﻿PETROLEUM 
  GEOLOGY 
  — 
  HEROY 
  189 
  

  

  basin 
  (Denison, 
  Oldham, 
  and 
  Kisling, 
  1933). 
  The 
  East 
  Texas 
  field, 
  

   in 
  the 
  same 
  basin, 
  is 
  a 
  trap 
  formed 
  in 
  the 
  Cretaceous 
  cycle, 
  the 
  outline 
  

   of 
  which 
  has 
  shifted 
  northward 
  as 
  a 
  result 
  of 
  recent 
  diastrophic 
  

   movement 
  (Levorsen, 
  1935). 
  

  

  In 
  conclusion, 
  we 
  may 
  accept 
  the 
  generalization 
  of 
  David 
  White 
  

   (1935, 
  p. 
  608) 
  that 
  the 
  great 
  migrations 
  of 
  oil 
  and 
  gas 
  were 
  accom- 
  

   plished 
  mainly 
  in 
  periods 
  of 
  orogeny. 
  

  

  DISPERSION 
  OF 
  PETROLEUM 
  

  

  It 
  is 
  probable 
  that 
  the 
  oil 
  and 
  gas 
  of 
  every 
  reservoir, 
  however 
  deeply 
  

   buried 
  and 
  covered 
  by 
  "impervious" 
  rocks, 
  is 
  escaping, 
  either 
  upward 
  

   through 
  the 
  overburden 
  or 
  laterally 
  along 
  the 
  bedding. 
  Generally 
  

   the 
  process 
  must 
  be 
  exceedingly 
  slow 
  and 
  almost 
  imperceptible, 
  else 
  

   most 
  oil 
  fields 
  would, 
  in 
  the 
  course 
  of 
  geologic 
  time, 
  have 
  been 
  de- 
  

   stroyed 
  by 
  such 
  leakage. 
  The 
  presence 
  in 
  Oklahoma 
  of 
  large 
  oil 
  

   fields 
  of 
  Ordovician 
  age 
  at 
  depths 
  of 
  less 
  than 
  a 
  mile 
  illustrates 
  how 
  

   effective 
  overlying 
  rocks 
  may 
  be 
  in 
  preventing, 
  through 
  many 
  mil- 
  

   lions 
  of 
  years, 
  the 
  dispersion 
  of 
  petroleum. 
  In 
  contrast, 
  the 
  loss 
  of 
  

   petroleum 
  from 
  underground 
  reservoirs 
  may 
  be 
  relatively 
  rapid 
  and 
  

   visible, 
  as 
  is 
  evidenced 
  by 
  the 
  large 
  quantities 
  of 
  petroleum 
  that 
  have 
  

   reached 
  the 
  surface 
  in 
  many 
  areas. 
  Such 
  asphalt 
  deposits 
  as 
  those 
  

   at 
  Pitch 
  Lake 
  in 
  Trinidad 
  are 
  proof 
  of 
  how 
  great 
  such 
  wastage 
  may 
  

   be 
  under 
  suitable 
  conditions. 
  

  

  In 
  most 
  petroliferous 
  regions 
  this 
  reservoir 
  loss 
  is 
  manifested 
  by 
  

   various 
  surface 
  indications, 
  such 
  as 
  oil 
  and 
  gas 
  seepage, 
  deposits 
  of 
  

   brea 
  and 
  asphalt, 
  bituminous 
  dikes, 
  tar 
  sands, 
  and 
  mud 
  volcanoes. 
  

   These 
  may 
  be 
  regarded 
  as 
  incidents 
  of 
  the 
  erosion 
  cycle 
  in 
  such 
  areas. 
  

   Where 
  uplift 
  and 
  erosion 
  have 
  exposed 
  the 
  margin 
  of 
  an 
  oil 
  reservoir, 
  

   so 
  that 
  a 
  direct 
  avenue 
  of 
  escape 
  to 
  the 
  surface 
  has 
  been 
  formed, 
  its 
  

   contents 
  will 
  soon 
  be 
  lost. 
  Light 
  oils 
  and 
  gas 
  may 
  be 
  completely 
  

   drained, 
  while 
  heavier 
  oils, 
  on 
  reaching 
  the 
  surface, 
  may 
  solidify, 
  seal 
  

   the 
  exposed 
  reservoir 
  beds, 
  and 
  thus 
  retard 
  the 
  process 
  of 
  dispersion. 
  

   Faults 
  which 
  in 
  some 
  cases 
  form 
  traps 
  for 
  petroleum 
  may 
  in 
  other 
  

   cases 
  produce 
  at 
  the 
  same 
  time 
  a 
  channel 
  along 
  which 
  some 
  of 
  the 
  

   trapped 
  oil 
  may 
  escape 
  to 
  the 
  surface. 
  The 
  deformation 
  which 
  pro- 
  

   duces 
  folded 
  structures 
  may 
  also 
  develop 
  faults 
  in 
  the 
  flexed 
  strata 
  

   along 
  which 
  the 
  oil 
  and 
  gas 
  may 
  pass 
  upward 
  to 
  shallower 
  reservoirs 
  

   or 
  to 
  the 
  surface. 
  An 
  example 
  is 
  the 
  Salt 
  Creek 
  anticline, 
  Wyoming, 
  

   to 
  which 
  attention 
  was 
  first 
  directed 
  because 
  of 
  the 
  presence 
  of 
  oil 
  

   seeps 
  near 
  the 
  axis 
  of 
  the 
  structure 
  and 
  the 
  development 
  of 
  which 
  has 
  

   revealed 
  the 
  presence 
  of 
  numerous 
  faults, 
  some 
  of 
  which 
  extend 
  to 
  

   the 
  surface 
  (Beck, 
  1929). 
  

  

  Another 
  possible 
  means 
  for 
  the 
  dissipation 
  of 
  petroleum 
  deposits 
  

   is 
  the 
  movement 
  of 
  underground 
  water. 
  Students 
  of 
  Rocky 
  Moun- 
  

  

  