﻿Williams 
  — 
  Devonian 
  Interval 
  in 
  northern 
  Arkansas, 
  151 
  

  

  manganese 
  bed. 
  The 
  relationship 
  existing 
  between 
  the 
  Syla- 
  

   more 
  sandstone, 
  which 
  is 
  the 
  phosphate-bearing 
  rock 
  of 
  this 
  

   region, 
  and 
  the 
  manganese 
  deposits 
  described 
  in 
  the 
  Batesville 
  

   region, 
  is 
  not 
  yet 
  clear. 
  

  

  As 
  Dr. 
  Branner 
  has 
  suggested 
  in 
  a 
  latter 
  discussion 
  of 
  the 
  

   subject,* 
  it 
  would 
  appear 
  that 
  the 
  Sylamore 
  sandstone, 
  and 
  

   the 
  manganese 
  deposits, 
  are 
  confused 
  in 
  some 
  of 
  the 
  sections. 
  

   "Whether 
  the 
  reason 
  for 
  this 
  is 
  the 
  wearing 
  down 
  of 
  the 
  

   Silurian 
  series, 
  so 
  that 
  the 
  Devonian 
  interval 
  deposits 
  were 
  laid 
  

   upon 
  the 
  surface 
  of 
  the 
  manganese 
  deposits 
  (the 
  Cason 
  shale), 
  

   or 
  whether 
  tliey 
  have 
  been 
  let 
  down 
  by 
  the 
  solution 
  of 
  an 
  

   originally 
  intervening 
  limestone, 
  it 
  is 
  difficult 
  to 
  determine 
  

   with 
  the 
  evidence 
  now 
  before 
  us. 
  

  

  There 
  seems 
  to 
  be 
  good 
  evidence 
  to 
  suppose 
  that 
  they 
  are 
  not 
  

   of 
  the 
  same 
  geological 
  age. 
  Further 
  study 
  of 
  the 
  whole 
  prob- 
  

   lem 
  of 
  the 
  deposits 
  filling 
  the 
  Devonian 
  interval 
  in 
  the 
  southf 
  

   has 
  led 
  to 
  the 
  conclusion 
  that, 
  however 
  much 
  erosion 
  of 
  the 
  

   underlying 
  Silurian 
  formation 
  took 
  place, 
  the 
  sediments 
  of 
  

   black 
  mud 
  forming 
  the 
  sliale 
  did 
  not 
  begin 
  till 
  after 
  the 
  

   beginning 
  of 
  the 
  Devonian 
  era. 
  The 
  association 
  of 
  the 
  frag- 
  

   ments 
  of 
  thick 
  bones 
  of 
  large 
  fish 
  with 
  the 
  worn 
  Sylamore 
  

   sandstone, 
  is 
  observed 
  on 
  the 
  eastern 
  margin 
  of 
  the 
  Cincinnati 
  

   plateau 
  in 
  Kentucky. 
  So 
  far 
  as 
  our 
  knowledge 
  of 
  the 
  range 
  

   of 
  species 
  goes, 
  these 
  fish 
  were 
  not 
  living 
  till 
  the 
  early 
  part 
  of 
  

   the 
  Devonian 
  era. 
  The 
  black 
  shale 
  following 
  such 
  worn 
  

   material 
  suggests 
  a 
  sinking 
  of 
  the 
  particular 
  region, 
  and 
  when 
  

   the 
  shale 
  and 
  the 
  worn 
  fragments 
  and 
  nodules 
  alternate, 
  as 
  

   they 
  appear 
  to 
  do 
  in 
  central 
  Tennessee, 
  it 
  may 
  be 
  taken 
  as 
  

   evidence 
  of 
  the 
  continuous, 
  shallow 
  condition 
  of 
  the 
  region, 
  

   which 
  was 
  at 
  that 
  time 
  the 
  southern 
  extension 
  of 
  the 
  Cincin- 
  

   nati 
  plateau. 
  

  

  Note. 
  — 
  While 
  preparing 
  this 
  report 
  for 
  publication, 
  I 
  have 
  

   seen 
  vol. 
  iii. 
  Part 
  II 
  of 
  the 
  Minnesota 
  Eeport,:}: 
  and 
  notice 
  a 
  

   remark 
  which 
  suggests 
  the 
  extension 
  of 
  this 
  peculiar 
  interval 
  

   deposit 
  as 
  far 
  north 
  as 
  Minnesota. 
  Describing 
  the 
  section 
  of 
  

   the 
  rocks 
  at 
  Prosser's 
  ravine 
  near 
  Wykoff, 
  Fitlmore 
  County, 
  

   the 
  authors 
  state 
  that 
  " 
  Succeeding 
  the 
  foregoing 
  bed 
  [which 
  

   was 
  of 
  uncertain 
  age, 
  of 
  6 
  feet 
  thickness, 
  regarded 
  as 
  Upper 
  

   Silurian, 
  the 
  passage 
  of 
  which 
  lithologically 
  from 
  the 
  Pich- 
  

   mond 
  group 
  (upper 
  Cincinnati 
  group) 
  is 
  described 
  as 
  exceed- 
  

   ingly 
  gradual] 
  and 
  followed 
  with 
  not 
  very 
  strong 
  evidence 
  of 
  

   unconformity 
  by 
  Devonian 
  strata, 
  is 
  a 
  sandstone 
  four 
  feet 
  thick, 
  

  

  * 
  See 
  the 
  Phosphate 
  Deposits 
  of 
  Arkansas, 
  by 
  J. 
  C. 
  Branner, 
  Am. 
  Inst. 
  Min., 
  

   Eng., 
  1896. 
  

  

  t 
  See 
  the 
  southern 
  Devonian. 
  

  

  X 
  G-eology 
  of 
  Minnesota, 
  vol. 
  iii, 
  Part 
  II, 
  of 
  the 
  final 
  report. 
  Paleontology, 
  

   1897, 
  p. 
  cv. 
  

  

  