QUARTZ  AND  FELDSPAR. 
FELDSPAR  AND  QUARTZ  DEPOSITS  OF  MAINE, 
By  Edson  S.  Bastin. 
INTRODUCTION. 
The  commercially  important  feldspar  and  quartz  deposits  of  Maine 
all  belong  to  a  single  type  of  rocks  known  to  the  geologist  as  pegma- 
tites. These  rocks  may  be  defined  as  coarse-grained  crystal  aggre- 
gates which  as  a  rule  have  the  composition  of  granite,  their  principal 
constituents  being  feldspar,  quartz,  and  mica,  usually  with  subordi- 
nate amounts  of  other  minerals.  The  pegmatites  of  Maine  were 
studied  by  the  writer  during  part  of  the  summer  of  1906,  the  work 
being  done  in  cooperation  between  the  State  Survey  Commission  and 
the  United  States  Geological  Survey. 
GEOGRAPHIC  DISTRIBUTION. 
These  deposits  are  confined  largely  to  Sagadahoc,  Cumberland, 
Androscoggin,  and  Oxford  counties,  in  southwestern  Maine,  though 
occurring  to  some  extent  in  association  with  all  the  large  granite 
masses  in  other  parts  of  the  State.  Excellent  exposures  occur  in 
many  open  pits,  from  which  feldspar,  quartz,  mica,  or  gem  minerals 
have  been  mined,  and  in  the  cliffs  along  the  seacoast,  especially  in  the 
Boothbay  Harbor  region. 
GEOLOGIC  OCCURRENCE. 
The  pegmatites  form  masses  that  are  plainly  intrusive  in  the  sur- 
rounding rocks.  The  latter  are  for  the  most  part  shaly  sediments, 
probably  of  early  Paleozoic  age,  which  have  been  closely  folded  and 
altered  to  slates  and  schists.  This  alteration  took  place  at  the  close 
of  Ordovician  time,  during  a  period  of  dynamic  or  regional  meta- 
morphism  which  affected  most  of  New  England.  In  many  of  the 
more  argillaceous  layers  the  regional  metamorphism  has  developed  a 
fissility  which  is  in  some  places  highly  inclined  to  the  bedding  planes 
and  in  others  nearly  parallel  to  them,  depending  on  the  character  of 
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