﻿334 
  J. 
  Barrell 
  — 
  The 
  Piedmont 
  Terraces 
  

  

  he 
  named 
  the 
  Harrisburg 
  peneplain. 
  20 
  In 
  the 
  vicinity 
  of 
  

   Harrisburg, 
  where 
  this 
  peneplain 
  is 
  well 
  developed 
  and 
  

   preserved 
  on 
  the 
  npper 
  Ordovician 
  slates, 
  it 
  has 
  an 
  eleva- 
  

   tion 
  slightly 
  over 
  500 
  feet. 
  Farther 
  np 
  the 
  Snsqnehanna 
  

   valley 
  in 
  the 
  vicinity 
  of 
  Sunbury, 
  Campbell 
  considered 
  

   that 
  the 
  Harrisbnrg 
  peneplain 
  had 
  an 
  elevation 
  of 
  800 
  

   feet, 
  near 
  Pittston 
  of 
  1,200 
  to 
  1,300 
  feet, 
  and 
  in 
  north- 
  

   western 
  Pennsylvania 
  of 
  abont 
  2,200 
  feet. 
  His 
  conclu- 
  

   sions 
  as 
  to 
  the 
  warping 
  of 
  the 
  peneplain 
  rested 
  on 
  the 
  

   fact 
  that 
  everywhere 
  he 
  was 
  able 
  to 
  recognize 
  at 
  least 
  two 
  

   erosion 
  surfaces. 
  The 
  npper 
  and 
  more 
  complete 
  of 
  

   these 
  he 
  correlated 
  with 
  the 
  Schooley 
  peneplain 
  of 
  

   " 
  Jura-Cretaceous 
  " 
  age; 
  the 
  second 
  was 
  regarded 
  as 
  the 
  

   Harrisburg, 
  formed 
  in 
  early 
  Tertiary. 
  In 
  addition, 
  the 
  

   Somerville 
  was 
  recognized 
  as 
  developed 
  only 
  on 
  the 
  

   softest 
  rocks. 
  The 
  recognition 
  by 
  Campbell 
  of 
  three 
  

   baselevels 
  in 
  Pennsylvania 
  represented 
  an 
  advance 
  in 
  the 
  

   physiographic 
  interpretation 
  of 
  this 
  part 
  of 
  the 
  Appala- 
  

   chians 
  similar 
  to 
  that 
  by 
  Keith 
  south 
  of 
  the 
  Potomac. 
  

  

  To 
  show 
  a 
  well 
  developed 
  and 
  well 
  preserved 
  pene- 
  

   plain 
  the 
  nature 
  of 
  the 
  rock 
  formations 
  must 
  be 
  closely 
  

   adjusted 
  to 
  the 
  time 
  elapsing 
  during 
  peneplanation 
  and 
  

   that 
  elapsing 
  after 
  uplift 
  of 
  the 
  peneplaned 
  surface. 
  

   Thus 
  the 
  remarkable 
  meanders 
  of 
  Conedoguinet 
  Creek 
  

   lie 
  partly 
  in 
  limestone 
  and 
  partly 
  in 
  slate 
  which 
  indicates 
  

   that 
  when 
  they 
  were 
  assumed 
  the 
  surface 
  must 
  have 
  been 
  

   a 
  very 
  perfect 
  plain. 
  In 
  fact, 
  the 
  breadth 
  of 
  the 
  mean- 
  

   ders 
  suggests 
  that 
  some 
  aggradation 
  had 
  taken 
  place 
  

   at 
  the 
  junction 
  of 
  the 
  creek 
  with 
  the 
  Susquehanna. 
  At 
  

   the 
  present 
  time 
  the 
  slate 
  outcrop 
  has 
  many 
  hills 
  rising 
  

   to 
  520-540 
  feet, 
  whereas 
  the 
  limestone 
  has 
  relatively 
  few 
  

   and 
  in 
  general 
  is 
  eroded 
  to 
  a 
  distinctly 
  lower 
  level 
  than 
  

   the 
  slate. 
  On 
  the 
  other 
  hand, 
  the 
  resistant 
  quartzite 
  of 
  

   the 
  Kittatinny 
  ridge 
  was 
  not 
  notably 
  eroded 
  during 
  the 
  

   Harrisburg 
  cycle 
  nor 
  later 
  except 
  by 
  undermining 
  

   through 
  the 
  removal 
  of 
  the 
  slate 
  at 
  its 
  base. 
  The 
  

   Newark 
  shales, 
  sandstones, 
  and 
  traps, 
  which 
  cover 
  most 
  

   of 
  the 
  New 
  Cumberland 
  quadrangle 
  and 
  lie 
  immediately 
  

   south 
  of 
  the 
  limestone 
  area, 
  must 
  have 
  been 
  peneplaned 
  

   in 
  large 
  part 
  during 
  the 
  Harrisburg 
  cycle, 
  but 
  consider- 
  

   able 
  areas 
  of 
  sandstone 
  and 
  trap 
  still 
  rise 
  above 
  600 
  feet 
  

   and 
  other 
  large 
  portions 
  have 
  been 
  reduced 
  to 
  below 
  520 
  

  

  20 
  M. 
  E. 
  Campbell. 
  Geographic 
  development 
  of 
  northern 
  Pennsylvania 
  

   and 
  southern 
  New 
  York. 
  Bull. 
  Geol. 
  Soc. 
  Am., 
  vol. 
  14, 
  277-296, 
  1903. 
  

  

  