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Show 398 PASSAGE OF COltDILLEI~i\. March, 1835. suppose that the animal fell with i~s head downward into a hole, when the stratum was contmuous, and that afterwards the surrounding parts were removed by the thaw. When nearly on the crest of the Portillo, we were enveloped in a cloud which was falling, under the f~rm of minute frozen spicula. This was very unfortunate,. as It continued the whole day, and quite intercepted our VIew. The pass takes its name of Portillo from a ~arrow cleft or doorway on the highest ridge, through whiCh the ro~d pas~es. From this point, on a clear day, those vast plams whJC.h extend from the base of the mountains towards the Atlantic can be seen. We descended to the upper limit of vegetation, and found good quarters for the night under the shelter of some large fragments of rock. W ~ here met some passengers, who made anxious inquiries about the state of the road. Shortly after it was dark, the clouds suddenly cleared away; and the effect was quite magical. The great mountains, bright with the full moon, seemed impending over us on all sides, as if we had been buried at the bottom of some deep crevice. One morning also, very early, I witnessed the same striking effect. As soon as the clouds were dispersed, it froze severely; but as there was no wind, we slept very comfortably. The increased brilliancy of the moon and stars at this elevation, owing to the perfect transparency of the atmosphere, was very remarkable. Travellers having observed the difficulty of judging heights and distances amidst lofty mountains, have generally attributed it to the absence of objects of comparison. It appears to me that it is fully as much owing to this transparency, confounding different distances, and partly, likewise, to the novelty of an unusual degree of fatigue arising from a little exertion,-habit being thus opposed to the evidence of the senses. I am sure that this extreme clearness of the air gives a peculiar character to the landscape; all objects app~aring to be brought nearly into one plane, as in a drawing or panorama. 'rhe transparency is, I presume, owing to the equable and nearly perfect March, 1835. PASSAGE OF CORDILLERA. 399 -state of atmosph. eric d. ryness. The latter quali'ty wa s sh own by the manner m whiCh woodwork shrunk (as I soon found by the trouble my geological hammer gave me); by articles of food, such as bre~d and sugar, becoming extremely hard; and by the preservatiOn of the skin and parts of the fl h f the beasts, which perish on the road To the samP. es 0 . · ,_, cause we mu~t attnbute the singul~r facility with which electricity is excited. My flannel-waistcoat, when rubbed in the d k d 'f . ar , ap~eare as I It had been washed with phosphorus ;-every ha1r on a dog's back crackled ;-even the linen sheets, and leathern straps of the saddle, when handled, emitted sparks. MARCH 23n.-The descent on the eastern side of the C _ d'll . or 1 era IS much shorter or steeper than on the Pac'fi 'd . . I c s1 e, m ?ther words, the mountains rise more abruptly from the plams, than from the alpine country of Chile. A level and brilliantly white sea of clouds was extended beneath our feet and thus squt out the view of the equally level Pampas~ We soon ent~red the band of clouds, and did not again emerg~ from It that day. About noon, finding pasture for the ammals and bushes for firewood, in a part of the valley called Los Arenales, we stopped for the night. This was near the uppermost limit of bushes, and the elevation, I suppose, was between seven and eight thousand feet. I was very much struck with the marked difference between t~e v~getation of t~ese eastern valleys and that of the oppo~ Ite s~de: yet the cl~mate, as well as the kind of soil, is nearly Identical, and the difference of longitude very trifling. The same re~ark holds good with the quadrupeds, and in a lesser degr~e Wit~ the bi~ds and insects. We must except certain species whiCh habitually or occasionally frequent elevated mountains ; and in the case of the birds, certain kinds, which have a range as far south as the Strait of Magellan. This fact is in perfect accordance with the geological history of the Andes; for these mountains 'have existed as a great b . . . arner, smce a period so remote that whole races of animals must subsequently have perished from the face of the earth. Therefore, unless we suppose the same species to have been |