﻿168 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  100 
  feet, 
  and 
  are 
  separated 
  from 
  each 
  other 
  by 
  masses 
  of 
  rock 
  from 
  

   10 
  or 
  20 
  to 
  200 
  or 
  300 
  feet 
  thick, 
  and 
  are 
  mined 
  in 
  yarious 
  ways 
  

   according 
  to 
  their 
  situation. 
  

  

  Geologic 
  investigation 
  in 
  all 
  coal 
  regions 
  has 
  led 
  to 
  the 
  conclu- 
  

   sion 
  that 
  the 
  strata 
  of 
  coal 
  are 
  composed 
  of 
  vegetable 
  matter, 
  

   which 
  during 
  the 
  Carboniferous 
  epoch 
  appears 
  to 
  have 
  reached 
  

   an 
  enormous 
  and 
  luxuriant 
  growth, 
  and 
  formed 
  vast 
  accumula- 
  

   tions, 
  which 
  after 
  being 
  buried 
  under 
  the 
  marine 
  sediments 
  of 
  

   clay 
  and 
  sand 
  which 
  now 
  form 
  the 
  shales 
  and 
  sandstones 
  over 
  

   them, 
  underwent 
  chemical 
  changes 
  which 
  transformed 
  them 
  

   to 
  their 
  present 
  condition. 
  The 
  proofs 
  of 
  this 
  are 
  found 
  in 
  the 
  

   fact 
  that 
  the 
  rocks 
  above 
  and 
  below 
  the 
  coal 
  seams 
  are 
  filled 
  

   with 
  vegetable 
  remains, 
  leaves, 
  stems, 
  roots, 
  etc.; 
  the 
  trunks 
  of 
  

   the 
  trees 
  being 
  in 
  some 
  places 
  found 
  still 
  erect 
  and 
  standing 
  

   upon 
  their 
  roots, 
  but 
  converted 
  into 
  coal 
  ; 
  and 
  that 
  even 
  the 
  coal 
  

   itself, 
  though 
  in 
  most 
  cases 
  it 
  is 
  solidified 
  into 
  one 
  mass 
  so 
  as 
  to 
  

   show 
  no 
  organic 
  structure, 
  displays 
  in 
  other 
  instances, 
  under 
  the 
  

   microscope, 
  all 
  the 
  structure 
  of 
  wood; 
  the 
  cells, 
  the 
  ducts 
  through 
  

   which 
  the 
  sap 
  once 
  circulated, 
  and 
  even 
  minute 
  markings 
  by 
  

   which 
  it 
  can 
  be 
  determined 
  whether 
  the 
  wood 
  belonged 
  to 
  one 
  

   or 
  another 
  general 
  class 
  of 
  trees. 
  

  

  The 
  vegetable 
  origin 
  of 
  all 
  coal 
  is 
  well 
  established; 
  but 
  the 
  

   mode 
  in 
  which 
  great 
  accumulations 
  of 
  it 
  were 
  made, 
  over 
  such 
  

   vast 
  areas, 
  is 
  yet 
  an 
  obscure 
  question. 
  A 
  single 
  bed 
  of 
  coal, 
  that 
  

   called 
  the 
  Pittsburgh 
  seam, 
  is 
  known 
  to 
  extend 
  over 
  no 
  less 
  than 
  

   14,000 
  square 
  miles, 
  with 
  a 
  usual 
  thickness 
  of 
  from 
  four 
  to 
  ten 
  

   feet. 
  Other 
  layers, 
  though 
  less 
  in 
  extent, 
  are 
  much 
  greater 
  in 
  

   thickness, 
  reaching 
  even 
  100 
  feet. 
  The 
  prevailing 
  opinion 
  is 
  that 
  

   it 
  grew 
  in 
  enormous 
  morasses 
  or 
  swampy 
  tracts, 
  resembling 
  on 
  

   a 
  larger 
  scale 
  the 
  Great 
  Dismal 
  swamp, 
  or 
  the 
  Okefinokee 
  swamp 
  

   of 
  Georgia, 
  in 
  which 
  the 
  annual 
  fall 
  of 
  leaves, 
  branches, 
  and 
  

   trunks 
  through 
  a 
  long 
  period 
  of 
  time 
  formed 
  thick 
  peaty 
  masses, 
  

   which, 
  being 
  submerged 
  under 
  the 
  sea 
  and 
  covered 
  with 
  sedi- 
  

   ments, 
  became 
  the 
  vast 
  deposits 
  of 
  fossil 
  fuel 
  wfeich 
  are 
  now 
  pf 
  

   so 
  great 
  importance. 
  

  

  