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Updated: May 7, 2025
Between these two transverse chains, contiguous to the Andes, an isolated group of granitic mountains is situated, from 3 to 7 degrees north latitude; which also runs parallel to the Equator, but, not passing the meridian of 71 degrees, terminates abruptly towards the west, and is not united to the Andes of New Grenada.
I may now with some confidence affirm, from my own observation, and from good information with regard to those places where I have not been, except the northwest corner, I may affirm, I say, that instead of the basis of the greatest part of Scotland being a granitic rock, which our author has maintained as an evident thing, there is very little of it that is so; not perhaps one five hundred part.
The grass is short and thick, yet the upper stratum of earth furnishes only a dry and parched granitic sand. The small herbaceous mimosas contribute in this zone to fatten the cattle, but are very rare between the Rio Jao and the mouth of the Guaviare.
Thus, for example, M. Fournet, in his description of some mines in Auvergne worked under his superintendence, observes that the granite of that country was first penetrated by veins of granite, and then dislocated, so that open rents crossed both the granite and the granitic veins. Into such openings, quartz, accompanied by sulphurets of iron and arsenical pyrites, was introduced.
In common sand, the quartz grains are the most numerous; but this is not a proof that the rocks from which these particles were derived were wholly, or even chiefly, quartzose in character; for, in many composite rocks, as, for example, in the granitic group, the mica, feldspar, and hornblende are more easily decomposed by chemical action, or disintegrated, comminuted, and reduced to an impalpable state by mechanical force, than the quartz.
It is probable, that the irruption of the waters towards the Llanos have given, by extraordinary rents, the form of ruins to the Morros of San Juan and of San Sebastian. The volcanic tract of Parapara and Ortis is now only 30 or 40 toises above the Llanos. The eruptions consequently took place at the lowest point of the granitic chain.
Inland, along the whole northern bank of the Plata, I saw, besides modern tertiary beds, only one small patch of slightly metamorphosed rock, which alone could have formed a part of the original capping of the granitic series.
The snow still covered the lofty granitic tops of the Guadarama; but in the deep valleys of Galicia, which resemble the most picturesque spots of Switzerland and the Tyrol, cistuses loaded with flowers; and arborescent heaths clothed every rock.
The aspect of the mountains of Paria, their colour, and especially their generally rounded forms, made us suspect that the coast was granitic; but we afterwards recognized how delusive, even to those who have passed their lives in scaling mountains, are impressions respecting the nature of rocks seen at a distance.
That an expedition with this end in view will soon be undertaken is, however, highly improbable, the survey of the Rattlesnake having completed all that was requisite for the immediate purposes of navigation in those parts. We saw no volcanoes, however, and the great central mountain chain appeared to me to be probably granitic.
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