A?unTe,uri'J7harm^        Methods  of  Studying  Coal 
273 
present  time  regards  coal  as  of  the  nature  of  modified  peat  and  as 
having  originated  in  most  cases  on  wet  land  as  the  result  of  the  root- 
ing, flourishing  and  falling  of  successive  generations  of  plants  on 
the  prostrate  remains  of  their  ancestors.  This  condition  is  realized 
in  the  cold,  temperate  regions  of  our  earth.  In  the  tropics,  how- 
ever, in  spite  of  a  luxuriance  of  vegetation,  with  which  that  of  the 
greatest  coal  age  (Carboniferous)  has  been  frequently  compared, 
there  are  no  accumulations  of  vegetable  matter  on  the  soil.  In  warm 
climates  the  hoarding  of  plant  remains  occurs  only  in  the  bottoms  of 
lakes  and  tranquil  estuaries,  since  the  high  temperature  makes  the 
destruction  of  dead  vegetable  matter  on  land  particularly  rapid. 
Even  in  this  country,  which,  as  a  whole,  is  neither  particularly  hot 
nor  especially  cold,  we  have  the  authority  of  the  United  States 
Bureau  of  Mines  (Peat  Investigations)  for  the  statement  that  by 
far  the  greater  accumulations  of  vegetable  matter  occur  under  open 
water,  which  by  its  relatively  constant  level,  safeguards  the  hoardings 
in  its  depths  from  the  ravages  of  destroying  fungi,  since  these  are 
unable  to  flourish  subaqueously. 
The  investigation  of  coals  from  all  parts  of  the  world  and  from 
every  geological  age,  by  the  methods  described  in  the  earlier  para- 
graphs, has  made  it  clear  that,  in  general,  coal  is  of  the  nature  of 
impude  cannel.  It  is  universally  conceded  that  cannel  coals,  oil  shales 
and  similar  combustibles,  which  constitute  a  small  proportion  of 
coals  mined,  were  laid  down  in  open  water.  We  can  best  picture 
their  mode  of  deposition  by  reference  to  a  lake  of  to-day.  Gener- 
ally in  the  month  of  June  the  forest  trees  shed  their  fertilizing  dust 
(pollen)  in  the  air,  to  be  borne  by  the  winds  to  the  waiting  seeds. 
Most  of  the  blossom  dust  is  spilled,  however,  on  the  bosoms  of  lakes, 
lying  in  sheltered  hollows,  where  the  air  currents  losing  their  driving 
force  drop  their  load  of  pollen,  which  falls  on  the  waters  as  so- 
called  "  sulphur  showers."  After  floating  for  a  while  in  circling 
windrows,  the  pollen  sinks  with  other  coarser  vegetable  matter  into 
the  depths  of  the  lake  or  estuary.  Where  the  pollen  or  spores  were 
relatively  abundant  in  the  depths  of  the  coal  lakes  of  the  past  the 
result  was  a  deposit  which  later  became  a  cannel  or  oil  shale.  In 
more  troubled  and  shallower  waters  a  greater  amount  of  the  vege- 
tative parts  of  plants  accumulated  with  the  spores  and  pollen,  to 
constitute  the  raw  material  of  a  "  fat"  bituminous  coal.  Where  the 
vegetative  parts  predominated  a  "  lean "  type  of  coal  is  the  final 
result.  Often  in  addition  to  spores  we  find  in  coal  wood  with  struc- 
ture preserved,  most  inappropriately  designated  "  Mother  of  Coal." 
