﻿of 
  the 
  Northern 
  Appalachians. 
  349 
  

  

  Marine 
  Peneplanes. 
  

  

  Competence 
  of 
  Marine 
  Denudation. 
  

  

  The 
  competence 
  of 
  heavy 
  waves 
  to 
  trim 
  off 
  headlands, 
  

   to 
  fill 
  up 
  bayheads, 
  to 
  transport 
  sand 
  and 
  mud, 
  and 
  to 
  

   build 
  up 
  a 
  profile 
  of 
  equilibrium 
  may 
  be 
  accepted 
  without 
  

   discussion. 
  On 
  the 
  other 
  hand, 
  the 
  ability 
  of 
  waves 
  both 
  

   offshore 
  and 
  on 
  the 
  shore 
  to 
  plane 
  across 
  hard 
  rocks 
  for 
  

   miles, 
  or 
  tens 
  of 
  miles, 
  is 
  not 
  so 
  generally 
  recognized. 
  

   In 
  the 
  past 
  twenty 
  years, 
  however, 
  important 
  examples 
  

   of 
  marine 
  denudation 
  have 
  been 
  described. 
  The 
  litera- 
  

   ture 
  has 
  been 
  recently 
  reviewed 
  by 
  D. 
  W. 
  Johnson 
  who 
  is 
  

   inclined, 
  from 
  the 
  field 
  evidence 
  as 
  well 
  as 
  on 
  theoretical 
  

   grounds, 
  to 
  assign 
  a 
  place 
  of 
  consequence 
  to 
  marine 
  pene- 
  

   planation. 
  24 
  

  

  The 
  fact 
  that 
  waves 
  and 
  wave-generated 
  currents 
  can 
  

   transport 
  sand 
  for 
  long 
  distances 
  and 
  build 
  up 
  sea 
  

   bottoms 
  to 
  a 
  profile 
  of 
  equilibrium 
  implies 
  that 
  the 
  same 
  

   forces, 
  acting 
  over 
  a 
  long 
  period, 
  can 
  erode 
  rock 
  to 
  nearly 
  

   the 
  same 
  profile. 
  But 
  the 
  question 
  is 
  the 
  practical 
  one 
  

   whether 
  the 
  land 
  is 
  ever 
  stationary 
  long 
  enough 
  for 
  this 
  

   to 
  be 
  accomplished 
  and 
  whether 
  fluvial 
  denudation 
  would 
  

   not 
  so 
  far 
  outstrip 
  marine 
  denudation 
  that 
  the 
  work 
  left 
  

   for 
  the 
  latter 
  would 
  be 
  inconsequential. 
  

  

  The 
  actuality 
  of 
  marine 
  planation 
  of 
  greater 
  or 
  less 
  

   extent 
  on 
  many 
  coasts 
  is 
  proved 
  by 
  old 
  sea 
  cliffs 
  with 
  an 
  

   uplifted 
  platform 
  at 
  their 
  bases. 
  On 
  the 
  other 
  hand, 
  it 
  is 
  

   ordinarily 
  difficult, 
  if 
  not 
  impossible, 
  to 
  determine 
  how 
  

   much 
  the 
  submerged 
  continental 
  margin 
  is 
  due 
  to 
  marine 
  

   denudation 
  and 
  how 
  much 
  to 
  aggradation. 
  It 
  appears 
  

   probable 
  that 
  deposition 
  of 
  sediment 
  and 
  outbuilding 
  are 
  

   more 
  important 
  at 
  the 
  present 
  time. 
  The 
  evidence 
  of 
  

   marine 
  planation 
  of 
  the 
  shores 
  bordering 
  the 
  North 
  

   Atlantic 
  is 
  summarized 
  by 
  Johnson 
  as 
  follows 
  : 
  

  

  "The 
  great 
  wave-cut 
  platform 
  ("strandfladen" 
  of 
  the 
  Nor- 
  

   wegians) 
  fringing 
  the 
  west 
  coast 
  of 
  Norway, 
  best 
  known 
  through 
  

   the 
  studies 
  of 
  Reusch, 
  Richter, 
  Vogt, 
  and 
  Nansen, 
  has 
  an 
  average 
  

   breadth 
  of 
  nearly 
  30 
  miles, 
  and 
  a 
  maximum 
  breadth 
  of 
  nearer 
  

   40 
  according 
  to 
  Vogt 
  and 
  Nansen, 
  if 
  we 
  include 
  the 
  portion 
  still 
  

   submerged. 
  Notwithstanding 
  the 
  doubt 
  implied 
  by 
  Reusch, 
  and 
  

   clearly 
  expressed 
  by 
  Nansen 
  and 
  Nussbaum, 
  regarding 
  the 
  essen- 
  

   tial 
  marine 
  origin 
  of 
  this 
  feature, 
  it 
  is 
  generally 
  considered, 
  and 
  

  

  24 
  D. 
  W. 
  Johnson. 
  Shore 
  Processes 
  and 
  Shoreline 
  Development, 
  chap. 
  V, 
  

   Development 
  of 
  the 
  shore 
  profile, 
  1919. 
  

  

  