﻿of 
  the 
  Northern 
  Appalachians. 
  233 
  

  

  further 
  than 
  other 
  workers 
  in 
  recognizing 
  a 
  much 
  larger 
  

   number 
  of 
  erosion 
  surfaces. 
  From 
  his 
  published 
  work 
  

   it 
  would 
  appear, 
  however, 
  that 
  he 
  did 
  not 
  consider 
  these 
  

   surfaces 
  as 
  representing 
  an 
  equal 
  number 
  of 
  erosion 
  

   cycles 
  but 
  rather 
  as 
  due 
  to 
  the 
  individual 
  conditions 
  

   under 
  which 
  different 
  rivers 
  eroded. 
  

  

  Professor 
  BarrelPs 
  conclusions 
  were 
  at 
  variance 
  with 
  

   the 
  older 
  views 
  on 
  many 
  points, 
  especially 
  as 
  to 
  the 
  num- 
  

   ber 
  of 
  erosion 
  cycles, 
  the 
  origin 
  of 
  the 
  erosion 
  surfaces, 
  

   and 
  the 
  age 
  of 
  those 
  surfaces. 
  His 
  work 
  in 
  Connecticut 
  

   had 
  convinced 
  him 
  that 
  the 
  number 
  of 
  erosion 
  cycles 
  

   was 
  considerably 
  greater 
  than 
  had 
  been 
  supposed, 
  a 
  view 
  

   that 
  was 
  supported 
  by 
  the 
  Mesozoic 
  and 
  Neozoic 
  sedi- 
  

   mentary 
  record. 
  The 
  complexity 
  of 
  this 
  record 
  is 
  strik- 
  

   ingly 
  at 
  variance 
  with 
  the 
  simplicity 
  of 
  the 
  accepted 
  

   physiographic 
  record 
  for 
  that 
  same 
  period. 
  He 
  differed 
  

   fundamentally 
  in 
  considering 
  the 
  terraces, 
  at 
  least 
  in 
  

   New 
  England, 
  as 
  initially 
  the 
  result 
  of 
  marine 
  denuda- 
  

   tion 
  and 
  in 
  assigning 
  to 
  the 
  majority 
  of 
  them 
  a 
  post- 
  

   Miocene 
  age. 
  The 
  only 
  point 
  in 
  common 
  with 
  the 
  older 
  

   view 
  was 
  the 
  recognition 
  of 
  a 
  " 
  Cretaceous" 
  topographic 
  

   plane 
  of 
  reference 
  whose 
  surface 
  had 
  been 
  shaped 
  by 
  

   fluvial 
  denudation. 
  It 
  was 
  over 
  this 
  surface 
  that 
  the 
  sea 
  

   made 
  its 
  first 
  advance. 
  He 
  considered 
  that 
  the 
  terraces 
  

   could 
  be 
  restored 
  from 
  their 
  existing 
  remnants 
  ; 
  on 
  the 
  

   other 
  hand, 
  he 
  believed 
  that 
  the 
  pre-Cretaceous 
  erosion 
  

   surfaces 
  in 
  all 
  probability 
  had 
  been 
  so 
  far 
  destroyed 
  as 
  

   to 
  be 
  unrecognizable 
  except 
  in 
  isolated 
  residual 
  masses. 
  

  

  The 
  process 
  of 
  marine 
  erosion 
  was 
  intimately 
  con- 
  

   nected 
  with 
  the 
  conception 
  of 
  a 
  rhythmic 
  oscillation 
  of 
  

   the 
  land 
  which 
  he 
  described 
  in 
  the 
  first 
  two 
  parts 
  of 
  

   "Rhythms 
  and 
  the 
  Measurement 
  of 
  Geologic 
  Time." 
  

   During 
  an 
  emergent 
  stage 
  the 
  land 
  would 
  be 
  subaerially 
  

   eroded 
  and 
  in 
  time 
  the 
  resistant 
  rock 
  formations 
  would 
  

   tend 
  to 
  become 
  interfluvial 
  ridges. 
  Upon 
  submergence 
  

   these 
  ridges 
  would 
  become 
  peninsulas, 
  islands, 
  and 
  reefs 
  

   which 
  would 
  be 
  planed 
  off, 
  though 
  not 
  completely, 
  by 
  the 
  

   sea 
  and 
  it 
  would 
  only 
  be 
  after 
  submergence 
  had 
  ceased 
  

   that 
  wave 
  planation 
  would 
  be 
  at 
  all 
  profound. 
  Such 
  a 
  

   process 
  would 
  give 
  beveled 
  ridges 
  grading 
  into 
  a 
  more 
  or 
  

   less 
  continuous 
  rock 
  terrace 
  which 
  would 
  terminate 
  in 
  a 
  

   seacliff. 
  Professor 
  Barrell 
  emphasized 
  the 
  importance 
  of 
  

   an 
  antecedent 
  fluvial 
  denudation 
  of 
  the 
  land 
  to 
  a 
  stage 
  

   of 
  advanced 
  maturity 
  or 
  old 
  age 
  ; 
  there 
  was 
  ' 
  l 
  not 
  whole- 
  

  

  