﻿164 
  Keyes 
  — 
  Carboniferous 
  and 
  Devonian 
  Strata. 
  

  

  The 
  blue 
  shales 
  below 
  the 
  Grassy 
  shales 
  and 
  above 
  the 
  

   Cedar 
  limestone 
  show 
  in 
  deep-well 
  sections 
  a 
  thickness 
  of 
  at 
  

   least 
  125 
  feet. 
  They 
  are 
  without 
  doubt 
  a 
  continuation 
  of 
  the 
  

   Lime 
  Creek 
  shales. 
  Along 
  the 
  Mississippi 
  river 
  they 
  become 
  

   attenuated 
  towards 
  the 
  northeast 
  ; 
  and 
  some 
  little 
  distance 
  

   south 
  of 
  Muscatine 
  and 
  to 
  the 
  south 
  of 
  Hannibal 
  they 
  fail 
  

   altogether. 
  Fifty 
  miles 
  southwest 
  of 
  the 
  last 
  mentioned 
  place, 
  

   near 
  Fulton, 
  they 
  appear 
  to 
  be 
  fully 
  represented 
  by 
  the 
  50 
  

   feet 
  of 
  Snyder 
  shales 
  which 
  immediately 
  overlie 
  the 
  Callaway 
  

   limestone. 
  From 
  Burlington 
  to 
  the 
  northwest 
  they 
  are 
  

   recognizable 
  as 
  far 
  as 
  Marshall 
  county 
  and 
  characteristic 
  Lime 
  

   Creek 
  fossils 
  have 
  been 
  taken 
  from 
  well-drillings 
  in 
  this 
  dis- 
  

   trict. 
  From 
  Marshall 
  the 
  belt 
  swerves 
  to 
  the 
  east 
  somewhat, 
  

   and 
  in 
  Floyd 
  county 
  the 
  Kinderhook 
  blue 
  shales 
  directly 
  cover 
  

   them. 
  

  

  In 
  the 
  delimitation 
  of 
  geologic 
  formations 
  I 
  place 
  far 
  more 
  

   weight 
  on 
  the 
  stratigraphic 
  evidence 
  of 
  a 
  well-marked 
  uncon- 
  

   formity 
  than 
  on 
  the 
  occurrence 
  of 
  a 
  fauna 
  of 
  Devonian 
  aspects 
  

   high 
  up 
  in 
  the 
  thick 
  shale-succession. 
  To 
  rne 
  unconformity 
  

   means 
  more 
  than 
  any 
  other 
  classificatory 
  or 
  correlative 
  

   criterion.* 
  

  

  * 
  American 
  Geologist, 
  vol. 
  xviii, 
  p. 
  289, 
  1898. 
  

  

  