Evidence derived from an inclined stream of lava at 

 the eastern base of the Portillo, might be adduced to show, that it 

 owes part of its great height to elevations of a still later date. 

 Looking to its earliest origin, the red granite seems to have been 

 injected on an ancient pre-existing line of white granite and mica- 

 slate. In most parts, perhaps in all parts, of the Cordillera, it may 

 be concluded that each line has been formed by repeated upheavals 

 and injections ; and that the several parallel lines are of different 

 ages. Only thus can we gain time, at all siifficient to explain the 

 truly astonishing amount of denudation, which these great, though 

 comparatively with most other ranges recent, mountains havo 

 suffered. 



Finally, the shells in the Peuquenes or oldest ridge, prove, as 

 before remarked, that it has been upraised 14,000 feet since a 

 Secondary period, which in Europe we are accustomed to consider 

 as far from ancient ; but since these shells lived in a moderately 

 deep sea, it can be shown that the area now occupied by the 

 Cordillera, must have subsided several thousand feet in northern 

 Chile as much as 6000 feet so as to have allowed that amount of 

 submarine strata to have been heaped on the bed on which the 

 shells lived. The proof is the same with that by which it was 

 shown, that at a much later period since the tertiary shells of 

 Patagonian lived, there must have been there a subsidence of 

 several hundred feet, as well as an ensuing elevation. Daily it is 



