﻿of 
  the 
  Northern 
  Appalachians. 
  359 
  

  

  east 
  and 
  south 
  coasts 
  of 
  England 
  where 
  the 
  rapid 
  advance 
  

   of 
  the 
  sea 
  has 
  raised 
  the 
  very 
  practical 
  and 
  important 
  

   problem 
  of 
  control. 
  The 
  shore 
  formations 
  consist 
  chiefly 
  

   of 
  unconsolidated 
  deposits 
  on 
  the 
  east 
  coast 
  and 
  of 
  chalk 
  

   on 
  the 
  south, 
  both 
  of 
  which 
  are 
  very 
  soft 
  and 
  unresistant. 
  

   The 
  cobbles 
  and 
  flints 
  from 
  the 
  chalk 
  are 
  ideal 
  material 
  

   for 
  grinding 
  up 
  the 
  associated 
  debris. 
  The 
  present 
  rapid 
  

   rate 
  of 
  erosion 
  and 
  the 
  spectacular 
  appearance 
  of 
  these 
  

   shores 
  thus 
  illustrate 
  a 
  case 
  where 
  the 
  normal 
  profile 
  of 
  

   submarine 
  denudation 
  has 
  not 
  yet 
  become 
  established. 
  

  

  Marine 
  denudation 
  working 
  against 
  a 
  land 
  already 
  

   dissected 
  by 
  fluvial 
  erosion 
  will 
  attack 
  islands 
  and 
  head- 
  

   lands 
  from 
  two 
  or 
  three 
  sides, 
  giving 
  rise 
  to 
  rock 
  stacks, 
  

   reefs, 
  and 
  shoals. 
  When 
  an 
  island 
  is 
  reduced 
  to 
  a 
  shoal 
  

   below 
  strong 
  surf 
  action 
  it 
  should 
  endure 
  for 
  a 
  long 
  time 
  

   because 
  the 
  supply 
  of 
  coarse 
  veneer 
  is 
  lacking; 
  erosion 
  

   would 
  be 
  at 
  the 
  base 
  and 
  tend 
  to 
  maintain 
  steep 
  slopes. 
  

   Shoals 
  will 
  persist 
  while 
  the 
  shore-line 
  is 
  pushed 
  inland, 
  

   as 
  is 
  shown 
  by 
  the 
  charts 
  of 
  many 
  regions 
  of 
  active 
  

   marine 
  denudation. 
  The 
  general 
  result 
  is 
  that 
  marine 
  

   peneplanes 
  should 
  exhibit 
  a 
  notable 
  irregularity 
  of 
  eleva- 
  

   tion 
  even 
  in 
  an 
  advanced 
  stage 
  of 
  development. 
  

  

  To 
  the 
  islands 
  of 
  a 
  marine 
  peneplane, 
  remaining 
  after 
  

   elevation, 
  D. 
  W. 
  Johnson 
  suggests 
  the 
  advisability 
  of 
  

   applying 
  the 
  name 
  monadnock. 
  The 
  hummocks 
  here 
  dis- 
  

   cussed, 
  however, 
  are 
  of 
  a 
  different 
  nature, 
  they 
  represent 
  

   fairly 
  normal 
  departures 
  from 
  the 
  uniformity 
  of 
  the 
  

   peneplaned 
  surface. 
  They 
  are 
  not 
  relics 
  from 
  a 
  previous 
  

   cycle 
  of 
  erosion, 
  but 
  correspond 
  to 
  the 
  low 
  interfluvial 
  

   ridges 
  normal 
  to 
  a 
  fluvial 
  peneplane. 
  Their 
  rounded 
  

   summits 
  may 
  have 
  been 
  some 
  fathoms 
  below 
  sea-level 
  

   and 
  their 
  bases 
  may 
  have 
  been 
  at 
  depths 
  of 
  20 
  to 
  40 
  

   fathoms 
  depending 
  upon 
  circumstances. 
  Thus 
  they 
  may 
  

   have 
  a 
  relief 
  of 
  100 
  or 
  more 
  feet, 
  and 
  their 
  summits 
  

   should 
  be 
  accordant, 
  even 
  more 
  so 
  than 
  their 
  bases. 
  

   They 
  may 
  be 
  expected 
  to 
  develop 
  along 
  the 
  outcrops 
  of 
  

   very 
  resistant 
  formations 
  and 
  may 
  be 
  a 
  direct 
  inheritence 
  

   from 
  an 
  interfluvial 
  land 
  ridge. 
  Cross 
  currents 
  between 
  

   them 
  may 
  scour 
  out 
  deeper 
  channels 
  than 
  the 
  normal, 
  

   permitting 
  a 
  cross 
  drainage 
  to 
  become 
  established 
  upon 
  

   emergence 
  without 
  the 
  necessity 
  for 
  complete 
  burial 
  of 
  

   the 
  whole 
  ridge. 
  

  

  The 
  critical 
  study 
  of 
  the 
  stratigraphic 
  series 
  indicates 
  

   with 
  increased 
  certainty 
  that 
  oscillations 
  of 
  sea-level 
  have 
  

  

  Am. 
  Jouh. 
  Sci.— 
  Fourth 
  Series, 
  Vol. 
  XLIX, 
  No. 
  293.— 
  May, 
  1920. 
  

   26 
  

  

  