﻿of 
  the 
  Northern 
  Appalachians. 
  339 
  

  

  important 
  to 
  recognize 
  that 
  the 
  gap 
  fixes 
  relatively 
  an 
  

   old 
  stream 
  level 
  and 
  that 
  the 
  form 
  of 
  a 
  gap 
  may 
  give 
  

   valuable 
  evidence 
  as 
  to 
  the 
  nature 
  of 
  at 
  least 
  one 
  and 
  

   perhaps 
  several 
  erosion 
  cycles. 
  The 
  last 
  point 
  is 
  further 
  

   treated 
  in 
  the 
  following 
  section. 
  

  

  In 
  this 
  connection 
  it 
  is 
  necessary 
  to 
  determine 
  as 
  

   closely 
  as 
  possible 
  the 
  elevation 
  of 
  the 
  original 
  bottom 
  of 
  

   the 
  wind 
  gaps. 
  It 
  is 
  evident, 
  on 
  account 
  of 
  the 
  age 
  of 
  

   the 
  gaps, 
  that 
  the 
  present 
  bottom 
  in 
  most 
  cases 
  does 
  not 
  

   coincide 
  with 
  the 
  original 
  one. 
  Glaciation 
  may 
  have 
  

   filled 
  in 
  or 
  scoured 
  out 
  a 
  gap 
  according 
  to 
  the 
  direction 
  

   of 
  ice 
  motion; 
  creep 
  from 
  the 
  sides 
  tends 
  to 
  fill 
  in 
  the 
  

   bottom. 
  More 
  important, 
  however, 
  brooks 
  may 
  flow 
  both 
  

   ways 
  from 
  a 
  gap 
  and 
  notch 
  it 
  below 
  the 
  original 
  level. 
  

   These 
  features 
  do 
  not 
  show 
  well 
  on 
  the 
  topographic 
  maps 
  

   but 
  usually 
  can 
  be 
  evaluated 
  on 
  the 
  ground. 
  In 
  general, 
  

   south 
  of 
  the 
  glacial 
  limit 
  the 
  cols 
  of 
  the 
  gaps 
  appear 
  to 
  

   be 
  not 
  more 
  than 
  fifty 
  feet 
  below 
  the 
  level 
  they 
  possessed 
  

   when 
  occupied 
  by 
  streams. 
  

  

  As 
  may 
  be 
  most 
  readily 
  determined 
  from 
  the 
  topogra- 
  

   phic 
  maps 
  more 
  than 
  one 
  system 
  of 
  gaps 
  cuts 
  through 
  the 
  

   Kittatinny 
  ridge. 
  The 
  gaps 
  of 
  a 
  higher 
  system 
  lying 
  

   between 
  1,300 
  and 
  1,400 
  feet 
  are 
  relatively 
  shallow, 
  their 
  

   cols 
  reaching 
  about 
  200 
  feet 
  below 
  the 
  mountain 
  crest. 
  

   Most 
  of 
  these 
  gaps 
  are 
  now 
  so 
  eroded 
  that 
  in 
  themselves 
  

   they 
  do 
  not 
  furnish 
  reliable 
  evidence 
  of 
  a 
  former 
  super- 
  

   posed 
  drainage. 
  They 
  acquire 
  significance, 
  however, 
  

   from 
  their 
  general 
  accordance 
  with 
  a 
  baselevel 
  otherwise 
  

   determined, 
  as 
  described 
  in 
  the 
  next 
  section. 
  The 
  con- 
  

   spicuous 
  system 
  lies 
  at 
  elevations 
  between 
  900 
  and 
  1,100 
  

   feet. 
  In 
  this 
  group 
  are 
  included 
  all 
  the 
  well-known 
  gaps 
  

   in 
  New 
  Jersey 
  and 
  Pennsylvania, 
  such 
  as 
  Culver's 
  and 
  

   Pen 
  Argyl. 
  

  

  In 
  addition 
  to 
  the 
  gaps 
  on 
  Kittatinny 
  Ridge 
  it 
  should 
  

   be 
  noted 
  that 
  on 
  minor 
  ridges 
  gaps 
  of 
  a 
  still 
  lower 
  set 
  are 
  

   found. 
  Two 
  such 
  wind 
  gaps 
  are 
  found 
  on 
  Rattlesnake 
  

   Ridge 
  at 
  an 
  elevation 
  of 
  750 
  feet 
  (New 
  Bloomfield 
  quad- 
  

   rangle). 
  These 
  appear 
  to 
  mark 
  the 
  Sunbury 
  baselevel. 
  

   In 
  general, 
  for 
  the 
  lower 
  baselevels, 
  the 
  gaps 
  show 
  a 
  

   greater 
  range 
  of 
  altitude 
  and 
  in 
  nearly 
  all 
  cases 
  repre- 
  

   sent 
  minor 
  stream 
  adjustments 
  due 
  to 
  strong 
  uplift 
  and 
  

   rapid 
  erosion. 
  

  

  The 
  sides 
  of 
  the 
  wind 
  gaps 
  when 
  compared 
  with 
  the 
  

   precipitous 
  slopes 
  of 
  the 
  present 
  water 
  gaps 
  indicate 
  the 
  

  

  