Vietnam or Thailand ? Vote for the TOP Country of the Week !
Updated: June 4, 2025
Hopkins, however, adds, that great irregularities and lateral thrusts might be expected in every great line of elevation, and that these would account for considerable deviations from the calculated results: considering that the granitic axis, as shown by the veins, has indisputably been injected after the perfect formation of the mica-slate, and considering the uniformity of the strike of the folia throughout the rest of the Archipelago, I cannot but still think that their anomalous position at this one point is someway directly and mechanically related to the intrusion of this W.N.W. and E.S.E. mountain-chain of granite.
Between Guasco and Copiapo, there are some siliceous and talcaceous slates cleaving in a north and south line, with an easterly dip of between 60 and 70 degrees: high up, also, the main valley of Copiapo, there is mica-slate with a high easterly dip. In the whole space between Valparaiso and Copiapo an easterly dip is much more common than an opposite or westerly one.
Farther to the south, the vast gulf Cariaco stretches away, like a longitudinal valley formed by the irruption of the sea, between the two small chains of Araya and the Cocollar, between the mica-slate and the Alpine limestone. We shall soon see that the direction of the strata, very regular in the first of these rocks, is not quite parallel with the general direction of the gulf.
In the Little Crau, the mouth of the Durance, are found prodigious numbers of green and crystalline rocks, granite and variolite brought down from the Alps of Briancon, but nine-tenths of the pebbles of the Great Crau are white quartz brought from the great chain of the Alps, together with mica-slate and calcareous stones, and only a few of the variolites of Mont Genevre.
The gneiss, the constituent parts of which are in a state of considerable disintegration, contains large crystals of feldspar; and, though it forms the body of the vein in the mica-slate, it is itself traversed by threads of quartz two inches thick, and of very recent formation. The aspect of this phenomenon is very curious: it appears as if cannon-balls were embedded in a wall of rock.
These transitions and alternating superpositions take place no doubt in formations of granite-gneiss and gneiss-mica-slate; but because these phenomena are observed in one region, it does not follow that in other regions we may not find very distinct circumscribed formations of granite, gneiss, and mica-slate.
To the east of the quarry which furnishes the clay is the ravine of La Mina. It is asserted that, a short time after the conquest, some Venetians extracted gold from the mica-slate. It appears that this metal was not collected in veins of quartz, but was found disseminated in the rock, as it is sometimes in granite and gneiss.
They would not confound Auvergne and the granitic valley of Caracas in the same denomination; that of a country of extinct volcanoes. I never could have pronounced the opinion, that the Silla and the Cerro de Avila, mountains of gneiss and mica-slate, were in dangerous proximity to the city of Caracas because they contained a great quantity of pyrites in subordinate beds of primitive limestone.
I believe this splendour, commonly reddish but sometimes silvery, to be a reflection produced by large plates of talc, or by gneiss passing into mica-slate. The whole of this country contains granitic rocks, on which here and there, in little plains, an argillaceous grit-stone immediately reposes, containing fragments of quartz and of brown iron-ore.
I have been informed that in the northern chain also, in the Montana de Paria, and near Carupana, secondary calcareous formations are found, and that they only begin to show themselves on the east of the ridge of rock called the Cerro de Meapire, which joins the calcareous group of Guacharo to the mica-slate group of the peninsula of Araya; but I have not had an opportunity of ascertaining the accuracy of this information.
Word Of The Day
Others Looking