﻿NIAGARA 
  FALLS 
  AND 
  VICINITY 
  39 
  

  

  downward, 
  i. 
  e. 
  till 
  the 
  grade 
  of 
  the 
  river 
  bottom 
  is 
  a 
  very 
  gentle 
  

   one, 
  when 
  lateral 
  swinging 
  widens 
  the 
  gorge 
  by 
  undercutting 
  the 
  

   banks, 
  and 
  atmospheric 
  degradation 
  quickly 
  destroys 
  the 
  steep 
  cliffs 
  

   which 
  the 
  river 
  does 
  not 
  keep 
  perpendicular. 
  

  

  During 
  the 
  process 
  of 
  drainage 
  development, 
  numerous 
  side 
  

   streams 
  come 
  into 
  existence, 
  which 
  join 
  the 
  main 
  stream 
  as 
  branches. 
  

   These 
  begin 
  as 
  gullies 
  formed 
  by 
  the 
  rainwater 
  running 
  over 
  the 
  

   sides 
  of 
  the 
  banks 
  into 
  the 
  main 
  stream. 
  A 
  slight 
  depression 
  in 
  the 
  

   surface, 
  or 
  a 
  difference 
  in 
  the 
  character 
  of 
  the 
  material 
  composing 
  

   the 
  banks, 
  may 
  determine 
  the 
  location 
  of 
  such 
  a 
  gully, 
  but, 
  

   once 
  determined, 
  it 
  will 
  become 
  the 
  cause 
  of 
  its 
  own 
  farther 
  

   growth. 
  For 
  the 
  existence 
  of 
  this 
  gully 
  will 
  determine 
  the 
  

   direction 
  of 
  flow 
  of 
  succeeding 
  surface 
  waters, 
  and 
  so 
  in 
  the 
  

   course 
  of 
  time 
  the 
  gully 
  will 
  become 
  longer 
  and 
  longer 
  by 
  

   headward 
  gnawing, 
  till 
  finally 
  a 
  channel 
  of 
  considerable 
  magni- 
  

   tude 
  is 
  produced. 
  Streams 
  of 
  this 
  type 
  are 
  known 
  as 
  subsequent 
  

   streams, 
  and 
  they 
  very 
  generally 
  have 
  a 
  direction 
  varying 
  from 
  a 
  

   moderately 
  acute 
  to 
  nearly 
  a 
  right 
  angle 
  with 
  reference 
  to 
  the 
  main 
  

   or 
  consequent 
  stream. 
  

  

  As 
  the 
  dissection 
  of 
  the 
  Niagara 
  coastal 
  plain 
  continued, 
  the 
  higher 
  

   portions 
  of 
  the 
  strata, 
  i. 
  e. 
  those 
  nearer 
  the 
  old-land, 
  were 
  slowly 
  re- 
  

   moved, 
  and 
  the 
  beds 
  lying 
  beneath 
  these 
  were 
  thus 
  exposed. 
  The 
  

   latter 
  strata 
  were 
  generally 
  of 
  a 
  more 
  destructible 
  character 
  than 
  

   the 
  overlying 
  ones, 
  and 
  on 
  this 
  account 
  great 
  lowlands, 
  parallel 
  

   to 
  the 
  old 
  shore 
  line, 
  or 
  the 
  line 
  of 
  strike 
  of 
  the 
  strata, 
  were 
  worn 
  

   in 
  them 
  by 
  subsequent 
  streams. 
  The 
  more 
  resistant 
  beds, 
  

   meanwhile, 
  favored 
  the 
  formation 
  of 
  more 
  or 
  less 
  prominent 
  cliffs 
  

   or 
  escarpments 
  which 
  faced 
  the 
  lowlands, 
  and 
  being 
  undermined 
  

   slowly 
  retreated 
  southward, 
  thus 
  increasing 
  the 
  width 
  of 
  the 
  low- 
  

   lands. 
  These 
  features 
  are 
  today 
  repeated 
  in 
  the 
  Niagara 
  escarp- 
  

   ment 
  which 
  faces 
  the 
  Ontario 
  and 
  Georgian 
  bay 
  lowlands, 
  and 
  the 
  

   escarpments 
  formed 
  by 
  the 
  outcrops 
  of 
  the 
  Ordovicic 
  limestones 
  

   farther 
  north. 
  The 
  diagram, 
  fig. 
  4, 
  illustrates 
  the 
  probable 
  con- 
  

   dition 
  during 
  early 
  Mesozoic 
  time. 
  The 
  great 
  master 
  consequent 
  

   streams 
  indicated 
  are: 
  the 
  Saginaw, 
  the 
  Dundas 
  and 
  the 
  Genesee, 
  

   flowing 
  from 
  the 
  old-land 
  on 
  the 
  northeast, 
  southward 
  or 
  southwest- 
  

  

  