﻿112 
  . 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  harmony 
  with 
  the 
  rock 
  structures 
  and 
  other 
  drainage 
  lines. 
  The 
  

   diversion 
  from 
  the 
  preglacial 
  course 
  was 
  due 
  to 
  heavy 
  glacial 
  accu- 
  

   mulations 
  between 
  the 
  villages 
  of 
  Black 
  River 
  and 
  Evans 
  Mills. 
  

  

  The 
  deep, 
  narrow 
  gorges 
  which 
  have 
  been 
  cut 
  through 
  the 
  steep 
  

   eastern 
  and 
  northeastern 
  fronts 
  of 
  the 
  Tug 
  Hill 
  plateau 
  are 
  com- 
  

   monly 
  called 
  "gulfs." 
  Of 
  these 
  the 
  Whetstone 
  gulf 
  (see 
  plate 
  8) 
  

   is 
  the 
  most 
  interesting 
  and 
  though 
  little 
  known 
  it 
  is 
  one 
  of 
  the 
  

   finest 
  examples 
  of 
  its 
  kind 
  in 
  the 
  State. 
  Its 
  length 
  is 
  two 
  miles, 
  

   and 
  for 
  one 
  mile 
  it 
  shows 
  a 
  depth 
  of 
  300 
  feet. 
  The 
  walls 
  are 
  

   very 
  steep-sided 
  to 
  nearly 
  vertical, 
  especially 
  in 
  the 
  upper 
  end 
  

   (narrows) 
  where 
  there 
  is 
  just 
  room 
  enough 
  for 
  the 
  swift 
  stream 
  

   at 
  the 
  bottom. 
  This 
  gulf 
  is 
  certainly 
  postglacial 
  in 
  origin 
  and 
  has 
  

   been 
  cut 
  into 
  the 
  soft 
  Lorraine 
  and 
  Utica 
  shales. 
  During 
  glacial 
  

   times 
  the 
  shales 
  were 
  eroded 
  back 
  by 
  the 
  ice 
  (see 
  above) 
  caus- 
  

   ing 
  the 
  development 
  of 
  the 
  steep 
  eastern 
  front 
  of 
  Tug 
  hill. 
  

   After 
  the 
  ice 
  disappeared, 
  all 
  east-bound 
  streams 
  from 
  Tug 
  hill, 
  

   not 
  in 
  their 
  preglacial 
  channels, 
  rushed 
  over 
  the 
  steep 
  shale 
  front 
  

   and 
  began 
  to 
  erode 
  notches 
  into 
  its 
  summit. 
  These 
  notches 
  were 
  

   rapidly 
  deepened 
  in 
  the 
  soft 
  shales 
  to 
  form 
  the 
  gulfs 
  whose 
  heads 
  

   have 
  since 
  been 
  cut 
  back 
  to 
  their 
  present 
  positions. 
  

  

  The 
  world 
  famous 
  Niagara 
  Falls 
  and 
  gorge 
  are 
  wholly 
  post- 
  

   glacial 
  in 
  origin. 
  After 
  plunging 
  167 
  feet 
  at 
  the 
  falls, 
  the 
  river 
  

   rushes 
  for 
  7 
  miles 
  through 
  the 
  gorge 
  whose 
  depth 
  is 
  between 
  200 
  

   and 
  300 
  feet 
  (plates 
  47, 
  48, 
  49 
  and 
  50). 
  When 
  the 
  glacial 
  waters 
  

   in 
  the 
  eastern 
  Great 
  Lakes 
  region 
  had 
  dropped 
  to 
  the 
  Iroquois 
  level, 
  

   the 
  Niagara 
  limestone 
  terrace 
  in 
  the 
  vicinity 
  of 
  Buffalo 
  and 
  with 
  

   steep 
  escarpment 
  or 
  northern 
  front 
  at 
  Lewiston 
  and 
  Queenston, 
  

   ceased 
  to 
  be 
  covered 
  by 
  lake 
  water, 
  and 
  the 
  Niagara 
  river 
  came 
  

   into 
  existence 
  by 
  flowing 
  northward 
  over 
  this 
  limestone 
  plain. 
  The 
  

   river 
  first 
  plunged 
  over 
  the 
  escarpment 
  at 
  Lewiston 
  and 
  Queenston, 
  

   thus 
  inaugurating 
  Niagara 
  Falls 
  there. 
  Since 
  that 
  time 
  the 
  falls 
  

   have 
  receded 
  the 
  7 
  miles 
  up 
  stream 
  to 
  their 
  present 
  position. 
  In 
  

   figure 
  38 
  we 
  see 
  that 
  soft 
  shales 
  underlie 
  the 
  hard 
  layer 
  of 
  Niagara 
  

   limestone, 
  and 
  the 
  recession 
  of 
  the 
  falls 
  has 
  clearly 
  been 
  caused 
  by 
  

   the 
  breaking 
  off 
  of 
  blocks 
  of 
  limestone 
  due 
  to 
  undermining 
  of 
  the 
  

   soft 
  shales. 
  A 
  glance 
  at 
  the 
  map 
  (plate 
  50) 
  will 
  show 
  that 
  the 
  

   gorge 
  development 
  is 
  really 
  taking 
  place 
  on 
  the 
  Horseshoe 
  falls 
  

   side 
  where 
  the 
  volume 
  of 
  water 
  is 
  much 
  greater, 
  and 
  that 
  in 
  a 
  

   short 
  time, 
  geologically 
  considered, 
  the 
  American 
  falls 
  will 
  be 
  dry. 
  

   The 
  rocks 
  exposed 
  in 
  the 
  gorge 
  walls 
  are 
  Niagara 
  limestone, 
  under 
  

   which 
  in 
  regular 
  order 
  come 
  Niagara 
  (Rochester) 
  shale, 
  Clinton 
  

  

  