514  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  [bull. 225. 
There  is  no  doubt  that  the  quartzites  form  a  definite  member  of  the 
metamorphosed  sediments  in  this  general  area,  but  the  region  is  so 
badly  broken  by  faults  and  the  outcrops  are  so  often  buried  in  the 
woods  that  it  is  impossible  to  say  whether  the  quartzite  appears  at 
one  or  more  horizons.  In  its  original  and  unmetamorphosed  condition 
it  was  probabl}r  a  very  bituminous  shale.  By  the  metamorphism  of 
such  a  deposit  the  abundant  feldspar  might  easily  have  resulted  and 
the  graphite  have  been  produced. 
•I.  Graphite  in  the  crystalline  limestones. — The  Algonkian  strata  of 
the  Adirondacks  contain  many  lenticular  beds  of  limestone,  which  vary 
from  a  maximum  of  about  100  feet  thick  down  to  a  few  inches. 
They  are  now  coarsely  crystalline  aggregates  of  calcite  or  dolomite, 
often  with  richly  disseminated  crystals  of  pyroxene,  and  not  infre- 
quently with  scales  of  graphite  more  or  less  abundantly  scattered 
through  the  mass.  The  crystalline  limestones  have  never  been  utilized 
as  a  commercial  source  of  the  mineral,  but  they  have  certain  advan- 
tages of  their  own  and  are  wortlry  of  serious  consideration.  The 
limestone  is  a  soft  rock,  easily  crushed,  and  in  separation  would  free 
itself  from  the  graphite.  The  presence  of  the  mica  (phlogopite) 
should  be  considered,  since  it  also  is  found  in  the  limestones  and  would 
present  difficulties  in  the  separation.  The  limestones  also  have  irreg- 
ular bunches  of  coarsely  crystalline  silicates  scattered  through  them, 
in  which  large  scales  of  graphite  are  common.  The  graphite  even 
presents  good  hexagonal  outlines,  each  an  inch  in  diameter. 
The  mineral  graphite  is  extremely  useful  and  of  increasing  impor- 
tance as  time  goes  on.  It  often  passes  by  the  name  of  plumbago,  or 
u  black  lead.''  A  "  lead  mine  "  in  the  usage  of  the  eastern  Adirondacks 
means  a  graphite  mine. 
In  the  trade  the  quality  of  the  mineral  depends  partly  on  the  size 
of  the  scales,  and  partly  on  its  adaptability  for  crucibles.  If  the  size  of 
the  scales  is  small  the  price  falls  and  the  difficulties  of  concentration 
are  increased. 
Contrary  to  the  general  impression  only  a  very  small  part  of  the 
graphite  produced  goes  into  lead  pencils,  and  practically  all  of  this  is 
obtained  from  Sonora,  Mexico.  Crucibles  for  the  manufacture  of 
crucible  steel  take  perhaps  most  of  the  product,  and  not  every  graphite 
can  be  used  for  them.  The  remainder  is  used  as  lubricants,  stove 
polish,  paints,  and  a  few  other  purposes. 
