286 
CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  [bull. 225. 
of  good  quality,  mine  water  may  be  utilized  to  advantage  during 
part  of  the  year  in  irrigation.  It  would  appear  from  their  elevations 
relative  to  the  valleys  that  many  mines  might  be  drained  without 
pumping,  at  least  in  the  early  stages  of  development. 
In  strip-pit  mining  no  outfit  is  necessary  beyond  a  plow  and  scraper, 
but  labor  conditions  render  the  use  of  mining  machinery  operated  by 
electricity  desirable  in  the  larger  underground  mines.  The  character 
of  the  lignite  renders  the  use  of  undercutting  machines  of  advantage 
in  some  places,  and  in  others  drilling  and  " shooting  from  the  solid" 
is  most  effective. 
Physical  properties. —  Physically,  these  lignites  do  not  differ  greatly 
from  the  Nebraska  lignites  previously  described.  The  content  of 
moisture,  31  per  cent,  is  somewhat  higher  than  that  of  the  Nebraska 
product,  and  the  same  tendency  to  slack  or  to  crumble  to  pieces  while 
drying  has  been  observed.  Another  objectionable  feature  is  the  pres- 
ence of  a  layer  of  "  slack"  which  often  forms  the  top  of  a  lignite  seam, 
sometimes  attaining  a  thickness  of  8  feet  and  sometimes  composing 
the  whole  of  a  thin  seam.  Such  material  is  soft,  gives  a  high  per- 
centage of  ash,  and  has  a  low  fuel  value.  It  is  apparently  due  to  the 
decay  of  lignite  which  was  exposed  to  the  air  during  a  large  part  of 
the  time  the  deposit  was  undergoing  alteration. 
Chemical  properties. — Analyses  of  60  samples  of  lignite  show  a  fair 
accordance  in  percentages,  computed  on  a  dry  basis,  of  hxed  carbon 
and  of  volatile  combustible  matter,  whether  taken  from  different  parts 
of  the  same  seam  or  from  seams  in  widely  separated  localities.  The 
percentage  of  ash  varies  more  widehT.  From  23  samples  fresh  from 
the  mine  the  moisture  ranges  high,  and  the  sulphur,  determined  in  5 
samples  only,  ranks  low.  No  data  are  given  showing  the  per  cent  of 
moisture  retained  in  dry  air,  but  inspection  of  analyses  of  37  samples, 
partly  dry  when  analyzed,  places  this  at  about  10  per  cent  as  the  mini- 
mum. Computed  on  this  basis,  which  is  the  usual  method  of  grouping 
the  proximate  constituents  of  a  coal,  a  general  estimate  of  percentages 
is  made. 
Analyses  of  North  Dakota  lignites. 
Fixed  carbon. 
Volatile  com- 
bustible matter. 
Ash. 
Sulphur. 
Moisture. 
Ranges  in  per- 
centages   
«43.  47-60!  95 
«31.  59-43. 18 
"1.  20-23.  92 
&0.  35-1. 10 
cl4.  25-35.  00 
Averages  of  per- 
centages   
«51. 21 
«35.  63 
«8.  50 
&.78 
<S1.  08 
Estimated  per- 
centages, 
usual  basis . . . 
47.88 
33.  32 
7.95 
.70 
<*10.  00 
a  60  samples,  dried. 
*>  5  samples,  dried. 
c  23  samples,  fresh  from  mines. 
d  Moisture  retained  in  dry  air. 
