﻿56 
  NEW 
  YORK 
  STATE 
  MUSEUM: 
  

  

  The 
  second 
  line 
  of 
  evidence 
  is 
  that 
  obtained 
  in 
  following 
  and 
  

   mapping 
  the 
  long 
  Potsdam 
  boundaries. 
  A 
  single 
  example, 
  that 
  of 
  

   the 
  Potsdam 
  margin 
  along 
  the 
  west 
  bank 
  of 
  Indian 
  river 
  in 
  the 
  

   southeast 
  corner 
  of 
  the 
  Alexandria 
  sheet 
  and 
  for 
  i 
  mile 
  southward 
  

   on 
  the 
  Theresa 
  sheet, 
  will 
  serve 
  as 
  well 
  as 
  a 
  multitude 
  of 
  illustra- 
  

   tions 
  to 
  indicate 
  what 
  the 
  evidence 
  is. 
  The 
  section 
  is 
  convenient 
  

   since 
  it 
  has 
  a 
  horizontal 
  base, 
  the 
  edge 
  of 
  the 
  Indian 
  river 
  marsh. 
  

   The 
  Potsdam 
  faces 
  the 
  river 
  in 
  a 
  prominent 
  bluff 
  which, 
  when 
  it 
  

   comes 
  down 
  to 
  the 
  marsh 
  level, 
  as 
  it 
  frequently 
  does, 
  forces 
  the 
  

   pedestrian 
  to 
  take 
  to 
  the 
  swamp, 
  so 
  that 
  the 
  walk 
  is 
  not 
  recom- 
  

   mended 
  as 
  a 
  pastime. 
  But 
  the 
  unbroken 
  clift 
  margin 
  renders 
  accu- 
  

   rate 
  mapping 
  of 
  the 
  Potsdam 
  base 
  possible, 
  and 
  underneath 
  it 
  Pre- 
  

   cambric 
  exposures 
  are 
  numerous. 
  At 
  the 
  south 
  end 
  of 
  this 
  section, 
  

   on 
  the 
  Theresa 
  sheet, 
  inspection 
  of 
  the 
  map 
  will 
  show 
  the 
  Potsdam 
  

   coming 
  down 
  to 
  the 
  river 
  level 
  in 
  a 
  point. 
  Going 
  northward 
  it 
  soon 
  

   runs 
  up 
  the 
  bank 
  until 
  the 
  base 
  is 
  40 
  feet 
  above 
  the 
  river, 
  with 
  

   Grenville 
  limestone 
  outcrops 
  showing 
  beneath, 
  then 
  it 
  returns 
  to 
  

   the 
  river 
  level 
  and 
  again 
  rises, 
  repeating 
  the 
  perform.ance 
  three 
  times 
  

   within 
  a 
  mile 
  of 
  distance. 
  Soon 
  after 
  passing 
  on 
  to 
  the 
  Alexandria 
  

   sheet 
  the 
  sandstone 
  retreats 
  prominently 
  up 
  the 
  bank 
  and 
  back 
  from 
  

   the 
  river, 
  showing 
  a 
  60 
  foot 
  thickness 
  of 
  limestone 
  underneath, 
  then 
  

   returns 
  to 
  marsh 
  level, 
  withdraws 
  30 
  feet 
  up 
  the 
  bank, 
  comes 
  back 
  

   again 
  forming 
  a 
  point, 
  retreats 
  quickly 
  for 
  60 
  feet 
  up 
  the 
  bank 
  and 
  

   again 
  returns 
  to 
  the 
  river, 
  all 
  the 
  while 
  with 
  limestone 
  underneath, 
  

   cut 
  by 
  occasional 
  granite 
  dikes, 
  so 
  that 
  all 
  these 
  oscillations 
  merely 
  

   represent 
  irregularities 
  of 
  the 
  limestone 
  surface. 
  Northward 
  from 
  

   this 
  last 
  point 
  of 
  reaching 
  the 
  river, 
  however, 
  the 
  limestone 
  is 
  cut 
  

   out 
  by 
  granite 
  gneiss, 
  and 
  this 
  turns 
  the 
  Potsdam 
  straight 
  up 
  the 
  

   bank 
  and 
  out 
  to 
  the 
  road, 
  with 
  a 
  rise 
  of 
  more 
  than 
  100 
  feet 
  in 
  the 
  

   level 
  of 
  the 
  Precambi^c 
  surface. 
  Equally 
  striking 
  are 
  the 
  oscilla- 
  

   tions 
  in 
  level 
  of 
  the 
  same 
  margin 
  when 
  followed 
  southward 
  on 
  the 
  

   Theresa 
  sheet, 
  and 
  this 
  margin 
  is 
  easy 
  to 
  follow, 
  using 
  the 
  railroad 
  

   as 
  a 
  base. 
  There 
  are 
  many 
  other 
  excellent 
  examples, 
  since 
  this 
  sort 
  

   of 
  thing 
  is 
  the 
  rule 
  throughout 
  the 
  district. 
  The 
  mapping 
  of 
  the 
  

   Potsdam 
  base 
  is 
  thereby 
  rendered 
  laborious 
  but 
  nothing 
  can 
  be 
  

   imagined 
  more 
  beautifully 
  demonstrative 
  of 
  the 
  character 
  of 
  the 
  

   surface 
  on 
  which 
  the 
  Potsdam 
  rests 
  and 
  its 
  identity 
  with 
  that 
  of 
  

   the 
  surface 
  from 
  which 
  the 
  Potsdam 
  has 
  been 
  removed. 
  

  

  Lastly 
  there 
  is 
  the 
  evidence 
  given 
  by 
  the 
  actual 
  contacts. 
  There 
  

   are 
  quite 
  a 
  number 
  of 
  these, 
  more 
  than 
  the 
  writer 
  has 
  seen 
  in 
  the 
  

   entire 
  remaining 
  border 
  of 
  the 
  Adirondack 
  region. 
  Besides 
  the 
  

   actual 
  contacts 
  there 
  are 
  a 
  host 
  of 
  others 
  where 
  but 
  a 
  few 
  feet 
  of 
  

  

  