there were above seven thousand Yanaconas, or Indian labourers, established in the neighbourhood, who were employed by their Christian masters in the various operations of these mines.  These men laboured with so much industry, that each Indian, by agreement, furnished two marks or sixteen ounces of silver weekly to their respective masters; and so rich was the mine, that they were able to do this and to retain an equal quantity to themselves[26].  Such is the nature of the ore extracted from the mineral veins of this mountain, that it cannot be reduced in the ordinary manner by means of bellows, as is customary in other places.  It is here smelted in certain small furnaces, called guairas by the Indians, which are supplied with a mixed fuel of charcoal and sheeps dung, and are blown up by the wind only, without the use of any mechanical contrivance.

[Footnote 25:  This produce is most extraordinarily large, being equal to four parts of pure silver from ten of ore, or 640 ounces of silver from the quintal or 1600 ounces of ore.  At the present time, the silver mines in Mexico, which are the most productive of any that have ever been known, are remarkable for the poverty of the mineral they contain.  A quintal or 1600 ounces of ore affording only at an average 3 or 4 ounces of pure silver.  The profit therefore of these must depend upon the abundance of ore, and the facility with which it is procured and smelted.—­E.]

[Footnote 26:  The gross amount of this production of silver, on the data in the text, is 11,648,000 ounces yearly; worth, at 5s. 6d. per ounce, L. 3,203,200 sterling; and, estimating silver in those days, at six times its present efficacy, worth L. 19,219,200 of modern value.  In the present day before the revolutionary troubles, Humboldt estimates the entire production of gold and silver from Spanish and Portuguese America at L. 9,787,500; only about three times the quantity said to have been at first extracted from Potosi alone, and only about half the effective value.—­E.]

These rich mines are known by the name of Potosi, which is that of the district, or province in which the mountain is situated.  Owing to the easy labour and great profit experienced by the Indians at these mines, when any of the Yanaconas was once established at this place it was found almost impossible to induce them to leave it or to work elsewhere; and indeed, they were here so entirely concealed from all dangers, and so much exempted from their usual severe drudgery and the unwholesome vapours they had been subjected to in other mines, that they preferred working at Potosi to any other situation.  So great was the concourse of inhabitants to Potosi, and the consequent demand for provisions, that the sack of maize was sold for twenty crowns, the sack of wheat for forty, and a small bag of coca_ for thirty dollars; and these articles rose afterwards to a higher price.  Owing to the astonishing productiveness of these new