climate of Zacatecas, as well as that of Catorce is much colder than the climate 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; and clay slate reposes on them, which from the beds of Lydian stone, grauwakke, 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

* Beschreibung der Bergwerks-refiere von Mexico, p. 166 -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.

and perpendicular rocks which the natives call buffas, covers in many places the clay slate, especially 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 amalgamation works of la Sauceda, compact limestone, in which Mr. Sonneschmidt also discovered Lydian stone, an old freestone (urfelsconglomerat) containing fragments of granite*, and a clayey and felspar agglomeration which is easily confounded with the grauwakke of the German mineralogists. The presence of the Lydian stone, with 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 kiesel slate forming subordinate beds in a limestone which was undoubtedly secondary.

The savage aspect of the metalliferous mountains of Zacatecas, are a singular contrast to the great wealth of the veins which they con

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

tain. 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 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 from 2500 to 3000 bars of silver, at 134 marcs each*.

an average,

The mass of the veins of this districtt con. tains a great variety of metals, viz: quartz, splintery hornstone, calcareous spar, a little of the sulfate of baryte and brown spar; prismatic black silver called in the country azul acerado; sulfuretted silver, (azul plomilloso) mixed with native silver; fuligenous silver (the silberschwärtze of the Germans, polvorilla of the Mexicans); pearl grey, blue, violet, and leek green muriated silver, (plata parda azul y verde) at very inconsiderable depths, a little red silver (petlangue or rosicler); and native gold, parti

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

+ Sonneschmidt, p. 185. The minerals called by the in-" habitants of Zacatecas copalillo, metal cenizo, and metal azul de plata, appear to this mineralogist mixtures of galena, sulfuretted silver, and native silver. I have thought proper to insert these synonimes 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.

cularly to the south west of the town of Zacatecas; argentiferous sulfuretted lead (soroche plomosa reluciente y tescatete); carbonated lead; black, brown, and yellow sulfuretted zinc, (estoraque and ojo de vivora); pyrite of copper and iron (bronze nochistle, or dorado, and bronze chino); magnetical oxydulated iron; blue and green carbonated copper, and sulfuretted antimony. The most abundant metals of the celebrated vein called the veta grande, are prismatic black silver (sprödglaserz), sulfuretted ro vitreous silver, mixed with native silver and silberschwärze.

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 grauwakke. According to the observation of M. Sonneschmidt, the rock is traversed there by an innumerable quantity of veins, rich in grey and green muriated silver. . 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

20 millions of livres tournois*. The most part of these veins are found in a compact limestone, which contains like that of the Sauceda kiesel slate, and lydian stone. The dull red silver particularly abounds in this district of mines; and it has been seen to form the whole mass of the veins which have more than a metre in extent† (puissance). Near Sombrerete the mountains of secondary calcareous formation, rise much above the porphyritic mountains. The Cerro de Papanton appears to be more than 3400 metres, above the level of the sea.

The mineral depository of Catorce, holds at present the second or third rank among the mines of New Spain, classing them according to the quantity of silver which they produce. It was only discovered in the year 1778. This discovery, and that of the veins of Gualgayoc, in Peru, vulgarly called the veins of Chota, are the most interesting in the history of the mines of Spanish America, for the last two centuries. The small town of Catorce, the true name of which is la Purissima Concepcion de Alamos de Catorce; is situated on the calcareous table land, which declines towards. the nuevo reyno de Leon, and towards the

* £ 833,400 Sterling. Trans.

+ More than 3 feet 3 inches. Trans.