LIME    INDUSTRY    OF    KNOX    COUNTY,    ME.  399 
On  the  whole,  the  shipment  of  magnesian  limes  for  building  purposes  is  to  be  encouraged, 
but  it  is  a  question  whether  a  product  of  more  merit  can  not  be  secured  by  the  hydration  of 
this  lime  before  it  is  placed  upon  the  market.  The  process  of  hydration  would  not  be 
greatly  slower  than  in  the  case  of  calcium  limes  and  the  danger  from  imperfect  slaking  at 
the  hands  of  the  mortar  mixer  would  be  completely  avoided.  The  result  should  be  a  lime 
which  is  superior  in  strength  to  the  calcium  limes. 
Recently  there  has  been  considerable  complaint  from  pulp-mill  operators  because  there 
has  often  been  much  dirt  mixed  with  the  raw  magnesia  rock  and  with  the  magnesian  lime 
which  was  shipped  to  them,  and  some  custom  has  been  lost  for  this  reason.  Owing  to  the 
clay  covering  which  usually  overlies  the  limestone  here,  it  is  difficult  to  keep  the  rock  per- 
fectly clean.  Probably  this  trouble  could  be  remedied  in  part  by  keeping  the  stripping  of 
the  clays  further  in  advance  of  the  quarrying,  but  it  is  worth  considering  whether  I  he  rock 
could  not  be  washed  before  shipment  or  burning  at  little  or  no  extra  expense  by  utilizing 
the  water  which  is  pumped  from  the  quarry,  but  which  usually  serves  no  useful  purpose. 
THE   MAIN    ROCKLAND-THOMASTON  BELT. 
The  diagram  (fig.  15)  brings  out  certain  features  of  importance  in  regard  to  the  distribu- 
tion of  the  different  kinds  of  limestone  within  the  main  belt.  These  may  be  enumerated  as 
follows,  always  bearing  in  mind  the  caution  already  given,  that  the  diagram  is  not  intended 
to  show  actual  thicknesses  or  sequence,  but  to  bring  out  correctly  the  principles  involved. 
(1)  Repetition  of  beds. — The  character  of  the  folding  is  such  that  the  same  bed  is  likely 
to  be  repeated  several  times  in  the  width  of  the  belt.  Thus  the  bed  E  (fig.  15)  appears 
again  at  E'  and  E",  and  the  bed  C  is  repeated  at  C.  As  a  result  we  may  have  within  the 
broad  limestone  area  several  nearly  parallel  belts  of  almost  identical  rock,  separated  by 
belts  of  poor  rock  or  of  good  rock  of  a  different  kind.  This  principle  finds  an  immediate 
application  in  the  prospecting  for  new  deposits.  This  search  should  be  conducted  by  tesl 
troughs  or  ditches  dug  through  the  surface  clays  and  gravels  at  a  right  angle  to  the  general 
trend  of  the  limestone  belts.  Such  prospect  ditches  are  likely  to  disclose,  beyond  the  walls 
of  poor  rock  which  bound  the  pits  now  worked,  a  repetition  of  the  same  profitable  bed  or 
the  presence  of  a  bed  of  good  rock  of  a  different  kind — that  is,  "hard"  instead  of  "soft" 
rock,  or  vice  versa. 
(2)  Width  of  surface  outcrops. — The  surface  width  of  the  bands  of  "hard  rock,"  "soft 
rock,"  and  impure  limestone  depend  not  only  on  the  original  thickness  of  1  hese  various  beds, 
but  also  on  the  character  of  the  folding  and  the  position  of  the  present  surface  with  respect 
to  these  folds.  Thus  the  "hard  rock"  as  it  outcrops  at  C  is  a  broad  band,  while  at  C  its 
outcrop  is  narrow.  The  same  is  true  of  the  impure  limestone,  which,  as  represented  at  I), 
has  a  broad  outcrop,  but  at  D'  a  very  narrow  one. 
(3)  Depth  of  the  folds. — As  already  stated,  the  folds  which  are  developed  in  these  rocks 
are  more  compressed  even  than  is  shown  in  the  diagram.  Their  depth  is  greater  than  their 
width;  in  many  cases  it  is  probably  two  or  three  times  as  great.  As  a  consequence  it  may 
be  expected  that  in  most  cases  a  "vein"  of  a  valuable  rock  can  be  worked  to  a  depth  which 
is  at  least  equal  to  its  width  and  which  may  be  twice  its  width.  In  only  a  few  eases,  as  at 
locality  C  (fig.  15),  is  the  depth  likely  to  be  less  than  the  surface  width. 
(4)  Prospecting  outside  the  limestone  area. — In  the  past  considerable  time  and  money  has 
been  expended  in  sinking  drill  holes  and  prospecting  in  other  ways  for  limestone  in  the 
schist  ("land  ledge")  areas  outside  the  limestone  belts.  Since  the  schists  lie  beneath  the 
limestones,  it  is  manifestly  useless  to  expect  to  find  limestone  by  drilling  through  the  schists. 
In  nearly  every  case,  if  limestone  is  present  at  all,  it  will  be  present  at  the  surface.^ 
The  field  studies  within  this  region  indicate  that  the  supply  of  valuable  rock  does  ik»! 
remotely  approach  exhaustion,  and  that  intelligent  prospecting  following  the  methods 
already  outlined  will  disclose  large  deposits  whose  presence  is  not  now  suspect  ed.     The  suc- 
a  Some  limestone  does  occur  locally  below  the  schists,  but  it  is  older  than  the  limestone  here  discussed 
and  is  not  of  economic  importance. 
