390  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1006,  PART    I. 
the  same  dimensions  to  a  considerable  depth.  A  number  of  other 
dikes  of  pegmatite  of  similar  size  and  shape  occur  in  this  vicinity  and 
some  of  them  have  been  worked  to  a  slight  extent.  None  of  these,  so 
far  as  seen,  showed  any  large  amount  of  feldspar  of  the  grade  required 
for  pottery  purposes. 
The  rock  now  quarried  is  mainty  a  coarse  graphic  intergrowth  of 
feldspar  and  quartz,  and  it  is  estimated  that  about  50  per  cent  of  the 
total  material  excavated  is  of  commercial  grade.  The  quarry  has 
been  worked  intermittently  for  over  thirty  years,  and  in  the  past  has 
produced  larger  amounts  of  perfectly  pure  spar  than  at  present.  It 
is  said  that  a  single  blast  would  sometimes  loosen  100  tons  of  almost 
pure  feldspar.  Black  mica  is  almost  wholly  absent.  Black  tourma- 
line is  somewhat  abundant,  but  is  so  aggregated  in  certain  parts  of 
the  deposit  that  it  can  be  easily  separated  in  mining.  Some  deep 
flesh-colored  garnet  is  also  present.  Muscovite  (white  mica)  is  only 
locally  abundant.  The  feldspar  is  cream  colored  and  is  largely  of 
the  potash  variety,  as  shown  by  the  following  analysis  made  by  the 
Pittsburg  testing  laboratory: 
Analysis  of  feldspar  from  Georgetown,   Mr. 
sin, '. 65.23 
A 1  ..<  )3 20.  09 
Fe203 71 
K20 11.  60 
Na2( ) 2.  00 
1  oss  "D  ignition 'M> 
99.99 
TOPSHAM,  SAGADAHOC  COUNTY. 
Twto  quarries  in  Topsham  are  operated  by  the  Trenton  Flint  and 
Spar  Company,  of  Trenton,  N.  J.  The  larger  quarry  is  about  1| 
miles  uorthwesl  of  Cathance  station  and  the  smaller  about  half  a 
mile  southwest  of  the  larger.  The  spar  is  hauled  by  teams  from  these 
mines  to  the  mill,  which  is  located  on  Cathance  River  near  Cathance 
station.  During  wet  seasons  the  water  power  of  the  river  is  utilized, 
hut  the  mill  is  also  equipped  with  steam.  The  grinding  machinery 
consists  of  three  chasers  and  four  ball  mills,  each  capable  of  grinding 
a  ton  ol  spar  in  four  to  five  hours.  The  capacity  of  the  mill  is  about 
L6  tons  a  day.  The  quarry,  which  is  the  largest  one  in  Maine,  covers 
an  area  of  several  acres  and  is  about  50  feet  in  maximum  depth.  In 
its  southern  portion  the  rock  is  very  similar  to  that  at  the  George- 
town quarry,  being  largely  a  graphic  intergrowth  of  feldspar  and 
quartz  in  greatly  varying  proportions.  At  the  north  end  of  the 
quany  the  pegmatite  is  much  coarser  and  graphic  texture  is  prac- 
tically absent.  At  one  place  a  continuous  bed  of  white  quartz  10 
feet  high  and  50  feet  long  is  exposed,  and  adjacent  to  it  is  a  mass  of; 
pure  feldspar  15  feet  across.     The  principal  iron-bearing  mineral  at 
