﻿J. 
  Barrell 
  — 
  Piedmont 
  Terraces. 
  327 
  

  

  .Art. 
  XXV. 
  — 
  The 
  Piedmont 
  Terraces 
  of 
  the 
  Northern 
  

   Appalachians 
  ; 
  by 
  Joseph 
  Barbell. 
  

  

  Edited 
  by 
  H. 
  H. 
  Kobinson. 
  

   [Continued 
  from 
  p. 
  258] 
  

  

  Indications 
  from 
  the 
  Coastal 
  Plain 
  of 
  Many 
  Baselevels. 
  

  

  The 
  view 
  that 
  there 
  are 
  frequent 
  oscillations 
  of 
  the 
  

   earth's 
  crust 
  rather 
  than 
  age-long 
  stability 
  is 
  based 
  on 
  

   several 
  lines 
  of 
  evidence 
  developed 
  in 
  recent 
  years. 
  The 
  

   numerous 
  baselevels 
  of 
  the 
  western 
  upland 
  of 
  Connect- 
  

   icut, 
  of 
  the 
  Piedmont 
  Plateau, 
  and 
  the 
  Coastal 
  Plain 
  con- 
  

   stitute 
  one 
  line 
  of 
  this 
  evidence. 
  

  

  The 
  shore-line 
  at 
  any 
  time 
  may 
  be 
  taken 
  as 
  the 
  axis 
  of 
  

   no 
  elevation. 
  It 
  separates 
  the 
  region 
  of 
  erosion 
  from 
  

   that 
  of 
  deposition. 
  During 
  emergence 
  the 
  shore-line 
  

   migrates 
  seaward 
  and 
  the 
  deposits 
  on 
  the 
  landward 
  side 
  

   suffer 
  erosion. 
  During 
  submergence 
  it 
  migrates 
  land- 
  

   ward 
  and 
  new 
  sediments 
  are 
  laid 
  down 
  on 
  an 
  erosion 
  sur- 
  

   face. 
  An 
  unconformity 
  results. 
  Over 
  the 
  continuously 
  

   submerged 
  portion 
  no 
  unconformity 
  separates 
  the 
  two 
  

   formations, 
  but 
  the 
  change 
  in 
  the 
  depth 
  of 
  water 
  and 
  in 
  

   the 
  kind 
  and 
  quantity 
  of 
  sediment 
  furnish 
  evidence 
  of 
  

   crustal 
  movement. 
  

  

  In 
  general, 
  unconformities, 
  changes 
  in 
  slope, 
  and 
  

   changes 
  in 
  formation 
  in 
  a 
  marine 
  series 
  correspond 
  to 
  a 
  

   migration 
  of 
  the 
  shore-line 
  and 
  a 
  change 
  of 
  baselevel 
  

   over 
  the 
  adjacent 
  regions 
  of 
  erosion. 
  It 
  should 
  be 
  noted, 
  

   however, 
  that 
  changes 
  in 
  the 
  nature 
  of 
  the 
  sediments 
  may 
  

   not 
  furnish 
  decisive 
  evidence, 
  for 
  they 
  may 
  be 
  due 
  to 
  

   other 
  causes 
  such 
  as 
  climate 
  or 
  bottom 
  scour. 
  

  

  In 
  the 
  development 
  of 
  the 
  Coastal 
  Plain 
  the 
  pre- 
  

   Comanche 
  surface 
  has 
  been 
  warped 
  on 
  an 
  axis 
  parallel 
  

   to 
  the 
  landward 
  margin. 
  The 
  region 
  of 
  the 
  Coastal 
  

   Plain 
  has 
  gone 
  down, 
  the 
  Piedmont 
  Plateau 
  and 
  moun- 
  

   tains 
  beyond 
  have 
  gone 
  up. 
  The 
  thickness 
  of 
  the 
  Coastal 
  

   Plain 
  deposits 
  increases 
  southeastward 
  from 
  the 
  margin 
  

   of 
  the 
  plateau, 
  whereas 
  the 
  elevation 
  of 
  the 
  plateau 
  in- 
  

   creases 
  toward 
  the 
  northwest. 
  But 
  the 
  motion 
  of 
  tilting 
  

   which 
  has 
  gone 
  forward 
  since 
  the 
  Jurassic 
  has 
  been 
  

   highly 
  variable 
  although 
  never 
  reversed. 
  Each 
  younger 
  

   formation 
  of 
  the 
  Coastal 
  Plain 
  has 
  a 
  lesser 
  slope 
  than 
  the 
  

   preceding 
  formation. 
  Most 
  of 
  the 
  warping 
  was 
  accom- 
  

  

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

   24 
  

  

  