INTRODUCTION.  7 
examined  and  classified.  The  work  was  done  with  two  purposes  in 
view,  namely,  (1)  to  classify  the  land  for  the  purpose  of  restoring  it  to 
coal  entry,  and  (2)  to  obtain  information  regarding  the  accessibility 
of  the  fields,  quality  of  coal,  correlation  of  coal  beds,  and  in  fact  all 
data  of  a  geologic  and  economic  character. 
It  is  proposed  to  publish  detailed  reports  of  the  work  of  each  party 
containing  the  information  thus  accumulated ;  but  inasmuch  as  many 
of  these  reports  could  not  be  written  until  the  completion  of  the 
work  it  has  been  thought  best  to  prepare  a  preliminary  statement  con- 
taining a  brief  account  of  the  investigation  made  by  each  party  dur- 
ing the  year.  These  papers,  which  make  up  the  present  volume,  give 
only  the  more  important  and  obvious  facts  for  immediate  use.  Simi- 
lar reports  were  published  in  Bulletin  316,  descriptive  of  fields  exam- 
ined during  the  year  1906-7,  and  in  Bulletin  285,  relative  to  fields 
examined  in  the  year  1905-6.  The  maps  accompanying  this  volume 
are  necessarily  on  a  small  scale  and  incomplete,  but  the  full  reports  on 
each  field  will  contain  contour  maps  in  colors,  on  a  uniform  scale  of  1 
to  125,000. 
The  field  work  on  which  these  reports  are  based  consisted  of  tracing 
and  mapping  outcrops  of  the  various  geologic  formations  and  coal 
beds  according  to  land  surveys,  care  being  taken  to  tie  such  meanders 
to  stones  and  other  monuments  marking  the  section  corners ;  of  exam- 
ining the  coal  beds  wherever  possible,  to  determine  the  thickness  and 
character  of  the  coal;  and  of  taking  samples  for  chemical  analysis. 
WESTERN    FIELDS. 
In  some  of  the  Western  States  the  geologic  parties  were  so  situated 
that  it  was  impossible  to  provide  for  field  supervision  except  by  the 
writer;  hence  in  a  large  measure  their  work  was  carried  on  independ- 
ently of  other  parties. 
In  central  Montana  and  northern  Wyoming  the  work  of  five  parties 
was  so  closely  related  that  they  were  placed  under  the  direct  super- 
vision of  Cassius  A.  Fisher,  and  similarly  four  parties  in  southern 
Wyoming  were  placed  under  the  control  of  A.  C.  Veatch.  Unfortu- 
nately during  the  field  season  Mr.  Veatch  was  detailed  to  other  work, 
and  the  parties  previously  under  his  direction  carried  on  their-  work 
independently  of  those  in  adjacent  regions.  The  work  done  by  the 
various  parties  is  briefly  summarized  as  follows: 
North  Dakota. — A  party  under  the  joint  direction  of  A.  G.  Leonard, 
State  geologist,  and  Carl  D.  Smith,  of  the  Federal  Survey,  made  an 
examination  of  the  Sentinel  Butte  lignite  field  of  western  North 
Dakota.  As  shown  by  area  No.  1  on  PL  I,  work  was  begun  a1  Medora 
and  carried  westward  along  the  Northern  Pacific  Railway  into  Mon- 
tana. Professor  Leonard  remained  with  tin*  party  only  while  ii 
in  North  Dakota,  and  after  that  it  was  in  charge  of  Mr.  Smith.     It 
