COAL  IN  NORTHWESTERN  COLORADO  AND  NORTHEASTERN  UTAH.       289 
Carbonaceous  shale  somewhat  resembling  coal  has  also  been  noted 
in  the  sandstone  in  the  lower  part  of  the  Mancos  in  the  same  general 
locality  as  that  of  the  Jurassic  coal  just  noted.  Coal  has  been  opened 
in  a  mine  3  or  4  miles  south  of  Lily  Park,  Colo.,  where  it  occurs  in 
beds  closely  adjacent  to  the  Dakota  sandstone. 
The  strata  overlying  the  Dakota  include  by  far  the  greater  part  of 
the  valuable  coal.  A  brief  summary  of  the  occurrences  of  the  coals  of 
the  various  formations  is  given  below;  this  will  be  followed  by  more 
detailed  descriptions  of  the  individual  coal  beds. 
The  coal  near  the  base  of  the  Mancos  shale  is  important  in  the  Vernal 
field  of  Utah,  where  it  is  mined  to  a  considerable  extent  for  domestic 
use. 
The  Mesaverde  is  the  most  important  coal-bearing  formation  in  the 
region,  constituting  by  far  the  largest  extent  of  coal  territory  and  con- 
taining the  greatest  thickness  of  workable  beds. 
The  Laramie  coal  is  found  in  the  Yampa  field  north  of  Yampa 
River  and  is  developed  to  a  very  moderate  extent  near  Hayden  and 
Craig. 
The  post-Laramie  coal  of  Fort  Union  or  earlier  age  is  also  found  in 
the  Yampa  field  and  is  developed  in  a  small  way  at  several  points 
north  of  Yampa  River. 
GENERAL    FEATURES    OF    THE    MESAVERDE    FORMATION. 
As  stated  above,  the  Mesaverde  is  the  most  important  of  the  coal- 
bearing  formations  in  these  fields.  On  account  of  the  magnitude  of 
this  formation,  which  is  approximately  a  mile  thick  in  many  parts  of 
the  Danforth  Hills  and  Grand  Hogback  fields,  the  arrangement  and 
character  of  its  beds  and  the  grouping  of  the  coals  are  important 
factors  in  influencing  the  areal  distribution  of  the  coal  available  for 
development. 
The  Mesaverde  formation  is  composed  predominantly  of  sandstone 
and  sandy  shale.  Among  these  strata  the  coal  beds  are  usually 
arranged  so  that  they  may  be  naturally  divided  into  three  groups. 
Recognition  of  these  groups  of  coal  beds  has  already  become  fairly 
established  in  the  local  usage,  especially  in  some  of  the  better-known 
districts,  where  the  whole  Mesaverde  section  is  exposed. 
In  the  Uinta  Basin  the  term  "lower  coal  group"  is  applied  to  coal 
beds  near  the  base  of  the  Mesaverde  formation.  In  the  fields  here 
discussed  this  group  usually  consists  of  a  few  unimportant  beds  of 
coal,  locally  of  fair  or  good  quality,  but  usually  too  thin  to  work. 
Where  thicker  beds  occur  they  are  commonly  broken  into  many  thin 
benches  by  bony  or  shaly  material,  so  that  the  coals  are  in  general  not 
workable.  Some  exceptions  to  this  rule  occur,  but  they  are  not  known 
in  the  area  here  described.  The  strata  associated  with  the  lower 
71497— Bull.  341     09  1!) 
