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Updated: June 8, 2025
I am strengthened in this conclusion of there having been two distinct, great periods of subsidence, by reflecting on the thick mass of coarse stratified conglomerate in the valley of Tenuyan, between the Peuquenes and Portillo lines; for the accumulation of this mass seems to me, as previously remarked, almost necessarily to have required a prolonged subsidence; and this subsidence, from the pebbles in the conglomerate having been to a great extent derived from the gypseous or Neocomian strata of the Peuquenes line, we know must have been quite distinct from, and subsequent to, that sinking movement which probably accompanied the deposition of the Peuquenes strata, and which certainly accompanied the deposition of the equivalent beds near the Puente del Inca, in this line of section.
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.
Valparaiso. Portillo Pass. Sagacity of mules. Mountain-torrents. Mines, how discovered. Proofs of the gradual elevation of the Cordillera. Effect of snow on rocks. Geological structure of the two main ranges, their distinct origin and upheaval. Great subsidence. Red snow. Winds. Pinnacles of snow. Dry and clear atmosphere. Electricity. Pampas. Zoology of the opposite sides of the Andes. Locusts.
In the Cordillera of South America, nearly under the equator, glaciers once extended far below their present level. In central Chile I examined a vast mound of detritus with great boulders, crossing the Portillo valley, which, there can hardly be a doubt, once formed a huge moraine; and Mr.
We carried a good deal of food in case we should be snowed up, as the season was rather late for passing the Portillo. We rode during this day to the last, and therefore most elevated, house in the valley. The number of inhabitants became scanty; but wherever water could be brought on the land, it was very fertile.
When Saragossa was besieged by the French during the Peninsular War, she carried food every afternoon to the soldiers who were defending the batteries. One day the attack was so fierce, and the fire so deadly, that by the gate of Portillo not a single man was left alive to repulse the terrible enemy.
The Teniente dismounted, evidently with the intention of joining us, but soon got back again into his saddle, having experienced, as H. explained, "a sudden recurrence of palpitation." Rejoining my companions, I dismissed our guide with a reward which surprised him, and we pursued our way to the Portillo.
Central Chile. Basal formations of the Cordillera. Origin of the porphyritic clay-stone conglomerate. Andesite. Volcanic rocks. Section of the Cordillera by the Peuquenes are Portillo Pass. Great gypseous formation. Peuquenes line; thickness of strata, fossils of. Portillo line. Conglomerate, orthitic granite, mica-schist, volcanic rocks of.
When nearly on the crest of the Portillo, we were enveloped in a falling cloud 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 narrow cleft or doorway on the highest ridge, through which the road passes.
Caldcleugh, who crossed on this same day of the month, was detained there for some time by a heavy fall of snow. Casuchas, or houses of refuge, have not been built in this pass as in that of Uspallata, and therefore, during the autumn, the Portillo is little frequented.
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