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I could not, however, distinctly ascertain whether a part of this pyritous diorite was not enclosed on the banks of the Orinoco, as it is at the bottom of the sea near Cabo Blanco, and at the Montana de Avila, in the rock which it covers.
Not only are those sparry and pyritous substances, which are more natural to coal strata, found forming veins traversing those strata in various directions, but also every other mineral vein may occasionally be found pervading coal mines, or traversing bituminous strata. Gold, silver, copper, lead, calamine, have all, in this manner, been found in coal.
The marls, as the smell indicates, are pyritous and bituminous at the same time; and the petroleum springs at the Buen Pastor, and in the island of Trinidad, proceed probably from these same beds of alpine limestone.
When the sulphur contents of pyritous ores are sufficiently high, and after the ore has been initially fired with auxiliary carbonaceous fuel, it is unnecessary, in a properly designed roasting furnace, to add fuel to the ore to enable the heat for oxidation to be obtained. The oxidation or burning of the sulphur will provide all the heat necessary to maintain the continuity of the process.
How much time did we not lose during five years' travels, in visiting, on the pressing invitations of our hosts, ravines, of which the pyritous strata have borne for ages the imposing names of 'Minas de oro! How often have we been grieved to see men of all classes, magistrates, pastors of villages, grave missionaries, grinding, with inexhaustible patience, amphibole, or yellow mica, in the hope of extracting gold from it by means of mercury!
A forty per cent pyritous or other sulphide ore should be roasted in a revolving furnace in thirty to forty minutes, and without any auxiliary fuel.
It affords the thickest stratum of pure vegetable matter hitherto detected in any secondary rock in England. One seam of coal of good quality has been worked three and a half feet thick, and there are several feet more of pyritous coal resting upon it. Terebratula fimbria, Sowerby. Inferior Oolite marl. Rhynchonella spinosa, Schloth. Pholadomya fidicula, Sowerby. One-third natural size.
But this is the case; we find those fissures filled both with calcareous, gypseous, and pyritous substances.
This rage for the search of mines strikes us the more in a climate where the ground needs only to be slightly raked to produce abundant harvests. After visiting the pyritous marls of the Rio Juagua, we continued following the course of the crevice, which stretches along like a narrow canal overshadowed by very lofty trees.
Conceive a stream or river fed by springs rising in a country intersected by auriferous reefs, and consequently in this case carrying gold in solution; the drift of such a country must be to a greater or lesser extent pyritous, so that the debris forming the beds of these streams or rivers will certainly contain nodules of such matters disseminated or even stopping them in actual contact with the flow of water.
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