58 Sketch of the Mine of Pasco. 
let, it meets a rock, which at first sight appears to be a porphyry, but up- 
on examimation, it is found to be a decomposed granite, in which the 
quartz, the mica and felspar which compose the green cement, are dis- 
covered. It contains a vitreous substance, yellowish green, like the pe- 
ridot, but in the other pieces it is found to be rather a garnet: on 
the other side of the rivulet, there is an elevated chain, called Chu- 
quitaniba, in which are found gold mines; this is composed of sand- 
stone, quartz, and hornstone porphyry, and forms a stratum of con- 
siderable extent and bulk; in this lie the auriferous cubic pyrites, 
and the green carbonate of copper. These pyrites have been ex- 
ploded for a long time back; it varies with the argillaceous slate, 
which also encloses the same cubic pyrites. The cajou of this metal 
yields from four to five ounces, the gold is of the best quality ; and 
the metal is so abundant in this, and the ridges of la Quina, Chiqui- 
rin, and Huanacuanea, that there is enough for many years. _ It is 
stated that there are found in the neighborhood, ores of quicksilver, of 
rather good quality. An interesting formation of granite, well cha- 
racterized, but of little extent, is found in the heights of Pargas, (see the 
map,) and appears similar to that of St. Gothard, of Hogblin, in Nor- 
way; and to that of the heights of Tucto, Cordillera of Yauli. It 
forms in both parts strata distinctly disposed, reposing upon a black, 
leafy slate, in Pargas, and upon the sandstone, in Yauli. The quartz 
is transparent, with conchoidal fracture ; the felspar “is white, in 
large and well formed crystals, and also in small ones, constituting 
the base of the rock; the mica is in very black hexahedral prisms. | 
The granite is not very fine, but that of Tucto is more so, and does 
hot contain the felspar, so well formed. This formation is to all ap- 
pearance modern, and always found in the summits of the Cordillera, 
as the learned geologist, Humboldt, has observed, serving as a base 
to the traquito, as in Hually, although this appears to be a granite, 
entirely decomposed, since it has all the substances which character- 
ize it. In Pargas, this formation is accompanied by a whitish com- 
pact limestone, towards the North; towards the South, by a black 
‘slate ; and towards the East and West, by the sandstone ; but pur- 
suing its direction, it extends to the pampas of St. Andrews, in which 
is found the black slate, upon which it probably lies. This granite 
decomposes, and changes to a white granular rock, in which the 
quartz abounds, and in other pieces is the felspar, without any signs 
of mica or quartz. The miners use this rock for the grinders of the 
