﻿310 
  W. 
  A. 
  Verwiebe 
  — 
  Correlation 
  of 
  the 
  

  

  Unconformity 
  between 
  Devonian 
  and 
  Mississippian, 
  

  

  It 
  will 
  be 
  noted 
  that 
  in 
  the 
  above 
  table 
  the 
  Berea 
  has 
  been 
  

   considered 
  the 
  basal 
  formation 
  of 
  the 
  Mississippian 
  system. 
  A 
  

   good 
  deal 
  has 
  been 
  written 
  to 
  determine 
  the 
  proper 
  place 
  to 
  

   put 
  the 
  dividing 
  line 
  between 
  the 
  Devonian 
  and 
  Mississippian 
  

   and 
  a 
  few 
  words 
  of 
  discussion 
  on 
  this 
  subject 
  may 
  therefore 
  

   not 
  seem 
  out 
  of 
  place. 
  In 
  the 
  article 
  by 
  Dr. 
  Grirty 
  discussed 
  

   above 
  some 
  excellent 
  reasons 
  are 
  given 
  for 
  drawing 
  the 
  line 
  at 
  

   the 
  base 
  of 
  the 
  Berea. 
  The 
  fact 
  that 
  the 
  Berea 
  inaugurates 
  a 
  

   new 
  series 
  of 
  rocks 
  as 
  a 
  basal 
  conglomerate 
  (though 
  it 
  is 
  most 
  

   commonly 
  a 
  coarse 
  sandstone), 
  secondly 
  the 
  fact 
  that 
  the 
  under- 
  

   lying 
  rocks 
  are 
  extensively 
  eroded 
  giving 
  rise 
  to 
  a 
  disconform- 
  

   ity, 
  are 
  strong 
  arguments 
  in 
  favor 
  of 
  this 
  view. 
  The 
  impor- 
  

   tance 
  of 
  this 
  disconformity 
  is 
  not 
  admitted 
  by 
  all 
  geologists. 
  

   Professor 
  dishing, 
  for 
  instance, 
  holds 
  that 
  it 
  is 
  merely 
  con- 
  

   temporaneous 
  erosion. 
  In 
  a 
  paper 
  published 
  in 
  the 
  Bulletin 
  

   of 
  the 
  Geological 
  Society 
  of 
  America* 
  he 
  states 
  certain 
  condi- 
  

   tions 
  which 
  should 
  be 
  present 
  in 
  order 
  to 
  indicate 
  a 
  gap 
  of 
  

   sufficient 
  length 
  of 
  time 
  to 
  entitle 
  the 
  break 
  to 
  be 
  considered 
  

   of 
  diastrophic 
  importance. 
  The 
  first 
  is 
  that 
  oscillation 
  upon 
  

   which 
  an 
  unconformity 
  depends 
  must 
  be 
  accompanied 
  by 
  some 
  

   warping. 
  He 
  finds 
  that 
  nowhere 
  does 
  the 
  Berea 
  rest 
  upon 
  any 
  

   formation 
  but 
  the 
  Bedford 
  (ranging 
  in 
  thickness 
  from 
  50 
  to 
  

   100 
  feet) 
  and 
  assumes 
  that 
  therefore 
  no 
  warping 
  has 
  taken 
  

   place. 
  This 
  reasoning 
  is 
  no 
  doubt 
  very 
  good. 
  Still, 
  would 
  it 
  

   not 
  be 
  perfectly 
  possible 
  that 
  a 
  negative 
  movement 
  of 
  the 
  

   strand 
  line 
  involving 
  a 
  narrow 
  strip 
  of 
  continent, 
  say 
  one 
  hun- 
  

   dred 
  miles 
  wide 
  and 
  extending 
  roughly 
  east 
  and 
  west, 
  might 
  

   be 
  caused 
  by 
  a 
  slight 
  lowering 
  of 
  the 
  sea 
  level 
  ? 
  Assuming 
  that 
  

   the 
  shore 
  line 
  during 
  the 
  Bedford 
  age 
  lay 
  to 
  the 
  north 
  approx- 
  

   imately 
  within 
  the 
  present 
  confines 
  of 
  Lake 
  Erie 
  and 
  that 
  the 
  

   shales 
  and 
  sandstones 
  of 
  that 
  age 
  were 
  being 
  accumulated 
  in 
  a 
  

   shallow 
  sea 
  gently 
  sloping 
  toward 
  the 
  south, 
  does 
  it 
  seem 
  unrea- 
  

   sonable 
  to 
  suppose 
  that 
  the 
  strand 
  line 
  shifted 
  slowly 
  south 
  

   until 
  it 
  reached 
  approximately 
  the 
  latitude 
  of 
  central 
  Ohio 
  ? 
  

   Such 
  a 
  shifting 
  would 
  explain 
  very 
  nicely 
  the 
  fact 
  that 
  the 
  

   Bedford 
  shale 
  increases 
  in 
  thickness 
  toward 
  the 
  south 
  and 
  that 
  

   1 
  the 
  sandstones 
  are 
  present 
  in 
  the 
  south 
  and 
  missing 
  toward 
  the 
  

   north. 
  The 
  Berea 
  formation 
  then 
  represents 
  the 
  coarse 
  phase 
  

   of 
  deposition 
  which 
  should 
  accompany 
  a 
  sea 
  transgressing 
  the 
  

   region 
  again 
  toward 
  the 
  north. 
  And 
  again 
  we 
  should 
  expect 
  

   that 
  the 
  Berea 
  would 
  show 
  a 
  less 
  thickness 
  in 
  central 
  Ohio 
  and 
  

   a 
  greater 
  thickness 
  in 
  northern 
  Ohio, 
  which 
  an 
  analysis 
  of 
  the 
  

   facts 
  proves 
  to 
  be 
  true. 
  If 
  we 
  accept 
  this 
  condition 
  of 
  affairs 
  

  

  * 
  Vol. 
  xxvi, 
  p. 
  205-216, 
  June 
  15, 
  1915. 
  Diastrophic 
  Importance 
  of 
  the 
  Un- 
  

   conformity 
  at 
  the 
  Base 
  of 
  the 
  Berea 
  Grit 
  in 
  Ohio. 
  

  

  