﻿336 
  J. 
  Barrell 
  — 
  The 
  Piedmont 
  Terraces 
  

  

  Clinton 
  shales 
  outcrop 
  west 
  of 
  Selinsgrove 
  and 
  show 
  a 
  

   very 
  thorough 
  leveling 
  at 
  600 
  to 
  630 
  feet. 
  The 
  relation 
  

   of 
  this 
  level 
  to 
  that 
  of 
  the 
  localities 
  of 
  Devonian 
  outcrops 
  

   is 
  the 
  same 
  as 
  for 
  the 
  Mauch 
  Chunk 
  shale. 
  This 
  surface 
  

   therefore 
  represents 
  the 
  Harrisburg 
  peneplain. 
  Far- 
  

   ther 
  northwest 
  the 
  Clinton 
  shales 
  again 
  outcrop 
  and 
  

   show 
  broad 
  hilltops 
  at 
  620 
  to 
  640 
  feet 
  which 
  are 
  the 
  last 
  

   clear 
  expression 
  of 
  the 
  Harrisburg 
  peneplain, 
  although 
  

   it 
  may 
  be 
  present 
  on 
  the 
  North 
  Fork 
  of 
  the 
  Susquehanna 
  

   at 
  an 
  elevation 
  of 
  about 
  700 
  feet 
  (Bloomsburg 
  quad- 
  

   rangle). 
  Throughout 
  a 
  straight-line 
  distance 
  of 
  about 
  

   sixty 
  miles 
  from 
  Harrisburg 
  to 
  Sunbury 
  the 
  Harrisburg 
  

   peneplain 
  maintains 
  itself 
  200 
  feet 
  above 
  the 
  present 
  

   river 
  level, 
  rising 
  two 
  feet 
  per 
  mile. 
  A 
  part 
  of 
  this 
  

   grade 
  may 
  be 
  assigned 
  to 
  warping 
  as 
  the 
  Susquehanna 
  

   presumably 
  has 
  a 
  considerably 
  steeper 
  grade 
  now 
  than 
  it 
  

   had 
  when 
  the 
  Harrisburg 
  peneplain 
  marked 
  its 
  level. 
  

  

  Campbell 
  correlated 
  the 
  Harrisburg 
  with 
  a 
  baselevel 
  

   in 
  the 
  vicinity 
  of 
  Sunbury 
  at 
  about 
  800 
  feet 
  embracing 
  the 
  

   localities 
  where 
  the 
  Devonian 
  formations 
  outcrop. 
  The 
  

   writer 
  has 
  come 
  to 
  the 
  conclusion, 
  however, 
  that 
  the 
  

   plane 
  at 
  this 
  level 
  is 
  not 
  equivalent 
  to 
  the 
  Harrisburg 
  

   and 
  he 
  has 
  called 
  it, 
  therefore, 
  the 
  Sunbury 
  peneplain. 
  

   This 
  newly 
  recognized 
  peneplain 
  is 
  not 
  an 
  entirely 
  satis- 
  

   factory 
  surface 
  to 
  trace 
  because 
  the 
  valley 
  flats 
  have 
  been 
  

   destroyed 
  and 
  it 
  is 
  possible 
  that 
  its 
  surface 
  has 
  been 
  

   lowered 
  by 
  later 
  erosion. 
  It 
  is 
  not 
  impossible 
  that 
  it 
  

   may 
  have 
  been 
  as 
  much 
  as 
  100 
  feet 
  higher 
  than 
  the 
  ele- 
  

   vation 
  assigned 
  to 
  it 
  and 
  thus 
  more 
  widely 
  separated 
  

   from 
  the 
  Harrisburg 
  peneplain. 
  

  

  The 
  following 
  tabulation 
  gives 
  in 
  descending 
  order 
  the 
  

   elevations 
  of 
  the 
  Susquehanna 
  and 
  North 
  Branch 
  which 
  

   appear 
  to 
  account 
  best 
  for 
  the 
  remnants 
  of 
  an 
  upland 
  — 
  

   the 
  Sunbury 
  peneplain 
  — 
  above 
  the 
  gentle 
  slopes 
  devel- 
  

   oped 
  in 
  the 
  later 
  Harrisburg 
  cycle. 
  

  

  Estimated 
  elevations 
  of 
  the 
  Sunbury 
  baselevel 
  on 
  the 
  Susque- 
  

   hanna 
  and 
  North 
  Branch, 
  and 
  present 
  river 
  levels. 
  

  

  

  

  

  

  Sunbury. 
  

  

  Present. 
  

  

  Pittston 
  

  

  Shickshinny 
  

  

  Shamokin 
  

  

  Sunbury 
  

  

  Millersburg 
  

  

  Harrisburg 
  

  

  quadrangle, 
  

  

  ab 
  

  

  out 
  

  

  i 
  

  

  1,200 
  

   1.000 
  

   900 
  

   850 
  

   750 
  

   650 
  

  

  560 
  

   500 
  

   450 
  

   425 
  

   400 
  

   340 
  

  

  