1835.] GEOLOGY OF THE CORDILLERA. 233 



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 con- 

 clude, 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 sand- 

 stone baked by it), we may feel sure, that the greater part of the injec- 

 tion 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 sufficient to explain the truly astonishing amount of 

 denudation, which these great, though comparatively with most other 

 ranges recent, mountains have 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 6,000 

 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 Patagonia lived, there must have been 

 there a subsidence of several hundred feet, as well as an ensuing 

 elevation. Daily it is forced home on the mind of the geologist, that 

 nothing, not even the wind that blows, is so unstable as the level of the 

 crust of this earth. 



I will make only one other geological remark : although the Portillo 

 chain is here higher than the Peuquenes, the waters, draining the 

 intermediate valleys, have burst through it. The same fact, on a 

 grander scale, has been remarked in the eastern and loftiest line of the 

 Bolivian Cordillera, through which the rivers pass : analogous facts 

 have also been observed in other quarters of the world. On the sup- 

 position of the subsequent and gradual elevation of the Portillo line, 

 this can be understood ; for a chain of islets would at first appear, and, 

 as these were lifted up, the tides would be always wearing deeper and 

 broader channels between them At the present day, even in the most 

 retired Sounds on the coast of Tierra del Fuego, the currents in the 



