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Updated: June 4, 2025
Do the neighbouring rocks of mica-slate and gneiss contain veins? or is the gold disseminated here, as in the granites of Guadarama in Spain, and of the Fichtelberg in Franconia, throughout the whole mass of the rock? Possibly the waters, in filtering through it, bring together the disseminated grains of gold; in which case every attempt to work the rock would be useless.
In these parts the bottom of the sea is evidently formed of mica-slate, and from it near Cape de la Brea, but at eighty feet distant from the shore, there issues a spring of naphtha, the smell of which penetrates into the interior of the peninsula. It is necessary to wade into the sea up to the waist, to examine this interesting phenomenon.
Although this watercourse was perfectly dry throughout yet it was an interesting feature in a valley enclosed on each side by undulating hills of mica-slate; and I thought of continuing in its course next morning, in hopes it might at last lead to some chain of ponds falling westward. May 4.
In our geognostical observation of the country round Caracas we found gneiss, and mica-slate containing beds of primitive limestone. The strata are scarcely more fractured or irregularly inclined than near Freyburg in Saxony, or wherever mountains of primitive formation rise abruptly to great heights.
The isthmus that divides these large masses of mica-slate was scarcely visible; its form appeared changed by the effect of the mirage and we recognized the intermediate part, through which runs the Laguna Grande, only by two small hills of a sugarloaf form, in the meridian of the Punta de Piedras.
Emeralds are found in Siberia, and some of the localities may have furnished to the ancients the Scythian gems which Pliny and others mention. In the Wald district magnificent crystals have been found embedded in mica-slate. One of these a twin-crystal, now in the Imperial Cabinet at St. Petersburg is seven inches long, four inches broad, and weighs four and a half pounds.
The coast is so very rugged that to attempt to walk in that direction requires continued scrambling up and down over the sharp rocks of mica-slate; and as for the woods, our faces, hands, and shin-bones all bore witness to the maltreatment we received, in merely attempting to penetrate their forbidden recesses. We stood out to sea.
Opposite the shore of the Guaricotos, we drew near another heap of rocks, which is very low, and three or four toises long. The shore, at this part of the Orinoco, is no longer of pure and quartzose sand; but is composed of clay and spangles of mica, deposited in very thin strata, and generally at an inclination of forty or fifty degrees. It looks like decomposed mica-slate.
The direction of the primitive rock near Cape Sotto is from north-east to south-west; its strata incline fifty degrees to the north-west. The mica-slate is silvery white, of lamellar and undulated texture, and contains garnets. Strata of quartz, the thickness of which varies from three to four toises, traverse the mica-slate, as we may observe in several ravines hollowed out by the waters.
There is some general resemblance to the chalk bluffs of England, especially about Beachy Head, but the rock here appears to be mica-slate, disposed in thin, vertical strata, with many violent transverse breaks. As we approached the end of the promontory which divides the Porsanger from the Laxe Fjord, the rocks became more abrupt and violently shattered.
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