﻿GEOLOGY. 
  5 
  1 
  

  

  The 
  likeness 
  of 
  varieties 
  of 
  the 
  burnt 
  shale 
  to 
  volcanic 
  rocks 
  is 
  indi- 
  

   cated 
  by 
  the 
  fact 
  that 
  Thomas 
  Antisell, 
  in 
  his 
  account 
  of 
  the 
  geology 
  

   of 
  the 
  Coast 
  Ranges 
  in 
  the 
  Pacific 
  Railroad 
  reports, 
  describes 
  "scori- 
  

   aceous" 
  and 
  " 
  amygdaloidal 
  lava," 
  " 
  whitish-gray 
  , 
  hard 
  trachytic 
  

   rock," 
  " 
  volcanic," 
  and 
  " 
  igneous 
  rocks" 
  in 
  the 
  region 
  of 
  Santa 
  Ynez 
  

   River, 
  evidently 
  having 
  reference 
  to 
  the 
  burnt 
  shale. 
  He 
  considered 
  

   these 
  rocks 
  to 
  be 
  eruptive 
  masses, 
  forming 
  the 
  oldest 
  and 
  axial 
  rocks 
  

   of 
  the 
  hill 
  ranges, 
  whereas 
  they 
  are 
  part 
  of 
  the 
  Monterey 
  shale, 
  which 
  

   overlies 
  the 
  basement 
  formation. 
  He 
  regarded 
  the 
  associated 
  diato- 
  

   maceous 
  shales 
  in 
  some 
  places, 
  although 
  not 
  in 
  others, 
  as 
  "magnesian" 
  

   and 
  "tremolite" 
  rocks 
  of 
  igneous 
  origin, 
  and 
  refers 
  to 
  the 
  places 
  

   where 
  the 
  shale 
  is 
  burning 
  as 
  examples 
  of 
  present 
  volcanic 
  activity. 
  

  

  CAUSE 
  OF 
  THE 
  ALTERATION. 
  

  

  There 
  can 
  be 
  little 
  doubt 
  that 
  the 
  burnt 
  condition 
  of 
  the 
  shale 
  is 
  

   in 
  all 
  places 
  the 
  result 
  of 
  heat 
  produced 
  by 
  combustion 
  of 
  its 
  hydro- 
  

   carbon 
  content. 
  The 
  phenomenon 
  is 
  confined 
  to 
  the 
  Monterey 
  shale, 
  

   which 
  is 
  the 
  source 
  of 
  a 
  large 
  part 
  of 
  the 
  California 
  petroleum, 
  and 
  

   to 
  those 
  regions 
  in 
  which 
  this 
  formation 
  is 
  extremely 
  bituminous. 
  

   The 
  shale 
  in 
  many 
  such 
  places 
  is 
  impregnated 
  with 
  petroleum 
  and 
  

   the 
  cracks 
  partially 
  filled 
  with 
  it. 
  The 
  areas 
  of 
  altered 
  shale 
  are 
  

   almost 
  invariably 
  situated 
  in 
  the 
  vicinity 
  of 
  oil 
  seepages, 
  which 
  

   usually 
  denote 
  a 
  fractured 
  condition 
  of 
  the 
  rocks 
  such 
  as 
  would 
  

   allow 
  fire 
  to 
  spread 
  and 
  be 
  supported. 
  The 
  observance 
  of 
  fires 
  

   actually 
  in 
  progress 
  in 
  the 
  shale 
  and 
  the 
  changes 
  that 
  have 
  taken 
  

   place 
  in 
  the 
  neighboring 
  rocks 
  — 
  changes 
  in 
  every 
  way 
  similar 
  to 
  

   those 
  in 
  localities 
  where 
  no 
  fire 
  exists 
  at 
  present 
  — 
  give 
  the 
  best 
  clues 
  

   to 
  the 
  manner 
  in 
  which 
  the 
  shale 
  has 
  been 
  baked 
  in 
  other 
  places. 
  It 
  

   is 
  difficult 
  to 
  conceive 
  another 
  source 
  of 
  heat 
  sufficient 
  to 
  cause 
  local 
  

   baking 
  of 
  the 
  shale 
  in 
  otherwise 
  unaltered 
  strata 
  at 
  a 
  depth 
  of 
  1,000 
  

   feet 
  below 
  the 
  surface 
  in 
  such 
  a 
  case 
  as 
  has 
  been 
  mentioned. 
  Prob- 
  

   ably 
  there, 
  as 
  on 
  the 
  surface, 
  it 
  was 
  due 
  to 
  ignition 
  of 
  bituminous 
  

   material. 
  It 
  is 
  probable 
  that 
  fire 
  started 
  in 
  the 
  petroliferous 
  shale 
  

   at 
  the 
  surface 
  and 
  threaded 
  its 
  way 
  downward 
  along 
  cracks 
  partially 
  

   filled 
  with 
  bitumen. 
  The 
  failure 
  to 
  smother 
  the 
  fire 
  in 
  the 
  shale 
  on 
  

   Graciosa 
  Ridge, 
  previously 
  noted, 
  indicates 
  that 
  such 
  fires 
  are 
  able 
  

   to 
  survive 
  with 
  a 
  small 
  air 
  supply. 
  On 
  the 
  other 
  hand, 
  if 
  the 
  above 
  

   theory 
  is 
  correct, 
  it 
  indicates 
  that 
  a 
  considerable 
  amount 
  of 
  oxygen 
  

   may 
  be 
  present 
  in 
  the 
  rocks 
  at 
  such 
  a 
  depth. 
  

  

  In 
  this 
  connection 
  it 
  may 
  be 
  mentioned 
  that 
  the 
  temperature 
  in 
  a 
  

   well 
  near 
  the 
  one 
  in 
  which 
  the 
  burnt 
  shale 
  was 
  found 
  was 
  152° 
  F., 
  

   at 
  a 
  depth 
  of 
  3,600 
  feet. 
  The 
  cause 
  of 
  ignition 
  may 
  be 
  kindled 
  fires, 
  

   lightning, 
  or 
  the 
  spontaneous 
  combustion 
  of 
  the 
  hydrocarbons 
  or 
  

  

  a 
  Explorations 
  and 
  surveys 
  for 
  the 
  Pacific 
  Railroad, 
  vol. 
  7, 
  1857, 
  pp. 
  65-72. 
  

  

  