Sketch of the Mine of Pasco. 53 
this esguito 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 those 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 line 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 calcming 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. Catalina, 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 voneemed; by 
that in the deep mines the metals are always accompanied 
by this stratum, 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 cireumference 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 the same wiiich 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, 
