They reckoned in 1803 in the whole district of mines of Guanaxuato, five thousand miners and workmen employed in picking the ores, in smelting, and amalgamating; eighteen hundred and ninety-six arastres, or machines for reducing the ores into powder; and fourteen thousand six hundred and eighteen mules destined to move the baritels, and to tread, for amalgamation, the pulverized ores mixed with mercury. The arastres of the town of Guanaxuato bray, when there is an abundance of mercury, eleven thousand three hundred and seventy quintals of ores per day. If we recollect that the produce in silver is annually from 5 to 600,000 marcs, we shall find by this datum, that the mean contents of the ores are extremely small.

The celebrated mines of Zacatecas, which Robertson*, from what motive I know not, calls Sacotecas, are, as we have already observed, older than the mines of Guanaxuato. They began to be worked immediately after the veins of Tasco, Zultepeque, Tlapujahua, and Pachuca. They are situated on the central table land of the Cordilleras, which lowers rapidly towards New Biscay, and towards the basin of the Rio del Norte. The climate of Zacatecas, as well as that of Catorce is much colder than the climate

* History of America, vol. ii. p. 389.

of Guanaxuato and Mexico. Barometrical measurements will one day determine whether this difference is owing to a more northern position, or to the elevation of the mountains.

The nature of the former has been examined by two very intelligent mineralogists, M. M. Sonneschmidt * and Valencia, the one a Saxon, and the other a Mexican. From the whole of their observations it appears, that the district of mines of Zacatecas bears great resemblance in its geological constitution to that of Guanaxuato. The oldest rocks which appear at the surface are syenitic; they are overlaid by clay slate, which from the beds of Lydian stone, grauwacke, and greenstone which it contains, has a resemblance to transition clay slate. The most part of the veins of Zacatecas are found in this clay slate. The veta grande, or principal vein, has the same direction as the veta madre of Guanaxuato; the others are generally in a direction from east to west. t A porphyry destitute of metals, and forming those naked and perpendicular rocks which the natives call buffas, covers in many places the clay slate, especially

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* Beschreibung der Bergwerks-refiere von Mexico, p. 237. Descripcion geognostica del real de Zacatecas, por Don Vicente Valencia. (M. S.)

+ Sobre la formacion de las vetas, por Don Andres del Rios. (Gazeta de Mexico.) T. xi. n. 51.

on the side of the Villa de Xeres, where a mountain rises in the midst of these porphyritic formations, in the form of a bell, the basaltic cone of the Campana de Xeres. Among the secondary rocks of Zacatecas we observe, near the works of la Sauceda, compact limestone, in which Mr. Sonneschmidt also discovered Lydian stone, an old sandstone (urfelsconglomerat) containing fragments of granite *, and a clayey and feldspar conglomerate which is easily confounded with the grauwacke of the German mineralogists. The presence of the Lydian stone in limestone, might tempt us to believe that this last rock belongs to transition limestone (übergangs kalkstein) which appears at the surface in the Cerro de la Tinaja, eight leagues to the north of Zacatecas; but I must observe here, that on the coast of South America, near the Morro of New Barcelona, I found flint-slate forming subordinate beds in a limestone which is undoubtedly secondary.

The savage aspect of the metalliferous mountains of Zacatecas, forms a singular contrast to the great wealth of the veins which they contain. This wealth is displayed, and the fact is very remarkable, not in the ravins, and where the veins run along the gentle slope of the

* In the ravin leading from Zacatecas to the convent of Guadalupe.

mountains, but most frequently on the most elevated summits, on points where the surface appears to have been tumultuously torn, in the antient revolutions of the globe. The mines of Zacatecas produce yearly at an average, from 2500 to 3000 bars of silver, at 134 marcs each. *

The mass of the veins of this district † contains a great variety of minerals, viz.: quartz, splintery hornstone, calcareous spar, a little sulphate of barytes and brown spar; prismatic black silver, called in the country azul acerado; sulphuret of silver, (azul plomilloso) mixed with native silver; black silver, (the silber-schwärtze of the Germans, polvorilla of the Mexicans); pearl grey, blue, violet, and leek green muriate of silver, (plata parda azul y verde) at very inconsiderable depths; a little red silver, petlangue or rosicler); and native gold, particularly to the south-west of the town of Zacatecas;

* From 219,866 to 263,839 lb. Troy. Trans.

+ Sonneschmidt, p. 185. The minerals called by the inhabitants of Zacatecas copalillo, metal cenizo, and metal azul de plàta, appear to this mineralogist mixtures of galena, sulphuret of silver, and native silver. I have thought proper to insert these synonyms of the Mexican minerals, because their knowledge is very important to the mineralogical traveller. See Garces, Nueva Theoria del beneficio de los metales, p. 87, 124, and 138.

argentiferous sulphuret of lead (soroche plomoso reluciente y tescatete); carbonate of lead; black, brown, and yellow sulphuret of zinc, (estoraque and ojo de vivora); copper and iron pyrites (bronze nochistle, or dorado, and bronze chino); magnetic oxydulated iron; blue and green carbonate of copper, and sulphuret of antimony. The most abundant metals of the celebrated vein called the veta grande, are prismatic black silver (sprödglaserz), sulphuret of silver, or vitreous silver, mixed with native and black silver..

The intendancy of Zacatecas contains the mines of Fresnillo, and those of Sombrerete. The former are very feebly wrought, and are situated in an insulated group of mountains which rise above the plains of the central table land. These plains are covered with porphyritic formations; but the metalliferous group itself is composed of grauwacke. According to the observation of M. Sonneschmidt, the rock is traversed there by an innumerable quantity of veins, rich in grey and green hornsilver.

The mines of Sombrerete have become celebrated, from the immense riches of the vein of the veta negra, which in the space of a few months left to the family of Fagoaga, (Marques del Apartado) a net profit of more than