284  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  [bull. 225. 
plateau,  a  little  east  of  the  middle  and  at  the  north  boundary  of  the 
State,  is  an  outlier  of  the  lignite  area.  Within  the  area  proper  are 
Williams,  Billings,  Stark,  Mercer,  Oliver,  Burleigh,  and  Morton 
counties,  the  greater  parts  of  Ward,  McLean,  and  Emmons,  and  por- 
tions of  Bottineau,  McHenry,  Wells,  and  Kidder  counties— an  area 
equal  to  at  least  half  of  the  State  of  Ohio. 
The  centers  of  mining  development  have  been  determined  mainly 
by  the  number  and  extent  of  local  outcrops  and  by  proximity  to  rail- 
roads or  a  market.  Lignite  is  mined  for  shipment  in  Burleigh, 
McLean,  Morton,  and  Stark  counties,  and  in  several  of  the  other 
counties  in  the  area  there  are  local  "banks"  from  which  lignite  is 
stripped  to  be  used  for  domestic  purposes  by  the  owners  or  is  sold  at 
the  mine  to  neighboring  ranchmen  who  haul  it  away,  perhaps  20  miles. 
General  geologic  relations. — The  badlands  with  their  characteristic 
topography  constitute  the  very  heart  of  the  lignite  area.  The  innu- 
merable "breaks,"  opening  into  larger  stream  valleys  and  presenting 
vertical  sections  of  hundreds  of  feet,  are  admirably  adapted  to  reveal 
the  stratigraphy  and  mineral  wealth  of  this  portion  of  the  State.  In 
the  lignite  area,  outlined  above,  the  rock  formations  are  restricted 
practically  to  the  uppermost  formation  of  the  Cretaceous,  the  Laramie, 
and  the  overlying  glacial  drift.  The  Laramie,  which  contains  all  the 
workable  lignite  of  North  Dakota,  consists  of  sands,  sandstones,  lignite, 
and  thin  bands  of  hematite,  clay  ironstone,  and  shaty  limestone.  The 
clays,  which  constitute  perhaps  three-fourths  of  the  entire  formation, 
are  in  part  of  great  purity,  and  such  are  of  considerable  value  for 
brickmaking.  The  strata  lie  practically  undisturbed,  with  a  broad 
slope  from  the  high  badlands  on  the  west  to  the  drift-covered  plains 
east  of  the  Missouri. 
Number,  thickness,  and  extent  of  the  seams. — In  the  western  part  of 
the  area  the  seams  are  most  numerous,  five  to  nine  being  reported  as 
observed  in  natural  exposes  along  the  Little  Missouri  and  Missouri 
valleys  and  other  stream  cuttings.  Their  number  decreases  toward 
the  eastern  edge  of  the  area,  where  one  to  three  seams  exist  at  certain 
points.  It  is  noteworthy  here  that  this  evidence  rests  solely  on  visible 
outcrops.  Future  deep  well  records  and  prospect  holes  doubtless  will 
reveal  the  existence  of  much  more  lignite  below  the  surface.  -  Already 
two  deep  wells,a  one  at  Medora,  the  other  at  Dickinson,  have  been 
sunk  about  1,000  feet,  and  each  passed  through  16  lignite  seams  vary- 
ing in  thickness  from  a  few  inches  to  over  23  feet,  the  total  aggregat- 
ing more  than  60  feet. 
In  thickness  the  seams  vary  from  1  inch  to  40  feet.  The  40-foot 
bed  outcrops  in  Billings  County,  in  sec,  31,  T.  135  N.,  R.  101  W.,  but 
thins  rapidly  to  15  feet  within  a  quarter  of  a  mile.     Near  Sentinel 
a  Darton,  N.  H.,  Preliminary  report  on  artesian  waters  of  a  portion  of  the  Dakotas:  Seventeenth 
Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  2,  1896,  p.  CG4. 
