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Show 392 PASSAGE OF CORDILLERA. March, 1835. action), I was astonished to find perfectly rounded masses of the black calcareous clay-slate with organic remains,-the same rock which I had just crossed in situ ori the Peuquenes. These phenomena compel us to arrive at the following conclusion :-that the Peuquenes existed as dry land for a long period anterior to the formation of the second range, and that, during this period, immense quantities of shingle were accumulated at its submarine flank. The action of a disturbing force then commenced : these more modern deposits were injected by dikes, altered by heat, and tilted towards the line whence, in the form of sediment and pebbles, they had originally proceeded,-thus making the offspring at first appear older than its parent. This second, grand, and subsequent line of elevation is parallel to the first and more ancient one. I will only make one other geological observation: the Portillo chain in the neighbourhood of the pass is rather more elevated than the Peuquenes, yet the waters of the intermediate district have burst a passage through it. On the supposition of a subsequent and gradual elevation of the second line, this can be understood ; for a chain of islets would at first appear, and as these were lifted up, the tides would always be working out deeper and broader channels between them. At the present day, even in the most retired sounds on the southern coast, the currents in the transverse breaks which connect the longitudinal channels, is so strong, that I have heard of one instance where a small vessel under sail was whirled round and round. Mr. Pentland,* when describing an hydrographical phenomenon of a nearly similar kind, but {)n an infinitely grander scale, which occurs in Bolivia, says, "This very curious fact, of rivers escaping through such an immense mountain-mass as the Bolivian Cordillera, is perhaps one of the most important points connected with the physical geography of this portion of the Andes, and deserves to be 1t Journal of the Royal Geograph. Society for 1835. March, 1835. PASSAGE OF CORDILLERA. 393 noticed at greater .length." It would be extremely rash to affirm that the eastern chain in Bolivia, like that of central Chile, must be of subsequent origin to the western one, or that nearer to the Pacific : but excepting through the explanation above offered, the circumstance that rivers flowing from a less elevated chain, should penetrate one far more lofty, appears to me quite inexplicable. About noon we began the tedious ascent of the Peuquenes, and then for the first time experienced some little difficulty in our respiration. The mules would halt every fifty yards, and then the poor willing animals after a few seconds started of their own accord again. The 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 here have puna;" others that "where there is snow there is puna ;"-and this no doubt is true. It is considered a kind of disease, and I was shown the crosses over the graves of some who had died "punado." Excepting perhaps in the case of a person suffering from some organic disease of the heart or chest, I should think this must be an erroneous conclusion. A person near death, would probably at this elevation experience a more unusual difficulty in breathing than others ; and hence the effect might be assumed as the cause. The only sensation I felt was a slight tightness over the head and chest; a feeling which may be experienced by leaving a warm room and running violently on a frosty day. There was much fancy even in this; for upon finding fossil shells on the highest ridge, I entirely forgot the puna in my delight. Certainly the exertion of walking was extreme, and the respiration became deep and laborious. It is incomprehensible to me, how Humboldt and others were able to ascend to the elevation of 19,000 fee~. No doubt a residence of some months in the lofty region of Quito would prepare the constitution for such an exertion; yet I am told that in Potosi (about 13,000 feet), strangers do not become quite accustomed to the atmosphere for an entire year. The inhabitants all recommend onions |