B. Silliman —Mineralogical Notes. 29 
bole, which have broken through sandstones and argillaceous 
shales. In Offenbanya, the tellurium ores oceur under very pe- 
culiar geological conditions ; that is, in veins in igneous rocks, 
and in segregated masses in granular limestone. The veins 
occupy thin clefts, fifteen of which on one property are tolerably 
parallel to each other (E. and W., dip 80°-40° N.), with an aver- 
age width of about an inch, and they carry chiefly sylvanite 
and nagyagite sparingly distributed, and more rarely native gold. 
The chief matrix is quartz and diallogite, associated with pyrite, 
galenite, sphalerite, stibnite, native silver and pyrargyrite. 
The gangue of the Nagyag lodes is diallogite, or brown spar, 
or calcite, or hornstone and quartz, it varying in the different 
lodes and in different parts of the same lode. The gold-bear- 
ing tellurium ores are scattered through this gangue with man- 
ganblende and pyrite. The chief ores worked are nagyagite, 
sylvanite, gold, auriferous iron pyrites, argentiferous tetrahe- 
drite, native silver and galenite. Associated with these are 
hessite, bournonite, jamesonite, barite, sphalerite, stibnite, native 
arsenic, realgar, orpiment, silver glance, chalcopyrite, marcasite, 
native copper, malachite, pyrrhotite, sulphur, &., with va- 
rious epigene species. In all, over forty mineral species are 
enumerated as found in the veins of Nagyag. Compared with 
this abundance, we find at the Red Cloud Mine only native 
tellurium, sylvanite, hessite, pyrite, chalcopyrite, and oly 
galenite and sphalerite, with native gold as an epigene species 
at s . The gangue stone is hornstone or chalcedonic 
quartz, with feldspar. 
Possibly explorations at greater depths may develop other 
species; but this result has not followed the deep workings of 
the silver mines in Nevada, where, at the depth of 1500 feet, the 
number of species found is not greater than it was at the sur- 
2. <A like paucity of species characterizes the metamorphic 
and voleanic rocks of the Sierra Nevada in California. 
Position and General Geology of the Gold Hill Mining Region ; 
by Arcu. R. Marvine, Geologist of the Geological Survey 
of the Territories in 1873.* 
THE accompanying map has been prepared to show the 
eral outlines of the country in the neighborhood of the Gold 
d F . . 
* These notes form part of Mr. Marvine’s Report, in the volume of Reports of 
pei, Be ERD eh ee oe 
