GLENKOCK    COAL   FIELD,    WYOMING.  161 
Ft.      in. 
Shale,  dark 29 
Shale,  blue 6 
Coal 2  2 
Shale,  with  hard  concretionary  layers,  weathering  to  very  dark 
brown 11 
Shale,  light  gray 4 
Concretions,  hard,  dark  brown 1-12 
Shale,  bluish,  massive 10 
Shale,  thin  bedded 1 
365+ 
The  outcrop  of  the  beds  at  Inez  trends  about  northwest  and 
southeast,  but  a  short  distance  farther  southeast  the  trend  changes 
to  nearly  east  and  the  beds,  crossing  the  river  near  Douglas,  con- 
tinue in  this  direction  to  the  east  end  of  the  field.  Just  west  of 
Douglas  there  are  six  or  eight  coal  prospects,  none  of  which  is 
worked  to  any  extent  at  present.  The  bed  ranges  in  thickness 
from  a  little  over  2  to  a  little  over  3  feet. 
Northwest  of  Inez  the  beds  are  exposed  almost  continuously  to 
the  river.  About  1  mile  north  of  the  river  they  probably  swing 
around  to  the  west  for  a  few  miles,  and  then  the  outcrop  trends  in 
a  general  northwesterly  direction  to  the  north  side  of  the  field.  The 
coal-bearing  zone  outcrops  only  here  and  there  north  of  the  river, 
and  there  are  few,  if  any,  prospects  except  those  at  Inez. 
QUALITY  OF  THE  COAL. 
The  coals  found  in  the  region  between  Casper  and  Douglas  are  all 
classed  as  subbituminous  (" black  lignite"),  but  some  are  almost 
good  enough  to  be  called  bituminous.  They  are  placed  in  the 
lower  class  because  all  yield  rapidly  to  weathering,  through  loss  of 
moisture  on  exposure  to  the  atmosphere,  and  because,  bedding 
planes  are  very  conspicuous,  showing  that  the  coal  has  not  reached 
an  advanced  stage  of  metamorphism.  The  development  of  joints 
varies  greatly  and  the  fracture  is  hackly  to  conchoidal.  The  coal 
is  black,  but  when  it  is  exposed  to  the  weather  it  cracks  and  the 
surface  becomes  slightly  brown.  At  the  mines  piles  of  slack  take 
fire  spontaneously;  however,  it  is  believed  that  the  coal  does  not 
slack  so  readily  or  take  fire  so  easily  as  that  found  100  to  150  miles 
to  the  north.  The  table  of  analyses  shows  that  the  moisture  con- 
tent of  air-dried  samples  ranges  from  13.50  to  20.0  1  per  cent,  and 
also  that  in  a  general  way  the  amount  of  moisture  varies  with  the 
geologic  age  of  the  coal,  the  youngest  having  the  most  moisture. 
The  samples  were  not  selected  lumps  of  coal,  bul  contained  coal 
from  all  parts  of  the  bed,  so  that  the  analyses  show  the  composi- 
tion of  the  average  output.  To  this  end  nothing  was  excluded  from 
the  samples  except  such  partings  as  are  excluded  in  mining.  I  ofor- 
71497— Bull.  341—09 11 
