202  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,    L906,  PART    I. 
deposited  long  before  the  produetion  of  the  peneplain,  which  preceded 
the  deposition  of  the  Guernsey  formation.  After  the  iron  ore  was 
deposited,  surface  waters  modified  the  deposit,  forming  considerable 
bodies  of  soft  ore  along  planes  of  maximum  circulation,  a  like  effect 
being  produced  by  movement  along  shear  zones.  Further,  limonite 
has  been  formed  along  some  of  the  water  channels  of  the  past  and  the 
present  day. 
RULES  FOR  PROSPECTING  AND  GROUND  FAVORABLE  FOR  PROSPECTING. 
The  restriction  of  the  important  ore  bodies  of  the  Hartvillc  iron 
range  to  a  single4  contact  has  already  been  mentioned  and  the  exten- 
sion of  this  contact  has  been  described.  In  prospecting  it  the 
diamond-drill  holes  should  be  located  in  the  schist  area  at  a  distance 
of  from  400  to  000  feel  from  the  foot  wall  of  limestone.  When4  the 
contact  is  covered  by  alluvium,  as  it  is  from  [ronton  to  Kline's 
ranch,  it  will  be  necessary  by  churn  or  diamond  drill  to  more  accu- 
rately locate  this  contact.  Drill  data  indicating  the  presence  of 
minor  folds  should  be  carefully  sought,  for  ore  will  probably  be 
found  in  minor  synclines.  Whether  this  portion  of  the  contact  will 
prove  as  rich  as  that  which  has  already  been  prospected  may  be 
questioned,  but  ore  bodies  probably  exist  within  this  new  prospect- 
ing ground.  The  proximity  of  the  detrital  Carboniferous  ore  bodies, 
later  to  be  described,  is  a  further  help  in  prospecting,  since  they  are 
apparently  confined  to  the  immediate  vicinity  of  iron-ore  lenses  in 
the  pre-Cambrian  rocks.  The  dial  compass  and  dip  needle  are 
valueless  I'm-  use  in  this  iron-ore  range,  since  considerable  bodies  of 
the  iron  ore  are  nonmagnetic  while  some  of  the  noniron-bearing  for- 
mations, such  as  the  gabbro,  ailed   the  needles  appreciably. 
The  conditions  that  determine  the  presence  of  iron  ore  along  the 
contact  already  described  appear  to  be  (1)  the  folding  to  which  the 
rocks  have  been  subjected  and  (2)  the  presence  of  a  thick  body  of 
schist  to  serve  as  a  source  of  the  ore  superimposed  upon  an  imper- 
vious body  of  limestone.  The  schist -limes)  one  contacts  throughout 
the  range  are  similar  to  this  one  as  regards  the  folding.  In  most 
places,  however,  the  schist  above  the  limestone  is  too  thin  to  be  the 
source  of  large  ore  bodies.  The  only  probable  exception  to  this 
statement  is  the  contact  between  the  schist  and  limestone  in  the 
west  half  of  sec.  26  and  the  east  half  of  sec.  27,  T.  27  N.,  R.  66  W. 
Along  this  contact  north  of  the  furnace  at  Fairbank  there  is  a  hill 
of  pre-Cambrian  limestone.  North  of  this  hill  is  a  wide  valley, 
beyond  which  pre-Cambrian  muscovitic  schist  is  exposed.  This 
schist  is  very  thick,  and  beneath  it  the  limestone  dips  northward  at 
an  angle  of  70°.  It  is  believed  that  this  contact,  which  is  hidden  in 
the  valley,  is  worth  careful  prospecting.  Farther  north  of  east,  in 
sec.  26,  hornblendic  schists  cut  out  the  muscovitic  schist.     The  large 
