﻿Williatns 
  — 
  Devonian 
  Interval 
  in 
  northern 
  Arkansas. 
  143 
  

  

  able. 
  The 
  bony 
  texture 
  is 
  preserved, 
  and 
  the 
  fragment, 
  2 
  by 
  

   3 
  inches 
  in 
  diameter, 
  is 
  J 
  to 
  ^ 
  inch 
  in 
  thickness. 
  

  

  In 
  Newton 
  County, 
  a 
  section 
  was 
  seen 
  near 
  the 
  Saltpetre 
  

   Cave, 
  Cave 
  Creek 
  P. 
  O. 
  

  

  No. 
  1277. 
  Cave 
  Creek, 
  Newton 
  Co. 
  

  

  The 
  first 
  specimens 
  seen 
  from 
  this 
  section 
  were 
  collected 
  by 
  

   Mr. 
  Hopkins 
  in 
  the 
  summer 
  of 
  1890, 
  and 
  were 
  marked 
  as 
  from 
  

   Saltpetre 
  Cave 
  at 
  Cave 
  Creek 
  P. 
  O. 
  In 
  the 
  next 
  season 
  Mr. 
  

   Weller 
  collected 
  from 
  the 
  same 
  section, 
  sending 
  in 
  enough 
  

   specimens 
  to 
  make 
  out 
  the 
  several 
  elements 
  of 
  the 
  section. 
  

   The 
  interval-material 
  of 
  this 
  section 
  is 
  a 
  hard, 
  black, 
  shaly 
  

   rock, 
  about 
  18 
  inches 
  thick 
  (A2) 
  separating 
  the 
  Polk 
  Bayou 
  

   limestone 
  (Al) 
  from 
  the 
  overlying 
  red 
  marble 
  (A3), 
  the 
  St. 
  

   Joe 
  marble, 
  which 
  is 
  here 
  10 
  feet 
  thick 
  ; 
  above 
  it 
  lies 
  the 
  

   cherty 
  limestone 
  (Al), 
  which 
  is 
  called 
  Boone 
  chert 
  in 
  the 
  

   Reports. 
  The 
  black 
  shale 
  (A2) 
  contains 
  Lingulas 
  as 
  in 
  the 
  St. 
  

   Joe 
  section. 
  

  

  The 
  typical 
  locality 
  for 
  the 
  black 
  shale 
  is 
  Eureka 
  springs, 
  

   from 
  which 
  the 
  formation 
  derives 
  its 
  name. 
  

  

  No. 
  1410. 
  Eureka 
  Springs, 
  Carroll 
  Co. 
  

  

  The 
  full 
  section 
  of 
  the 
  rocks 
  at 
  Eureka 
  Springs 
  is 
  given 
  in 
  

   volume 
  iv 
  of 
  the 
  Annual 
  Reports 
  of 
  the 
  Geological 
  Survey 
  

   of 
  Arkansas 
  for 
  1890." 
  The 
  part 
  of 
  it 
  interesting 
  in 
  this 
  

   place 
  is 
  that 
  given 
  in 
  my 
  section 
  1410 
  A. 
  A' 
  is 
  the 
  top 
  of 
  the 
  

   saccharoidal 
  sandstone 
  ; 
  resting 
  immediately 
  upon 
  this 
  and 
  

   without 
  any 
  apparent 
  change 
  in 
  the 
  plane 
  of 
  bedding 
  is 
  the 
  

   black 
  shale 
  (A2). 
  In 
  the 
  section, 
  in 
  the 
  midst 
  of 
  the 
  city, 
  the 
  

   thickness 
  of 
  black 
  shale 
  is 
  about 
  four 
  feet, 
  with 
  a 
  foot 
  above 
  it 
  

   of 
  green 
  shale. 
  In 
  some 
  places 
  the 
  green 
  shale 
  is 
  several 
  feet 
  

   thick. 
  When 
  I 
  visited 
  the 
  locality, 
  an 
  excavation 
  for 
  the 
  cel- 
  

   lar 
  of 
  a 
  building 
  exposed 
  a 
  fresh 
  cut 
  of 
  about 
  six 
  feet 
  of 
  the 
  

   greenish 
  shale, 
  from 
  which 
  a 
  few 
  fossils 
  were 
  obtained. 
  The 
  

   black 
  shale 
  ran 
  up 
  into 
  the 
  green 
  without 
  any 
  sharp 
  line 
  of 
  

   sudden 
  change, 
  showing 
  a 
  continuous 
  deposition. 
  The 
  black 
  

   part 
  is, 
  however, 
  the 
  typical 
  Eureka 
  shale 
  (A2), 
  while 
  the 
  

   upper 
  green 
  part 
  is 
  a 
  representative 
  of 
  the 
  formation 
  which 
  in 
  

   Tennessee 
  is 
  much 
  more 
  important 
  and 
  constitutes 
  in 
  that 
  

   region 
  the 
  lower 
  member 
  of 
  the 
  Carboniferous 
  system. 
  The 
  

   sandstone 
  (A') 
  below 
  the 
  Eureka 
  shale 
  is 
  the 
  Ordovician 
  rock 
  

   lying 
  below 
  the 
  Polk 
  Bayou 
  limestone. 
  It 
  will 
  be 
  noticed 
  that 
  

   where 
  the 
  black 
  shale, 
  tilling 
  the 
  interval, 
  is 
  present 
  and 
  

   thickest 
  in 
  the 
  northwest 
  it 
  rests 
  on 
  the 
  lower 
  formations, 
  

   below 
  the 
  Polk 
  Bayou 
  limestone, 
  and 
  the 
  erosion 
  has 
  cut 
  into 
  

   the 
  saccharoidal 
  sandstones. 
  It 
  seems 
  probable 
  that 
  these 
  

   sandstones 
  were 
  the 
  source 
  of 
  the 
  polished 
  siliceous 
  grains 
  

  

  * 
  Marbles 
  and 
  other 
  limestones, 
  by 
  T. 
  C. 
  Hopkins. 
  1893. 
  

  

  