﻿424 
  J. 
  Barrel! 
  — 
  The 
  Piedmont 
  Terraces 
  

  

  The 
  sea 
  thus 
  advanced 
  over 
  a 
  subaerially 
  denuded 
  land 
  

   in 
  the 
  Oligocene 
  cutting 
  the 
  Cornwall 
  terrace 
  and 
  again 
  

   in 
  the 
  Pliocene 
  cutting 
  the 
  Goshen 
  terrace. 
  The 
  land 
  in 
  

   both 
  instances 
  was 
  supposed 
  to 
  have 
  been 
  reduced 
  to 
  

   old 
  age, 
  for 
  "slight 
  submergences 
  and 
  crustal 
  rest 
  are 
  

   sufficient 
  to 
  account 
  for 
  the 
  planing 
  inland 
  by 
  the 
  sea." 
  

   The 
  initial 
  advance 
  of 
  the 
  sea, 
  in 
  any 
  instance, 
  was 
  sup- 
  

   posed 
  to 
  be 
  due 
  to 
  a 
  depression 
  of 
  the 
  land 
  and 
  from 
  

   this 
  it 
  may 
  be 
  inferred 
  that 
  wave 
  planation 
  during 
  this 
  

   stage 
  did 
  not 
  produce 
  a 
  great 
  amount 
  of 
  change 
  in 
  the 
  

   form 
  of 
  the 
  surface 
  ; 
  it 
  may 
  have 
  been 
  restricted 
  to 
  the 
  

   beveling 
  of 
  the 
  tops 
  of 
  interfluvial 
  ridges. 
  On 
  the 
  other 
  

   hand, 
  after 
  the 
  downward 
  movement 
  of 
  the 
  land 
  had 
  

   ceased, 
  planation 
  would 
  have 
  been 
  more 
  pronounced, 
  but 
  

   the 
  advance 
  of 
  the 
  sea 
  would 
  have 
  been 
  slower 
  and 
  finally 
  

   must 
  have 
  been 
  checked 
  by 
  the 
  initiation 
  of 
  an 
  emergent 
  

   movement. 
  Under 
  these 
  conditions 
  it 
  would 
  seem 
  that 
  

   the 
  degradation 
  effected 
  by 
  the 
  sea 
  should 
  have 
  been 
  

   moderate 
  and 
  as 
  a 
  result 
  the 
  outcrops 
  of 
  rock 
  formations 
  

   should 
  not 
  have 
  been 
  greatly 
  changed. 
  

  

  It 
  would 
  also 
  appear 
  on 
  this 
  interpretation 
  that 
  the 
  

   volume 
  of 
  the 
  sediments 
  brought 
  down 
  by 
  the 
  rivers 
  

   would 
  have 
  been 
  moderate 
  and 
  that 
  the 
  production 
  of 
  

   marine 
  conglomerates 
  would 
  have 
  been 
  small 
  except, 
  

   perhaps, 
  during 
  the 
  stage 
  when 
  the 
  sea 
  was 
  working 
  

   against 
  a 
  stationary 
  coast. 
  37 
  

  

  If 
  the 
  marine 
  plain 
  were 
  uplifted 
  with 
  little 
  change 
  

   in 
  slope 
  the 
  main 
  streams, 
  under 
  the 
  given 
  conditions, 
  

   would 
  tend 
  to 
  become 
  located 
  again 
  on 
  much 
  the 
  same 
  

   courses 
  they 
  had 
  before 
  the 
  terrace 
  was 
  cut. 
  On 
  the 
  

   other 
  hand, 
  if 
  the 
  plain 
  were 
  somewhat 
  tilted 
  and 
  

   warped, 
  as 
  would 
  seem 
  more 
  probable, 
  then 
  a 
  notable 
  

   amount 
  of 
  drainage 
  along 
  new 
  lines 
  should 
  be 
  expected 
  

   which 
  at 
  first 
  would 
  be 
  consequent 
  on 
  the 
  sedimentary 
  

   cover 
  and 
  later 
  would 
  be 
  superimposed 
  upon 
  the 
  under- 
  

   lying 
  crystalline 
  floor. 
  As 
  is 
  well 
  known, 
  the 
  courses 
  

   of" 
  several 
  of 
  the 
  large 
  rivers 
  of 
  the 
  Appalachian 
  region 
  

   in 
  part 
  have 
  been 
  explained 
  as 
  superimposed; 
  Davis 
  

   considered, 
  for 
  example, 
  that 
  the 
  lower 
  course 
  of 
  the 
  

   Connecticut 
  was 
  so 
  located 
  upon 
  the 
  metamorphic 
  and 
  

   igneous 
  rocks 
  from 
  a 
  cover 
  of 
  Cretaceous 
  sediments. 
  

   Such 
  an 
  explanation 
  also 
  holds 
  under 
  Professor 
  BarrelPs 
  

  

  37 
  As 
  bearing 
  on 
  this 
  point 
  see 
  section 
  "Relations 
  of 
  rate 
  [of 
  denuda- 
  

   tion] 
  to 
  the 
  cycle 
  of 
  erosion," 
  pp. 
  760-761 
  in 
  "Rhythms 
  and 
  the 
  Measure- 
  

   ment 
  of 
  Geologic 
  Time. 
  " 
  

  

  