﻿COHOES 
  MASTODON. 
  131 
  

  

  floods 
  of 
  the 
  following 
  spring 
  washed 
  away 
  the 
  debris 
  that 
  then 
  

   covered 
  a 
  group 
  of 
  smaller 
  holes 
  (one 
  to 
  three 
  feet 
  in 
  diameter), 
  

   situated 
  six 
  or 
  eight 
  feet 
  above 
  the 
  plateau, 
  in 
  the 
  notch 
  where 
  

   the 
  stream 
  enters. 
  This 
  notch 
  indents 
  the 
  cliff 
  so 
  deeply 
  as 
  to 
  

   afford 
  an 
  easy 
  descent 
  to 
  its 
  base. 
  It 
  now 
  conveys 
  only 
  some 
  

   leakage 
  of 
  the 
  mill-race, 
  and 
  its 
  proper 
  stream 
  is 
  so 
  entirely 
  cut 
  

   off 
  b}' 
  canals 
  and 
  roads 
  that 
  it 
  is 
  even 
  doubtful 
  with 
  what 
  notch 
  

   in 
  the 
  clay 
  hill 
  it 
  was 
  originally 
  connected. 
  The 
  exceptional 
  posi- 
  

   tion 
  of 
  these 
  holes 
  suggests 
  that 
  they 
  were 
  formed 
  by 
  the 
  stream 
  

   that 
  cut 
  the 
  notch. 
  The 
  last, 
  however, 
  has 
  the 
  form 
  and 
  dimen- 
  

   sions 
  of 
  the 
  valley 
  of 
  a 
  very 
  small 
  stream, 
  and 
  I 
  have 
  yet 
  no 
  other 
  

   evidence 
  of 
  the 
  formation 
  of 
  pot-holes 
  by 
  small 
  streams. 
  The 
  

   large 
  depression 
  may 
  be 
  the 
  bottom 
  of 
  an 
  ancient 
  pot-hole. 
  

  

  Plateaux. 
  — 
  A 
  striking 
  peculiarity 
  of 
  the 
  river 
  bed 
  is 
  its 
  

   evenness 
  — 
  not 
  in 
  the 
  space 
  of 
  a 
  few 
  feet, 
  but 
  when 
  a 
  broad 
  area 
  

   is 
  considered. 
  The 
  flood-plain 
  of 
  a 
  river 
  freshly 
  upturned 
  by 
  the 
  

   plow 
  affords 
  a 
  comparison. 
  Exclusive 
  of 
  pot-holes, 
  the 
  greatest 
  

   depressions 
  and 
  elevations 
  vary 
  but 
  a 
  few 
  inches 
  from 
  the 
  general 
  

   level,* 
  and 
  this 
  level 
  does 
  not 
  sensibly 
  vary 
  in 
  the 
  width 
  of 
  

   the 
  river 
  bed. 
  I 
  ascertained 
  that 
  at 
  a 
  point 
  near 
  the 
  fall 
  it 
  is 
  

   ItVo 
  f 
  ee 
  ^ 
  higher 
  than 
  at 
  a 
  point 
  480 
  feet 
  further 
  down 
  stream 
  — 
  

   the 
  rate 
  of 
  fall 
  of 
  the 
  stream. 
  All 
  the 
  features 
  of 
  this 
  floor 
  indi- 
  

   cate 
  that 
  it 
  depends, 
  like 
  a 
  flood-plain, 
  upon 
  the 
  w 
  r 
  ater 
  level, 
  with 
  

   the 
  difference 
  that 
  it 
  indicates 
  a 
  minimum, 
  instead 
  of 
  a 
  maximum 
  

   stage 
  of 
  water. 
  In 
  summer 
  it 
  is 
  now 
  bared; 
  but, 
  on 
  Sundays, 
  when 
  

   less 
  water 
  is 
  taken 
  from 
  the 
  river 
  by 
  the 
  mill 
  races, 
  its 
  hollow 
  T 
  s 
  are 
  

   flooded, 
  and 
  I 
  am 
  confident 
  that 
  the 
  natural 
  summer 
  stage 
  would 
  

   just 
  cover 
  it. 
  The 
  jagged 
  detail 
  of 
  this 
  surface 
  forbids 
  the 
  theory 
  

   that 
  it 
  is 
  caused 
  by 
  wearing 
  of 
  water 
  or 
  of 
  materials 
  moved 
  by 
  water. 
  

   I 
  conceive 
  that 
  the 
  upper 
  mass 
  of 
  rock 
  has 
  been 
  disintegrated 
  by 
  

   frost 
  and 
  removed 
  by 
  the 
  current 
  down 
  to 
  the 
  limit 
  of 
  perpetual 
  

   protection 
  by 
  water. 
  This 
  floor 
  characterizes 
  the 
  bed 
  of 
  the 
  river 
  

   from 
  the 
  basin 
  of 
  the 
  fall 
  down 
  to 
  the 
  rift 
  above 
  the 
  bridge 
  of 
  the 
  

  

  * 
  Exception 
  must 
  be 
  made 
  of 
  an 
  oval 
  hill 
  — 
  about 
  75 
  X 
  35 
  feet, 
  and 
  rising 
  5 
  8-10 
  

   feet 
  above 
  the 
  plateau 
  — 
  which 
  adjoins 
  the 
  basin 
  a 
  little 
  west 
  of 
  the 
  channel. 
  Its 
  upper 
  

   end 
  is 
  some 
  — 
  feet 
  from 
  the 
  base 
  of 
  the 
  fall. 
  Wet 
  by 
  spray 
  half 
  the 
  year, 
  exposed 
  to 
  the 
  

   blows 
  of 
  ice 
  blocks 
  just 
  from 
  the 
  fall, 
  washed 
  clean 
  by 
  every 
  flood, 
  its 
  endurance 
  is 
  diffi- 
  

   cult 
  to 
  comprehend. 
  Its 
  greatest 
  elevation 
  above 
  the 
  plateau 
  was 
  carefully 
  noted, 
  with 
  

   the 
  thought 
  that 
  another 
  observation, 
  ten 
  years 
  hence, 
  might 
  show 
  some 
  alteration. 
  The 
  

   standard 
  of 
  comparison, 
  however, 
  may 
  be 
  undergoing 
  alteration. 
  A 
  natural 
  result 
  of 
  

   the 
  lessening 
  by 
  human 
  agency 
  of 
  the 
  minimum 
  volume 
  of 
  the 
  Mohawk, 
  would 
  be 
  a 
  

   gradual 
  disintegration 
  and 
  lowering 
  of 
  the 
  surface 
  of 
  the 
  plateau. 
  

  

  