Sketch of the Mine of Pasco. 57 
The grés lies distinetly upon this in horizontal strata, from north to 
south, inclining to the east and varying with the limestone just like 
that of the Pasco Ridge. 
A stratum of green porphyry with crystals of felspar, presents 
itself at the entrance of the break through the road of Junin; it 
is about a yard wide, and varies more or less in its inflections. In 
this calcareous and sandy formation, are the mines of our Senora de 
la O, Chiriquiquira, Descubridora, Copacabana, Trinidad, &c. In 
the first, the stratum has for covering a loose grés; for a wall, a 
dark ealcareois sandstone, half a yard wide, and extremely vitreous ; 
the metal is an argentiferous oxide of iron, with copper pyrites, with 
pavonine spots. ‘The summits of these ridges are all of limestone, 
and in it is found the notable stratum of lignite, a league and a half 
from the place, and which has been wrought by the miner Loli, after 
having at first extracted large pieces of this fossil, which plainly in- 
dicate its origin. Also the limestone varies with a stratum of white 
compact yeso, in the road to Tarma, half a league from Huaypacha, 
along the shores of the river. This yeso is like that which exists at 
the foot of the ridge of Chiacha, near Hualley ; from which a brack- 
ish water issues. In all the breaks which surround the ledge of 
Pasco, the limestone is seen changing with the sandstone, in strata, 
sometimes horisontal, sometimes perpendicular, according to the 
directions the s assume; in the ridges of Sacra-familia, and 
anton Riiainclechs, sinuosities plainly appear. In the breaks of 
and Tulluranca, a limestone is found which appears of 
more recent formation than that of the chain ; it is’a mass which 
contains separate pieces of black limestone, semicompact, united by 
a.dirty black cement, similar, on the whole, to the puddingstone. 
With this rock they make the grindstones of the engines, which last 
two or three months ; descending by these breaks on the north, you 
go as far as the gold mine of Quinau, distant two leagues from Pas- 
co. In the bottom of the valley, you meet with a very interesting 
formation, seen only here and there, because the sandstone covers it. 
‘On entering the valley, (even i in the break itself,) you find a white 
semisaccharoidal rock, in which are distinctly — shining 
plates, which reflect the light. It contains fragments of the white 
conchoidal, hyaline quartz, spangles of green talc, and small pieces 
of pyrites 5 jdt —— to be of felspar. It serves for the stones of 
the engines which grind the gold — Inclining towards the riva- 
Vou. XVI.—No. 1. 
