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Updated: June 24, 2025
These conformably stratified porphyries, though none are either vesicular are amygdaloidal, have evidently flowed as submarine lavas: some of them are separated from each other by seams of indurated tuff, which, however, are quite insignificant in thickness compared with the porphyries.
Elena, Camerones, Malaspina, and as far south as the Paps of Pineda, is a purplish-pink or brownish claystone porphyry, sometimes laminated, sometimes slightly vesicular, with crystals of opaque feldspar and with a few grains of quartz; hence these porphyries resemble those immediately to be described at Port Desire, and likewise a series which I have seen from P. Alegre on the southern confines of Brazil.
These garnets re-appear in the trachytic porphyries that crown the celebrated metalliferous mountain of Potosi, and in the black and pyroxenic masses of the small volcano of Yana-Urca, at the back of Chimborazo.
Bed 4; a dull purplish-red, hard conglomerate, with crystallised particles and veins of carbonate of lime, from three hundred to four hundred feet in thickness. The pebbles are of claystone porphyries of many varieties; they are tolerably well rounded, and vary in size from a large apple to a man's head.
The gravel-bed near the Rio Negro is, on an average, about ten or twelve feet in thickness; and the pebbles are larger than on the northern side of the Colorado, being from one or two inches in diameter, and composed chiefly of rather dark-tinted porphyries.
This, Sloggett explained, was the characteristic flame of both cyanogen and hydrocyanic acid vapour, which, being inflammable, may have become locally ignited in the passage over cities, and only burned in that limited and languid way on account of the ponderous volumes of carbonic anhydride with which they must, of course, be mixed: the dark empurpled colour was due to the presence of large quantities of the scoriae of the trappean rocks: basalts, green-stone, trachytes, and the various porphyries.
We saw gold, silver, copper, tin, and iron, as well as metals which were quite new to us. Some of these had a purple, blue, or green colour, and emitted a most agreeable fragrance. There are granites and porphyries, marbles and petrifactions of the most exquisite grain or tints.
If well polished it fully equals many of the highly prized antique porphyries. The dyke is of great thickness and runs for fully a mile, so is practically inexhaustible. Blocks of very large size could be raised, and from the situation of the dyke on the side of two steep hills, it would be very easy to open up large quarries if needful."
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.
The lower beds of the Peuquenes ridge, and of the several great lines to the westward of it, are composed of a vast pile, many thousand feet in thickness, of porphyries which have flowed as submarine lavas, alternating with angular and rounded fragments of the same rocks, thrown out of the submarine craters.
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