1 82 The American Geologist. September, 1902 
in the dark-colored gneisses, and held ore-bodies in the pink or 
white feldspaihic gneiss. My own observations enabled me 
to confirm this in a general way, and also showed that in am- 
phibolyte the vein was barren as well as narrow, and that no 
workable ore-bodies had been found in the dior)^te. In quartz- 
yte and in the intrusive rhyolyte porphyry the veins have proved 
rich near the surface, but the values have gone down but a 
few yards. It is believed, however, that this is because of struc- 
tural conditions, with secondary enrichment of a shattered zone, 
rather than because of a mineralogical condition due to the 
nature of the enclosing rock. These conditions are indicated 
in Fig. 7, reproduced from my report on the district.* 
Furstenbiirg. — A similar example is quoted from Four- 
net by De la Beche.t The Wenzal vein at Furstenburg 
is nearly vertical and cuts down through many beds of gneiss, 
about 60 ft. thick, that dip east. In the micaceous gneiss the 
vein is a nearly imperceptible string of clay. In argillaceous 
slates it suddenly becomes 12 to 18 in. thick, consisting of 
baryta, ruby-silver, large masses of antimonial silver, and ar- 
gentiferous copper. In the hornblende-gneiss it continues, but 
the silver-ores are wanting and galena is the only c^re. In the 
fourth series, of slightly micaceous beds of gneiss, the silver- 
ores are as abundant as in the argillaceous slates ; but they 
gradually disappear in depth, being replaced by relenite and 
galena. 
It will be noted that the Xeihart veins present several con- 
tradictions to the rule observed in the Butte district. The ores 
occur in the feldspathic rocks, carrying little ferro-magnesian 
minerals. The basic araphibolyte and the diorite are both bar- 
ren. It should be noticed also, in this connection, that the 
ore-depositing solutions were markedly different in the two 
cases. In the Neiliart veins the gangue is mainly a mixture of 
carbonates of lime, iron and manganese. The ores are also 
markedly different, as they consist primarily of galena wath 
sphalerite and pyrite, which is secondarily enriched in the 
upper parts of some veins. The solutions have been of such 
a character as to react with the feldspars rather than with the 
ferro-magnesian silicates. 
OtJicj' Montana Localities. — In the silver-lead camp of 
Barker in the Little Belt Alts., near Xeihart, as at the mines 
•"Geologv of the Little Pelt Mts., Mont.," 20th Ann. Rept. U. S. GeoU 
Surv., 1900. Part lii. p. 419. 
t Geological Observer, p. 6H0 
