burchard.]     LIGNITES  OF  MEDDLE  AND  UPPER  MISSOURI  VALLEY.      279 
below  the  lignite  was  a  gray,  sandy  clay.  Very  little  water  was 
encountered  in  this  shaft,  its  elevation  being  above  the  horizon  of 
copious  ground  water.  The  lignite  at  the  bottom  of  the  shaft  was 
drifted  into  for  about  10  feet,  but  in  this  distance  it  did  not  vary  in 
character  or  thickness.  This  development  was  carried  no  further,  the 
fruitlessness  of  such  work  becoming  readily  apparent. 
It  is  evident  that  this  bed  is  represented  in  the  second  horizon 
exploited  in  sec.  22,  T.  29  N.,  R.  7  E.,  and  at  Sargents  Bluff's,"  on  the 
Iowa  side  of  the  river,  11  miles  northwest  of  Homer,  Nebr. 
Owing  to  the  distance  between  the  two  localities  where  lignite  has 
been  shown  to  exist  in  Dakota  County  and  the  absence  of  intermediate 
prospecting  or  outcrops,  it  may  not  positively  be  stated  that  there  is  a 
continuity  of  the  beds  from  one  locality  to  the  other.  Stratigraphically 
the  two  second  beds  are  equivalent,  and  it  is  probable  that  a  seam  of 
lignite  at  that  horizon  should  be  fairly  constant  through  the  whole 
strip  of  land  bordering  the  escarpment,  except  where  removed  by  the 
erosion  of  the  lateral  drainage.  The  bed  should,  however,  thin  and 
disappear  to  the  west.  Conditions  favorable  to  the  origin  and  develop- 
ment of  such  a  bed  of  lignite  probably  prevailed  in  Dakota  time,  the 
shallow,  swampy  area  being  delimited  by  the  shore  line  to  the  east 
and  deeper  waters  to  the  west. 
Further  well  drilling  will  shed  more  light  on  the  extent  of  the  lignite, 
and  it  is  likely,  now  that  some  interest  has  been  aroused  in  the  matter, 
that  drillers  will  more  carefully  preserve  future  records. 
Physical  character. — When  freshly  mined  the  lignite  is  very  moist, 
and  by  drying  in  the  air  loses  15  to  18  per  cent  in  weight.  When  thus 
dried  its  specific  gravity  is  1.28  to  1.35.  It  is  nearly  black,  has  not  a 
uniform  texture,  as  it  contains  many  fragments  and  streaks  of  soft, 
charcoal-like  matter  with  woody  structure,  and  its  average  hardness  is 
much  less  than  that  of  bituminous  coal.  Its  most  significant  character- 
istic is  its  disintegration  upon  exposure.  When  the  material  has  given 
up  the  greater  part  of  its  moisture  the  consequent  shrinkage  of  the 
particles  and  opening  of  joints  causes  it  to  lose  its  cohesiveness  and  to 
fall  to  pieces  at  the  slightest  jar.  If  exposed  again  to  moist  air  the 
movement  between  the  particles  consequent  upon  the  rapid  absorption 
of  water  still  further  aids  disintegration  of  the  mass,  so  that  after  a 
few  alternations  of  wetting  and  drying  it  can  be  carried  only  in  dust- 
tight  receptacles. 
Chemical  composition. — Both  proximate  and  ultimate  analyses  of  the 
lignite  from  the  second  horizon  were  made  by  the  writer.  The  results 
of  the  ultimate  analyses  were  used  as  a  basis  for  calculating  the  heating 
value  of  the  fuel.    Tests  were  also  made  of  the  relative  gas-producing 
oBain,  H.  F.,  The  geology  of  Woodbury  County:  Iowa  Geol.  Survey,  vol.  5,  1895,  pp.  259-260,  and 
fig.  35. 
