A very considerable quantity of silver is produced from the smelting of iron pyrites (gemeiner schwefelkies) of which New Spain sometimes exhibits varieties richer than the glaserz itself. It has been found in the Real del Monte, on the vein of Biscaina, near the pit of San Pedro, the quintal of which contained even so much as three marcs of silver. At Sombrerete, the great abundance of pyrites disseminated in the red silver ore, is a great obstacle to the process of amalgamation.

We have described the ores which produce the Mexican silver, and it remains for us to examine into the mean riches of these minerals, considering them as all mixed together. It is a very common prejudice in Europe, that great masses of native silver are extremely common in Mexico and Peru, and that in general the mineralised silver ores destined to amalgamation or smelting, contain more ounces, or more marcs of silver to the quintal, than the poor ores of Saxony and Hungary. Full of this prejudice, I was doubly surprised on my arrival in the Cordilleras to find that the number of poor mines greatly surpasses those of the mines to which in Europe we give the name of rich. A traveller who visits the famous mine of Valenciana in Mexico, after having examined the metalliferous repositories of Clausthal, Freiberg,

and Schemnitz, can scarcely conceive how a vein which, for a great part of its extent contains the sulphuret of silver disseminated in the gangue in almost imperceptible particles, can regularly supply thirty thousand marcs per month, a 'quantity of silver equal to the half of what is annually furnished by all the mines of Saxony. It is no doubt true that blocks of native silver (papas de plata) of an enormous weight, have been extracted from the mines of Batopilas in Mexico and Guantahajo in Peru; but when we study attentively the history of the principal mines of Europe, we find that the veins of Kongsberg in Norway, Schneeberg in Saxony, and the famous metallic repository of Schlangenberg in Siberia, have produced masses of much more considerable bulk. We are not in general to judge from the size of the blocks, of the wealth of the mines of different countries. France does not altogether produce more than 8000 marcs of silver annually; and yet there are veins in that country. (those of Sainte-Marie-aux-Mines) from which amorphous masses of native silver have been extracted, of the weight of 30 kilogrammes. *

A

It appears that at the period of the formation of veins in every climate, the distribution of

66lb. avoird. Trans.

silver has been very unequal; sometimes concentrated in one point, and at other times disseminated in the gangue, and allied with other metals. Sometimes in the midst of the poorest ores we find very considerable masses of native silver; a phenomenon which appears to depend on a particular operation of chemical affinities, the mode of action and laws of which we are completely ignorant of. The silver instead of being concealed in galena, or in pyrites in a small degree argentiferous, or of being distributed throughout all the mass of the vein over a great extent, is collected into a single mass. In that case the riches of a point may be considered as the principal cause of the poverty of the neighbouring ores; and hence we may conceive why the richest parts of a vein are found separated from one another by portions of gangue almost altogether destitute of metals. In Mexico, as well as in Hungary, large masses of native silver and glaserz, appear only in nests or kidneys, (par rognons ;) and the compound rocks exhibit the same phenomena as the masses of veins. When we examine with care the structure of granites, syenites, and porphyries, we discover the effects of a particular attraction in the crystals of Mica, amphibole and feldspar, of which a great number are accumulated in

one point, while the neighbouring parts are almost entirely destitute of them.

Although the New Continent, however, has not hitherto exhibited native silver in such considerable blocks as the Old, this metal is found more abundantly in a state of perfect purity in Peru and Mexico, than in any other quarter of the globe. In laying down this opinion, I am not considering the native silver which appears in the form of lamellæ, branches, or cylindrical filaments in the mines of Guantahajo, Potosi, and Gualgayoc, or in Batopilas, Zacatecas, and Ramos. I found my opinion rather on the enormous abundance of the ores called pacos and colorados, in which silver is not mineralised, but disseminated in such small particles, that they can only be perceived by means of a micro

scope.

The result of the investigations made by Don Fausto d'Elhuyar, the director general of the mines of Mexico, and by several members of the superior council of mines, is, that in uniting together all the silver minerals annually extracted, it would be found from the mixture, that their mean produce is from 0.0018 to 0.0025 of silver, that is to say in the common language of miners, that a quintal of ore (of one hundred pounds, or 16,000 ounces) contains from three to four ounces of silver. This im

portant result is confirmed by the testimony of an inhabitant of Zacatecas, who dad the direc tion of considerable metallic operations, in several districts of mines of New Spain, and who has lately published a very interesting work, on the American amalgamation. M. Garces*, whom we have already had occasion to quote, expressly says, "that the great mass of Mexican "ores is so poor, that the three millions of marcs "of silver annually produced by the kingdom "in good years, are extracted from ten millions "of quintals of mineral, partly smelted, and "partly amalgamated." According to these numbers, the mean riches would only amount to 23 ounces per quintal, a result which differs very much from the assertion of a traveller, very estimable in other respects †, who relates that the veins of New Spain are of such extraordinary wealth, that the natives never think of working them when the minerals contain less than a third of their weight in silver, or seventy marcs per quintal. As the most erroneous ideas have

* Nueva Theorica del beneficio de los metales, por Don Joseph Garces y Eguia, Perito facultativo de minas y primario de beneficios de la mineriu de Zacatecas (Mexico, 1802,) p. 121 & 125.

+ The Jesuit Och (Murrs Nachrichten vom Spanischen America, t. i. p. 236.)