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1835.] GEOLOGY OF THE CORDILLERA. 



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 con- 

 sider 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 subsi- 

 dence of several hundred feet, as well as an ensuing elevation. 

 Daily it is forced home on the mind of the geologist, that no- 

 thing, 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 supposition of the sub- 

 sequent 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 transverse breaks which connect the longitudinal 

 channels, are very strong, so that in one transverse channel even 

 a small vessel under sail was whirled round and round. 



About noon we began the tedious ascent of the Peuquenes 

 ridge, and then for the first time experienced some little difficulty 

 in our respiration. The mules would halt every fifty yards, and 



Y 



