228         CONTRIBUTIONS   TO   ECONOMIC   GEOLOGY,    1907,   PART    II. 
LARAMIE    FORMATION. 
The  Laramie  formation  is  composed  of  soft  carbonaceous  shale  and 
white  to  brown  sandstone  and  appears  as  a  prominent  ridge  through- 
out most  of  the  field.  It  is  separated  from  the  Mesaverde  by  the 
soft,  calcareous  shale  of  the  Lewis.  The  basal  portion  of  the  Laramie 
as  mapped  contains  marine  invertebrates  which  are  referred  to  upper 
Montana  (Lewis)  age.  This  condition  is  common  throughout  much 
of  southern  Wyoming  and  northern  Colorado  (see  pp.  224-225),  and 
has  led  to  the  inclusion  in  the  Laramie  of  these  massive  beds  on  the 
ground  of  their  lithologic  similarity  to  the  other  part  of  that  formation. 
The  Laramie  formation  is  prolifically  coal  bearing  throughout.  In 
sees.  29  and  30,  T.  25  N.,  R.  89  W.,  about  1,800  feet  of  strata  contain 
a  total  thickness  of  about  54  feet  of  coal,  nearly  28  feet  of  which  is 
of  workable  thickness.  The  following  section  shows  the  number  and 
thickness  of  the  beds  and  their  relative  positions: 
Section  of  a  part  of  the  Laramie  formation  in  sees.  29  and  30,  T.  25  N.,  R.  89  W. 
Ft.  in. 
Sandstone,  gray,  and  drab  shale 45 
Coal 1  10 
Sandstone  and  shale,  brown  to  drab 58  10 
Coal -1  3 
Shale  and  sandstone,  brown 84  3 
Coal,  good 2  3 
Shale,  brown  and  drab 18  9 
Coal,  good 4  1 
Shale,  drab 5 
Coal '. 1  7 
Shale  and  sandstone,  brown  and  drab 35  3 
Coal 2 
Shale,  brown,  carbonaceous 78 
Coal 1  3 
Shale 4 
Coal 3 
Sandstone  and  shale,  brown 29  3 
Coal 9 
Shale  and  sandstone 46  6 
Coal 2  4 
Shale  and  sandstone,  alternating 76  6 
Coal 1  6 
Shale  and  sandstone,  brown 23  8 
Coal 6 
Shale  and  shaly  sandstone 75  1 
Coal 2 
Sandstone  and  shale,  carbonaceous  and  brown 123  7 
Coal 10 
Shale  and  sandstone 65  5 
Coal .' 1  4 
Shale,  brown  and  drab 9  9 
Coal 1  3 
