﻿138 
  

  

  TWENTY-FIRST 
  REPORT 
  ON 
  THE 
  STATE 
  CABINET. 
  

  

  years 
  ; 
  which 
  period 
  I 
  consider 
  a 
  minimum 
  for 
  the 
  time 
  that 
  has 
  

   elapsed 
  since 
  Cohoes 
  Falls 
  were 
  opposite 
  the 
  Mastodon 
  pot-hole. 
  

  

  Fig. 
  

  

  a 
  

  

  «• 
  

  

  '%gmm 
  

  

  Illlllfl* 
  

  

  ' 
  .. 
  -\- 
  ,> 
  

  

  m^^^m^mmsm^m 
  

  

  Falls. 
  — 
  The 
  water 
  makes 
  no 
  clear 
  leap 
  in 
  Cohoes 
  Falls. 
  The 
  

   fall 
  (properly 
  speaking) 
  commences 
  at 
  a 
  (fig. 
  9). 
  From 
  a 
  to 
  c, 
  a 
  

   distance 
  of 
  400 
  feet, 
  the 
  descent 
  is 
  14 
  feet 
  ; 
  from 
  c 
  (crest) 
  to 
  b 
  

   (base), 
  57 
  feet 
  ; 
  making 
  a 
  total 
  of 
  71 
  feet. 
  The 
  slope 
  c 
  b 
  is 
  a 
  

   little 
  less 
  steep 
  than 
  the 
  dip 
  of 
  the 
  strata. 
  From 
  a 
  to 
  c 
  is 
  the 
  

   region 
  of 
  pot-holes 
  now 
  forming. 
  Most 
  of 
  them 
  must 
  disappear 
  at 
  c 
  

   by 
  the 
  destruction 
  of 
  their 
  walls 
  ; 
  a 
  few 
  of 
  the 
  larger, 
  wearing 
  

   as 
  rapidly 
  at 
  bottom 
  as 
  at 
  top, 
  are 
  being 
  carried 
  down 
  to 
  take 
  

   positions 
  in 
  future 
  basins. 
  The 
  slope 
  a 
  c 
  displays 
  such 
  rapid 
  

   erosion, 
  that 
  it 
  has 
  occurred 
  to 
  me 
  that 
  it 
  may 
  be 
  wearing 
  more 
  

   rapidly 
  than 
  c 
  b, 
  and 
  thus 
  converting 
  the 
  cataract 
  into 
  a 
  rapid. 
  

   Is 
  it 
  not 
  possible 
  that 
  rapids 
  constitute 
  the 
  normal 
  mode 
  of 
  

   descent 
  of 
  a 
  river 
  over 
  these 
  upturned 
  shales, 
  and 
  the 
  falls 
  are 
  

   merely 
  an 
  episode 
  occasioned 
  by 
  preexisting 
  pot-holes 
  ? 
  

  

  Slips. 
  — 
  All 
  the 
  slips 
  observed 
  strike 
  across 
  the 
  gorge, 
  and 
  dip 
  

   S. 
  E. 
  at 
  various 
  angles, 
  all 
  less 
  than 
  the 
  inclination 
  of 
  the 
  strata. 
  

  

  West 
  of 
  the 
  channel, 
  opposite 
  the 
  new 
  

   mill, 
  I 
  observed 
  a 
  combination 
  of 
  three 
  

   slips 
  in 
  slightly 
  different 
  directions, 
  and 
  

   separated 
  by 
  quartz 
  (fig. 
  10). 
  They 
  seem 
  

   to 
  record 
  three 
  movements 
  along 
  the 
  same 
  

   fault-plane, 
  with 
  intervals 
  of 
  time 
  sufficient 
  

   for 
  the 
  deposition 
  of 
  crystalline 
  quartz. 
  

   Some 
  exposures 
  of 
  surfaces 
  of 
  faults 
  are 
  

   very 
  finely 
  shown 
  on 
  the 
  plateau, 
  and, 
  

   if 
  cleaned 
  from 
  river 
  slime, 
  might 
  show 
  the 
  direction 
  of 
  the 
  

   slide. 
  I 
  have 
  drawn 
  one 
  (fig. 
  11) 
  that 
  can 
  be 
  traced 
  quite 
  across 
  

   the 
  river 
  near 
  the 
  mill. 
  While 
  the 
  section 
  given 
  in 
  the 
  cliff 
  g 
  is 
  

   straight 
  (dipping 
  about 
  25°), 
  that 
  in 
  the 
  plateau 
  b 
  is 
  devious. 
  

   Joining 
  with 
  it 
  is 
  a 
  fault 
  curved 
  in 
  the 
  direction 
  of 
  the 
  movement. 
  

  

  Fi£. 
  10. 
  

  

  ^^MSSMM 
  

  

  