﻿240 
  J. 
  Barrell 
  — 
  The 
  Piedmont 
  Terraces 
  

  

  country 
  by 
  a 
  shallow 
  sea, 
  burying 
  the 
  previously 
  base- 
  

   leveled 
  Blue 
  Ridge. 
  Following 
  uplift 
  of 
  the 
  region 
  

   above 
  sea 
  level, 
  the 
  streams 
  would 
  flow 
  in 
  general 
  courses 
  

   along 
  the 
  dip 
  [of 
  the 
  deposits] 
  and 
  only 
  later 
  in 
  eroding 
  

   their 
  beds 
  would 
  discover 
  that 
  their 
  courses 
  lay 
  across 
  

   the 
  Blue 
  Ridge. 
  Even 
  after 
  every 
  trace 
  of 
  the 
  cover 
  had 
  

   been 
  removed 
  the 
  streams 
  by 
  their 
  discordance 
  with 
  the 
  

   structural 
  features 
  would 
  still 
  betray 
  the 
  fact 
  of 
  its 
  pre- 
  

   vious 
  existence. 
  " 
  

  

  This 
  hypothesis 
  is 
  developed 
  under 
  a 
  number 
  of 
  head- 
  

   ings, 
  as 
  follows: 
  (1) 
  The 
  epoch 
  of 
  submergence; 
  (2) 
  

   Details 
  of 
  discordance 
  as 
  shown 
  by 
  wind 
  gaps 
  at 
  numer- 
  

   ous 
  localities 
  in 
  Pennsylvania 
  and 
  New 
  Jersey; 
  (3) 
  Dis- 
  

   cussion 
  of 
  the 
  details 
  of 
  the 
  discordance 
  illustrated 
  by 
  the 
  

   previous 
  examples, 
  in 
  which 
  the 
  generally 
  accordant 
  level 
  

   of 
  the 
  wind 
  gap 
  bottoms 
  is 
  considered; 
  (4) 
  The 
  age 
  of 
  

   the 
  cover; 
  (5) 
  Argument 
  for 
  a 
  Cretaceous 
  cover, 
  and 
  (6) 
  

   Conclusion 
  as 
  to 
  age 
  and 
  extent 
  of 
  cover. 
  

  

  Under 
  the 
  last 
  topic 
  he 
  wrote: 
  "From 
  the 
  preceding 
  

   discussion 
  we 
  find 
  that 
  during 
  the 
  late 
  Cretaceous 
  a 
  

   slight 
  submergence 
  caused 
  the 
  sea 
  to 
  move 
  far 
  inland; 
  

   its 
  shallow 
  waters 
  spreading 
  a 
  littoral 
  deposit 
  over 
  [the 
  

   region 
  of] 
  the 
  Great 
  Valley 
  and 
  the 
  Blue 
  Ridge. 
  The 
  

   submergence 
  did 
  not 
  extend 
  over 
  the 
  whole 
  Coast; 
  the 
  

   Highlands 
  [of 
  New 
  Jersey] 
  formed 
  an 
  axis 
  which 
  was 
  

   not 
  submerged, 
  but 
  ran 
  far 
  southward 
  forming 
  a 
  fiat 
  

   peninsula 
  like 
  the 
  present 
  eastern 
  shore 
  of 
  Maryland. 
  

  

  "The 
  bay 
  on 
  the 
  inside 
  of 
  this 
  peninsula 
  did 
  not 
  extend 
  

   very 
  far 
  over 
  the 
  Appalachians, 
  being 
  restricted 
  by 
  the 
  

   limits 
  of 
  the 
  submergence. 
  It 
  covered 
  the 
  Blue 
  Ridge 
  

   at 
  least 
  from 
  Culver's, 
  Gap 
  in 
  New 
  Jersey 
  to 
  Perry 
  

   County, 
  Penna., 
  but 
  did 
  not 
  extend 
  over 
  any 
  part 
  of 
  the 
  

   mountain 
  in 
  New 
  York. 
  The 
  depth 
  of 
  the 
  material 
  was 
  

   at 
  least 
  thick 
  enough 
  to 
  bury 
  from 
  sight 
  the 
  Blue 
  Ridge, 
  

   requiring 
  probably 
  a 
  depth 
  between 
  one 
  hundred 
  and 
  

   four 
  hundred 
  feet. 
  

  

  "Upon 
  uplift 
  at 
  the 
  beginning 
  of 
  the 
  Tertiary 
  the 
  

   streams 
  flowed 
  at 
  random 
  over 
  the 
  nearly 
  level 
  coastal 
  

   plain, 
  as 
  do 
  now 
  the 
  streams 
  east 
  of 
  the 
  'fall 
  line.' 
  It 
  

   was 
  only 
  later 
  that 
  they 
  discovered 
  the 
  hidden 
  barrier 
  

   to 
  their 
  courses 
  and 
  began 
  to 
  toil 
  for 
  their 
  existence. 
  

  

  "Thus, 
  the 
  wind 
  gaps 
  of 
  eastern 
  Penna. 
  have 
  been 
  

   taken 
  as 
  circumstantial 
  evidence 
  of 
  a 
  once 
  wide 
  reaching 
  

   mantle 
  of 
  late 
  Cretaceous 
  sediments. 
  The 
  observations 
  

  

  