﻿Appalachian 
  Geosyncline. 
  449 
  

  

  coarser 
  marginal 
  deposits, 
  such 
  as 
  the 
  Bellvale 
  flags 
  of 
  the 
  

   Green 
  Pond 
  Mountain 
  syncline, 
  are 
  also 
  carbonaceous 
  and 
  con- 
  

   tain 
  their 
  iron 
  chiefly 
  in 
  ferrous 
  form. 
  In 
  this 
  respect 
  the 
  

   Rensselaer 
  grit 
  resembles 
  the 
  Bellvale 
  flags 
  much 
  more 
  than 
  

   it 
  does 
  the 
  Oneonta 
  or 
  Catskill 
  formation. 
  In 
  the 
  Hamilton 
  

   formation 
  a 
  thick 
  and 
  widespread 
  sand 
  and 
  mud 
  mantle 
  holding 
  

   marine 
  fossils 
  was 
  spread 
  over 
  the 
  northeastern 
  part 
  of 
  the 
  geo- 
  

   syncline, 
  synchronous 
  with 
  the 
  deposition 
  of 
  the 
  Bellvale 
  flags. 
  

   Erosion 
  was 
  therefore 
  active, 
  and 
  coarser 
  flags 
  and 
  grits 
  should 
  

   mark 
  the 
  marginal 
  deposits. 
  The 
  reference 
  of 
  the 
  Rensselaer 
  

   grit 
  to 
  the 
  Middle 
  Devonian 
  seems 
  then 
  more 
  probable 
  from 
  

   both 
  its 
  color 
  and 
  its 
  arenaceous 
  character. 
  The 
  presence 
  of 
  

   calcareous 
  beds 
  gives 
  a 
  further 
  contrast 
  to 
  the 
  adjacent 
  upper 
  

   Devonian 
  deposits. 
  

  

  Interpreted 
  as 
  of 
  Middle 
  Devonian 
  age, 
  the 
  formation 
  would 
  

   not 
  fall 
  within 
  the 
  limits 
  of 
  this 
  article, 
  save 
  for 
  its 
  indications 
  

   of 
  the 
  extension 
  of 
  the 
  basin 
  of 
  sedimentation 
  in 
  this 
  direction 
  

   and 
  the 
  possibility 
  that 
  truly 
  Upper 
  Devonian 
  sediments 
  may 
  

   have 
  constituted 
  the 
  upper 
  part 
  of 
  the 
  sequence. 
  If 
  such 
  was 
  

   the 
  case 
  they 
  have 
  been 
  subsequently 
  eroded 
  because 
  lying 
  

   during 
  the 
  Mesozoic 
  above 
  the 
  baselevels 
  of 
  the 
  time. 
  

  

  The 
  Pocono 
  sandstone. 
  

  

  The 
  Mississippfan 
  period 
  was 
  opened 
  by 
  the 
  development 
  in 
  

   the 
  Appalachian 
  geosyncline 
  of 
  a 
  great 
  sandstone 
  formation, 
  

   the 
  Pocono 
  sandstone. 
  In 
  character 
  it 
  is 
  distinct 
  from 
  the 
  pre- 
  

   ceding 
  Catskill, 
  though 
  grading 
  into 
  it 
  through 
  a 
  thick 
  transi- 
  

   tion 
  series. 
  It 
  consists 
  in 
  the 
  east 
  almost 
  entirely 
  of 
  coarse, 
  

   clean, 
  gray-green 
  sandstone, 
  verging 
  into 
  conglomerates. 
  

   These 
  sandstones 
  in 
  some 
  beds 
  become 
  white 
  and 
  platy 
  on 
  

   weathered 
  surfaces. 
  Other 
  beds 
  are 
  massive. 
  On 
  account 
  of 
  

   the 
  uniformity 
  of 
  the 
  material 
  such 
  features 
  as 
  crossbedding 
  

   are 
  not 
  easily 
  detected. 
  Red 
  shales 
  are 
  absent 
  except 
  as 
  very 
  

   minor 
  developments 
  ; 
  but 
  the 
  argillaceous 
  material 
  gives 
  rise, 
  

   on 
  the 
  contrary, 
  to 
  olive-green 
  or 
  dull 
  yellow 
  shales. 
  Toward 
  

   the 
  west 
  and 
  southwest 
  the 
  formation 
  thins 
  down, 
  becomes 
  

   more 
  shaly, 
  and 
  breaks 
  up 
  into 
  a 
  group 
  of 
  alternating 
  shales 
  

   and 
  conglomeratic 
  sandstones. 
  Thin 
  coal 
  seams 
  become 
  more 
  

   abundant, 
  but 
  there 
  are 
  also 
  larger 
  members 
  of 
  red 
  shale 
  than 
  

   to 
  the 
  northeast. 
  

  

  In 
  Allegheny 
  and 
  Cattaraugus 
  counties 
  of 
  New 
  York 
  the 
  

   Oswayo 
  formation 
  is 
  lithologically 
  equivalent 
  to 
  the 
  Pocono 
  and 
  

   carries 
  a 
  marine 
  fauna. 
  Marine 
  fossils 
  also 
  occur 
  in 
  Bedford 
  

   County 
  in 
  southern 
  Pennsylvania. 
  These 
  and 
  other 
  occurrences 
  

   show 
  truly 
  marine 
  phases 
  occurring 
  in 
  the 
  Pocono 
  in 
  the 
  two- 
  

   fifths 
  of 
  Pennsylvania 
  west 
  of 
  the 
  seventy-eighth 
  meridian. 
  

  

  