250         CONTRIBUTIONS   TO   ECONOMIC    GEOLOGY,    1907,    PART   II. 
Green  River  Basin.  In  the  north  end  of  the  field  the  beds  change 
gradually  from  a  dip  of  25°  on  the  eastern  margin  of  the  coal  field  to 
a  practically  horizontal  position  along  the  Union  Pacific  Railroad 
west  of  Latham,  forming  here  the  south  end  of  the  shallow  syncline 
which  is  the  main  structural  feature  of  the  Great  Divide  Basin.  All 
the  westward -dipping  formations  south  of  a  line  drawn  roughly 
from  Red  Desert  station  through  Echo,  Coal  Bank,  and  Chicken 
springs  lie  on  the  eastern  slope  of  what  King  a  called  the  Washakie 
Basin,  the  northeast  corner  of  which  is  indicated  by  the  angle  of  the 
Laney  Rim.  The  beds  composing  this  rim  strike  parallel  to  the  rail- 
road with  a  very  low  southerly  dip  as  far  east  as  a  point  south  of 
Red  Desert,  where  they  turn  southeastward,  dipping  from  2°  to 
4°  SW.  Throughout  the  south  end  of  the  area  the  Mesaverde  and 
Laramie  formations  dip  12°  or  less  to  the  west.  Near  the  top  of  the 
Laramie  the  dip  increases  to  28°,  and  this  dip  prevails  to  the  place 
where  the  lower  beds  disappear  beneath  the  overlapping  upper 
Wasatch,  which  here,  as  farther  north,  dips  1°  to  4°  W. 
The  simplicity  of  structure  and  general  low  dips  of  the  field  favor 
easy  and  economic  development  of  the  coals.  So  far  as  observed  no 
faults  of  any  appreciable  magnitude  disturb  the  continuity  of  the 
coal  beds  anywhere  in  the  field.  That  minor  faults  are  present  in  the 
region  of  folded  rocks  near  Rawlins  is  shown  by  the  following  state- 
ment by  M.  W.  Dillon  regarding  the  Dillon  mine:  "The  first  fault  is 
a  downthrow  of  4  feet  about  200  feet  from  the  portal,  the  next  is  an 
upthrow  of  4  feet  240  feet  from  the  portal,  and  the  next  a  downthrow 
of  6  feet  about  450  feet  from  the  portal  of  the  slope." 
THE   COAL. 
PHYSICAL  PROPERTIES. 
The  Mesaverde  coal  as  exposed  at  the  Dillon  mine  is  very  compact 
and  hard.  As  there  are  no  surface  exposures  of  this  bed  in  the  vicin- 
ity, it  was  impossible  to  determine  the  effects  of  surface  weathering, 
but  in  the  mine  the  coal  is  black  and  clean,  with  a  submetallic  luster, 
showing  a  smooth,  unweathered  face  down  to  the  water  which  at 
present  fills  the  bottom  of  the  slope.  At  the  Robertson  opening  the 
Mesaverde  coal  presents  a  clean,  compact  face  without  partings  or 
inferior  streaks. 
The  Laramie  coal  bed  exposed  at  the  Nebraska  mine  is  composed  of 
alternations  of  clean,  firm  coal  and  softer,  slightly  crumbly  layers 
which  weather  rapidly.  The  coal  in  the  harder  benches  is  black  and 
compact,  and  has  a  slightly  resinous  luster. 
The  beds  of  the  basal  member  of  the  upper  coal  group  are  made  up 
of  benches  of  coal  with  thin  partings  of  bone.  The  coals  are  not  so 
compact,  clean,  or  black  as  those  of  the  Mesaverde,  and  they  weather 
oU.  S.  Geol.  Explor.  40th  Par.,  Atlas,  1876,  Map  II. 
