1 Cerro de San Ignacio, serves for base to the secondary formations. The result of this general view of the metalliferous repositories (erzführende lagerstätte) is, that the cordilleras of Mexico contain veins in a great variety of rocks, and that those rocks, which at present furnish almost the whole silver annually exported from Vera Cruz, are, primitive slate, grauwacke, and alpine lime stone, intersected by the principal veins of Guanaxuato, Zacatecas, and Catorce. It is also in primitive slate (urthon-schiefer), on which rests a clayey porphyry containing garnets, that the wealth of Potosi, in the kingdom of Buenos Ayres, is contained. On the other hand, in Peru the mines of Gualgayoc or Chota, and that of Yauricocha or Pasco, which together yield annually double the quantity of all the German mines, are found in an alpine limestone. The more we study the geological constitution of the globe on a large scale, the more we perceive that there is scarcely a rock which has not in certain countries been found eminently metalliferous. The wealth of the veins is for the most part totally independent of the nature of the beds which they intersect. We observe in the most celebrated mines of Europe, that the mining operations are either directed to a multitude of small veins, as in the primitive mountains of Saxony, or to a very small number of depositories of minerals of an extraordinary power, as at Clausthal, the Harz, and near Schemnitz in Hungary. The cor dilleras of Mexico offer frequent examples of these two methods of operation; but the districts of mines of the most constant and considerable wealth, Guanaxuato, Zacatecas, and the Real del Monte, contain only one principal vein each (veta madre). The vein called halsbrükner spath, of which the extent is two metres*, and which has been traced for a length of 6200 metrest, is spoken of as a remarkable phenomenon at Freiberg. The veta madre of Guanaxuato, from which there has been extracted, during the course of the last ten years, more than six millions of mares of silver, is of the extent of from 40 to 45 metres §, and it is wrought from Santa Isabella and San Bruno to Buena-Vista, a length of more than 12,700 metres. In the Old Continent, the veins of Freiberg and Clausthal, which intersect mountains of gneiss and grauwacke, are visible in table lands of which the elevation above the level of the sea is only from 350 to 570 metres; and this * 6 feet. Trans. † 20, 341 feet. Trans. § From 131 to 147 feet. Trans. | 41,665 feet. Trans. ¶ From 1148 to 1869 feet. Trans. 7 elevation may be regarded as the mean height of the most abundant mines in Germany. But in the New Continent the metallic wealth is deposited by nature by nature on the very ridge of the cordilleras, and sometimes in situations within a very small distance from the limit of perpetual snow. The most celebrated mines in Mexico are at absolute heights of from 1800 to 3000 metres. * In the Andes, the districts of mines of Potosi, Oruro, Paz, Pasco and Gualgayoc, are in regions of which the elevation surpasses that of the highest summits of the Pyrenees. Near the small town of Micuipampa, the great square of which, according to my measurement, is 3618 metres † above the level of the sea, a depôt of silver ore known by the name of Cerro de Gualgayoc was found to yield immense wealth at an absolute height of 4100 metres. ‡ We have mentioned in another place § the advantage which in working the Mexican mines, is derived from the most important veins being in a middle region, where the climate is not unfavourable to agriculture and vegetation. The large town of Guanaxuato is placed in a ravin, the bottom of which is somewhat lower than the level of the lakes of the valley of Tenochtitlan. We are ignorant of the absolute heights of Zacatecas and the Real de Catorce; but these two places are situated on table lands seemingly more elevated than the level of Guanaxuato. However, the temperate climate of these Mexican towns, which are surrounded with the richest mines in the world, is a contrast to the cold and exceedingly disagreeable climate of Micuipampa, Pasco, Huancavelica and other Peruvian towns. When in a district of small extent, for instance, in that of Freiberg in Saxony, we compare the quantity of silver annually coined, with the great number of mines constantly worked, we perceive, on the slightest examination, that this produce is derived from a very small part of the mining operations, and that nine tenths of the mines possess almost no influence on the total mass of ores extracted from the bowels of the earth. In the same manner, in Mexico, the 2,500,000 marcs* of silver which are annually sent to Europe and Asia, from the ports of Vera Cruz and Acapulco, are the produce of a very small number of mines. `The three districts which we have frequently had occasion to name, Guanaxuato, Zacatecas, and Catorce, supply more than the half of that sum. * 1,640,791 lb. troy. Trans. The vein of Guanaxuato alone yields more than a fourth part of the whole silver of Mexico, and a sixth part of the produce of all America. In the general view already presented by us, the principal mines are confounded with those from which a very small quantity of metal is extracted. The disproportion between the two classes is so great, that more than 2 of the Mexican mines belong to the latter, of which the total produce does not probably amount to the sum of 200,000 marcs. * In Saxony also the mines which surround the town of Freiberg produce annually nearly 50,000 marcs of silver, while all the rest of the Erzgebirge does not yield more than from seven to eight thousand mares, The following is the order in which the richest mines of New Spain follow one another, arranging them according to the quantity of money actually drawn from them: Guanaxuato, in the Intendancy of the same name. Catorce, in the Intendancy of San Luis Potosi, Zacatecas, in the Intendancy of the same name. Real del Monte, in the Intendancy of Mexico. Bolaños, in the Intendancy of Guadalaxara. * 131,263 lb. troy. Trans. 1 |