eansome] ORIGIN OF THE LODE AND STOCK ORES. 137 
review briefly the characteristic features of these ore bodies which 
bear upon this question. 
The ore first struck, in some cases actually at the surface, consisted 
chiefly of argentiferous galena. At a depth which varied somewhat 
in different mines, but which appears to have been usually less than 
200 feet, this galena changed to an ore consisting chiefly of highly 
argentiferous stromeyerite. At a still greater depth — usually about 
500 feet — the stromeyerite changed to argentiferous bornite, still 
deeper to chalcopyrite and pyrite, and finally to low-grade aurifer- 
ous and argentiferous pyrite. These changes were more or less irreg- 
ular and overlapping. Thus pyrite was found a1 nearly all levels, and 
punches of galena were met with far below the levels at which it ceased 
to be 1 he dominant ore. Small rich streaks of bornite were also found, 
with chalcopyrite and pyrite, below the levels where it occurred in 
large masses. According to Schwarz, 1 who opened and worked many 
bf the ore bodies of the Red Mountain district, the rich portions of 
the ore bodies were always associated with open water-bearing fis- 
sures, and he apparently regarded the entire deposits as formed pri- 
marily by deposition from the water entering through these fractures. 
It seems to be a well attested fad thai at a depth of about 500 feet 
there was encountered in the Yankee Girl and Guston mines a fault 
or "slip plane" with low westerly dip, and, further, that the richest 
ore occurred just above this seam, which was filled with clay-like 
gouge. Moreover, most of the water entering the mines came in at or 
above this fault. The acid character of this water was well known, 
and it carried in solution large amounts of the sulphates of iron and 
copper. Lastly, the mines are situated within a valley of erosion, 
within which the ore bodies outcrop at different levels. It is not 
known what thickness of material has been removed in the shaping of 
the present topography, but il probably exceeds 2,1100 feet. It is 
hardly conceivable that the observed relation between the vertical 
variations in the ore bodies and the present topographic surface is a 
haphazard one. It is without much doubt genetic. 
Ore deposits which show a fairly orderly vertical succession from 
rich sulphides near the ground-water level down to poor sulphides at 
greater depth are in nearly all cases regarded as the product of two 
concentrations — a concentration by ascending waters and a further 
concentration by descending waters. 2 By the former are deposited 
lean ores, found in the deepest workings, which are enriched to a 
greater or less depth by the downward-moving solutions. As Van 
llise has pointed out, these two processes may go on at the same 
time, or they may have operated successively on any given vertical 
section of the ore body. The facts obtainable in the Bed' Mountain 
region point to the original deposition of bodies consisting chiefly of 
1 Trans. Am. Inst. Min. Eng., Vol. XVIII, 1890, p. 144. 
2 Van Hise, op. cit., p. 101. 
