MINES OF MEXICO. 



341 



mg minerals, such as fibrous zeolite, stilbite, gram- 

 matite, pycnite, native sulphur, fluor, barytes, corky 

 asbestus, green garnets, carbonate and chromate of 

 lead, orpiment, chrysoprase, and fire-opal. 



Among the transition rocks, containing ores of 

 silver, may be mentioned the limestone of the Real 

 del Cardonal, Xacala, and Lomo del Toro, to the 

 north of Zuriapan. In Mexico graywacke is also 

 rich in metals. 



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

 as those of El Doctor and Xaschi, near Zuriapan trav- 

 erse alpine limestone, which rests on a conglome- 

 rate 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 these calcareous rocks the metalli- 

 ferous veins display the greatest wealth. 



It thus appears that the cordilleras of Mexico con- 

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

 deposites which furnish almost all the silver exported 

 from Vera Cruz are primitive slate, graywacke, and 

 alpine limestone. The mines of Potosi, in Buenos 

 Ayres, are contained in primitive clay-slate, and the 

 richest of those of Peru in alpine limestone. Oar 

 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 Mexi- 

 can mines, from the circumstance that the most im- 

 portant of them are situated in temperate regions 

 where the climate is favourable to agriculture. Gua- 

 naxuato 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 Ca- 

 torce are a little higher ; but the mildness of the 

 air at these towns, which are surrounded by the 

 richest mines in the world, is a contrast to the cold 

 Ff 2 



