﻿6o 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  away 
  of 
  the 
  sandstone 
  ; 
  in 
  other 
  words 
  that 
  it 
  is 
  the 
  reappearance 
  at 
  

   the 
  surface 
  of 
  a 
  topography 
  of 
  tremendous 
  antiquity. 
  

  

  It 
  further 
  shows 
  that 
  this 
  surface 
  was 
  httle 
  affected 
  by 
  the 
  ice 
  

   sheets 
  of 
  Pleistocene 
  times, 
  otherwise 
  this 
  identity 
  of 
  character 
  could 
  

   not 
  have 
  been 
  so 
  well 
  retained. 
  

  

  Except 
  for 
  the 
  local 
  accumulation 
  of 
  a 
  very 
  scanty 
  amount 
  ot 
  

   residual 
  material 
  in 
  small 
  pockets 
  in 
  the 
  depressions 
  (and 
  this 
  almost 
  

   exclusively 
  quartzose) 
  the 
  Precambric 
  surface, 
  as 
  it 
  passes 
  under 
  

   the 
  Paleozoics, 
  is 
  remarkably 
  free 
  from 
  signs 
  of 
  surface 
  decay, 
  

   even 
  the 
  weak 
  rocks 
  being 
  astonishingly 
  fresh. 
  In 
  this 
  respect 
  also 
  

   the 
  conditions 
  are 
  like 
  those 
  noted 
  in 
  many 
  places 
  in 
  Canada 
  and 
  

   the 
  United 
  States, 
  as 
  described 
  by 
  numerous 
  observers. 
  

  

  The 
  relief 
  of 
  the 
  Precambric 
  surface 
  under 
  the 
  Potsdam 
  is 
  much 
  

   the 
  same 
  in 
  character 
  here 
  as 
  elsewhere 
  along 
  the 
  northern 
  and 
  

   eastern 
  borders 
  of 
  the 
  Adirondacks, 
  but 
  is 
  apparently 
  less 
  in 
  amount 
  

   than 
  it 
  is 
  further 
  east, 
  where 
  there 
  are 
  differences 
  in 
  level 
  of 
  three 
  

   or 
  four 
  hundred 
  feet 
  at 
  least. 
  The 
  evidence 
  there, 
  however, 
  is 
  com- 
  

   plicated 
  by 
  the 
  presence 
  of 
  numerous 
  large 
  faults 
  and 
  is 
  by 
  no 
  

   means 
  so 
  well 
  shown 
  as 
  it 
  is 
  here. 
  On 
  the 
  south 
  border, 
  in 
  the 
  Mo- 
  

   hawk 
  valley 
  region, 
  the 
  surface 
  was 
  much 
  smoother 
  than 
  here, 
  ex- 
  

   ceedingly 
  smooth 
  in 
  fact. 
  

  

  Potsdam 
  sandstone 
  

  

  The 
  first 
  deposits 
  laid 
  down 
  upon 
  the 
  worn 
  Precambric 
  surface 
  

   consisted 
  of 
  medium 
  grained, 
  quite 
  pure 
  quartz 
  sand, 
  now 
  firmly 
  

   cemented 
  to 
  sandstone. 
  On 
  the 
  Alexandria 
  quadrangle 
  tlie 
  forma- 
  

   tion 
  attains 
  a 
  maximum 
  thickness 
  of 
  about 
  125 
  feet. 
  This 
  thickness 
  

   diminishes 
  both 
  southward 
  and 
  westward, 
  but 
  shows 
  a 
  steady 
  in- 
  

   crease 
  to 
  the 
  eastward 
  of 
  the 
  area 
  mapped. 
  Within 
  that 
  the 
  thick- 
  

   ness 
  of 
  the 
  sandstone 
  is 
  not 
  greatly 
  in 
  excess 
  of, 
  or 
  else 
  does 
  not 
  

   quite 
  equal, 
  the 
  variation 
  of 
  level 
  shown 
  by 
  its 
  floor, 
  so 
  that 
  it 
  is 
  

   subject 
  to 
  continual 
  variation 
  from 
  place 
  to 
  place, 
  and 
  thins 
  to 
  20 
  

   feet 
  or 
  less 
  over 
  the 
  old 
  ridge 
  summits. 
  On 
  the 
  Theresa 
  quad- 
  

   rangle, 
  and 
  on 
  Wellesley 
  island, 
  it 
  locally 
  failed 
  to 
  overtop 
  the 
  

   highest 
  of 
  these, 
  and 
  the 
  Theresa 
  dolomite 
  is 
  found 
  resting 
  directly 
  

   on 
  the 
  Precambric. 
  

  

  The 
  bulk 
  of 
  the 
  formation 
  consists 
  of 
  a 
  very 
  pure 
  quartz 
  sand, 
  

   quite 
  thoroughly 
  cemented 
  with 
  a 
  silicious 
  cement. 
  The 
  general 
  

   color 
  is 
  light 
  gray 
  to 
  buff^ 
  weathering 
  white, 
  but 
  in 
  the 
  northern 
  

   portion 
  of 
  the 
  mapped 
  area 
  there 
  is 
  much 
  red, 
  or 
  banded 
  red 
  and 
  

   white 
  rock 
  in 
  the 
  lower 
  half 
  of 
  the 
  formation. 
  The 
  bulk 
  of 
  the 
  

   formation 
  is 
  evenly 
  bedded, 
  and 
  the 
  greater 
  part 
  is 
  thick 
  bedded, 
  

  

  