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with grauwac/ce-slate is equally rich in metals in Mexico as in several parts of Germany. In this rock, the formation of which immediately preceded that of the secondary rocks, several of the veins of Zacatecas appear to be found. .~ ‘ '
In proportion as the north of Mexico shall be examined I by intelligent geologists, it will be perceived that ,the metallick wealth of Mexico does not exclusively belong to primitive formations and transition rocks, but extend 'also to those of secondary jbrmation. A I know not whether the lead which is procured in the eastern parts of the intendancy of San Luis Potosi is found in veins or beds; but it appears certain, that the veins of silver of the Real de Catorce, as well as those of the Doctor and Xaschi near Zimapan, traverse alpine limestone (alpenlral/rstein); and this rock rests on pudding-stone, with silicious cement, which may be considered as the most antient of secondary formations. ‘The alpine limestone; and the jura limestone (jurakallcstein), contain the ‘celebrated silver mines of Tasco and Tehuilotepec, in the intendancy of Mexico; and it is in these calcareous rocks that the numerous veins which in this country have been verygearly wrought, display the greatest wealth. Theypare less productive in the strata of primitive slate (urthon-schiefer), which is as seen in the
Cerro de San Ignacio, serves for base to the secondary formations.
The result of this general view of the metalliferous repositories (erzfiihrende lagerstiitte) 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, grawwacke, and alpine lime stone, intersected by the principal veins of Guanaxuato, Zacatecas, and Catorce. It is also in primitive slate (urtkon-sclzie/er), 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 intthe primitive mountains of Saxony, or to a very
cmir. XL] KINGDOM OF NEW SPAIN. I35
small number of depositories of minerals of an extraordinary power, as at Clausthal, the H_arz, and near Schemnitz in Hungary. The cordilleras 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 uein each (veta madre). The vein called halsbrzlkner spath, of which the extent is two metres ‘*‘, and which has been traced for a length of 6200 metresf, 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’rn_arcs_of siIve11I,__is of
the extent of from 40 to 4~5 metres §,‘ and it is wrought from Santa Isabella and San Bruno to Buena-Vista, a length of more than 12,700 metres." I u 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 850 to 570 metres'1|' ; and‘this
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 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 8000’metres.*" In the Andes, the districts of mines of Potosi, -Oruro, P-az, 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 metresi above the level of the sea, a depot of silver ore known by the name of Cerro de Gualgayoc was found to yield immense wealth at an absolute height of 4.400 metres. I I '
We have mentioned in another place§ the advantage which in working the Mexican mines, is derived fr0m ihfl. 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
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lower than the level of the lakes of the valley
When in a district of small extent, fbr