276 PER U. 
given above. The part of the ground that has been broken up, and 
in which ores have been found, is about half a mile in length in a 
north and south direction, and about one-fourth of a mile east and 
west. Within the whole of this extent ores have been mined of 
greater or less value, and the number of mines worked and now 
deserted are said to amount to upwards of a thousand : some of these 
are represented on the plan by round marks. 
The town of Pasco is surrounded on three sides — northeast and 
south by hills of blue limestone ; on the west the hills are of sand- 
stone, and on the southwest of a blue slate. Through the latter rock 
the adit wmich comes up from the lake of Quilacocha has been 
driven, until it reached the metalliferous ground in the district of 
Santa Rosa. All the ores of the Cerro are ferruginous, and the silver 
nearest to the surface is contained in an ochreous iron-stone. In 
particular spots the silver is found mixed with lead and copper, and 
at variable depths in different localities the ores rest on a bed of solid 
iron pyrites, which in some mines yield silver and in others not. 
Although there appeared to be two veins, crossing each other at 
right angles, yet strictly speaking there is but one, the great vein of 
Colquijirca. This vein comes in from the hill of Uliachim, on the 
south of the town, and runs through the whole metalliferous ground 
to the edge of the plain of San Juan on the north. 
On the course of this lode, generally speaking, the richest ores are 
met with. On each side of the vein an extensive deposit of ore is 
generally found, with little regard to the ordinary regularity of metal- 
liferous formation. 
The plain of San Juan is divided into many mining districts, to 
which names are given to distinguish them more readily. The 
southernmost of these is called Zauricocha, and contains several 
mines, from which great wealth has been produced since the Revo- 
lution. This is the district from which all the richest ores have been 
produced, and it has been always looked upon as the most important 
district in the Cerro. It is believed that farther south, between this 
point and the hill of Uliachim, some good ores exist, but no attempt 
has yet been made to mine there. 
In the district of Santa Rosa, lying west of Zauricocha, the greatest 
quantity of ore has been raised : it has been worked down to the level 
of the adit; and in several mines, where good ore has been discovered, 
they have descended to a lower level, drainage having been effected 
by hand-pumping. 
