^AMPA    COAL    FIELD,    COLORADO. 
237 
The  heat  accompanying  the  intrusion  of  the  molten  rock  has  influenced  to  varying 
legrees  the  character  of  near-by  coals.  In  general  the  result  of  this  baking  process  has 
>een  the  driving  off  of  the  volatile  hydrocarbons.  In  this  way  all  intermediate  grades  of 
■oal  ranging  from  bituminous  to  anthracite  have  been  fo  med. 
l!  is  evident  that  where  the  source  of  the  heat  was  fairly  uniform  in  its  relation  to  the 
•oal  seams  the  resulting  alteration  of  the  coal  may  be  expected  to  be  correspondingly 
jniform  over  a  like  area.  This  result  is  best  attained  in  the  cases  of  the  intruded  sills. 
Two  reasons  may  be  given  for  the  fact  that  many  of  these  intrusions  have  taken  the  form 
)f  sheets  lying  parallel  to  the  coal  seams:  (1)  The  basalt,  when  molten,  is  a  comparatively 
luid  magma  and  more  readily  forces  its  way  into  thin  crevices  than  would  the  magmas 
)f  more  acidic  rocks.  (2)  These  crevices  would  more  easily  open  in  the  sedimentary  series 
between  the  beds  than  across  them. 
On  the  other  hand,  the  intruded  lava  sheets  do  not  seem  to  have  exerted  an  influence 
dirough  more  than  50  to  70  feet  of  intervening  strata,  and  probably  not  often  so  far  as 
his.  A  contact  of  coal  and  lava  would  probably  have  resulted  in  burning  or  complete 
joking  of  the  coal.  In  order  that  any  given  seam  may  be  changed  to  good  anthracite 
here  is  necessary  a  comparatively  delicate  adjustment  of  this  relation  of  coal  seam  and 
ava  sheet,  the  achievement  of  which  depends  on  purely  accidental  circumstances. 
The  property  known  as  the  Crawford  tract  is  situated  on  the  county  road  that  crosses 
ihe  Anthracite  Range  west  of  Anthracite  post-office.  Openings  on  the  seams  of  this  tract 
'urnish  perhaps  the  best  known  of  the  anthracized  coals.  Three  entries  are  located  close 
;o  the  public  road.  The  two  uppermost  on  the  road  and  one  on  a  side  gulch  to  the  north 
ippear  to  be  on  the  same  seam.  This  measures  at  least  11  feet  in  thickness,  with  a  part- 
ng  of  6  to  8  inches  near  its  middle.  A  massive  sheet  of  basalt  is  plainly  exposed  on  the 
lorth  side  of  the  creek,  dipping  under  the  lower  seam  at  an  interval  of  about  50  feet. 
The  coal  seam  shows  varying  degrees  of  anthracization.  It  is  thought  that  this  seam  cor- 
esponds  to  the  lowest  seam  of  the  middle  coal  group  as  exposed  at  the  mouth  of  Wolf 
.reek,  both  in  details  of  its  measurements  and  in  position  at  the  base  of  the  group.  Sam- 
ples (E  and  G)  from  two  entries  on  this  seam  were  taken  for  analysis.  They  were  obtained 
yy  making  cuts  across  the  face  from  top  to  bottom  of  the  lower  bench  of  6  to  7  feet  of  coal. 
Analyses  of  coals  from  11-foot  seam  on  Crawford  tract. 
|  K.  M.  Stanton,  analyst.] 
Sample  E. 
Sample  G. 
Moisture 
Per  cent. 
0.  94 
3.  42 
75.  61 
14.03 
Per  cent. 
6.85 
Volati le  matter 
23.  84 
Fi  xed  carbon 
00. 00 
Ash 
9.31 
Sulphur 
100. 00 
.57 
4.20 
100.  00 
4.20 
A  comparison  of  these  results  with  analyses  of  typical  Pennsylvania  coals,  both  anthra- 
cite and  bituminous,  shows  that  Sample  E  is  an  exceptionally  high  grade  of  anthracite, 
so  far  as  its  percentages  of  fixed  carbon  and  volatile  matter  are  concerned,  but  that  its 
commercial  value  as  such  is  materially  impaired  by  the  high  percentage  of  ash. 
Sample  G  was  taken  from  an  entry  on  the  same  seam,  only  40  rods  distant.  Its  com- 
position would  class  it  as  a  bituminous  coal  of  good  quality. 
A  smaller  seam,  measuring  about  28  inches,  has  been  opened  in  a  number  of  places  a 
ort  distance  beneath  the  large  seam  just  described.     Reports  of  analyses  of  this  coal 
