Principal Silver Mimes of Mexico and South America. 227 



torce, and many others near Zimapan, are in the alpine limestone, 

 as well as those of Tasco and Tehuilotepec, and the veins are rich- 

 er in this limestone than in the argillaceous slate, which serves as a 

 basis for it. 



The three most productive mining districts have their veins situa- 

 ted in different rocks, viz. those of Guanaxuato in primitive argillite, 

 (" schiste argileux primitif,") those of Zacatecas in grauwacke, and 

 those of Catorce in alpine limestone, ("calcaire alpin.") The mines 

 of Pasco and Hualgaj^oc, in Peru, are also in the alpine limestone,* 

 but that of Potosi is in primitive slate, ("schiste primitif.") 



M. Humboldt remarks, that the more we study the geological con- 

 struction of the globe, the more are we led to observe, that there 

 hardly exists any rock, which, in certain countries, has not been 

 found eminently metalliferous. 



The most common ores of silver, in Mexico, are the sulphuret, 

 the antimonial sulphuret, the prismatic black ore, the chloride, and 

 gray copper. It is rare not to find native silver, in small quantity, in 

 connection with the sulphuret of silver, and one mass of native silver 

 was found at Batopilas, weighing more than four hundred pounds. 

 Red silver ore and chloride of silver, which are rare in Europe, are 

 abundant ores in Mexico and South America. There are some 

 earthy ores of silver, called colorados, and in Peru pacos, which con- 

 tain imperceptible particles of silver ores, disseminated in a basis, 

 which is mostly oxide of iron. This ore is generally found where 

 a vein of silver ore approaches the surface of the earth. Among 

 the other ores explored for the silver they contain, are the argentif- 

 erous sulphurets of lead, iron, and copper. 



The quantity of silver in the ores, averages from three to four 

 ounces to the quintal, or from ^jj to ^-^^ of the weight of the ore. 

 The annual produce of silver, during the last years of the eighteenth 

 century, by Mexico, was 537,512 kilogrammes, or 1,134,424 lbs., a 

 kilogramme being 2 lbs. 3 oz."5 dr.; but -}§ of the mines do not 

 produce j\ of this amount. Thus we see -^\ of the mines, being 

 the most productive, give more than j-i of the whole amount. 



Most of the mines of Mexico are situated either upon the back 

 or sides of the Cordilleras, and particularly on the west side, and 

 they are the most abundant between the eighteenth and twenty fourth 

 degrees of north latitude. 



* Annales des Mines, t. xxis, p. 113. 



