﻿Appalachian 
  Geosyncline. 
  459 
  

  

  ceous 
  sandstone, 
  and 
  this 
  in 
  turn 
  into 
  red 
  sandy 
  shale. 
  In 
  the 
  

   sandstones 
  the 
  bedding 
  is 
  usually 
  smooth 
  and 
  even 
  but 
  with 
  

   considerable 
  oblique 
  lamination. 
  The 
  shales 
  commonly 
  crum- 
  

   ble 
  rapidly 
  to 
  a 
  hackly 
  rubbish 
  without 
  relation 
  to 
  bedding 
  

   planes. 
  In 
  these 
  respects 
  the 
  sandstones 
  and 
  shales 
  conform 
  

   to 
  the 
  normal 
  widespread 
  character 
  of 
  the 
  Catskill 
  formation. 
  

  

  To 
  turn 
  to 
  the 
  evidences 
  of 
  subaerial 
  origin, 
  for 
  which 
  the 
  

   section 
  was 
  especially 
  investigated, 
  it 
  is 
  to 
  be 
  noted 
  that 
  

   mud-cracks 
  or 
  rain 
  prints 
  were 
  found 
  at 
  intervals 
  through- 
  

   out 
  the 
  entire 
  section, 
  always 
  in 
  horizons 
  of 
  red 
  shales. 
  

   The 
  section 
  was 
  in 
  fact 
  chosen 
  for 
  study 
  because 
  the 
  beds 
  

   from 
  top 
  to 
  bottom 
  are 
  here 
  best 
  exposed 
  in 
  detail 
  of 
  any 
  

   which 
  the 
  writer 
  has 
  seen. 
  In 
  the 
  bulk 
  of 
  the 
  red 
  shales 
  the 
  

   uniformity 
  of 
  the 
  material, 
  the 
  absence 
  of 
  bedding 
  planes, 
  and 
  

   the 
  rapidity 
  of 
  weathering 
  prevent 
  the 
  detection 
  of 
  subaerial 
  

   exposure 
  even 
  if 
  such 
  was 
  the 
  condition 
  of 
  origin, 
  but 
  even 
  in 
  

   such 
  beds 
  a 
  number 
  of 
  mud-crack 
  patterns 
  were 
  detected. 
  It 
  

   is 
  where 
  well-bedded 
  shales 
  are 
  interstratified 
  with 
  sandstones, 
  

   however, 
  that 
  the 
  opportunities 
  for 
  the 
  detection 
  of 
  mud 
  cracks 
  

   and 
  rainprints 
  are 
  the 
  best. 
  This 
  feature 
  of 
  the 
  stratigraphy 
  

   as 
  noted 
  applies 
  especially 
  to 
  the 
  upper 
  750 
  feet. 
  In 
  all 
  of 
  the 
  

   mud-cracks 
  of 
  the 
  Catskill 
  the 
  filling 
  was 
  a 
  mud 
  of 
  nearly 
  the 
  

   same 
  quality 
  as 
  the 
  cracked 
  stratum 
  and 
  the 
  result 
  is 
  usually 
  a 
  

   shadowy 
  pattern, 
  chiefly 
  visible 
  through 
  a 
  duller 
  luster 
  of 
  the 
  

   fillings. 
  In 
  rare 
  cases 
  the 
  filling, 
  however, 
  has 
  become 
  deoxi- 
  

   dized 
  and 
  shows 
  as 
  a 
  yellow 
  pattern 
  on 
  the 
  red 
  shale. 
  The 
  

   shale 
  surfaces 
  are 
  flat, 
  the 
  polygons 
  not 
  being 
  concave 
  upward 
  

   as 
  is 
  commonly 
  the 
  case 
  in 
  the 
  Mauch 
  Chunk 
  and 
  Newark 
  

   shales. 
  On 
  a 
  part 
  of 
  the 
  mud-cracked 
  surfaces 
  the 
  pattern 
  is 
  

   obvious 
  to 
  the 
  casual 
  observer, 
  but 
  in 
  more 
  than 
  half 
  it 
  requires 
  

   careful 
  search 
  and 
  observation 
  to 
  find 
  the 
  evidences 
  and 
  make 
  

   certain 
  that 
  the 
  irregularities 
  are 
  not 
  mere 
  weathering 
  simula- 
  

   tion 
  of 
  mud-crack 
  structures. 
  In 
  this 
  respect 
  the 
  Catskill 
  is 
  

   much 
  more 
  difficult 
  to 
  study 
  than 
  certain 
  formations 
  in 
  which 
  

   mud-cracks 
  are 
  a 
  conspicuous 
  feature. 
  

  

  The 
  Catskill 
  on 
  the 
  Potomac 
  River. 
  

  

  The 
  Catskill 
  appears 
  at 
  the 
  surface 
  on 
  the 
  flanks 
  of 
  succes- 
  

   sive 
  folds 
  in 
  western 
  Maryland 
  and 
  is 
  described 
  in 
  the 
  geologic 
  

   reports 
  of 
  that 
  region. 
  From 
  the 
  southeasternmost 
  exposure 
  

   of 
  Upper 
  Devonian 
  rocks 
  in 
  the 
  Hancock 
  quadrangle 
  of 
  Mary- 
  

   land 
  to 
  the 
  northwestern 
  in 
  the 
  Union 
  town 
  quadrangle 
  of 
  

   Pennsylvania 
  is 
  a 
  distance 
  of 
  about 
  80 
  miles 
  across 
  the 
  strike. 
  

   Having 
  discussed 
  the 
  character 
  in 
  the 
  Schuylkill 
  River 
  section 
  

   it 
  is 
  desirable 
  to 
  compare 
  it 
  with 
  these 
  localities 
  farther 
  south 
  

   and 
  west 
  toward 
  the 
  open 
  Chemung 
  sea. 
  

  

  