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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.
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.
The lava-streams at the eastern foot of the Portillo are interesting, not so much from the great denudation which they have suffered at a comparatively late period as from the evidence they afford by their inclination taken conjointly with their thickness and compactness, that after the great range had assumed its present general outline, it continued to rise as an axis of elevation.
Traces of Indian habitations have been discovered in many other parts, where it does not appear probable that they were used as mere resting-places, but yet where the land is as utterly unfit for any kind of cultivation, as it is near the Tambillos or at the Incas Bridge, or in the Portillo Pass, at all which places I saw ruins.
Traces of Indian habitations have been discovered in many other parts, where it does not appear probable that they were used as mere resting-places, but yet where the land is as utterly unfit for any kind of cultivation as it is near the Tambillos or at the Incas Bridge, or in the Portillo Pass, at all which places I saw ruins.
To the west and east the wall has broken down, but the Fortaleza, as the Canary men call it, stands yet, scarred into chimneys, shining, half glassy, half like fired clay. And further to the east, beyond the gap called the Portillo, the cliffs rise again as one follows the trail over that high desert to Vilaflor. White pumice lies under these cliffs, looking like a beach.
Concluding remarks on the denudation and elevation of the Portillo line. Section by the Cumbre, or Uspallata Pass. Porphyries. Gypseous strata. Section near the Puente del Inca; fossils of. Great subsidence. Intrusive porphyries. Plain of Uspallata. Section of the Uspallata chain. Structure and nature of the strata. Silicified vertical trees. Great subsidence. Granitic rocks of axis.
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.
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.
Eden states that in the year 1705 he saw little flames, which, according to the doctrine of the naturalists of his time, he attributes to sulphurous exhalations igniting spontaneously. We continued to ascend, till we came to the rock of La Gayta and to Portillo: traversing this narrow pass between two basaltic hills, we entered the great plain of Spartium.
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