lie 
166         CONTRIBUTIONS   TO    ECONOMIC    GEOLOGY,  1906,  PART   T. 
extend  more  nearly  parallel  with  the  range  and  have  greater  eifec 
upon  the  topography  than  the  normal  faults.     Most  of  the  norm 
faults  in  this  district  are  of  slight  displacement,  but  some  of  the  thrul 
faults  have  a  throw  of  a  thousand  feet  or  more. 
The  ore  occurs  in  two  forms;  the  first  rather  hard,  massive,  an 
quartzitic;  the  second  soft,  crumbly,  and  slaty.     The  soft  ore  is  gen 
erally  higher  in  iron  and  is  more  easily  mined.      It  undoubtedly  h 
been  formed  by  the  replacement  of  slate  by  iron.     The  hard,  massiv 
ore  breaks  into  angular  blocks  bounded  by  joints.      On  freshly  fra 
tured  surfaces  the  ore  is  seen  in  glistening  small  crystals  intersperse 
with  quartz  grains.      Much  of  the  quartz  is  of  a  bluish  color  but  o 
long  exposure  becomes  white  and   opaque.     The  quartz  grains  ar 
crushed  and  elongated  in  the  plane  of  the  cleavage.     The  ore  is  dark 
nearly  black,  but   becomes  gray  on  exposure.     This  change  of  color 
is  especially  noticeable  in  the  slaty  ore. 
At   the  Mesaba  mine  there  are  two  main  veins  of  ore,  which  differ: 
but   slightly  from  each  other  either  in  character  or  thickness.     Th 
eastern  vein  varies  from   lo  to  1.1  feel   in  thickness.     At  two  place 
however,  its  thickness  has  been  increased  by  thrust   faulting,  whiq 
took   place  before   the   block   faulting  occurred.      This   vein   has  been 
uncovered  for  about  600  feel  along  the  strike.      Beyond  the  point  thus  nil 
exposed  the  evidence  afforded  by  scattered  pits  is  too  incomplete  to  *\\ 
permit   valuable  deductions  as  to  the  structure  which  may  be  encounUc 
tered    in   furl  her  development . 
A  vein  of  ore  that  has  been  slightly  prospected  extends  from  the'  ) 
mine  nearly  due  south  for  a  quarter  of  a  mile  and  then  swings  around  I'.i 
toward   the  southeast.      It    may  be  traced   for  about   half  a   mile,  but!, 
near  the  junction  of  the  spur  1  rack  with  the  mainline  of  the  Louisville 
and  Nashville  Railroad  it  is  cut  oil*  by  the  fault  along  the  south  and  iL 
easl  -id''  of  the  range  which  brings  the  limestone  to  the  surface.     This'-lfi 
vein  has  an  exposed  thickness  ranging  from  :\\  to  5  feet.     The  ore  is  |„ 
of  the   hard    variety,   being  quartzitic,   with   numerous   flattened   and    , 
crushed  grains  of  quart  /.. 
The  second  vein  at  Tallaseehatch.ee  lies  about  75  paces  west  of  the  (  \ 
eastern  one.  Toward  the  south  the  western  vein  diverges  slightly,  so  ■  j e: 
that  the  distance  between  the  two  veins  increases  in  that  direction.  !i 
In  the  extreme  southern  part  of  the  area  that  has  been  opened  at  the  n 
mine  on  this  vein  about  42  feel  of  ore  is  exposed.  This  unusual 
thickness  is  due  to  the  reduplication  of  beds  by  thrust  faulting.  Roth  h 
the  eastern  and  western  veins  are  cul  by  normal  faults  that  have  east- 
west  strikes,  no  less  than  five  having  been  recognized  in  a  distance  of 
only  200  paces. 
The  entire  area  that  has  been  opened  up  at  the  Mesaba  mine  i 
included  within  a  square  thai  measures  200  yards  on  aside.  Nodept 
greater  than  20  or  25  feel  below  the  surface  has  yet  been  attained, 
