GEAPHITE    m   MAINE.  481 
side  relatively  barren,  even  at  the  point  of  contact  with  the  pegmatite.  This  pegmatite- 
schist  contact  is  well  defined,  and  while  the  muscovite  selvage  contains  a  small  content  of 
graphite,  the  muscovite  does  not  apparently  extend  into  the  schist. 
Microscopic  examination  of  thin  sections  of  these  rocks  simply  confirms  the  field  evi- 
dence. The  schist  contains  varying  amounts  of  graphite,  adjoining  beds  also  differing 
considerably  in  their  other  constituents.  A  specimen  collected  at  a  distance  of  several 
feet  from  the  pegmatite  contact  is  a  quartz-biotite  schist  in  which  graphite  is  present  as 
very  fine  dust,  which  gives  the  gray  color  to  the  rock.  A  thin  section  cut  from  another 
rock,  apparently  relatively  barren  of  graphite  although  close  to  the  contact,  shows  a 
similar  small  content  of  graphite  dust,  the  mass  of  the  schist  being  composed  of  musco- 
vite, quartz,  tourmaline,  and  pyrite.  The  adjoining  bed,  which  was  mentioned  above  as 
graphitic,  is  a  schist  darker  in  color,  but  when  the  rock  is  studied  in  thin  section  the 
amount  of  graphite  present  is  found  to  be  small.  The  abundance  of  needles  of  brown 
tourmaline  doubtless  contributes  to  the  dark  color,  and  pyrite  is  again  present,  in  close 
association  with  the  tourmaline. 
A  thin  section  of  the  best  grade  of  graphitic  rock  collected  at  the  Madrid  cut  shows  this 
schist  to  contain  small  grains  of  graphite  evenly  distributed  throughout  the  rock.  This 
is  in  most  intimate  association  with  muscovite,  the  small  folia  of  muscovite  being  thor- 
oughly interwoven  with  the  graphite  flakes  and  grains.  In  other  bands  fine  grains  of  quartz 
form  the  matrix  for  the  graphite  particles.  The  schist  is  beautifully  foliated  and  a  glance 
at  either  the  hand  specimen  or  the  thin  section  leads  the  observer  to  overestimate  the 
amount  of  graphite  present.  This  is  due  to  the  fineness  of  grain  and  the  thorough  dissem- 
ination of  the  graphite  throughout  the  rock.  Although  it  is  evenly  distributed  in  the  rock, 
the  foliated  character  of  the  graphite  causes  the  surface  of  this  graphitic  schist  to  seem 
very  rich  in  graphite.  The  graphite  particles  are  in  reality  minute  and  range  from  0.20 
to  0.01  mm.  in  diameter,  the  average  size  being  less  than  0.04  mm. 
A  sample  was  collected  of  the  best  of  the  graphite  schist  as  exposed  in  October  on  the 
face  of  the  cut  at  Madrid.  The  amount  of  graphite  in  this  sample  was  determined  in  the 
Survey  laboratory  by  E.  C.  Sullivan  as  8.5  per  cent. 
YARMOUTH    OCCURRENCE. 
In  the  town  of  Yarmouth  the  graphite  locality  is  about  one-half  mile  northwest  of  the 
village.  The  country  rock  in  the  southern  part  of  Cumberland  County  is  a  fissile  schist,  fine 
grained,  but  apparently  not  at  all  carbonaceous.  This  schist  in  the  town  of  Yarmouth  is 
cut  by  large  intrusions  of  granite,  and  in  one.  of  the  large  masses  of  granite  graphite-bearing 
pegmatite  occurs.  This  pegmatite  has  been  prospected  at  several  points  within  200  yards 
and  occurs  in  the  form  of  a  dike  with  an  average  width  of  1  foot.  The  exposures  were  not 
sufficient  to  determine  whether  there  is  not  a  possibility  of  two  parallel  dikes  being  present 
rather  than  a  single  dike.  At  one  point  a  basaltic  dike  is  in  contact  with  the  pegmatite, 
and,  though  the  contact  relations  are  not  at  all  plain,  the  pegmatite  is  presumably  the 
older. 
The  pegmatite  is  for  the  most  part  of  medium  grain,  and  quartz  and  feldspar  are  the 
principal  constituents.  Small  amounts  of  mica  occur,  but  only  sporadically,  while  graphite 
is  an  important  constituent.  A  few  nests  of  graphite  about  an  inch  in  diameter  occur  in 
the  pegmatite,  but  the  most  of  the  graphite  is  in  the  form  of  disseminated  flakes  evenly 
distributed  throughout  the  rock.  No  definite  difference  between  the  content  of  graphite 
near  the  walls  of  the  dike  and  that  at  the  center  could  be  noted,  nor  was  any  variation 
noticed  in  the  amount  near  the  contact  with  the  basaltic  rock. 
Examined  microscopically,  this  pegmatite  is  found  to  resemble  other  pegmatites  except 
in  the  presence  of  the  graphite.  Quartz,  orthoclase,  and  plagioclase  form  a  mosaic  similar 
to  that  typical  for  granite.  The  only  other  constituent  present  is  biotite,  which  occurs 
in  small  amounts  and  is  largely  altered  to  chlorite.  The  graphite,  as  already  mentioned, 
occurs  in  the  larger  masses  and  in  flakes.     These  lustrous  flakes  are  disseminated  in  the 
