404  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1906,   PART    T. 
gneiss  is  composed  <>!'  hornblende  gneiss  and  hornblende  schist  with 
smaller  beds  of  mica  gneiss  and  mica  schist  included.  Large  areas 
of  the  other  rocks  mentioned  above  are  mapped  as  separate  forma- 
tions. These  are  principally  granites  and  granite  gneisses  of  Arehean 
age.  In  the  mica  regions  by  far  the  most  important  formation  is  the 
Carolina  gneiss.  It  extends  from  the  northwestern  side  of  the 
Cowee-Black  Mountain  belt  to  and  beyond  the  southeastern  side  of 
the  Piedmont  belt.  In  a  northeast-southwest  direction  it  extends 
far  beyond  the  State  boundaries.  The  age  of  the  Carolina  gneiss  is 
greater  than  that  of  any  other  formation  in  the  region.  Igneous 
rocks  <)i'  later  epochs  have  been  intruded  into  this  gneiss,  which  has 
been  gashed  and  cut  by  them  into  irregular-shaped  masses,  in  many 
places  forking  out  into  long  tongues  or  occurring  as  long,  narrow 
streaks  in  the  intrusives,  or  vice  versa.  This  feature  is  common  to 
both  the  granite  intrusives  and  the  Roan  gneiss,  which  is  the  next 
oldest  formation  n(  the  region.  Rocks  of  still  later  age,  as  Cam- 
brian sediments,  have  been  metamorphosed  into  gneiss  and  schist 
and  folded  with  the  older  formations  by  movements  associated  with 
the  Appalachian  uplift.  The  Carolina  and  Roan  gneiss  formations 
have  been  interbanded  with  and  cut  at  all  angles  by  numerous 
streaks  of  granitic  or  pegmatitic  material.  These  range  from  a  frac- 
tion of  an  inch  upward  in  thickness,  and  locally  pass  into  mica- 
bearing  pegmatites.  In  some  place-  pegmatization  is  so  thorough 
that  mica  gneisses  become  strikingly  like  granite  gneisses.  This  is 
especially  characteristic  of  the  Carolina  gneiss  in  the  Piedmont 
region. 
The  study  of  the  geology  in  this  region  i>  exceedingly  difficult, 
because  the  rocks  have  been  so  intensely  folded,  faulted,  and  meta- 
morphosed. The  enormous  amount  of  erosion  the  region  has  under- 
gone and  the  present  depth  •>('  atmospheric  decomposition  also  com- 
plicate the  t ask. 
OCCURRENCE   OF   MICA. 
Mica  deposits  ot  commercial  value  in  this  State  are  confined  to 
pegmatites.  These  rocks  vary  considerably  in  form,  some  being 
typically  lenticular  in  shape  and  others  more  or  less  persistent  in 
length.  The  lens-shaped  bodies  are  generally  conformable  with  the 
schistosity  of  the  inclosing  rock.  They  may  lie  in  the  same  line  of 
bedding  or  schistosity  and  be  connected  by  smaller  streaks  or  string- 
ers of  pegmatite  or  by  mere  seams  in  the  rock.  Many  of  them,  on 
the  other  hand,  lie  in  planes  of  schistosity  more  or  less  separated 
from  one  another  and  form  parallel  or  overlapping  bodies.  In  cross- 
section  some  of  these  lenses  are  short  and  bulky,  with  a  length  only 
two  or  three  times  the  thickness;  others  are  long  and  tapering,  and 
may  constitute  simply  a  bulge  in  a  sheet  of  pegmatite.  In  most 
places  the  schistosity  of  the  inclosing  rock  bends  around   the  lenses. 
