ran some] DEPOSITS OF RED MOUNTAIN REGION. 233 
a description of the secondary or oxidized ores of the American Belle 
and neighboring mines. They "occur above a former water line, 
either attached to walls of caves, as broken detached masses, or as a 
bed of clayey mud or sand, more or less completely filling the cave. 
The cave formation is identified with the massive outcroppings or 
knolls of silicified andesite ordinarily termed 'quartz.' These knolls 
* * * present a rough mass of quartz, cut up by cross fractures, 
and showing small vugs and cavities on the exposed cliff faces. The 
ore-bearing caves, which ramify throughout the mass, generally come 
to the surface along the cliff base." The caves are stated to come 
together in depth. The ores were mainly carbonates of lead and iron, 
with iron oxide, lead sulphate, and arsenates. Kaolinite and zinc 
blends were common. Galena occurred, but usually as a residue 
core. Such were the ores of the National (American) Belle, Grand 
Prize, and Yanderbilt mines, according to Schwarz. He briefly sum- 
marizes the characteristics of these secondary ores as follows: 
1. The secondary ores are richer than the sulphide ores occurring below them. 
2. The ores of adjoining or connecting caves are sometimes greatly different in 
grade. 
3. In some cases the formation of the caves along fracture or cleavage planes is 
evident, but in others all traces of such planes are quite obliterated. 
4. The cave walls are a porous sandy quartz, the sand from the disintegration of 
which forms part of the cave filling. 
5. The line of change from oxidized to unoxidi/.ed ores, or the former water 
level, is very marked. It varies as much as 100 feet in elevation in properties 
within 1 .000 feet of each other, rising to the south and west. The quartz outcrop 
rarely rises more than 200 feet above it. 
6. In isolated cases may be found masses of the unoxidized ore, the euargite (i.e., 
in National Belle), above the line of change, in the vicinity of the secondary ores. 
Mr. Schwarz ascribes the formation <>f the caves and the secondary 
ores within them to "surface waters" which "dissolved" sulphide 
ores and country rock as they moved along fracture planes. 
In 1S99 no thorough examination of the mine was possible, the 
croppings and an adit tunnel constituting the only accessible places 
for observation. The knob, or "blow-out," as the miners commonly 
term it, is in many places plainly an altered igneous rock, probably 
andesite or andesitie breccia. Hut the material in which the original 
porphyritic structure is still recognizable passes with no discoverable 
line of demarcation into a rock consisting chief!}' of quartz, in the 
condition of a tine-granular crystalline aggregate. On 1 lie northwest- 
ern side of the knoll the country rock was originally a monzonite- 
porphyry mass of the same kind as that exposed just south of the 
Yankee Girl, or forming the cliffs just east of Summit Station. This 
intrusive rock has been altered in a similar manner to the andesitie 
breccia. The comparatively fresh facies in which the orthoclase and 
quartz phenocrysts lie in a fine greenish groundmass may be traced 
into a medium stage of alteration in which the orthoclase phenocrysts 
