watson.]  THE    SEMINOLE    COPPER    DEPOSIT    OF    GEORGIA.  183 
to  white  in  accordance  with  the  amount  and  mineralogical  form  of  the 
bisilicate  present. 
In  general  the  strike  of  the  schistosity  is  northeast-southwest,  with 
considerable  local  variation  observed  from  place  to  place.  The  dip  is 
northwest.  The  schists  are  intersected  by  two  major  sets  of  joints 
which  strike  about  east-west  and  north-south,  with  minor  jointing 
developed  at  various  angles  to  the  major  jointing.  Slickensides 
usually  characterize  the  joint-plane  surfaces,  indicating  subsequent 
movement  in  the  rocks. 
Dike  rocks. — Dikes,  mostly  of  altered  basic  igneous  rocks,  intersect 
the  schists  in  large  numbers.  They  vary  from  a  few  feet  to  several 
hundred  feet  in  width.  Where  exposed  in  the  underground  workings 
they  are  completely  schistose  and  broken  at  close  intervals  by  joints. 
They  are  very  dark  and  are  composed  chiefly  of  altered  feldspar,  some 
biotite,  hornblende,  and  much  quartz,  which  in  most  cases  at  least  is 
probably  secondary.  Furthermore,  they  are  in  general  abundantly 
impregnated  with  large  and  small  crystals  of  pyrite. 
In  the  stream  bed,  about  700  feet  west  of  the  shaft,  is  exposed  an 
igneous  rock,  which  is  entirely  distinct  in  mineral  type  from  the  dikes 
exposed  in  the  underground  workings.  The  rock  is  moderately  dark 
and  fine  to  medium  textured,  and  contains  innumerable  conspicuously 
developed  rounded  quartzes  of  opalescent  appearance.  Under  the 
microscope  large  phenocrysts  of  both  potash  and  plagioclase  feldspars 
are  recognized.  Fresh  exposures  of  the  rock  in  the  stream  bed  indicate 
a  degree  of  mineralization  with  pyrite  equal  to  the  schistose-hornblende 
dikes  in  the  mine  openings.  On  the  opposite  side  of  the  stream  from 
the  mine  the  rock  is  deepby  decayed,  but  can  be  readily  traced  by  means 
of  the  rounded  quartzes  which  litter  the  surface. 
Both  underground  and  on  the  surface  the  dikes  strike  in  two  general 
directions,  namely,  about  N.  75°  W.  and  N.  20°  E.  So  far  as  could 
be  determined  from  the  underground  working  the  dikes  striking 
N.  20°  E.  are  the  oldest,  since  they  are  cut  across  by  those  striking 
N.  75°  W.  The  rocks  are  so  completely  altered  that  no  contact  phe- 
nomena could  be  definitely  made  out,  though  the  contacts  between  the 
dikes  and  inclosing  rocks  are  at  all  times  entirely  sharp.  Neither  was 
there  apparent  evidence  for  regarding  the  dikes  striking-  N.  20°  E.  as 
apophyses  from  those  striking  N.  75°  W.  The  dikes  vary  but  little 
from  the  vertical,  though  the  dikes  striking  N.  75°  W.  show  local 
variations  in  the  dip  of  as  much  as  15°  N.  in  some  places,  while  those 
striking  N.  20°  E.  indicate  a  tendency  in  dip  toward  the  west. 
At  the  time  the  mine  was  examined  the  shaft  had  penetrated  to  a 
depth  of  approximately  200  feet,  with  ore  worked  on  the  90-,  125-, 
145-,  and  185-foot  levels.  Where  the  levels  had  been  opened  for  a 
long  enough  distance  from  the  shaft  the  same  dikes  could  be  readily 
traced  penetrating  the  rocks  in  each  of  the  levels. 
