THE  NORTHERN  PART  OF  THE  ROCK  SPRINGS  COAL 
FIELD,  SWEETWATER  COUNTY,  WYOMING. 
By  A.  R.  Schultz. 
INTRODUCTION. 
This  paper  is  a  brief  preliminary  statement  of  the  results  of  a  geo- 
logic survey  of  the  northern  part  of  the  Rock  Springs  coal  field,  Wyo- 
ming, made  during  the  summer  of  1907.a  The  region  mapped,  with 
the  exception  of  two  townships,  was  covered  by  the  public-land  sur- 
veys. A  considerable  tract  was  resurveyed  by  the  General  Land 
Office  in  1906  and  twenty-four  townships  were  resurveyed  in  1907. 
As  economic  considerations  demanded  that  the  work  be  based  pri- 
marily on  the  Land  Office  subdivisions,  because  these  subdivisions  are 
the  units  of  economic  importance,  it  was  necessary  to  do  different 
kinds  of  work  in  different  parts  of  the  field. 
In  the  areas  where  resurvey  inspection  work  was  carried  on,  the 
geologic  work  was  executed  in  connection  with  the  inspection.  All 
geologic  locations  along  the  land  lines,  as  well  as  within  the  township 
sections,  were  measured  by  stadia.  An  idea  of  the  accuracy  of  the 
location  of  coal  prospects,  outcrops  of  coal  beds,  and  fossil  localities 
may  be  had  from  the  fact  that  approximately  ninety  locations  were 
obtained  in  each  square  mile. 
In  the  unsurveyed  townships,  T.  23  N.,  Rs.  103  and  104  W.,  it  was 
necessary  to  establish  Government  corners  before  the  lands  could  be 
classified.  In  this  area  detailed  geologic  mapping  was  carried  on 
in  connection  with  the  subdivision  work,  and  a  complete  geologic 
map,  showing  all  the  coal  croppings  and  prospect  pits,  was  made  as 
that  work  progressed.  The  geologic  and  topographic  locations,  as 
well  as  the  line  measurements,  were  made  by  stadia. 
Outside  of  the  areas  of  detailed  mapping  all  locations  were  made  by 
pacing  section  lines  or  from  land  corners  found  by  such  pacing.  Lines 
were  run  one-fourth  to  one-half  mile  apart,  and  all  the  more  important 
coal  beds  were  traversed  and  the  traverses  tied  to  land  corners. 
a  The  personnel  of  the  parties  engaged  in  mapping  the  geology  changed  from  time  to  time,  as  they 
were  transferred  to  other  fields  or  left  in  order  to  take  up  other  work.  The  men  assisting  in  the  geo- 
logic mapping  were  V.  H.  Barnett,  G.  E.  Burton,  J.  L.  Rich,  G.  C  Matson,  J.  J.  Galloway,  E.  B.  Hop- 
kins, W.  B.  Heroy,  and  J.  T.  Singewald.  Of  these,  only  the  first  two  were  with  the  party  for  the  entire 
season. 
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