﻿K. 
  F. 
  Mather 
  — 
  Pottsville 
  Formations 
  and 
  Faunas. 
  1 
  33 
  

  

  Art. 
  XIII. 
  — 
  Pottsville 
  Formations 
  and 
  Fatmas 
  of 
  Arkansas 
  

   and 
  Oklahoma 
  • 
  by 
  Kirtley 
  F. 
  Mather. 
  

  

  Pottsville 
  formations 
  of 
  the 
  Boston 
  Mountains. 
  

  

  The 
  Boston 
  Mountains 
  form 
  an 
  escarpment 
  which 
  overlooks 
  

   the 
  Ozark 
  Plateau 
  and 
  extends 
  from 
  the 
  vicinity 
  of 
  Muskogee, 
  

   Oklahoma, 
  eastward 
  past 
  Fayetteville, 
  Arkansas, 
  to 
  Batesville, 
  

   Arkansas. 
  Their 
  structure 
  is 
  monoclinal, 
  the 
  beds 
  dipping 
  

   gently 
  toward 
  the 
  south. 
  The 
  strata 
  exposed 
  in 
  the 
  outlying 
  

   erosion 
  remnants 
  and 
  the 
  terraced 
  front 
  of 
  the 
  mountains 
  are 
  

   in 
  the 
  main 
  shales 
  and 
  sandstones 
  with 
  occasional 
  limestones. 
  

   Of 
  these, 
  the 
  Morrow 
  group 
  embraces 
  two 
  units, 
  the 
  Hale 
  

   formation 
  and 
  the 
  Bloyd 
  shale. 
  The 
  latter 
  contains 
  two 
  lime- 
  

   stone 
  members, 
  the 
  Brentwood 
  and 
  the 
  Kessler. 
  The 
  Morrow 
  

   group 
  rests 
  unconformably 
  upon 
  the 
  Pitkin 
  limestone, 
  or 
  in 
  

   places 
  on 
  the 
  Fayetteville 
  shale, 
  and 
  is 
  overlain 
  unconformably 
  

   by 
  the 
  Winslow 
  formation. 
  Both 
  unconformities 
  are 
  more 
  

   pronounced 
  toward 
  the 
  north 
  and 
  practically 
  disappear 
  toward 
  

   the 
  south 
  where 
  the 
  group 
  is 
  lost 
  to 
  sight 
  beneath 
  the 
  Wins- 
  

   low. 
  From 
  east 
  to 
  west 
  there 
  is 
  a 
  change 
  in 
  lithologv 
  ; 
  in 
  

   Oklahoma 
  the 
  Morrow 
  is 
  largely 
  limestone 
  while 
  toward 
  Bates- 
  

   ville 
  it 
  is 
  dominantly 
  clastic. 
  Limestone 
  lenses 
  in 
  the 
  Hale 
  

   formation 
  and 
  the 
  Brentwood 
  and 
  Kessler 
  limestone 
  members 
  

   of 
  the 
  Bloyd 
  carry 
  an 
  abundant 
  marine 
  fauna 
  which 
  has 
  been 
  

   described 
  elsewhere.* 
  A 
  thin 
  seam 
  of 
  coal 
  in 
  the 
  shales 
  be- 
  

   tween 
  the 
  two 
  upper 
  limestone 
  members 
  contains 
  a 
  fossil 
  flora 
  

   of 
  Sewanee 
  affinities. 
  The 
  early 
  Pottsville 
  age 
  of 
  the 
  group 
  

   is 
  further 
  demonstrated 
  by 
  the 
  marine 
  fauna, 
  in 
  which 
  a 
  large 
  

   number 
  of 
  residual 
  Mississippian 
  invertebrates 
  are 
  associated 
  

   with 
  forms 
  of 
  distinctly 
  Pennsylvanian 
  aspect. 
  

  

  Pottsville 
  formations 
  south 
  of 
  Arkansas 
  River. 
  

  

  Arkansas 
  Biver 
  and 
  its 
  tributaries 
  in 
  eastern 
  Oklahoma 
  and 
  

   western 
  Arkansas 
  occupy 
  a 
  geosynclinal 
  basin 
  composed 
  of 
  

   Pennsylvanian 
  strata. 
  The 
  lowest 
  beds 
  of 
  the 
  series 
  are 
  

   exposed 
  along 
  the 
  southern 
  margin 
  of 
  the 
  basin, 
  between 
  the 
  

   Arbuckle 
  Mountains 
  in 
  south 
  central 
  Oklahoma 
  and 
  the 
  Oua- 
  

   chita 
  Mountains 
  farther 
  east. 
  Throughout 
  this 
  region 
  the 
  

   Atoka 
  formation 
  is 
  especially 
  conspicuous, 
  both 
  because 
  of 
  its 
  

   great 
  thickness, 
  3000 
  to 
  6000 
  feet, 
  and 
  because 
  of 
  the 
  recur- 
  

   rence 
  of 
  massive 
  sandstone 
  beds 
  in 
  the 
  midst 
  of 
  the 
  shales 
  of 
  

   which 
  it 
  is 
  dominantly 
  composed. 
  Toward 
  the 
  north 
  it 
  is 
  

  

  * 
  Mather, 
  K. 
  F., 
  The 
  fauna 
  of 
  the 
  Morrow 
  group 
  of 
  Arkansas 
  and 
  Okla- 
  

   homa. 
  Denison 
  Univ., 
  Sci. 
  Lab. 
  Bull., 
  vol. 
  xviii, 
  pp. 
  59-284, 
  1915. 
  

  

  