Sketch of the Mine of Pasco. 53 



this esquito is fine, of a darkish color, and very hard : it contains 

 particles of mica, and small veins of iron pyrites and white quartz, 

 run indistinctly through it. The miners, on account of the yellow 

 pyrites, and of the hardness of the rock, which does not permit the 

 four men who work in the excavation to advance more than two 

 yards, call it bronze. The stratum in the mass, bears the same 

 name, and in the extension of it, pyrites are found in mass, in almost 

 all the mines, and especially in tliose of St. Catalina, St. Rita, the 

 excavation of Yauacancha, and the mines north of the church of the 

 same name, since all those in this Hne are perforated with this sub- 

 stance. The pyrites are decomposed as much in the interior as the 

 exterior of the mines, and produce sulphate of iron, or a whitish sort 

 of copperas ; this salt is found in abundance, chiefly in the excava- 

 tions of Yauacancha. The magustral is made of these pyrites, by 

 first calcining it, in order to reduce it to an oxide ; it also contains a 

 considerable quantity of silver, and would defray the expense of 

 working it, if they knew how to extract the precious metal from this 

 kind of ore. 



The esquitoso soil mentioned, which, from all the qualities and cir- 

 cumstances attending it, belongs to the transition class, ought to contain 

 the pyritose strata, and with them the silver, since those which Trin- 

 idad, St. Catahna, St. Rita, St. Philip, &;c. afford, prove, that from, 

 the decomposition of this, proceeds the silver now extracted ; and 

 although the miners do not think so, this supposition is confirmed, by 

 observing that in the deep mines the metals are always accompanied 

 by this straturh, and very often they unite and form a mass. Upon^ 

 this soil rests the gres, as in the neighborhood of Lake Quinlacocha,. 

 in Uliachin, Pargas, Suco, and in the whole circumference compre- 

 hending the formations known to be metallic. The horizontal strata 

 have a direction from north to south, inclining to the east, and are 

 plainly seen in the hills of Uliachin and St. Juan, in which is observed 

 a certain correspondence in the opposite strata, which are interrupted 

 only by the mineral bed, in the cavity of which the diluvian waters 

 remained a longer time ; for this conclusion is naturally founded upon 

 what remains in the lakes existing in this cavity, and the many which 

 are scattered about at a short distance from the place. This forma- 

 tion extends many leagues, being tlie same which I have observed in 

 Punco, Lampa, Chucuito, Huaypacha, Yauli, and the neighborhood 

 of Tarine. It contains every where stone coal in considerable beds, 

 as in the exploded mine in Raucas, in Curaopuero, road to Vinchos, 



