Copper and Lead in Netv Mexico. — Herrick. 
289 
ous stratum formed by the granite, becomes the collector of 
the iron leeched from the rocks above, forming a band of var- 
iable width in which the sand grains are coated with iron ox- 
ide or replaced by it. In this case the collection is not so 
complete at this horizon as in the San Andreas by reason of 
the fact that the metamorphism of the sandy lower layers of 
the limestone has been so complete as to form water-bearing 
horizons above, and there has been a good deal of accimiul?- 
tion of iron in the same way at these higher levels. Along the 
axis of uplift the effect on the silicious materials has been very 
great, and there has been a thickening of these bands. The 
lime, on the other hand, has been abruptly turned on edge 
and the selvedge has been wedged in between the less altered 
lime and the granite till from a distance it appears in sections 
as though there had been an igneous intrusive thrust up at 
this point. Such an appearance is very deceptive in the sec- 
tion in the Palomas Gap canon and affords a most interesting 
geological object lesson. The general conditions are repro- 
duced in the accompanying diagram. 
CoLbo^llo Mt 
C..^o../e 
erc(^ceoui 
The whole series is subject to the same system of frac- 
ture lines so much in evidence in the San Andreas and the 
collection of copper at the intersection of the veins with the 
iron band is similar, with this difference that, inasmuch as 
the iron is also to some extent precipitated in the lower mem- 
bers of the limestone series, the sulphides are also more ex- 
tended in the vertical direction. This fact will also probably 
militate against the collection of very large bodies even at the 
intersection. The chemistry of the copper precipitation mav 
well be a subject for speculation. That the iron is leeched 
from above can hardly be doubted and it is e(|ually probable 
that the copper came up in some form from the depths along 
the fissures. It is obvious too that no considerable part of 
