﻿356 
  

  

  J. 
  Barrell 
  — 
  The 
  Piedmont 
  Terraces 
  

  

  to 
  a 
  depth 
  of 
  600 
  feet 
  and 
  disturb 
  clay, 
  mud, 
  and 
  probably 
  

   the 
  very 
  finest 
  sands. 
  Oscillatory 
  waves, 
  however, 
  would 
  

   have 
  practically 
  no 
  erosive 
  power 
  at 
  that 
  depth, 
  but 
  waves 
  

   of 
  translation 
  would 
  appear 
  to 
  be 
  capable 
  of 
  producing 
  

   noteworthy 
  erosion 
  and 
  transportation. 
  30 
  On 
  the 
  other 
  

   hand, 
  the 
  actual 
  forms 
  of 
  the 
  profiles 
  of 
  the 
  shelf 
  seas 
  

   seem 
  to 
  show 
  that 
  bottom 
  transportation 
  becomes 
  ineffec- 
  

   tive 
  at 
  somewhat 
  lesser 
  depths. 
  The 
  rise 
  of 
  sea-level 
  

   since 
  late 
  Glacial 
  times, 
  which 
  is 
  estimated 
  at 
  as 
  much 
  as 
  

   20 
  fathoms, 
  has 
  overdeepened 
  the 
  ocean 
  profiles 
  and 
  they 
  

   have 
  been 
  adjusted 
  to 
  the 
  present 
  higher 
  water-level 
  only 
  

   where 
  there 
  is 
  a 
  great 
  abundance 
  of 
  unconsolidated 
  

   bottom 
  material. 
  The 
  lack 
  of 
  recognition 
  of 
  this 
  condi- 
  

   tion 
  has 
  created 
  the 
  impression 
  that 
  wave 
  action 
  in 
  

  

  Fig. 
  16. 
  

  

  Fig. 
  16. 
  — 
  Successive 
  stages 
  of 
  marine 
  erosion 
  on 
  a 
  stationary 
  coast. 
  

  

  general 
  is 
  effective 
  to 
  a 
  greater 
  depth 
  than 
  is 
  actually 
  the 
  

   case. 
  A 
  depth 
  of 
  50 
  fathoms 
  seems 
  more 
  probable 
  than 
  

   the 
  limit 
  of 
  100 
  fathoms, 
  for 
  coast 
  charts 
  commonly 
  show 
  

   a 
  downward 
  curvature 
  of 
  the 
  bottom 
  profile 
  at 
  about 
  the 
  

   former 
  depth, 
  indicating 
  the 
  cessation 
  of 
  effective 
  wave 
  

   action. 
  

  

  Various 
  Cases 
  of 
  Marine 
  Denudation. 
  

  

  In 
  an 
  analysis 
  of 
  the 
  features 
  of 
  marine 
  denudation, 
  

   when 
  acting 
  on 
  a 
  surface 
  previously 
  shaped 
  by 
  fluvial 
  

   denudation, 
  there 
  are 
  several 
  cases 
  to 
  be 
  considered. 
  

  

  Case 
  I. 
  Let 
  submergence 
  bring 
  the 
  sea 
  against 
  mod- 
  

   erate 
  hill 
  slopes, 
  as 
  illustrated 
  by 
  fig. 
  16. 
  Successive 
  

   stages 
  of 
  erosion 
  are 
  shown 
  by 
  A, 
  B, 
  C, 
  and 
  D. 
  During 
  

   the 
  youth 
  of 
  the 
  shore-line, 
  erosion 
  will 
  be 
  concentrated 
  

  

  30 
  Loc. 
  cit., 
  pp. 
  81-83. 
  

  

  