﻿344 
  J. 
  Barrell 
  — 
  The 
  Piedmont 
  Terraces 
  

  

  and 
  flows 
  on 
  the 
  soft 
  beds 
  between 
  the 
  Oriskany 
  and 
  the 
  

   Hamilton 
  sandstones. 
  The 
  northwest 
  dip 
  of 
  the 
  strata 
  

   is 
  flatter 
  here 
  than 
  elsewhere 
  and 
  consequently 
  the 
  out- 
  

   crops 
  are 
  wider. 
  The 
  Catskill 
  beds 
  of 
  hard 
  sandstones 
  

   and 
  shales 
  stand 
  up 
  on 
  the 
  northwestern 
  wall 
  to 
  1,330 
  

   feet. 
  The 
  Hamilton 
  sandstone, 
  a 
  hard 
  siliceous 
  silt, 
  

   rises 
  to 
  900 
  feet 
  and 
  except 
  where 
  cut 
  by 
  ravines 
  is 
  all 
  

   above 
  600 
  feet. 
  East 
  of 
  the 
  river 
  is 
  the 
  Oriskany 
  sand- 
  

   stone, 
  a 
  coarse 
  quartz 
  rock 
  with 
  calcareous 
  cement. 
  It 
  

   is 
  less 
  resistant 
  than 
  the 
  Hamilton 
  and 
  only 
  at 
  two 
  locali- 
  

   ties 
  in 
  seven 
  miles 
  does 
  it 
  rise 
  to 
  900 
  feet 
  ; 
  on 
  the 
  other 
  

   hand 
  the 
  outcrops 
  of 
  this 
  formation 
  do 
  not 
  fall 
  below 
  an 
  

   elevation 
  of 
  about 
  550 
  feet. 
  The 
  hard 
  Oneida-Medina 
  

   quartzite, 
  forming 
  the 
  Kittatinny 
  ridge, 
  rises 
  to 
  1,600 
  

   feet. 
  The 
  Delaware 
  has 
  an 
  elevation 
  of 
  325 
  to 
  355 
  feet 
  

   and 
  Flat 
  Brook 
  flows 
  at 
  345 
  to 
  500 
  feet. 
  

  

  In 
  explanation 
  of 
  these 
  differences 
  in 
  the 
  elevations 
  of 
  

   the 
  belts 
  of 
  different 
  rocks 
  an 
  older 
  generation 
  of 
  geolo- 
  

   gists 
  would 
  have 
  said 
  that 
  they 
  were 
  due 
  merely 
  to 
  dif- 
  

   ferences 
  in 
  resistance 
  of 
  the 
  rocks 
  to 
  erosion. 
  In 
  fact, 
  

   that 
  would 
  doubtless 
  be 
  the 
  offhand 
  comment 
  of 
  most 
  

   present 
  day 
  geologists. 
  However, 
  the 
  subject 
  will 
  bear 
  

   a 
  closer 
  examination 
  and 
  it 
  will 
  be 
  seen 
  that 
  differing 
  

   resistance 
  is 
  only 
  part 
  of 
  the 
  explanation. 
  

  

  The 
  Hamilton 
  forms 
  a 
  shelf 
  a 
  mile 
  broad 
  cut 
  across 
  

   the 
  basset 
  edges 
  of 
  the 
  beds. 
  This 
  shelf, 
  although 
  some- 
  

   what 
  dissected, 
  shows 
  many 
  summits 
  between 
  900 
  and 
  950 
  

   feet, 
  as 
  illustrated 
  in 
  fig. 
  10. 
  It 
  clearly 
  represents 
  an 
  

   ancient 
  erosion 
  surface, 
  and 
  lying 
  so 
  near 
  the 
  present 
  

   river 
  it 
  must 
  represent 
  very 
  closely 
  the 
  actual 
  valley 
  floor 
  

   over 
  which 
  the 
  river 
  once 
  meandered 
  in 
  a 
  stage 
  of 
  ad- 
  

   vanced 
  local 
  baselevel. 
  This 
  old 
  valley, 
  then, 
  may 
  be 
  

   given 
  an 
  elevation 
  of 
  about 
  950 
  feet 
  and 
  in 
  confirmation 
  

   it 
  should 
  be 
  noted 
  that 
  this 
  level 
  corresponds 
  very 
  closely 
  

   to 
  those 
  of 
  the 
  original 
  bottoms 
  of 
  the 
  conspicuous 
  wind 
  

   gaps 
  which 
  cut 
  Kittatinny 
  ridge. 
  The 
  slightly 
  lower 
  ele- 
  

   vation 
  of 
  Culver 
  ? 
  s 
  Gap, 
  just 
  east 
  of 
  the 
  northern 
  end 
  of 
  

   the 
  projected 
  area, 
  is 
  probably 
  due 
  to 
  later 
  glacial 
  scour- 
  

   ing. 
  

  

  The 
  Hamilton 
  sandstone 
  still 
  shows 
  this 
  level 
  because 
  

   it 
  has 
  been 
  resistant 
  enough 
  to 
  withstand 
  erosion 
  during 
  

   the 
  time 
  which 
  has 
  elapsed 
  since 
  it 
  was 
  thoroughly 
  lev- 
  

   eled 
  by 
  the 
  Delaware 
  during 
  the 
  950 
  foot 
  cycle 
  of 
  erosion. 
  

   It 
  also 
  appears 
  to 
  have 
  been 
  eroded 
  to 
  a 
  state 
  of 
  early 
  

  

  

  