the metalliferous veins of Clausthal, Freiberg, and Schemnitz, can scarcely conceive how a vein which, for a great part of its extent contains sulfuretted 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 mass of minerals of Schlangenberg in Siberia, have produced much more considerable quantities. 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 unshapen masses of native silver have been extracted, of the weight of 30 kilogrammes*.

It appears that at the formation of veins

*66lb. avoird. Trans.

in every climate, the distribution of 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 minerals we find very considerable masses of native silver; a phenomenon which appears to depend on a particular operation of chemical affinities, with the mode of action, and laws of which we are completely ignorant. The silver in place of being concealed in galenæ, 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 minerals; 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 a reniform shape (par rognons ;) the composed 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 par ticular attraction in the chrystals of Mica, amphibole and felspar, of which a great num

ber are accumulated in one point, while the neighbouring parts are almost entirely destitute.

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 minerals called pacos and colorados, in which silver is not mineralized, but disseminated in such small particles, that they can only be perceived by means of a microscope.

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 riches 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 important result is confirmed by the testimony of an inhabitant of Zacatecas, who had the direction 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 minerals is so poor, that the three "millions of marcs of silver annually produced

66

by the kingdom in good years, are extracted "from ten millions of quintals of mineral,

66

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

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

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

have been spread through Europe respecting the contents of the minerals of America, I shall procecd to give a more minute description of the districts of mines of Guanaxuato, Tasco, and Pachuca, which I had occasion to visit.

At Guanaxuato, the mine of the count de la Valenciana produced between the 1st January, 1787, and the 11th June, 1791, the sum of 1,737,052 marcs of silver, which were extracted from 84,368 montones of minerals. In the table* containing the general state of the mine, a monton is estimated at 32 quintals, or at 91 cargas; from whence it follows that the mean riches of the minerals, was, twenty years ago 5 ounces of silver per quintal. Applying the same calculation to the

* Estado de la mina Valenciana, remitido por mano del Excellentiss. Señor virey de Nueva España al Secretario de Estado Don Antonio Valdes. (Manuscript.) (Manuscript.) I have followed the numbers contained in the table drawn up by Don Joseph Quixano, the administrator of Valenciana. A monton (a heap of minerals reduced to powder) is reckoned at 35 quintals at Guanaxuato; at thirty at the Real del Monte, Pachuca, Zultepeque, and Tasco; at Zacatecas and Sombrerete, at 20; at Fresnillo at 18; and at 15 quintals at Bolaños. The carga is generally estimated at Guanaxuato at 14 arrobas; so that 10 cargas amount there to smonton (Garces, p. 92.)

of the ore is determined from the contents

As the wealth

of the monton,

the exact knowledge of the measure is of great importance in metallurgical calculations.