3r{(i 



METALLIl'KROUS DEPOSITES. 



Variety of 

 veins. 



CiiAP.XXVi barytes, corky aslicstus, green garnets, carbonate and 



chroniate of lead, orpinient, chrysoprasc, and fire-opal. 

 Silver ores. Among the transition rocks containing ores of silver, 



may be mentioned the limestone of tlie Real del Car- 

 donal, Xaeala, and Lonio del Toro, to the north of 

 Zimapan, In Mexico graywacke is also rich in metals. 



Tlie silver-mines of the Real de Catorce, as well as 

 those of El Doctor and Xaschi, near Zimapan, traverse 

 Alpine limestone, which rests on a conglomerate with 

 siliceous cement. In that and the Jura limestone are 

 contained the celebrated silver-mines of Tasco and 

 Tehuilotepec, in the intendancy of Mexico ; and in 

 the.se calcareous rocks the metalliferous veins display 

 the greatest wealth. 



It thus appears that the cordilleras of Mexico contain 

 veins in a great variety of rocks, and that the deposites 

 which furnish almost all tlie silver exported from Vera 

 Cruz are primitive slate, graywacke, and Alpine lime- 

 stone. The mines of Potosi in Buenos Ayres are con- 

 tained in primitive clay-slate, and the richest of those of 

 Peru in Alpine limestone. Our author here observes, 

 that there is scarcely a variety of rock which has not in 

 some country been found to contain metals, and that 

 the richness of the veins is for the most part totally 

 independent of the nature of the beds which they 

 intersect. 



Great advantage is derived in working the Mexican 

 mines, from the circumstance that the most important 

 of them are situated in temperate regions where the 

 climate is favourable to agriculture. Guanaxuato is 

 placed in a ravine, the bottom of which is somewhat 

 lower than the level of the lakes of the valley of 

 Mexico. Zacatecas and the Real de Catorce are a little 

 hig'her ; but the mildness of the air at these towns, 

 which are surrounded l)y the richest mines in the 

 world, is a contrast to the cold and disagreeable atmo- 

 sphere of tlie Peruvian districts. 



The produce of the Mexican mines is very unequally 

 pportioned. The 2,500,000 marks, or l,6il,015 troy 



AdTantage- 

 ous sitiuition 

 ot mines. 



Irn'quaJlty. 



