﻿PETROLEUM 
  GEOLOGY 
  — 
  HEROT 
  163 
  

  

  but 
  it 
  remained 
  for 
  Orton 
  (1888) 
  to 
  publish 
  the 
  first 
  treatise 
  which 
  

   critically 
  studied 
  and 
  compared 
  the 
  evidence 
  and 
  reached 
  consistent 
  

   conclusions 
  on 
  this 
  subject. 
  As 
  this 
  report 
  best 
  presents 
  the 
  state 
  

   of 
  knowledge 
  of 
  petroleum 
  geology 
  as 
  of 
  50 
  years 
  ago, 
  its 
  conclusions 
  

   will 
  be 
  extensively 
  quoted. 
  

  

  ORIGIN 
  

  

  After 
  reviewing 
  the 
  various 
  theories 
  that 
  had 
  been 
  advanced 
  by 
  geol- 
  

   ogists 
  and 
  chemists 
  to 
  accownt 
  for 
  the 
  origin 
  of 
  petroleum 
  and 
  natural 
  

   gas, 
  Orton 
  presented 
  the 
  following 
  summary 
  (1888, 
  pp. 
  82, 
  83) 
  : 
  

  

  1. 
  Petroleum 
  is 
  derived 
  from 
  organic 
  matter. 
  

  

  2. 
  It 
  is 
  much 
  more 
  largely 
  derived 
  from 
  vegetable 
  than 
  from 
  animal 
  substances. 
  

  

  3. 
  Petroleum 
  of 
  the 
  Pennsylvania 
  type 
  is 
  derived 
  from 
  the 
  organic 
  matter 
  of 
  

   bituminous 
  shales 
  and 
  is 
  of 
  vegetable 
  origin. 
  

  

  4. 
  Petroleum 
  of 
  the 
  Canada 
  type 
  is 
  derived 
  from 
  limestones, 
  and 
  is 
  probably 
  of 
  

   animal 
  origin. 
  

  

  5. 
  Petroleum 
  has 
  been 
  produced 
  at 
  normal 
  rock 
  temperatures 
  (in 
  Ohio 
  fields) 
  

   and 
  is 
  not 
  a 
  product 
  of 
  destructive 
  distillation 
  of 
  bituminous 
  shales. 
  

  

  6. 
  The 
  stock 
  of 
  petroleum 
  in 
  the 
  rocks 
  is 
  already 
  practically 
  complete. 
  

  

  After 
  showing 
  that 
  petroleum 
  is 
  almost 
  universally 
  present 
  in 
  small 
  

   quantities 
  throughout 
  the 
  limestones 
  and 
  shales 
  of 
  Pennsylvania 
  and 
  

   Ohio, 
  he 
  concluded 
  : 
  

  

  It 
  is 
  obvious 
  that 
  the 
  total 
  amount 
  of 
  petroleum 
  in 
  the 
  rocks 
  underlying 
  the 
  

   surface 
  of 
  Ohio 
  is 
  large 
  beyond 
  computation, 
  but 
  in 
  its 
  diffused 
  and 
  distributed 
  

   state, 
  it 
  is 
  entirely 
  without 
  value. 
  It 
  must 
  be 
  accumulated 
  in 
  rocks 
  that 
  serve 
  as 
  

   reservoirs 
  before 
  it 
  becomes 
  of 
  economic 
  interest. 
  

  

  RESERVOIRS 
  

  

  He 
  then 
  summarized 
  the 
  existing 
  knowledge 
  concerning 
  petroleum 
  

   reservoirs. 
  As 
  to 
  sandstone 
  reservoirs, 
  he 
  contrasted 
  those 
  of 
  Pennsyl- 
  

   vania, 
  as 
  described 
  by 
  Carll, 
  with 
  those 
  of 
  Ohio. 
  The 
  Venango 
  sands 
  

   of 
  Pennsylvania 
  were 
  standstones 
  of 
  medium 
  or 
  coarse 
  grain, 
  or 
  even 
  

   in 
  some 
  cases 
  conglomerates, 
  ranging 
  from 
  a 
  shell 
  to 
  100 
  feet 
  in 
  thick- 
  

   ness. 
  The 
  productive 
  fields 
  were 
  found 
  to 
  extend 
  in 
  length 
  for 
  a 
  score 
  

   or 
  more 
  miles 
  in 
  some 
  cases, 
  while 
  their 
  width 
  was 
  confined 
  to 
  1 
  or 
  2 
  

   miles. 
  The 
  reservoirs 
  were 
  lenticular 
  in 
  transverse 
  section. 
  The 
  

   coarser 
  the 
  sand 
  and 
  the 
  more 
  open, 
  the 
  greater 
  the 
  amount 
  of 
  oil 
  ; 
  and, 
  

   in 
  like 
  manner, 
  the 
  thicker 
  the 
  stratum, 
  the 
  larger 
  was 
  its 
  production 
  

   likely 
  to 
  be, 
  other 
  things 
  being 
  equal. 
  The 
  sandstone 
  reservoir 
  of 
  east- 
  

   ern 
  Ohio 
  was 
  "a 
  stratum 
  of 
  sandstone 
  that 
  rests 
  on 
  and 
  is 
  covered 
  by 
  

   shales, 
  but 
  the 
  stratum, 
  so 
  far 
  from 
  being 
  lenticular 
  in 
  character, 
  is 
  

   wonderfully 
  persistent, 
  though 
  varying 
  in 
  thickness 
  and 
  grain 
  from 
  

   point 
  to 
  point 
  and 
  occasionally 
  nearly 
  disappearing 
  for 
  short 
  spaces." 
  

   He 
  concluded 
  his 
  remarks 
  on 
  sandstones 
  as 
  reservoirs 
  with 
  the 
  

   following 
  : 
  

  

  