﻿NIAGARA 
  FALLS 
  AND 
  VICINITY 
  

  

  37 
  

  

  sidence. 
  The 
  present 
  surface 
  of 
  the 
  Niagara 
  plateau 
  is 
  therefore 
  

   not 
  to 
  be 
  considered 
  as 
  identical 
  with 
  the 
  old 
  surface 
  of 
  deposition, 
  

   but 
  as 
  due 
  to 
  prolonged 
  peneplanation, 
  or 
  erosion 
  to 
  near 
  sealevel, 
  

   completed 
  probably 
  toward 
  the 
  close 
  of 
  Mesozoic 
  or 
  the 
  beginning 
  

   of 
  Cenozoic 
  time. 
  The 
  following 
  diagram 
  (fig. 
  3) 
  will 
  illustrate 
  the 
  

   relation 
  between 
  the 
  strata 
  and 
  the 
  surface 
  of 
  the 
  land 
  at 
  i) 
  the 
  close 
  

   of 
  Siluric 
  time, 
  2) 
  late 
  Mesozoic 
  or 
  early 
  Cenozoic 
  time, 
  after 
  the 
  

   completion 
  of 
  the 
  last 
  cycle 
  of 
  erosion 
  and 
  the 
  reduction 
  of 
  the 
  land 
  

   to 
  peneplain 
  condition, 
  and 
  3) 
  the 
  present 
  surface. 
  

  

  Fig. 
  3 
  Diagram 
  of 
  ancient 
  Paleozoic 
  coastal 
  plain, 
  and 
  its 
  relation 
  to 
  the 
  Mesozoic 
  peneplain 
  sur- 
  

   face 
  and 
  the 
  present 
  land 
  surface. 
  The 
  numbering 
  of 
  the 
  beds 
  corresponds 
  to 
  that 
  of 
  the 
  table. 
  

  

  Between 
  the 
  close 
  of 
  the 
  Siluric 
  and 
  beginning 
  of 
  Mesozoic 
  time 
  

  

  a 
  long 
  period 
  intervened, 
  during 
  which 
  this 
  region 
  was 
  at 
  first 
  a 
  

  

  land 
  surface, 
  suffering 
  considerable 
  erosion, 
  but 
  later 
  was 
  resub- 
  

  

  merged, 
  and 
  covered 
  with 
  extensive 
  deposits 
  of 
  Devonic 
  limestones, 
  

  

  shales 
  and 
  sandstones. 
  The 
  final 
  emergence 
  took 
  place 
  at 
  the 
  close 
  

  

  of 
  Paleozoic 
  time, 
  the 
  succeeding 
  Mesozoic 
  time 
  being 
  in 
  this 
  region 
  

  

  probably 
  an 
  uninterrupted 
  period 
  of 
  erosion, 
  during 
  which 
  the 
  land 
  

  

  suffered 
  the 
  combined 
  attacks 
  of 
  the 
  atmosphere 
  and 
  of 
  running 
  

  

  water. 
  

  

  Development 
  of 
  the 
  drainage 
  features 
  . 
  

  

  The 
  water 
  which 
  falls 
  as 
  rain 
  or 
  snow 
  on 
  the 
  land 
  either 
  evapor- 
  

   ates, 
  runs 
  off 
  on 
  the 
  surface, 
  or 
  sinks 
  into 
  the 
  ground, 
  where 
  it 
  con- 
  

   stitutes 
  the 
  ground 
  water. 
  That 
  which 
  evaporates, 
  accomplishes 
  lit- 
  

   tle 
  or 
  no 
  direct 
  geologic 
  work, 
  but 
  both 
  the 
  surface 
  and 
  under- 
  

   ground 
  waters 
  are 
  important 
  geologic 
  agents. 
  If 
  the 
  surface 
  on 
  

   which 
  the 
  water 
  falls 
  is 
  a 
  perfectly 
  smooth 
  but 
  inclined 
  plain, 
  the 
  

   water 
  will 
  run 
  of¥ 
  in 
  the 
  form 
  of 
  a 
  thin 
  sheet. 
  A 
  perfectly 
  smooth 
  

  

  