﻿of 
  the 
  Northern 
  Appalachians. 
  361 
  

  

  able 
  to 
  marine 
  attack. 
  Upon 
  emergence 
  the 
  old 
  valley 
  

   lines 
  in 
  part 
  would 
  be 
  re-established 
  and 
  the 
  flat-topped 
  

   interfluves 
  would 
  be 
  on 
  the 
  kinds 
  of 
  rocks 
  and 
  in 
  the 
  situ- 
  

   ations 
  favorable 
  to 
  the 
  preservation, 
  for 
  a 
  long 
  time, 
  of 
  

   the 
  surfaces 
  of 
  marine 
  denudation. 
  

  

  From 
  the 
  geologic 
  standpoint 
  the 
  strand-line 
  is 
  ever 
  

   shifting 
  and 
  neither 
  the 
  land 
  nor 
  sea 
  maintains 
  a 
  stability 
  

   of 
  level 
  between 
  the 
  periods 
  of 
  marked 
  and 
  rapid 
  change. 
  

   Minor 
  oscillations 
  and 
  halts 
  occur 
  at 
  all 
  stages. 
  The 
  

   mind 
  tends 
  to 
  dwell 
  on 
  the 
  more 
  conspicuous 
  features 
  

   and 
  to 
  over-simplify 
  nature. 
  In 
  formulating 
  the 
  criteria 
  

   for 
  the 
  recognition 
  of 
  marine 
  denudation 
  regard 
  must 
  be 
  

   had 
  for 
  this 
  inconstancy 
  of 
  baselevel. 
  

  

  The 
  situation 
  is 
  illustrated 
  by 
  the 
  shores 
  of 
  the 
  extinct 
  

   Lake 
  Bonneville. 
  The 
  highest 
  and 
  most 
  conspicuous 
  

   shore-line 
  is 
  the 
  Bonneville, 
  on 
  the 
  average 
  1,000 
  feet 
  

   above 
  the 
  level 
  of 
  Great 
  Salt 
  Lake. 
  On 
  the 
  other 
  hand, 
  

   the 
  one 
  which 
  represents 
  the 
  longest 
  stand 
  of 
  the 
  water 
  

   and 
  the 
  greatest 
  volume 
  of 
  shore 
  work 
  is 
  the 
  Provo, 
  which 
  

   has 
  an 
  elevation 
  about 
  600 
  feet 
  below 
  the 
  Bonneville 
  

   strand. 
  The 
  entire 
  slope, 
  however, 
  from 
  the 
  Bonneville 
  

   level 
  to 
  that 
  of 
  Great 
  Salt 
  Lake 
  is 
  modified 
  by 
  wave 
  

   action 
  and 
  under 
  the 
  proper 
  slant 
  of 
  sunlight 
  the 
  many 
  

   horizontal 
  scorings 
  from 
  temporary 
  water 
  levels 
  may 
  be 
  

   observed. 
  The 
  causes 
  of 
  the 
  changing 
  water 
  level 
  of 
  

   Lake 
  Bonneville 
  were 
  the 
  cutting 
  down 
  of 
  the 
  outlet 
  and 
  

   variations 
  in 
  climate, 
  but 
  the 
  results 
  in 
  shore 
  action 
  are 
  

   comparable 
  in 
  some 
  respects 
  to 
  those 
  of 
  a 
  shifting 
  sea- 
  

   level. 
  

  

  In 
  temporary 
  and 
  transitional 
  stages 
  of 
  sea-level 
  two 
  

   aspects 
  should 
  be 
  called 
  to 
  attention. 
  During 
  a 
  tem- 
  

   porary 
  stage 
  of 
  submergence 
  wave 
  action 
  may 
  be 
  recorded 
  

   only 
  by 
  lines 
  of 
  minor 
  cliffs 
  and 
  benches 
  developed 
  on 
  

   headlands. 
  During 
  a 
  temporary 
  stage 
  of 
  emergence 
  the 
  

   work 
  of 
  the 
  waves 
  will 
  be 
  confined 
  to 
  the 
  flat 
  bottom, 
  

   moving 
  finer 
  material 
  to 
  deeper 
  water, 
  throwing 
  up 
  off- 
  

   snore 
  bars 
  and 
  barrier 
  beaches. 
  No 
  sea 
  cliff 
  would 
  result 
  

   unless 
  the 
  stand 
  of 
  the 
  water 
  were 
  so 
  prolonged 
  that 
  a 
  

   new 
  profile 
  of 
  equilibrium 
  became 
  established 
  and 
  the 
  

   shore 
  eroded 
  inland 
  for 
  some 
  distance 
  A 
  conspicuous 
  

   cliff 
  and 
  bench 
  would 
  require 
  erosion 
  to 
  or 
  beyond 
  the 
  

   former 
  shore-line. 
  

  

  In 
  the 
  later 
  Tertiary 
  and 
  the 
  Pleistocene 
  the 
  land 
  

   along 
  the 
  Atlantic 
  Coast, 
  on 
  the 
  whole, 
  was 
  rising, 
  and 
  

   each 
  submergent 
  phase 
  permitted 
  the 
  sea 
  to 
  advance 
  

  

  