Principal Silver Mines in Mexico aud South America. 231 



The mines of the district of Sombrerete, which approaches that 

 of Fresnillo on the north west, are in a compact limestone, which 

 contains siliceous slate and lydian stone. There are some veins of 

 from three to four feet in thickness, whose entire mass is formed of 

 antimonial sulphuret of silver. One of these veins gave, in six 

 months, seven hundred thousand marcs* of silver. The limestone, 

 in this vicinity, is much more elevated than the porphyry. 



The district of Catorce is situated about 24° N. latitude, one hun- 

 dred miles east of Sombrerete, and about three hundred miles north 

 of Mexico. A great number of small and very variable veins have 

 been explored. The masses of the veins are disintegrated, so that 

 the ores are earthy, and most of them are colorados, or earthy fer- 

 ruginous ores. The veins traverse a compact secondary limestone, 

 which covers argillaceous slate, (schiste argileux de transition.) 

 Masses of basalt and cellular amygdaloid, which contain olivine, 

 zeolite and obsidian, are protruded above the limestone. 



III. PacJmca, Real del Monte, and Moran. 



These mining districts are very near each other. Four great 

 veins, viz. la Biscaina, le Rosario, la Cabrera and I'Encino, traverse 

 all these districts, to great distances, without changing their direc- 

 tion, and almost without being crossed or deranged by any other 

 vein. 



The veins traverse a decomposed porphyry, whose basis is some- 

 times a scaly hornstone, and sometimes an earthy mass. Common 

 and glassy feldspar, and some spots of green hornblende, are ob- 

 served, but no quartz. Tn the vicinity of these rocks, on the high- 

 est summits, are other porphyritic rocks, with a basis of pearl stone, 

 mingled with beds and nodules of obsidian. 



Upon the first or metalliferous porphyry, reposes the alpine lime- 

 stone, (calcaire alpin,) which contains some veins of galena. This 

 is covered by Jura limestone, which, in its turn, is covered by slaty 

 sandstone, and finally, gypsum, mingled with clay, completes the 

 series observed. From the vein Biscaina, in the district of Real del 

 Monte, the Count de Regla, in twelve years, cleared |5,000,000. 



These mining districts have enjoyed great celebrity, both on ac- 

 count of their great wealth and their vicinity to the capital. The 



* A Spanish marc is equal to 7 oz. 3 dwt. 14 grs. troy.— Mier's Travels, II, 405. 



