dillek.]  INDIAN    VALLEY    REGION,    CALIFORNIA.  47 
sediments,  the  other  between  Crescent  and  Greenville,  cutting  the 
quartz-porphyries  of  that  district.  The  metalliferous  deposits  are 
confined  chiefly  but  not  wholly  to  the  igneous  rocks,  and  in  none  of 
the  cases  examined  are  they  definite  contact  deposits,  such  as  occur 
in  a  portion  of  the  Genesee  belt.  The  deposits  throughout  the 
Crescent  belt  are  in  more  or  less  well-defined  quartz  veins,  running 
generally  parallel  to  the  course  of  the  belt,  but  in  a  few  cases  there 
are  small  veins  at  nearly  right  angles  to  the  others.  The  ore  is 
auriferous  pyrite,  sometimes  in  small  bodies,  but  generally  dissemi- 
nated in  the  narrow  strip  of  sheared  rock  of  the  partially  formed 
vein,  in  which  there  is  usually  some  quartz.  The  pyrite  is  nearly 
always  changed  to  limonite,  setting  the  gold  free  and  staining  the 
incomplete  vein  as  well  as  its  walls.  One  of  the  best  defined  and 
most  complete  quartz  veins  of  the  Crescent  belt  occurs  in  the  Pre- 
mium mine.  It  is  vertical,  about  2  feet  in  thickness,  and  cuts 
granodiorite. 
In  the  Green  Mountain  mine  one  subordinate  vein  carries  a  small 
amount  of  chalcopyrite,  but  in  general  copper  is  absent  in  the  belt, 
except  at  the  Petti nger  mine,  near  Taylors ville,  where  a  small  imper- 
fect vein  in  the  Taylorsville  slates  is  impregnated  with  carbonates  of 
copper,  sometimes  blue,  but  generally  green. 
An  exceptional  deposit  for  the  Crescent  belt,  and,  indeed,  for  the 
whole  region,  is  a  mass  of  pyrrhotite  a  mile  and  a  half  nearly  south  of 
Taylorsville.  It  lies  in  a  narrow  strip  of  sheared  sandstone  running 
north  and  south,  but  the  largest  body,  about  10  feet  in  thickness,  is  at 
a  point  where  the  sheared  sediments  end  against  serpentine.  The 
pyrrhotite  was  tested  for  nickel  by  Mr.  Hillebrand.  but  none  was 
found. 
GEOLOGY    OF    THE    GENESEE    BELT    OF    MINES. 
The  Genesee  mining  belt  folloAVs  approximately  the  northeastern 
limit  of  the  Mesozoic  sediments  where  they  come  in  contact  with  the 
granodiorite  and  other  igneous  rocks.  The  deposits  are  variable  in 
form;  some  are  more  or  less  complete  veins  following  narrow  belts 
along  which  the  rock  has  been  crushed  and  sheared ;  others  follow  the 
line  of  contact  bounding  the  granodiorite.  In  some  deposits  the  ore 
is  auriferous  quartz  and  limonite,  but  in  others  it  is  chiefly  bornite, 
chalcopyrite,  chalcocite,  or  copper  carbonates.  Quartz  is  the  most 
common  gangue  mineral,  but  in  one  case  barite  appears,  and  in  an- 
other a  green  mineral  like  actinolite. 
The  Gruss  mine,  on  Wards  Creek,  is  on  both  sides  of  the  contact 
(between  andesite-porphyry  and  slaty  shale.  In  the  shale  the  partially 
formed  veins  follow  narrow  shear  zones,  in  which  there  is  some  aurif- 
erous quartz  associated  with  limonite  that  deeply  stains  the  richest 
portions  of  the  crushed  mass,     The  adjacent  andesite  is  often  decid- 
I 
