Sketch of the Mine of Pasco. 51 



The gres lies distinctly upon this in horizontal strata, from north to 

 south, inclining to the east and varying with the limestone just hke 

 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 gres ; for a wall, a 

 dark calcareous 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 thfe 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 horizontal, sometimes perpendicular, according to the 

 directions the breaks assume ; in the ridges of Sacra-familia, and 

 shore of Quinlachocha, sinuosities plainly appear. In the breaks of 

 Pucayau and TuUuranca, 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 in the break itself,) you find a white 

 semisaccharoidal rock, in wliich are distinctly perceived shining 

 plates, which reflect the light. It contains fragments of the white 

 conchoidal, hyaline quartz, spangles of green talc, and small pieces 

 of pyrites ; it appears to be of felspar. It serves for the stones of 

 the engines which grind the gold metal. Inclining towards the rivu- 



VoL. XVII.— No. 1. 8 



