﻿118 
  R. 
  R. 
  Rice 
  — 
  Inner 
  Gorge 
  Terraces 
  of 
  the 
  

  

  This 
  view 
  of 
  the 
  benches 
  is 
  in 
  harmony 
  with 
  the 
  facts 
  as 
  shown 
  

   on 
  the 
  Beaver. 
  The 
  rock 
  benches 
  at 
  Beaver 
  Falls 
  and 
  New 
  

   Brighton, 
  where 
  the 
  Beaver 
  is 
  catting 
  its 
  new 
  channel, 
  lie 
  

   nearer 
  stream 
  level 
  than 
  the 
  benches 
  at 
  Wampum 
  and 
  Mora- 
  

   via, 
  where 
  the 
  Beaver 
  is 
  re-excavating 
  its 
  buried 
  channel. 
  It 
  

   may 
  also 
  be 
  added 
  that 
  the 
  greatly 
  increased 
  fall 
  of 
  the 
  Beaver 
  

   in 
  the 
  last 
  four 
  miles 
  of 
  its 
  course 
  where 
  it 
  drops 
  down 
  from 
  

   the 
  rock 
  channel 
  into 
  its 
  buried 
  one, 
  and 
  thence 
  into 
  the 
  Ohio, 
  

   is 
  sufficient 
  to 
  compensate 
  for 
  the 
  greater 
  elevation 
  of 
  the 
  

   benches 
  on 
  the 
  Ohio. 
  

  

  It 
  would 
  seem 
  therefore 
  that 
  sufficient 
  is 
  now 
  known 
  to 
  jus- 
  

   tify 
  the 
  conclusion 
  that 
  the 
  cutting 
  of 
  the 
  inner 
  gorge 
  is 
  to 
  be 
  

   subdivided 
  into 
  two 
  periods. 
  (1) 
  The 
  time 
  required 
  to 
  cut 
  

   from 
  the 
  level 
  of 
  the 
  lowest 
  of 
  the 
  upper 
  rock 
  benches 
  to 
  the 
  

   level 
  of 
  the 
  inner 
  rock 
  benches, 
  when 
  erosion 
  seems 
  to 
  have 
  

   approached 
  a 
  base 
  level, 
  and 
  (2) 
  a 
  second 
  period 
  of 
  cutting 
  

   from 
  the 
  inner 
  rock 
  benches 
  to 
  the 
  bottom 
  of 
  the 
  buried 
  chan- 
  

   nel. 
  The 
  first 
  period 
  evidently 
  much 
  the 
  longer. 
  The 
  bench 
  

   at 
  Homewood, 
  for 
  example, 
  is 
  some 
  seventy 
  feet 
  above 
  the 
  

   bottom 
  of 
  the 
  inner 
  gorge 
  (the 
  bottom 
  of 
  the 
  buried 
  channel), 
  

   and 
  about 
  one 
  hundred 
  feet 
  below 
  the 
  lowest 
  of 
  the 
  upper 
  

   benches. 
  The 
  work 
  of 
  erosion 
  in 
  the 
  first 
  period 
  was 
  here 
  

   through 
  the 
  Homewood 
  sandstone 
  in 
  great 
  measure, 
  while 
  the 
  

   cutting 
  of 
  the 
  second 
  period 
  was 
  in 
  shales 
  to 
  a 
  great 
  extent 
  ; 
  

   the 
  lower 
  portion 
  of 
  the 
  gorge 
  is 
  also 
  narrower 
  than 
  the 
  upper 
  

   portion. 
  It 
  seems 
  safe 
  to 
  say, 
  therefore, 
  the 
  first 
  period 
  repre- 
  

   sents 
  two 
  thirds 
  to 
  three-fourths 
  of 
  the 
  entire 
  work 
  of 
  excava- 
  

   tion, 
  and 
  probably 
  a 
  larger 
  proportion 
  in 
  time. 
  

  

  After 
  the 
  excavation 
  of 
  the 
  buried 
  channel, 
  the 
  next 
  chapter 
  

   of 
  the 
  river 
  history 
  was 
  the 
  silting 
  of 
  the 
  valleys 
  to 
  the 
  top 
  of 
  

   the 
  inner 
  terraces. 
  It 
  is 
  not 
  purposed 
  in 
  this 
  paper 
  to 
  discuss 
  

   the 
  inner 
  alluvium, 
  further 
  than 
  to 
  call 
  attention 
  to 
  a 
  mistake 
  

   regarding 
  it, 
  evidently 
  due 
  to 
  a 
  study 
  of 
  the 
  gravel 
  escarp- 
  

   ments, 
  without 
  examination 
  of 
  the 
  structure 
  back 
  from 
  the 
  

   face. 
  It 
  has 
  been 
  described 
  as 
  quite 
  coarse, 
  ranging 
  up 
  to 
  two 
  

   feet 
  in 
  diameter, 
  and 
  the 
  impression 
  prevails 
  that 
  it 
  is 
  uni- 
  

   formly 
  of 
  this 
  character, 
  from 
  top 
  to 
  bottom, 
  and 
  from 
  escarp- 
  

   ment 
  to 
  the 
  base 
  of 
  the 
  hills 
  bounding 
  the 
  inner 
  gorge. 
  

  

  It 
  seems 
  evident, 
  and 
  generally 
  admitted, 
  that 
  the 
  alluvium 
  

   should 
  be 
  considered 
  as 
  a 
  whole, 
  from 
  the 
  top 
  of 
  the 
  highest 
  

   terraces 
  s 
  to 
  the 
  bottom 
  of 
  the 
  buried 
  channel. 
  The 
  records 
  

   that 
  determined 
  the 
  existence 
  of 
  the 
  buried 
  channel 
  were 
  not 
  

   sufficient 
  to 
  furnish 
  any 
  knowledge 
  of 
  the 
  character 
  of 
  the 
  fill- 
  

   ing, 
  and 
  it 
  is 
  only 
  recently 
  any 
  real 
  knowledge 
  has 
  come 
  to 
  

   light, 
  and 
  rendered 
  it 
  possible 
  to 
  form 
  a 
  correct 
  idea 
  of 
  the 
  

   filling 
  material 
  and 
  consequently 
  of 
  the 
  stream 
  that 
  deposited 
  

   it. 
  

  

  