﻿460 
  J. 
  Barrell 
  — 
  Upper 
  Devonian 
  Delta 
  of 
  the 
  

  

  On 
  the 
  eastern 
  side, 
  in 
  the 
  Hancock 
  quadrangle, 
  according 
  

   to 
  Stose 
  and 
  Schwartz, 
  the 
  Catskill 
  attains 
  a 
  thickness 
  of 
  about 
  

   3800 
  feet. 
  Fifteen 
  miles 
  west, 
  in 
  the 
  Pawpaw 
  quadrangle, 
  its 
  

   thickness 
  is 
  about 
  2000 
  feet, 
  a 
  diminution 
  of 
  more 
  than 
  a 
  

   hundred 
  feet 
  to 
  the 
  mile. 
  Below 
  this 
  are 
  some 
  500 
  feet 
  of 
  

   beds 
  separately 
  mapped 
  and 
  transitional 
  into 
  the 
  Jennings 
  

   formation, 
  4000 
  to 
  4800 
  feet 
  thick. 
  Some50 
  miles 
  farther 
  

   west, 
  G. 
  C. 
  Martin 
  reports 
  the 
  Catskill 
  as 
  1200 
  to 
  1400 
  feet 
  

   thick. 
  Only 
  the 
  upper 
  part 
  of 
  the 
  Jennings 
  is 
  exposed 
  here, 
  

   but 
  in 
  the 
  columnar 
  section 
  it 
  is 
  estimated 
  at 
  3500 
  feet 
  in 
  

   thickness. 
  In 
  the 
  Uniontown 
  quadrangle, 
  20 
  miles 
  northwest 
  

   of 
  the 
  last 
  locality, 
  M. 
  R. 
  Campbell 
  reports 
  that 
  fossiliferous 
  

   green 
  shales 
  of 
  Chemung 
  age 
  directly 
  underlie 
  the 
  Pocono 
  

   sandstone. 
  But 
  beginning 
  about 
  700 
  feet 
  below 
  the 
  Pocono 
  

   sandstone, 
  wells 
  have 
  penetrated 
  about 
  150 
  feet 
  of 
  red 
  shale. 
  

   In 
  character 
  the 
  rocks 
  of 
  the 
  Maryland 
  sections 
  are 
  more 
  argil- 
  

   laceous 
  than 
  in 
  Schuylkill 
  County, 
  Pennsylvania, 
  the 
  great 
  

   thicknesses 
  of 
  olive 
  sandstones 
  of 
  the 
  latter 
  region 
  apparently 
  

   being 
  replaced 
  by 
  red 
  argillaceous 
  sandstones 
  and 
  red 
  shales. 
  

   Cross-bedding 
  and 
  ripple 
  marking 
  are 
  common. 
  Stose 
  and 
  

   Schwartz 
  mention 
  furthermore 
  in 
  the 
  Pawpaw-Hancock 
  folio 
  

   in 
  1912 
  the 
  presence 
  of 
  mud-cracks. 
  

  

  For 
  discussions 
  of 
  the 
  conditions 
  of 
  origin 
  it 
  is 
  important 
  to 
  

   determine 
  to 
  what 
  extent 
  these 
  marks 
  of 
  subaerial 
  exposure 
  

   extend 
  south 
  westward 
  from 
  eastern 
  Pennsylvania 
  and 
  are 
  coin- 
  

   cident 
  with 
  the 
  Catskill 
  phase 
  of 
  sedimentation. 
  For 
  this 
  pur- 
  

   pose 
  the 
  writer 
  in 
  1908 
  studied 
  the 
  section 
  between 
  Frostburg 
  

   and 
  Cumberland, 
  Maryland, 
  longitude 
  78° 
  51' 
  W. 
  This 
  is 
  forty 
  

   miles 
  west 
  of 
  the 
  eastern 
  outcrop 
  in 
  Maryland, 
  fully 
  sixty 
  

   miles 
  west 
  of 
  the 
  strike 
  of 
  the 
  Schuylkill 
  River 
  sections, 
  and 
  

   160 
  to 
  170 
  miles 
  distant 
  from 
  the 
  latter 
  in 
  a 
  southwest 
  by 
  west 
  

   direction. 
  

  

  Ascending 
  through 
  the 
  Upper 
  Devonian 
  section, 
  the 
  olive 
  

   shales 
  are 
  observed 
  to 
  give 
  place 
  to 
  red 
  shales 
  of 
  the 
  Catskill 
  

   type, 
  some 
  thin 
  layers 
  of 
  olive 
  shale 
  and 
  gray 
  sandstone 
  being 
  

   interstratified 
  near 
  the 
  base 
  with 
  the 
  red 
  shales. 
  Gradations 
  

   into 
  argillaceous 
  red 
  sandstones 
  are 
  common. 
  Twenty-five 
  feet 
  

   above 
  the 
  top 
  of 
  the 
  olive 
  shales* 
  well-defined 
  mud-cracked 
  

   surfaces 
  were 
  noted 
  and 
  continued 
  to 
  appear 
  through 
  about 
  140 
  

   feet 
  of 
  beds. 
  The 
  polygons 
  range 
  from 
  three 
  to 
  twelve 
  inches 
  

   in 
  diameter 
  on 
  different 
  surfaces, 
  the 
  fillings 
  from 
  one-fourth 
  

   to 
  one-half 
  inch 
  across, 
  and 
  differing 
  from 
  the 
  polygons 
  chiefly 
  

   in 
  luster. 
  No 
  concavity 
  of 
  the 
  polygonal 
  plates 
  is 
  observed, 
  

  

  * 
  The 
  olive 
  shales 
  stop 
  about 
  fifty 
  feet 
  southeast 
  of 
  the 
  east 
  portal 
  of 
  the 
  

   tunnel 
  of 
  the 
  Cumberland 
  and 
  Pennsylvania 
  Eailroad. 
  The 
  tunnel 
  is 
  cut 
  

   through 
  red 
  shale 
  and 
  sandstone 
  and 
  its 
  waste 
  offered 
  a 
  good 
  opportunity 
  for 
  

   the 
  study 
  of 
  the 
  basal 
  Catskill. 
  

  

  