﻿of 
  the 
  Northern 
  Appalachians. 
  357 
  

  

  upon 
  headlands. 
  A 
  mature 
  profile 
  of 
  equilibrium 
  will 
  be 
  

   established 
  while 
  the 
  strand-line 
  is 
  still 
  young. 
  As 
  the 
  

   shore 
  retreats, 
  the 
  sea 
  operates 
  against 
  a 
  larger 
  and 
  

   larger 
  proportion 
  of 
  higher 
  land 
  and 
  brings 
  about 
  a 
  

   notable 
  change 
  in 
  the 
  character 
  of 
  the 
  coast. 
  The 
  char- 
  

   acter 
  of 
  the 
  sea-bottom 
  profile, 
  however, 
  changes 
  much 
  

   less. 
  

  

  Increase 
  in 
  the 
  depth 
  of 
  erosion 
  for 
  equal 
  distances 
  

   inland, 
  due 
  to 
  increasing 
  height 
  of 
  sea 
  cliff, 
  must 
  tend 
  to 
  

   slow 
  down 
  the 
  rate 
  of 
  advance, 
  but 
  the 
  slowing 
  down 
  is 
  

   probably 
  much 
  less 
  than 
  a 
  simple 
  inverse 
  proportion 
  to 
  

   the 
  volume 
  of 
  material 
  to 
  be 
  removed. 
  The 
  reasons 
  are 
  

   (1) 
  that 
  not 
  all 
  the 
  wave 
  energy 
  is 
  expended 
  in 
  the 
  

   erosion 
  of 
  headlands, 
  for 
  much 
  is 
  wasted 
  in 
  bays 
  without 
  

   proportionate 
  effect, 
  (2) 
  for 
  equal 
  stages 
  of 
  advance 
  the 
  

   depth 
  of 
  bottom 
  erosion 
  increases 
  very 
  slowly, 
  and 
  (3) 
  

   although 
  the 
  sea 
  cliff 
  increases 
  in 
  height 
  and 
  more 
  

   material 
  must 
  be 
  removed, 
  yet 
  the 
  process 
  of 
  undercut- 
  

   ting 
  maintains 
  a 
  very 
  rapid 
  rate 
  because 
  the 
  greater 
  

   quantity 
  of 
  coarse 
  angular 
  debris 
  is 
  competent 
  to 
  erode 
  

   the 
  abrasion 
  platform 
  much 
  faster 
  than 
  would 
  a 
  lesser 
  

   amount 
  of 
  material. 
  It 
  is 
  by 
  the 
  oscillation 
  of 
  the 
  veneer 
  

   of 
  waste 
  that 
  the 
  platform 
  is 
  worn 
  down. 
  A 
  superabun- 
  

   dance 
  of 
  waste 
  would 
  temporarily 
  protect 
  the 
  rock 
  

   below, 
  but 
  when 
  the 
  whole 
  amount 
  can 
  be 
  moved 
  by 
  

   storms, 
  increase 
  of 
  moving 
  debris 
  presumably 
  increases 
  

   the 
  corrasion 
  of 
  the 
  rock 
  below. 
  The 
  maximum 
  volume 
  

   of 
  denudation 
  for 
  equal 
  time 
  intervals 
  is 
  reached 
  when 
  

   the 
  shore-line 
  has 
  attained 
  maturity. 
  

  

  Case 
  II. 
  Another 
  case 
  which 
  needs 
  discussion 
  is 
  that 
  

   of 
  marine 
  denudation 
  against 
  a 
  sinking 
  land 
  with 
  a 
  hilly 
  

   topography. 
  Such 
  a 
  surface 
  is 
  commonly 
  regarded 
  as 
  

   favoring 
  marine 
  planation 
  ; 
  it 
  permits 
  the 
  waves 
  to 
  act 
  

   more 
  strongly 
  against 
  the 
  shore 
  because 
  less 
  of 
  their 
  

   energy 
  is 
  spent 
  on 
  the 
  offshore 
  bottom. 
  

  

  The 
  work 
  of 
  marine 
  planation 
  is 
  shallower 
  in 
  this 
  case 
  

   than 
  in 
  the 
  preceding 
  one, 
  as 
  shown 
  in 
  fig. 
  17. 
  Let 
  AM 
  be 
  

   the 
  initial 
  profile 
  of 
  equilibrium. 
  As 
  submergence 
  and 
  

   planation 
  are 
  going 
  forward 
  together 
  the 
  shore-line 
  will 
  

   retreat 
  from 
  A 
  to 
  C 
  and 
  the 
  profile 
  of 
  equilibrium 
  will 
  

   advance 
  from 
  AM 
  to 
  CO. 
  Instead 
  of 
  erosion 
  on 
  the 
  off- 
  

   shore 
  bottom, 
  as 
  in 
  Case 
  I, 
  there 
  is 
  aggradation. 
  Let 
  the 
  

   slope 
  of 
  the 
  rising 
  strand-line 
  be 
  AC. 
  Draw 
  TT' 
  parallel 
  

   to 
  AC 
  and 
  tangent 
  to 
  the 
  profile 
  AM. 
  It 
  will 
  be 
  tangent 
  

  

  