Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 2 - By Alexander Von Humboldt And Aime Bonpland.
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Here, However, As In Every Place Where Native
Gold And Auriferous Pyrites Are Disseminated In The Rock, Or By The
Destruction Of The Rocks, Are Deposited In Alluvial Lands, The People
Conceive The Most Exaggerated Ideas Of The Metallic Riches Of The
Soil.
But the success of the workings, which depends less on the
abundance of the ore in a vast space of land than on its accumulation
in one point, has not justified these favourable prepossessions.
The
mountain of Chacao, bordered by the ravine of Tucutunemo, rises seven
hundred feet above the village of San Juan. It is formed of gneiss,
which, especially in the superior strata, passes into mica-slate. We
saw the remains of an ancient mine, known by the name of Real de Santa
Barbara. The works were directed to a stratum of cellular quartz,*
full of polyhedric cavities, mixed with iron-ore, containing
auriferous pyrites and small grains of gold, sometimes, it is said,
visible to the naked eye. (* This stratum of quartz, and the gneiss in
which it is contained, lie hor 8 of the Freyberg compass, and dip 70
degrees to the south-west. At a hundred toises distance from the
auriferous quartz, the gneiss resumes its ordinary situation, hor 3 to
4, with 60 degrees dip to the north-west. A few strata of gneiss
abound in silvery mica, and contain, instead of garnets, an immense
quantity of small octohedrons of pyrites. This silvery gneiss
resembles that of the famous mine of Himmelsfurst, in Saxony.) It
appears that the gneiss of the Cerro de Chacao also furnishes another
metallic deposit, a mixture of copper and silver-ores. This deposit
has been the object of works attempted with great ignorance by some
Mexican miners under the superintendance of M. Avalo. The gallery*
directed to the north-east, is only twenty-five toises long. (* La
Cueva de los Mexicanos.) We there found some fine specimens of blue
carbonated copper mingled with sulphate of barytes and quartz; but we
could not ourselves judge whether the ore contained any argentiferous
fahlerz, and whether it occurred in a stratum, or, as the apothecary
who was our guide asserted, in real veins. This much is certain, that
the attempt at working the mine cost more than twelve thousand
piastres in two years. It would no doubt have been more prudent to
have resumed the works on the auriferous stratum of the Real de Santa
Barbara.
The zone of gneiss just mentioned is, in the coast-chain from the sea
to the Villa de Cura, ten leagues broad. In this great extent of land,
gneiss and mica-slate are found exclusively, and they constitute one
formation.* (* This formation, which we shall call gneiss-mica-slate,
is peculiar to the chain of the coast of Caracas. Five formations must
be distinguished, as MM. von Buch and Raumer have so ably demonstrated
in their excellent papers on Landeck and the Riesengebirge, namely,
granite, granite-gneiss, gneiss, gneiss-mica-slate, and mica-slate.
Geologists whose researches have been confined to a small tract of
land, having confounded these formations which nature has separated in
several countries in the most distinct manner, have admitted that the
gneiss and mica-slate alternate everywhere in superimposed beds, or
furnish insensible transitions from one rock to the other.
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