MICA    DEPOSITS    OF    WESTERN    NORTH    CAROLINA.  421 
was  formed.  It  is  thought  that  pegmatite  veins  may  have  formed  in 
very  much  the  same  way  as  these  auriferous  quartz  veins.  Under 
similar  conditions  heated  solutions,  carrying  the  constituents  of  peg- 
matite instead  of  those  of  gold-bearing  quartz  veins,  would  form  regu- 
lar veins  of  pegmatite.  Any  irregularities  in  the  composition  of  the 
solutions  would  produce  the  banding  already  described  as  of  common 
occurrence  in  pegmatites. 
It  is  difficult  to  conceive  of  the  formation  by  injection,  as  an  ordi- 
nary magma,  of  pegmatite  in  streaks  or  bands  a  fraction  of  an  inch 
thick  in  gneissic  rocks,  in  many  places  having  no  visible  connection 
with  other  pegmatite  bodies.  On  the  other  hand,  it  is  easy  to  conceive 
of  a  solution  being  forced  through  the  smallest  fractures  or  working  its 
way  between  the  mineral  particles  and  depositing  its  load.  The  latter 
process  would  not  require  such  high  temperatures,  either  in  the  solu- 
tion or  country  rock,  as  would  be  required  for  the  injection  of  a  magma 
in  order  that  it  might  not  be  cooled  so  quickly  as  to  prevent  coarse 
crystallization.  The  possibility  of  the  formation  of  these  smaller  peg- 
matites by  the  injection  of  a  highly  fluid  aqueo-igneous  magma  is  not 
denied,  especially  if  the  magma  approaches  closely  the  conditions  of  a 
solution.  It  is  thought,  however,  that  aqueous  pr  >cesses  afford  a 
simpler  and,  therefore,  more  reasonable  explanation. 
Pegmatization  of  rock  masses,  so  common  in  the  Carolina  gneiss, 
especially  in  the  Piedmont  Plateau  region,  has  probably  resulted  from 
one  or  both  of  two  causes — namely,  either  recrystallization  due  to 
aqueous  agencies  or  the  addition  of  more  material  from  solutions  pass- 
ing through  the  formations.  In  the  first  process  occluded  water  in  the 
rock,  aided  by  the  heat  generated  during  regional  metamorphism,ma}^ 
have  caused  recrystallization  and  consequent  pegmatitic  texture.  In 
the  second  process  it  is  probable  that  pegmatization  has  resulted  from 
solutions  which  were  forced  through  the  rock  along  cracks,  seams,  or 
bedding  planes  and  there  deposited  their  load.  Where  pegmatization 
is  characterized  by  much  feldspar,  it  is  probable  that  these  solutions 
were  of  magmatic  origin,  and  one  generally  does  not  have  to  look  far 
to  find  a  granite  intrusion  in  the  neighborhood. 
It  is  thought  that  pegmatites  occurring  in  irregular  masses,  streaks, 
lenses,  augen,  or  balls,  and  having  no  visible  connection  with  other 
pegmatite  bodies,  are  generally  the  result  of  aqueous  action.  A  solu- 
tion could  be  readily  forced  through  fractures  or  seams  along  the  bed- 
ding planes  and  deposit  its  load  only  in  the  more  favorable  places.  If 
such  bodies  were  formed  by  intrusions,  it  would  be  necessary  to  con- 
sider that  the  walls  of  the  dike  had  been  forced  together,  closing  the 
passage  through  which  the  magma  had  passed.  Though  the  possi- 
bility of  such  conditions  is  not  denied,  a  simpler  method  of  formation, 
as  deposition  from  solution,  is  considered  more  probable.  In  augen 
and  ball-shaped  bodies  of  pegmatite  without  visible  connection  with 
