118 (Ge I, SEI BL ICIM CIE 
These veins are so regular that it is conceived that they may be 
best explained as the result of warping or shrinking in the sedi- 
mentary series and it seems certain that they have been filled 
from above. The vein matter is chiefly calcite, fluor spar, 
siderite and barite and it is chiefly at the intersection of the vein 
with a band of iron-filled quartzite, reposing on the granite and 
forming a definite selvedge to the sedimentary series, that the 
copper is deposited. The ores include nearly all the common 
copper compounds, calchocite, malachite, azurite, bournite and 
cuprite predominating. Here, as in Hannover and Santa Rita, 
it seems indubitable that the iron, accumulated by leaching, has 
been the agent in precipitating the copper. 
Between the Organ and San Andreas mountains there is an 
area on either side where the granite is laid bare and it is true 
that some show of copper may be found in crevices and basins 
superficially on the granite. It is probable that all, or a great 
part, of the copper of the two ranges has been originally 
derived from the red-bed series (Permian and Triassic) by 
infiltration, for the original existence of the cupriferous series on 
top of the strata now remaining in the ranges is indubitable. 
Dikes of diorite cutting through the granite and sedimentaries 
along or near the fault line have caused portions of the latter to 
lie in irregular fragments along the foot of the escarpment to the 
east, the strata dipping towards the dike which served to pry 
them from their original position. 
Standing upon a jutting eminence of the San Andreas and 
turning eastward one looks out upon a scene difficult to parallel. 
At one’s feet 1s an enormous plain, apparently as level as a floor,. 
over forty miles wide and extending as far as eye can reach to 
north and south. On the southern horizon rise the Jarillas 
Mountains which only partially interrupt the plain, while to the 
northeast are the snow-capped peaks of the Sierra Blanca. 
Northward the plain is narrowed by the eastward intrusion of 
the Oscuro range while it is possible to make out the dark area 
of basalt which covers that part of the plain to the east and south- 
east of that range. This is the widely-know ‘‘mal pais” of 
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