490  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY;  1904.         [bull.  2G0. 
color,  although  locally,  as  in  the  northern  part  of  Deer  Isle  and  in 
the  vicinity  of  Stonington,  it  has  a  light-pink  tint.  The  granite  con- 
tains both  hornblende  and  biotite,  but  usually  the  darker  minerals 
are  not  abundant,  although  evenly  distributed  throughout  the  rock. 
The  grain  of  the  granite  ranges  from  fine  to  coarse,  although  most 
of  the  rock  quarried  might  be  termed  medium  grained.  It  is  worthy 
of  mention,  as  showing  the  uniformity  of  the  granite  both  in  color 
and  in  grain,  that  often  work  on  the  same  contract  is  done  at  quarries 
several  miles  apart. 
At  a  few  localities  dark  knots  are  found  in  the  granite,  and  in 
some4  quarries  bands  of  aplitic  material  cut  the  coarser  granite. 
Neither  the  basic  segregations  nor  aplitic  dikes  are  common  enough, 
however,  to  materially  affect  the  amount  of  clear  stone  available  in 
the  quarries.  The  granite  of  this  area  is  also  remarkably  free  from 
mineral  constituents  of  a  nature  to  cause  staining  of  the  rock.  This 
is  shown  in  the  slight  amount  of  discoloration  on  the  weathered  sur- 
face of  the  ledge.  In  most  of  the  quarries  only  a  few  inches  of  the 
surface  rock  is  slightly  weathered,  so  that  a  very  small  amount  of 
work  is  necessary  to  develop  a  quarry,  and,  indeed,  often  even  the 
surface  blocks  are  used. 
A  most  important  feature  affecting  the  granite  industry  is  the 
distribution  of  joints  in  the  rock  mass.  The  rift,  or  plane  along 
which  the  granite  splits  most  readily,  varies  in  direction  in  the 
different  quarries.  In  the  vicinity  of  Stonington  the  rift  ranges  from 
north-south  to  X.  40°  W.,  while  the  joints  in  the  same  localities 
range  from  N.  50°  W.  to  N.  85°  W.  The  "  bottom;'  or  approxi- 
mately horizontal,  joints,  are  perhaps  the  most  conspicuous  features 
in  the  granite,  as  it  is  exposed  in  the  quarry  face.  The  presence  and 
spacing  of  these  well-defined  planes  are  often  what  determine  the 
location  of  a  new  quarry.  The  spacing  of  these  parting  planes  in 
the  rock  determines  the  kind  of  work  for  which  each  quarry  is  espe- 
cially adapted,  and  while  in  a  few  quarries  in  the  Penobscot  Bay 
area  the  joints  are  so  close  together  that  only  material  for  curbing 
and  paving  blocks  can  be  quarried,  in  many  other  quarries  excep- 
tionally large  blocks  suitable  for  monoliths  can  be  easily  taken  out. 
Examples  of  these  will  be  given  in  a  later  paragraph. 
Equipment  of  quarries. — The  largest  of  the  granite  quarries  of  the 
Penobscot  Bay  area  are  those  in  the  vicinity  of  Stonington  and  Vinal- 
haven,  including  the  Crotch  Island  and  Hurricane  Island  quarries. 
Several  of  these  quarries  doubtless  rank  as  the  largest  in  the  United 
Slates,  and  are  well  equipped  for  a  large  output  of  both  rough  blocks 
and  dressed  granite.  The  works  of  the  Bodwell  Granite  Company  at 
Sand  Cove  on  Vinalhaven  has  an  equipment  comprising  travelings 
cranes,  lathes,  pneumatic  hand  tools,  and  plug  drills,  in  addition  to 
the  usual  number  of  derricks,  hoisting  engines,  steam  drillers,  and  sur- 
