﻿154 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  The 
  cataract 
  of 
  Niagara 
  is 
  produced 
  by 
  the 
  passage 
  of 
  the 
  river 
  

   over 
  this 
  limestone 
  and 
  shale; 
  and 
  from 
  being 
  a 
  well 
  known 
  and 
  

   extremely 
  interesting 
  locality, 
  as 
  well 
  as 
  exhibiting 
  the 
  greatest 
  

   natural 
  development 
  of 
  these 
  rocks 
  within 
  the 
  limits 
  of 
  the 
  state, 
  

   this 
  name 
  has 
  been 
  adopted 
  for 
  its 
  designation. 
  

  

  Standing 
  on 
  the 
  upper 
  suspension 
  bridge 
  at 
  Niagara 
  Falls, 
  one 
  

   sees 
  in 
  the 
  precipice, 
  above 
  the 
  Clinton 
  limestone, 
  a 
  sloping 
  bank 
  

   of 
  soft 
  gray 
  shale 
  about 
  80 
  feet 
  thick, 
  above 
  which 
  succeeds 
  a 
  

   thick 
  series 
  of 
  layers 
  of 
  limestone 
  forming 
  the 
  brink 
  of 
  the 
  

   rocky 
  wall: 
  these 
  are 
  the 
  Niagara 
  shale 
  and 
  the 
  Niagara 
  lime- 
  

   stone. 
  The 
  great 
  cataract 
  pours 
  over 
  their 
  edges; 
  and 
  its 
  ver- 
  

   tical 
  descent 
  is 
  owing 
  to 
  the 
  fact 
  that 
  the 
  soft 
  shale 
  below 
  wears 
  

   away 
  more 
  rapidly 
  than 
  the 
  hard 
  limestone 
  which 
  forms 
  the 
  top 
  

   of 
  the 
  fall, 
  thus 
  maintaining 
  a 
  recess 
  behind 
  the 
  descending 
  sheet 
  

   of 
  water. 
  These 
  rocks 
  are 
  perfectly 
  exhibited 
  in 
  the 
  gorge 
  of 
  

   the 
  Niagara 
  river, 
  especially 
  along 
  the 
  Niagara 
  Falls 
  and 
  Lewis- 
  

   ton 
  railroad. 
  

  

  The 
  limestone 
  at 
  Niagara 
  is 
  about 
  160 
  feet 
  thick 
  (of 
  which 
  only 
  

   the 
  lower 
  part 
  is 
  seen 
  at 
  the 
  falls); 
  at 
  Rochester 
  it 
  is 
  about 
  70 
  

   feet 
  thick. 
  The 
  shale 
  decomposes 
  rapidly 
  where 
  exposed 
  to 
  the 
  

   air, 
  until 
  it 
  resembles 
  a 
  deposit 
  of 
  gray 
  clay. 
  It 
  contains 
  thin 
  

   layers 
  of 
  limestone 
  in 
  many 
  places, 
  the 
  surfaces 
  of 
  which 
  are 
  

   often 
  covered 
  with 
  beautiful 
  small 
  corals 
  of 
  several 
  species, 
  and 
  

   the 
  shale 
  itself 
  contains 
  them 
  in 
  great 
  numbers. 
  The 
  ^ 
  deep 
  cut 
  ^ 
  

   of 
  the 
  canal 
  above 
  Lockport 
  is 
  through 
  the 
  Niagara 
  limestone, 
  

   some 
  layers 
  of 
  which 
  there 
  form 
  a 
  massive 
  and 
  beautiful 
  build- 
  

   ing 
  stone. 
  The 
  same 
  limestone 
  and 
  shale 
  form 
  the 
  upper 
  falls 
  

   of 
  the 
  Genesee 
  at 
  Rochester. 
  

  

  Salina 
  Group, 
  or 
  Onondaga 
  Salt 
  Group 
  

   The 
  next 
  series 
  of 
  strata 
  in 
  upward 
  succession 
  is 
  a 
  group 
  of 
  

   shales 
  and 
  thin 
  limestones, 
  the 
  whole 
  of 
  which 
  in 
  central 
  and 
  

   western 
  New 
  York 
  attains 
  a 
  thickness 
  of 
  nearly 
  1,000 
  feet. 
  

   Its 
  lower 
  part 
  in 
  central 
  New 
  York 
  is 
  composed 
  for 
  sevei'al 
  

   hundred 
  feet 
  of 
  a 
  soft 
  red 
  shale 
  or 
  hardened 
  clay, 
  especially 
  

   conspicuous 
  along 
  the 
  Erie 
  canal 
  in 
  Madison 
  county. 
  Its 
  upper 
  

  

  