70 GEOLOGY OF THE CORDILLERA. 



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 Por- 

 tillo 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 east- 

 ern 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 sufficient 

 to explain the truly astonishing amount of denu- 

 dation which these great, though, comparatively 

 with most other ranges, recent mountains have suf- 

 fered. 



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 Coi-dillera must have subsi- 

 ded several thousand feet — in northera 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 peiiod since the tertiary shells of 



