1835.] GEOLOGY OF THE CORDILLERA. 319 



we gain time, at all sufficient to explain the truly astonish- 

 ing" 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 6000 feet — so as to have allowed that amount of sub- 

 marine 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 supposition 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 

 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 Httio 

 difficulty in our respiration. The mules would halt every 

 fifty yards, and after resting for a few seconds the poor 

 willing animals started of their own accord again. TIk- 

 short breathing from the rarefied atmosphere is called by 

 the Chilenos "puna"; and they have most ridiculous 

 notions concerning its origin. Some say, " all the waters 



