﻿of 
  the 
  Northern 
  Appalachians. 
  353 
  

  

  bottom 
  friction 
  and 
  can 
  only 
  stir 
  the 
  material 
  at 
  a 
  lesser 
  

   depth. 
  The 
  resnlt 
  is 
  that 
  nearer 
  shore 
  the 
  wave 
  work 
  is 
  

   in 
  equilibrium 
  on 
  a 
  shallower 
  bottom. 
  Farther 
  inshore 
  

   the 
  water 
  shallows 
  until 
  the 
  waves 
  break 
  and 
  surf 
  results. 
  

   The 
  remaining 
  energy 
  is 
  there 
  concentrated; 
  beach 
  

   material 
  is 
  thrown 
  up, 
  a 
  distinct 
  bench 
  may 
  be 
  cut, 
  and 
  

   the 
  base 
  of 
  a 
  sea 
  cliff 
  undermined. 
  The 
  main 
  divisions 
  

   of 
  the 
  marine 
  profile 
  are 
  shown 
  diagrammatically 
  in 
  fig. 
  

   14 
  and 
  are 
  in 
  conformity 
  with 
  those 
  adopted 
  by 
  Dr. 
  D. 
  W. 
  

   Johnson. 
  27 
  

  

  In 
  so 
  far 
  as 
  wave 
  action 
  and 
  the 
  currents 
  generated 
  by 
  

   waves 
  move 
  a 
  veneer 
  of 
  material 
  back 
  and 
  forth 
  over 
  

   the 
  abrasion 
  platform 
  there 
  must 
  be 
  wear 
  both 
  of 
  the 
  

   veneer 
  and 
  the 
  rock 
  below. 
  In 
  times 
  of 
  gentle 
  wave 
  

   action 
  the 
  profile 
  tends 
  to 
  become 
  shallower 
  because 
  

   aggradation 
  instead 
  of 
  erosion 
  tends 
  to 
  occur 
  over 
  the 
  

   abrasion 
  platform; 
  consequently 
  erosion 
  is 
  mainly 
  the 
  

   result 
  of 
  the 
  higher 
  intensity 
  of 
  action 
  during 
  storms, 
  as 
  

   it 
  is 
  on 
  the 
  land 
  surface. 
  The 
  direction 
  of 
  storm 
  winds, 
  

   as 
  well 
  as 
  their 
  intensity, 
  affects 
  the 
  character 
  of 
  work 
  

   done 
  over 
  the 
  sea 
  bottom. 
  The 
  latter 
  can 
  never 
  be 
  in 
  

   perfect 
  equilibrium 
  but 
  adapts 
  itself 
  to 
  ever 
  changing 
  

   conditions, 
  oscillating 
  about 
  a 
  mean. 
  At 
  one 
  time 
  a 
  shore 
  

   may 
  be 
  stripped 
  temporarily 
  of 
  its 
  beach 
  material, 
  at 
  

   another 
  time 
  an 
  unusual 
  amount 
  may 
  be 
  piled 
  up. 
  The 
  

   profile, 
  however, 
  remains 
  the 
  same 
  in 
  character 
  for 
  shores 
  

   exposed 
  to 
  different 
  intensity 
  of 
  wave 
  action 
  but 
  differs 
  

   in 
  scale 
  ; 
  it 
  reaches 
  equilibrium 
  soonest 
  and 
  displays 
  the 
  

   typical 
  form 
  on 
  shores 
  of 
  weak 
  resistance 
  and 
  on 
  bottoms 
  

   of 
  alluvial 
  material. 
  

  

  From 
  an 
  inspection 
  of 
  the 
  bathymetric 
  charts 
  of 
  the 
  

   margins 
  of 
  many 
  water 
  bodies, 
  the 
  following 
  data 
  have 
  

   been 
  derived 
  and 
  previously 
  published. 
  28 
  

  

  Generalized 
  Profile 
  of 
  Equilibrium 
  for 
  Shelf 
  Sea. 
  

  

  Distance 
  from 
  shore 
  in 
  miles 
  1 
  2 
  3 
  5 
  10 
  20 
  100 
  

  

  Depth 
  of 
  water 
  in 
  fathoms 
  7-5 
  11 
  13-5 
  15-5 
  18 
  23 
  50 
  

  

  The 
  symmetry 
  of 
  this 
  profile 
  is 
  greatly 
  disturbed 
  by 
  a 
  

   number 
  of 
  factors 
  which 
  are 
  always 
  present 
  to 
  some 
  

   degree. 
  The 
  profile 
  is 
  flatter 
  on 
  a 
  shore 
  toward 
  which 
  

   sediment 
  is 
  driven, 
  undertow 
  sweeps 
  the 
  bottom 
  material 
  

  

  27 
  Shore 
  Processes 
  and 
  Shoreline 
  Development, 
  pp. 
  159-163, 
  1919. 
  

  

  28 
  Joseph 
  Barrell 
  : 
  Bhythms 
  and 
  the 
  Measurement 
  of 
  Geologic 
  Time, 
  

   Bull. 
  Geol. 
  Soc. 
  Am., 
  vol. 
  28, 
  pp. 
  779-780, 
  1917. 
  

  

  