260         CONTRIBUTIONS    TO   ECONOMIC   GEOLOGY,    1907,   PART   II. 
Section  of  Cretaceous  and  Tertiary  rocks  of  Sweetwater  County,  Wyo. — Continued. 
Formation. 
Lewis  shale. 
Mesaverde 
Economic 
designa 
Almond 
coal 
group. 
Rock 
Springs 
coal 
group. 
750 
800 
800 
940 
■550 
Description. 
Economic  value. 
Dark  gray,  drab,  and  black 
shales,  highly  gypsiferous, 
with  some  soft  shaly  sand- 
stones and  large  concre- 
tions. Produces  region  of 
low  relief. 
Possible  source  of  clay  beds. 
Natural  routes  of  travel. 
Not  known  to  be  coal 
bearing. 
Soft  white  and  brown  sand- 
stones, sandy  shale,  and 
clay,  with  numerous  beds 
of  "coal  and  bitumiuous 
shale. 
Massive  white  and  yellowish 
sandstones,  with  little  shale 
and  ferruginous  matter. 
Upper  third  conglomeratic, 
with  fine  black  and  gray 
quartz  pebbles.  Sandstone 
forms  pronounced  escarp- 
ments and  hogback  ridges. 
White  to  yellow  sandstone, 
interbedded  shale  and  clay 
with  several  large  coal  beds 
and  numerous  thin  beds 
ranging  from  a  few  inches 
to  2  or  3  feet.  The  heaviest 
sandstones  are  grouped 
near  the  base  of  the  forma- 
tion. 
Drab,  yellow,  and  brown 
sandstones  and  interbed- 
ded shale  and  shaly  sand- 
stone with  little  or  no  bitu- 
minous matter.  Massive 
sandstones  are  grouped 
near  top  of  formation,  giv- 
ing rise  to  the  "Golden 
Wall." 
Shaly  sandstone  and  arena- 
ceous shale,  in  places  highl  y 
gypsiferous.  Much  of  it 
very  friable,  producing  low 
benches  and  badland  ridges. 
Black  and  drab  shales,  very 
soft  and  friable. 
Coal  bearing. 
Many  coal  beds.  Numer- 
ous prospects  throughout 
the  field.  Coal  from  these 
beds  has  been  mined  at 
Rock  Springs  and  Point 
of  Rocks. 
Yields    artesian 
parts  of  field. 
Prolifically  coal  bearing. 
Many  large  coal  beds  and 
numerous  smaller  beds. 
Best  coal  in  the  Rock 
Springs  field.  Important 
mines  at  Rock  Springs 
and  Superior.  Many 
prospects  and  drifts 
opened.  Artesian- water 
zone.  Flowing  wells  at 
Superior  and  Rock 
Springs. 
Important    artesian- water 
zone. 
COAL-BEARING    FORMATIONS. 
MESAVERDE. 
The  oldest  coal-bearing  rocks  exposed  in  this  area  are  of  Montana 
age.  It  is  possible  that  the  Frontier  formation  of  the  Colorado  group 
may  contain  workable  beds  of  coal,  and  that  along  the  axis  of  the 
