geaton.]  THE    CAROLINA   TIN    BELT.  191 
north  of  the  State  line,  and  there  turns  more  nearly  northward,  cor- 
responding very  closely  with  the  axis  of  the  Blacksburg  anticline. 
But  the  correspondence  is  not  exact,  for  at  Gatfney  the  pegmatite  dikes 
occur  on  the  southeast  side  of  the  axis  and  hence  dip  to  the  southeast, 
while  from  Blacksburg  northward  they  occur  where  the  rocks  dip 
northwestward,  indicating  that  the  belt  crosses  the  axis  of  the  anti- 
cline at  some  intervening  point.  The  structure  of  the  northern  part 
of  the  area  is  much  confused  and  has  not  been  deciphered. 
The  pegmatite  masses  are  called  dikes,  but  they  are  very  irregular. 
In  dip,  strike,  and  width  individual  bodies  exhibit  great  variations. 
Forking  or  branching  is  rather  common.  Frequently  a  dike  pinches 
out  completely  and  it  is  not  found  again,  but  sometimes  it  reap- 
pears in  the  same  plane  or  to  one  side.  These  variations  take  place 
both  horizontally  and  vertically.  For  instance,  a  dike  which  may 
have  a  considerable  continuous  extent  upon  the  surface  may  pinch 
out  at  a  comparatively  small  depth  and  perhaps  be  found  again 
below  or  at  one  side.  Conversely,  a  dike  which  is  short  horizontally 
may  be  deep.  Some  of  the  dikes  are  more  persistent  than  others, 
but  it  is  probably  only  a  matter  of  distance  or  depth  when  they,  too, 
will  show  irregularities.  In  actual  width  the  dikes  vary  from  nu- 
merous small  streaks,  a  few  millimeters  wide,  injected  into  the  coun- 
try rock  and  collectively  forming  what  may  be  considered  an  individ- 
ual dike,  to  bodies  probably  30  or  more  feet  wide.  One  of  the  wider 
dikes  occurs  about  a  mile  south  of  Kings  Mountain  village.  The 
common  width  of  the  dike  thus  far  exploited  for  tin  ore  is  from  2  to 
6  feet. 
CHARACTER  OF  THE  PEGMATITE  AND  THE  ORE. 
There  are  two  varieties  of  pegmatite.  One  is  composed  almost  ex- 
clusively of  quartz  and  microcline,  and,  so  far  as  known,  carries  no 
tin.  It  occurs  rather  commonly  in  the  neighborhood  of  the  Ross 
mine  at  Gaffney.  The  tin-bearing  variety  is  particularly  character- 
ized by  abundant  muscovite-mica  in  large  foils,  in  feathery  aggre- 
gates, or  in  small,  irregular  grains  mixed  with  quartz.  It  is  not  a 
lithium-bearing  species.  The  amount  of  quartz  varies,  but  is  always 
considerable.  Feldspar  is  sparingly  present,  and  is  largely  of  the 
plagioclase  variety.  In  general  appearance  the  rock  is  of  light  color 
and  of  variable  grain. 
It  seems  beyond  question  that  these  masses  of  rock  are  of  igneous 
origin.  There  is  no  indication  of  their  being  the  result  of  deposition 
from  solution.  The  contact  with  the  surrounding  rocks  is  sharp  and 
distinct,  and  no  impregnation  has  taken  place.  On  the  other  hand, 
the  effect  of  the  dikes  on  the  wall  rock,  wherever  it  could  be  studied, 
has  been  exceedingly  typical  of  the  contact  metamorphism  due  to  an 
intruded  igneous  mass. 
