CONTRIBUTIONS  TO  ECONOMIC  GEOLOGY. 
1907,  PART  II. 
COAL  AND  LIGNITE. 
Marius  R.  Campbell,  Geologist  in  Charge. 
INTRODUCTION. 
By  Marius  R.  Campbell. 
GENERAL   STATEMENT. 
During  the  year  1907  a  greater  addition  was  made  to  existing  knowl- 
edge regarding  the  outline,  extent,  quality,  and  tonnage  of  the  western 
coal  fields  than  had  been  made  in  any  previous  year.  This  was  due 
largely  to  the  fact  that  during  the  latter  part  of  1906  and  the  early 
part  of  1907  supposed  coal  lands  to  the  extent  of  67,000,000  acres,  or 
104,000  square  miles,  were  withdrawn  from  entry,  and  the  United 
States  Geological  Survey  was  called  upon  to  examine  and  to  classify 
these  lands  so  that  they  might  be  restored  to  coal  entry. 
Before  this  work  was  done  it  was  impossible  to  determine  with  any 
degree  of  accuracy  the  positions  of  many  of  the  coal  fields  in  the 
Rocky  Mountain  region,  or  to  say  what  were  their  sizes  and  shapes 
and  the  extent  of  their  coal  resources.  Now,  however,  the  coal  areas 
are  much  better  known,  and  a  map  representing  them  has  been  pre- 
pared^ A  copy  of  this  map  on  a  small  scale,  in  black  and  white,  is 
here  given  (PL  I)  for  the  purpose  of  showing  the  extent  of  the  coal 
fields  and  the  areas  in  which  surveys  were  carried  on  during  the  last 
year. 
In  preparing  this  map  it  was  deemed  necessary  to  revise  and 
systematize  the  nomenclature  of  the  coal  areas.  Accordingly  a 
committee  consisting   of   George  H.   Ashley,  Joseph    A.    Tall',    and 
a  Map  of  coal  fields  of  the  United  States,  U.  S.  Geol.  Survey,  1908 
