﻿PETROLEUM 
  GEOLOGY 
  — 
  HEROY 
  169 
  

  

  derived 
  from 
  organic 
  matter 
  deposited 
  in 
  sedimentary 
  rocks. 
  Some 
  

   chemists 
  and, 
  more 
  rarely, 
  geologists 
  have 
  sought 
  to 
  explain 
  the 
  origin 
  

   of 
  these 
  hydrocarbons 
  as 
  due 
  to 
  inorganic 
  processes. 
  Through 
  the 
  

   years 
  this 
  smaller 
  group 
  has 
  diminished 
  in 
  numbers, 
  and 
  at 
  the 
  present 
  

   time 
  the 
  organic 
  origin 
  of 
  petroleum 
  is 
  "generally 
  accepted" 
  (Snider, 
  

   1934, 
  p. 
  51). 
  But 
  agreement 
  on 
  the 
  general 
  principle 
  has 
  proven 
  much 
  

   simpler 
  than 
  the 
  collection 
  of 
  pertinent 
  and 
  adequate 
  supporting 
  evi- 
  

   dence. 
  Like 
  the 
  broader 
  biologic 
  principle 
  of 
  evolution, 
  precise 
  knowl- 
  

   edge 
  of 
  its 
  mechanism 
  is 
  attained 
  only 
  by 
  many 
  years 
  of 
  intensive 
  

   investigation. 
  

  

  The 
  general 
  problem 
  of 
  the 
  conversion 
  of 
  the 
  organic 
  material 
  de- 
  

   posited 
  in 
  sedimentary 
  rocks 
  into 
  oil 
  and 
  gas 
  may 
  be 
  divided 
  into 
  more 
  

   specialized 
  fields 
  of 
  investigation, 
  such 
  as 
  : 
  

  

  1. 
  The 
  character 
  of 
  the 
  organic 
  material 
  which 
  ultimately 
  becomes 
  petroleum. 
  

  

  2. 
  The 
  characteristics 
  which 
  give 
  to 
  a 
  sedimentary 
  deposit 
  the 
  capacity 
  to 
  pro- 
  

   duce 
  petroleum. 
  

  

  3^ 
  The 
  steps 
  of 
  chemical 
  change 
  whereby 
  the 
  organic 
  matter 
  of 
  animals 
  and 
  

   plants 
  has 
  been 
  converted 
  into 
  the 
  various 
  hydrocarbons 
  of 
  which 
  petroleum 
  is 
  

   composed. 
  

  

  4. 
  The 
  nature 
  of 
  the 
  forces 
  which 
  have 
  been 
  instrumental 
  in, 
  or 
  have 
  con- 
  

   tributed 
  to, 
  the 
  transformation 
  of 
  organic 
  matter 
  into 
  petroleum. 
  

  

  5. 
  The 
  manner 
  in 
  which 
  widely 
  disseminated 
  and 
  minute 
  quantities 
  of 
  such 
  

   derivatives 
  have 
  been 
  aggregated 
  into 
  appreciable 
  quantities 
  of 
  fluid. 
  

  

  In 
  attacking 
  these 
  problems 
  most 
  geologists 
  and 
  chemists 
  have 
  con- 
  

   sidered 
  that 
  the 
  doctrine 
  of 
  uniformity 
  of 
  Lyell 
  (1842, 
  pp. 
  323-327), 
  

   which 
  assumes 
  that 
  the 
  geologic 
  processes 
  and 
  conditions 
  of 
  the 
  present 
  

   are 
  essentially 
  the 
  same 
  as 
  those 
  of 
  the 
  past, 
  was 
  applicable 
  to 
  the 
  

   formation 
  of 
  petroleum. 
  This 
  is 
  questioned 
  by 
  Woolnough 
  (1937, 
  p. 
  

   1 
  106) 
  who 
  considers 
  that 
  petroleum 
  may 
  have 
  been 
  formed 
  under 
  "con- 
  

   ditions 
  of 
  accumulation 
  not 
  now 
  exhibited, 
  on 
  a 
  major 
  scale, 
  in 
  any 
  part 
  

   of 
  the 
  world." 
  Any 
  progress 
  in 
  the 
  solution 
  of 
  problems 
  of 
  origin 
  

   must, 
  however, 
  rest 
  upon 
  detailed 
  examination 
  of 
  present 
  processes 
  on 
  

   the 
  assumption 
  that, 
  at 
  least 
  in 
  kind 
  if 
  not 
  in 
  degree, 
  they 
  were 
  opera- 
  

   tive 
  in 
  past 
  ages. 
  

  

  NATURE 
  OF 
  ORGANIC 
  MATERIAL 
  

  

  As 
  to 
  the 
  kind 
  of 
  organic 
  matter 
  that 
  is 
  requisite 
  to 
  the 
  production 
  

   of 
  petroleum, 
  there 
  is 
  much 
  divergence 
  of 
  view. 
  Trask 
  (1938, 
  p. 
  384) 
  

   considers 
  that 
  petroleum 
  is 
  a 
  very 
  special 
  substance 
  and 
  that 
  only 
  

   certain 
  types 
  of 
  organic 
  material 
  can 
  be 
  changed 
  into 
  petroleum, 
  while 
  

   Snider 
  (1934, 
  p. 
  62) 
  holds 
  the 
  opinion 
  that 
  almost 
  any 
  kind 
  of 
  organic 
  

   matter 
  buried 
  in 
  sediments 
  may, 
  under 
  proper 
  conditions, 
  be 
  changed 
  

   to 
  petroleum 
  and 
  natural 
  gas. 
  These 
  are 
  wide 
  extremes 
  of 
  thought 
  

   which 
  have 
  been 
  developed 
  through 
  quite 
  different 
  lines 
  of 
  approach. 
  

  

  Trask 
  (1932), 
  in 
  an 
  intensive 
  study 
  of 
  the 
  organic 
  constituents 
  of 
  

   recent 
  sediments, 
  found 
  that 
  oils 
  and 
  fats 
  form 
  a 
  very 
  small 
  part 
  of 
  the 
  

  

  