GRANITE-BIMETALLIC    AND    CABLE    MINES,   MONTANA.  47 
concentrating  machinery  to  the  plant.  The  concentrates,  though 
low  in  gold,  carried  sufficient  copper  and  iron  to  make  them  a 
by-product  of  value. 
GEOLOGY. 
Country  rock.- — The  ore  deposits  occur  in  the  Wolsey  shale  and 
Meagher  limestone.  The  Wolsey  shale  is  in  most  places  a  rather 
fissile  olive-green  to  black  formation  from  100  to  300  feet  thick.  The 
Meagher  limestone  is  a  thick-bedded  medium-grained,  nearly  white 
to  dark-gray  limestone,  somewhat  gritty  on  weathered  surfaces.  Its 
usual  thickness  is  about  400  feet.  The  Wolsey  shale  rests  upon  the 
Flathead  quartzite  and  in  turn  is  overlain  by  the  Meagher  limestone. 
The  relation  of  these  rocks  with  later  ones  is  given  in  the  geologic 
section  (p.p  33-34). 
These  formations  have  been  cut  by  two  intrusive  masses  of  granite 
in  such  a  manner  as  to  form  a  long  narrow  belt  of  sedimentary  rocks, 
chiefly  Meagher  limestone,  closely  confined  between  granite  walls. 
The  southwestern  granite  mass  covers  an  area  of  several  square 
miles  and  extends  nearly  to  the  Southern  Cross  and  Gold  Coin  mines. 
This  granite  body  forms  the  south  wall  of  the  ore  zone.  The  northern 
intrusive  is  much  smaller  and  its  outcrop  is  relatively  long  and  nar- 
row, so  that  its  form  suggests  that  of  a  dike  approximately  parallel  to 
the  contact  of  the  larger  mass.  These  two  intrusives  are  in  the  main 
from  50  to  360  feet  apart,  and  though  each  sends  off  small  apophyses 
toward  the  other,  connection  between  the  two  has  not  yet  been 
found.  The  strike  of  the  ore  zone,  as  determined  by  the  granite  con- 
tacts which  limit  it,  is  about  northwest.  The  attitude  of  the  sedi- 
mentary rocks  in  the  mine  can  not  everywhere  be  made  out,  but  their 
general  strike  is  probably  close  to  that  of  the  ore  zone  and,  locally  at 
least,  their  dip  is  nearly  90°.  The  granite  is  medium  grained  and 
composed  essentially  of  feldspar,  quartz,  mica,  and  hornblende.  It 
is  in  most  places  fresh  and  very  much  resembles  the  granite  that  forms 
the  country  rock  of  the  Granite  mine,  near  Philipsburg,  though  the 
two  bodies  are  not  connected  in  outcrop. 
Contact  metamorp?iis?n. — The  sedimentary  rocks  are  greatly  meta- 
morphosed near  their  contact  with  the  granite.  The  upper  part  of 
the  Wolsey  formation  is  a  calcareous  shale  and  changed  very  readily 
to  a  rock  composed  chiefly  of  pyroxene,  amphibole,  garnet,  magnetite, 
epidote,  and  mica.  Rocks  of  this  composition  outcrop  on  the  surface 
north  of  the  ore  zone,  and  angular  masses  of  garnet  rock  more  than  a 
foot  in  diameter  occur  at  several  places  in  the  lower  levels  of  the 
mine.  They  are  especially  numerous  on  the  north  wall  of  the  214- 
foot  level.  The  contact-met  amorphic  minerals,  especially  garnet  and 
epidote,  are  in  many  places  concentrated  along  the  bedding  planes  of 
the  altered  shale  to  a  certain  extent,  and  this  is  also  true  of  pyrite. 
