﻿of 
  the 
  Northern 
  Appalachians. 
  337 
  

  

  The 
  Susquehanna 
  would 
  reach 
  a 
  low 
  grade 
  after 
  uplift 
  

   more 
  quickly, 
  because 
  of 
  its 
  size, 
  than 
  would 
  a 
  smaller 
  

   stream, 
  and 
  consequently 
  peneplains 
  would 
  be 
  best 
  devel- 
  

   oped 
  along 
  its 
  course. 
  On 
  minor 
  streams 
  peneplains 
  

   comparable 
  with 
  those 
  along 
  master 
  streams 
  would 
  be 
  

   developed 
  only 
  during 
  periods 
  of 
  prolonged 
  crustal 
  rest 
  

   and 
  widespread 
  planation. 
  Other 
  factors 
  which 
  must 
  be 
  

   taken 
  into 
  account, 
  however, 
  are 
  the 
  attitude 
  of 
  the 
  rocks 
  

   and 
  the 
  amount 
  of 
  uplift 
  separating 
  successive 
  base- 
  

   levels. 
  Sedimentary 
  rocks 
  with 
  steep 
  dips 
  offer 
  less 
  

   resistance 
  to 
  erosion 
  than 
  when 
  horizontal 
  so 
  that 
  a 
  pro- 
  

   nounced 
  uplift 
  leads 
  to 
  a 
  deeper 
  dissection 
  and 
  more 
  

   rapid 
  destruction 
  of 
  a 
  peneplain 
  developed 
  on 
  them. 
  

   The 
  Devonian 
  strata 
  in 
  the 
  Pittston 
  quadrangle, 
  for 
  ex- 
  

   ample, 
  are 
  nearly 
  horizontal 
  whereas 
  in 
  the 
  Harrisburg 
  

   quadrangle 
  they 
  are 
  nearly 
  vertical. 
  The 
  amount 
  of 
  up- 
  

   lift 
  at 
  Pittston 
  was 
  the 
  greater 
  but 
  the 
  river 
  took 
  appre- 
  

   ciably 
  longer 
  after 
  uplift 
  to 
  reach 
  stable 
  grade. 
  

  

  Let 
  the 
  Harrisburg 
  peneplain 
  now 
  be 
  followed 
  north- 
  

   east 
  on 
  the 
  belt 
  of 
  slate 
  from 
  the 
  Susquehanna 
  to 
  the 
  

   Delaware. 
  Near 
  the 
  Schuylkill 
  Campbell 
  assigned 
  it 
  a 
  

   level 
  of 
  about 
  500 
  feet 
  and 
  on 
  the 
  Delaware 
  700 
  feet 
  and 
  

   he 
  noted 
  that 
  near 
  both 
  streams 
  monadnocks 
  rise 
  above 
  

   the 
  general 
  level, 
  as 
  they 
  do 
  also 
  in 
  the 
  intervening 
  

   region. 
  

  

  To 
  the 
  writer 
  there 
  appears 
  to 
  be 
  considerable 
  doubt 
  

   as 
  to 
  whether 
  the 
  significance 
  of 
  these 
  monadnocks 
  has 
  

   been 
  correctly 
  interpreted. 
  Near 
  the 
  Schuylkill 
  the 
  

   monadnocks 
  are 
  both 
  higher 
  and 
  more 
  numerous 
  than 
  

   near 
  the 
  Susquehanna. 
  The 
  slopes 
  above 
  the 
  500 
  foot 
  

   level 
  look 
  like 
  post-mature 
  valley 
  sides 
  eroded 
  with 
  re- 
  

   spect 
  to 
  a 
  lower 
  baselevel. 
  In 
  order 
  that 
  the 
  surface 
  

   might 
  reach 
  the 
  degree 
  of 
  planation 
  shown 
  near 
  Harris- 
  

   burg 
  an 
  elevation 
  of 
  550 
  to 
  600 
  feet 
  w^ould 
  have 
  to 
  be 
  

   taken 
  and 
  on 
  the 
  Lehigh 
  and 
  Delaware 
  the 
  corresponding 
  

   elevation 
  would 
  be, 
  respectively, 
  650 
  and 
  700 
  feet. 
  In 
  

   this 
  connection 
  it 
  should 
  be 
  noted 
  that 
  although 
  in 
  gen- 
  

   eral 
  near 
  the 
  Susquehanna 
  the 
  Harrisburg 
  (520-540 
  feet) 
  

   is 
  well 
  marked, 
  isolated 
  hills 
  rise 
  to 
  640 
  feet 
  four 
  miles 
  

   from 
  the 
  river 
  and 
  350 
  feet 
  above 
  it 
  (southwest 
  corner 
  

   of 
  Harrisburg 
  quadrangle). 
  Near 
  the 
  Schuylkill 
  hills 
  

   rise 
  to 
  740 
  feet 
  one 
  mile 
  from 
  the 
  river 
  and 
  500 
  feet 
  above 
  

   it; 
  near 
  the 
  Lehigh 
  940 
  feet 
  one 
  to 
  two 
  miles 
  from 
  the 
  

   river 
  and 
  600 
  feet 
  above 
  it; 
  near 
  the 
  Delaware 
  840 
  feet 
  

  

  