Mineral Deposits <>/ Eastern California. — Fairbanks. 157 
quartz. The shattering of the country rock along a fissure 
and the substitution of silica seems to the writer to absolutely 
demand the removal of some of the crushed mass. If the re- 
moval of any material is admitted it is impossible to limit the 
extent to which the process might be carried under favorable 
circumstances. The occasional presence of large bunches or 
chimneys of quartz along the course of a vein and the fre- 
quent slight divergence of short veins fi*om this into the 
country rock point to local conditions favoring more ener- 
getic action. 
In many districts the quartz veins are quite localized. On 
the theory that the lenses of quartz along a vein are due either 
to an opening of the wall or to movements bringing two con- 
cave portions opposite, it cannot be conceived why quartz 
veins are frequently of so limited extent longitudinally. 
Faulting is a very common phenomenon in disturbed re- 
gions, but quartz veins or mineral deposits of any kind occur 
only here and there, so that it would seem that in addition to 
the formation of fissures there must accompany it in the local 
centres of deposition more or less removal of crushed rock. 
It can hardly be disputed that the large bodies of manga- 
nese, chrome iron and quicksilver in the Coast ranges, as well 
as the galena ores of eastern California, have been formed 
by replacement. 
In this discussion the writer does not wish to be under- 
stood as arguing that open fissures have not at times played 
an important part in mineral deposition, but that there are 
many reasons against that view of the origin of the most of 
the gold quartz veins as well as the other mineral deposits of 
( talifornia. 
(/>) Silver Deposits. Silver bearing galena is more often 
found associated with limestone in irregular chamber-like 
deposits along mineralized zones. Exceptionally it occurs in 
other sedimentary rocks and in granite, in the latter case 
forming well defined veins. Calcite and iron oxides form 
much of the gangue. 
Enargite is found only in the Tertiary lavas and more 
ancient rocks of Alpine county. 
Tetrahedrite,bornite,chalcocite, chalcopyrite,and etromeyer- 
ite occur characteristically in well defined veins with quartz 
