3i8 GEOLOGY OF THE CORDILLERA, [chap. xv. 



covered in the central parts, by a great thickness of 

 red sandstone, conglomerate, and calcareous clay-slate, 

 associated with, and passing into, prodigious beds of 

 gypsum. In these upper beds shells are tolerably frequent ; 

 and they belong to about the period of the lower chalk of 

 Europe. It is an old story, but not the less wonderful, to 

 hear of shells which were once crawling on the bottom of 

 the sea, now standing nearly 14,000 feet above its level. 

 The lower beds in this great pile of strata have been dis- 

 located, baked, crystallised, and almost blended together, 

 through the agency of mountain masses of a peculiar white 

 soda-granitic rock. 



The other main line, namely, that of the Portillo, is of a 

 totally different formation ; it consists chiefly of grand bare 

 pinnacles of a red potash-granite, which low down on the 

 western flank are covered by a sandstone, converted by the 

 former heat into a quartz-rock. On the quartz, there rests 

 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 Peuquenes line. I was astonished 

 to find 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 in- 

 jected 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 



