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The southern part of Wollaston Island and the whole of Hermite and Horn Islands, seem formed of cones of greenstone; the outlying islets of Il Defenso and D. Raminez are said to consist of porphyritic lava. Brooke's Paper in the "London Philosophical Magazine" volume 10. No recent volcanic district has been observed in any part of Tierra del Fuego.
Relations between ancient orifices of eruption and subsequent axes of injection. Iquique, Peru, fossils of, salt-deposits. Metalliferous veins. Summary on the porphyritic conglomerate and gypseous formations. Great subsidence with partial elevations during the cretaceo-oolitic period. On the elevation and structure of the Cordillera. Recapitulation on the tertiary series.
The highest peaks of the Cordillera appear to consist of active or more commonly dormant volcanoes, such as Tupungato, Maypu, and Aconcagua, which latter stands 23,000 feet above the level of the sea, and many others. The next highest peaks are formed of the gypseous and porphyritic strata, thrown into vertical or highly inclined positions.
From this point, great mountains of purplish and greenish, generally thinly stratified, highly porphyritic conglomerates, including many strata of amygdaloidal and greenstone porphyries, extend up the valley to the junction of the rivers Yeso and Volcan.
A narrow path winding under high rocks of porphyritic gneiss brought me to the cascade called the Saut de la Saule, where the river, divided into two branches by a vast block, leaps fifteen or twenty feet into a deep basin to whirl and boil with fury, then dashes onward down the stony channel, to leap again into the air and fall into another basin.
Within the horseshoe and close up to it stand the famous blue-stones, now twelve in number, but originally perhaps more. These stones are not so high as the trilithons, the tallest reaching only 7-1/2 feet. They are nearly all of porphyritic diabase.
With the exception of the grauwacke being here more abundant, and the clay-slate less altered, this formation closely resembles that unconformably underlying the porphyries at the western foot of this same range; and likewise that alternating with the porphyritic conglomerate in the main Cordillera.
My notes of our ride mention a great water-wheel: sections of porphyritic rocks, with enormous masses of alluvial soil lying upon them: steep ravines: arroyos, cut by mountain-streams, and forests of pine-trees a thoroughly Alpine district altogether. At Regla it became evident that our letter of introduction was not a mere complimentary affair.
Colour red, coarse-grained. Composed of Quartz, Feldspar, and Mica. Granite, Porphyritic. Colour light red. Both occurring in the bed of New Year's Creek, traversing it obliquely, and are visible for a few hundred yards only. This granite occurs about 16 miles from the Range in a N. by E. direction. Old Red Sandstone. Old Red Sandstone. Composition of D'Urban's group.
But when he further read that its capital was three million five hundred thousand, and that its total resources amounted to forty-seven million three hundred thousand dollars, his breath came in shorter gasps of excitement. He began to realize the colossal wealth which lay guarded behind the great porphyritic granite pillars. He also began to realize some new and as yet undefined responsibility.
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