﻿of 
  the 
  Northern 
  Appalachians. 
  333 
  

  

  farther 
  than 
  is 
  indicated 
  by 
  the 
  present 
  ontcrops 
  of 
  for- 
  

   mations. 
  How 
  far 
  they 
  may 
  have 
  extended 
  can 
  not 
  be 
  

   said 
  because 
  erosion 
  has 
  removed 
  the 
  plainest 
  and 
  most 
  

   commonly 
  accepted 
  evidence, 
  namely, 
  the 
  deposited 
  sedi- 
  

   ments. 
  When 
  this 
  situation 
  exists 
  the 
  problem 
  of 
  deter- 
  

   mining 
  the 
  position 
  of 
  a 
  former 
  shore-line 
  becomes 
  a 
  

   physiographic 
  one. 
  For 
  a 
  proper 
  solution 
  it 
  is 
  neces- 
  

   sary 
  to 
  recognize 
  that 
  the 
  sea 
  is 
  as 
  competent 
  as 
  sub- 
  

   aerial 
  agencies 
  to 
  produce 
  extensive 
  peneplanes, 
  that 
  

   marine 
  denudation, 
  like 
  fluvial 
  denudation, 
  has 
  its 
  char- 
  

   acteristic 
  features, 
  and 
  that 
  some 
  of 
  these 
  features 
  may 
  

   endure 
  for 
  long 
  periods 
  even 
  though 
  the 
  peneplaned 
  sur- 
  

   face 
  be 
  modified 
  by 
  later 
  subaerial 
  erosion. 
  

  

  Fluvial 
  peneplanes. 
  

   Editorial 
  Note. 
  

  

  It 
  should 
  be 
  understood 
  that 
  the 
  following 
  three 
  sec- 
  

   tions, 
  namely, 
  "Re-examination 
  of 
  the 
  Harrisburg 
  pene- 
  

   plain," 
  "Significance 
  of 
  present 
  valley 
  forms,' 
  ' 
  and 
  

   "Evidence 
  of 
  baselevels 
  given 
  by 
  wind 
  gaps" 
  are 
  based 
  

   in 
  part 
  on 
  map 
  study 
  and 
  although 
  Professor 
  Barrell 
  

   was 
  well 
  acquainted 
  with 
  region, 
  he 
  had 
  planned 
  to 
  fur- 
  

   ther 
  test 
  his 
  conclusions 
  in 
  the 
  field. 
  The 
  results 
  as 
  they 
  

   stand, 
  therefore, 
  should 
  be 
  considered 
  tentative 
  in 
  char- 
  

   acter 
  ; 
  they 
  illustrate 
  the 
  complexity 
  introduced 
  into 
  the 
  

   problem 
  by 
  many 
  rather 
  than 
  few 
  baselevels 
  of 
  erosion. 
  

  

  Ee-examination 
  of 
  the 
  Harrisburg 
  Peneplain. 
  

  

  In 
  a 
  study 
  of 
  the 
  later 
  Appalachian 
  history, 
  as 
  re- 
  

   vealed 
  by 
  the 
  land 
  forms, 
  a 
  re-examination 
  of 
  previous 
  

   work 
  should 
  be 
  made 
  beginning 
  with 
  the 
  basal 
  postulates. 
  

   The 
  criteria 
  for 
  tracing 
  a 
  warped 
  and 
  elevated 
  erosion 
  

   surface 
  must 
  be 
  reviewed 
  and 
  ultimately 
  those 
  for- 
  dis- 
  

   tinguishing 
  fluvial 
  and 
  marine 
  peneplanes 
  must 
  be 
  taken 
  

   up. 
  In 
  this 
  section 
  a 
  fluvial 
  peneplane 
  will 
  be 
  examined 
  . 
  

   and 
  in 
  doing 
  this 
  the 
  methods 
  employed 
  will 
  be 
  made 
  

   clear. 
  

  

  It 
  has 
  been 
  seen 
  that 
  Davis 
  in 
  1889 
  recognized 
  the 
  

   presence 
  of 
  an 
  old 
  baseleveled 
  surface, 
  represented 
  by 
  

   uplands, 
  which 
  he 
  named 
  the 
  Schooley 
  peneplain 
  and 
  a 
  

   younger 
  one, 
  represented 
  by 
  broad 
  valley 
  lowlands, 
  

   which 
  he 
  called 
  the 
  Somerville. 
  In 
  1903 
  Campbell 
  pre- 
  

   sented 
  evidence 
  of 
  an 
  intermediate 
  erosion 
  surface 
  which 
  

  

  