420  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  19(H),  PART    T. 
can  be  drawn.  Van  Ilise  further  cites  the  occurrence  of  pegmatite  in 
metamorphic  rocks  in  the  Marquette  district  of  the  Lake  Superior 
region,  where  no  parent  granite  mass  was  found,  and  concludes  that 
the  pegmatite  was  formed  by  the  metamorphism  of  the  rocks  through 
mechanical  action  aided  by  aqueous  agencies. 
It  is  thought  that  these  views  are  applicable  to  the  pegmatites  of 
North  Carolina.  Some  are  so  clearly  associated  with  large  granite 
intrusions  and  are  so  like  granite  in  their  behavior  toward  the  country 
rock  that  the  theory  of  intrusive  origin  seems  particularly  appropriate. 
Others  also  in  regions  of  granite  masses  exhibit  structures  so  similar 
to  those  generally  attributed  to  vein  formations  that  they  must  be 
considered  of  aqueous  origin.  Still  others  show  structures  common 
to  both  igneous  masses  and  vein  formations  and  must  be  placed  in 
the  intermediate  stage  sei  forth  by  Van  Hise.  There  are  pegmatites 
within  the  areas  of  the  Carolina  and  Roan  gneisses  which  are  so  far 
removed  from  any  known  granite  masses  that  it  seems  probable  that 
they  were  produced  during  the  metamorphism  of  the  inclosing  rocks, 
like  those  of  the  Marquette  district.  This  theory  is  more  plausible 
when  the  great  extent  of  the  regional  metamorphism  of  the  Carolina 
and  Roan  gneiss  formations  and  the  large  number  of  small  pegmatite 
streaks  cutting  them  at  all  angles  are  taken  into  consideration. 
The  occurrence  of  drusv  cavities,  comb  st  met  ure,  and  regular  band- 
ing, such  as  is  common  in  many  fissure-vein  deposits,  is  observed  in 
few  places,  if  anywhere,  in  the  mica-bearing  pegmatites  of  North  Caro- 
lina. This  is  not  to  be  wondered  at  when  the  condit  ions  of  the  forma- 
tion of  pegmatite  are  considered.  'Fhe  materials  are  probably  derived 
from  deep-seated  magmatic  or  metamorphic  sources,  and  the  pegma- 
tite was  formed  at  great  depth  under  condit  ions  of  heat  and  pressure. 
If  1  he  material  was  itself  a  magma,  the  resulting  form  would  be  a  dike, 
in  which  formation  cavities  are  never  looked  for,  except  near  the  sur- 
face. If  the  material  was  a  solution,  either  of  magmatic  or  metamor- 
phic origin,  a  vein  would  be  produced.  That  veins  do  not  necessarily 
have  banded  structure  nor  drusy  cavities  is  plainly  shown  by  many  of 
the  auriferous  quart/  veins  of  the  southern  Appalachians,  in  which 
genuine  banding  or  crustification  is  rare  and  the  majority  show  no 
trace  of  either.  These  veins  are  the  mere  stumps  of  a  once  extensive 
vein  system  that  has  been  eroded  away  along  with  several  thousand 
feet  of  the  formations  in  which  they  occurred.  According  to  Graton,a 
these  veins  were  formed  by  heated  solutions  forced,  under  great  pres- 
sure, into  what  in  many  cases  may  have  been  the  merest  fractures  and 
depositing  their  loads.  The  force  of  crystallization  may  also  have 
aided  in  expanding  the  openings,  but  the  principal  force  is  supposed 
to  be  due  to  the  pressure  exerted  by  the  weight  of  overlying  forma- 
tions on  these  solutions  at  a  lower  depth  than  that  at  which  the  vein 
aGraton,  L.  C,  Gold  and  tin  deposits  of  the  southern  Appalachians:   Hull.  U.  S.  Geol.  Survej  No, 
293,  1906,  p.  60. 
