*nsome.] THE STOCKS OR MASSES. HI 
National Belle mine, p. 231), the sand from the disintegration of which 
orms part of the cave filling. 
5. The line of change from oxidized to unoxidized ores, or the for- 
mer water level, is very marked. It varies as much as 100 feet in ele- 
ction in properties within 1,000 feet of each other, rising to the south 
,nd west. The quartz outcrop rarely rises more than 200 feet above it. 
(5. In isolated cases may be found masses of the unoxidized ore, the 
nargite, 1 above the line of change, in the vicinity of the secondary 
res. 
Mr. Schwarz considered the caves and secondary ores to have been 
ue to surface waters, which dissolved the sulphide ores and country 
ock as they moved along fracture planes. It appears unlikely, how- 
ver, that the surface waters exercised much solvent action upon the 
ountry rock. Their function was probably limited to the oxidation 
f the ore and to the removal of some of its constituents. 
CHANGES IN THE ORE WITH DEPTH. 
As indicated in the preceding section, the ores of some of the stocks 
/ere partially oxidized down to the ground-water surface. This sec- 
ndary alteration was particularly noticeable in the National Belle 
line, and to some extent in the VanderbiH mine, but was a much 
3ss conspicuous feature in the Yankee Girl, Guston, and other mines, 
he ore bodies of which outcropped nearer the bottom of the valley of 
led Creek. The oxidation apparently presented no unusual fea- 
ares, and seems to have consisted chiefly of the transformation of 
alena to carbonate and sulphate of lead, with removal of more solu- 
le constituents, reduction in the bulk of the ores, and the consequent 
Urination of caves. Even when, as in the case of the National Belle, 
tie ore of the deeper workings was chiefly enargite, the oxidized ores 
earer the surface were evidently largely composed of lead com- 
ounds, as no reference is found to the occurrence of copper carbon- 
tes. This result is probably less a consequence of any peculiar 
rocess of oxidation than of the relative disposition of the sulphide 
r unoxidized ores prior to superficial weathering. It is with the 
hanges in these latter ores relative to depth that this section has 
hiefly to do. 
In spite of the diversity shown by the different ore bodies, there is 
fter all remarkable uniformity to be found in the change at very 
loderate depths — usually less than 300 feet — from an ore consisting 
tiiefly of argentiferous galena to highly argentiferous silver-copper 
res, and then a gradual diminution of value downward through the 
lcreasing proportion of low-grade pyrite in the ore bodies. These 
aanges are best recorded in the Yankee Girl, Guston, and Silver Bell 
»It is evident that in this description Mi-. Schwarz has the National Belle deposit most in 
ind. 
