30 QUICKSILVER DEPOSITS OP THE PACIFIC SLOPE. 



ore, and spots of bituminous matter are sometimes found. I found quartz 

 gangue abundant both in the reserves and in tlie newer exposures. 



The deposits of the Ahiiaden mine consist of three tabular masses of 

 ore, nearl}' GOO feet long and from 12 to 25 feet in thickness. They stand 

 almost vertically and nearly coincide in position with the surfaces of strat- 

 ification. The southernmost body is called San Pedro y San Diego ; then 

 come the San Francisco and, still farther to the north, the San Nicolas. 

 The first of the three consists of a stratum of sandstone (or quartzite, as it is 

 called by some authors) impregnated to a large extent with cinnabar. The 

 impregnation diff"ers in degree and is sometimes so complete that de Prado 

 infers a partial replacement of the material of the rock by the metallic sul- 

 phide. ]\rost later writers have accepted de Prado's view, but I could find 

 no evidence to sustain it. In the two more northerly bodies the deposits 

 consist of quartzite intersected by stringers and seams of cinnabar. The 

 seams are sometimes parallel to one another and sometimes intersect the 

 rock in every direction. Occasionally portions of the quartzite appear to 

 be impregnated with cinnabar. The walls of the deposits are formed by 

 quartzite and slate. When quartzite is the wall rock the ore dies out into 

 it gradually, but scarcely a trace is to be found in the slate. Diabase in a 

 highly decomposed condition is said to cut off tlie San Nicolas and the San 

 Francisco to the east. 



The ore does not always follow a single stratum, but, according to 

 Kuss, sometimes passes abruptly from one stratum to another. Slicken- 

 sides are noted in the schists by Caron, who also mentions small faults in 

 the San Nicolas, which did not reappear in tlie San Francisco. 



There has been much difference of opinion as to the classification of 

 these deposits. Early authors regarded them as veins ; de Prado, who con- 

 sidered tliat the ore was introduced fi-om below after the formation of the 

 beds, regarded the deposits as ore-bearing strata, but not as veins. Nog- 

 gerath assents to this opinion, pointing out that many phenomena common 

 in veins are not found here. Caron calls them impregnations and denies 

 that they are veins or beds. Kuss says: "So soon as one admits, with Mr. 

 de Prado, that the mercury is derived from the earth's interior, so soon as 

 one recognizes that tlie deposits of Alniaden form relatively narrow belts, 



