﻿40 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Because 
  of 
  the 
  deep 
  mantle 
  of 
  sand 
  and 
  gravel 
  which 
  now 
  covers 
  

   the 
  Precambric 
  surface 
  east 
  of 
  Black 
  river, 
  the 
  configuration 
  of 
  that 
  

   surface 
  can 
  not 
  be 
  studied 
  to 
  the 
  best 
  advantage. 
  But 
  so 
  far 
  as 
  

   can 
  be 
  judged, 
  if 
  the 
  stream 
  channels 
  in 
  the 
  Precambric 
  surface 
  

   were 
  filled 
  up 
  the 
  resulting 
  surface 
  would 
  be 
  comparatively 
  smooth 
  

   and 
  even 
  which 
  strongly 
  argues 
  for 
  that 
  sort 
  of 
  a 
  surface 
  before 
  the 
  

   stripping 
  off 
  of 
  the 
  sediments 
  and 
  later 
  erosion. 
  Any 
  prominent 
  

   elevations 
  on 
  the 
  old 
  floor 
  ought 
  now 
  to 
  be 
  recognizable, 
  especially 
  in 
  

   the 
  valley 
  bottom, 
  and 
  near 
  the 
  Paleozoic 
  boundary, 
  but 
  none 
  occur 
  

   there. 
  The 
  distinct 
  rock 
  ridge 
  southeast 
  of 
  Fowlersville 
  seems 
  to 
  

   be 
  the 
  only 
  example 
  of 
  such 
  an 
  elevation. 
  This 
  ridge 
  rises 
  about 
  

   80 
  feet 
  above 
  the 
  general 
  level 
  but 
  its 
  hight 
  is 
  thought 
  to 
  have 
  been 
  

   somewhat 
  accentuated 
  by 
  ice 
  action. 
  Again, 
  if 
  there 
  had 
  been 
  any 
  

   marked 
  depressions 
  in 
  the 
  old 
  floor 
  they 
  would 
  have 
  been 
  filled 
  

   up 
  with 
  Paleozoic 
  sediments 
  and 
  we 
  might 
  well 
  expect 
  to 
  find 
  such 
  

   protected 
  sediments 
  as 
  isolated 
  patches 
  or 
  outliers 
  within 
  the 
  gen- 
  

   eral 
  Precambric 
  area 
  as, 
  indeed, 
  the 
  Potsdam 
  sandstone 
  does 
  occur 
  

   some 
  30 
  or 
  40 
  miles 
  farther 
  northward. 
  The 
  available 
  evidence, 
  

   however, 
  points 
  to 
  a 
  complete 
  removal 
  of 
  the 
  sediments. 
  

  

  The 
  conclusion 
  for 
  the 
  Port 
  Leyden 
  quadrangle- 
  is 
  that 
  the 
  Pre- 
  

   cambric 
  floor 
  upon 
  which 
  the 
  sediments 
  were 
  laid 
  down 
  was 
  com- 
  

   paratively 
  smooth 
  and 
  even, 
  with 
  only 
  one 
  known 
  elevation 
  rising 
  

   above 
  the 
  general 
  level. 
  This 
  is 
  substantially 
  the 
  conclusion 
  reached 
  

   by 
  Professor 
  Gushing 
  and 
  the 
  writer 
  for 
  the 
  Little 
  Falls 
  and 
  Rem- 
  

   sen 
  quadrangles 
  respectively 
  and 
  it 
  is 
  true 
  of 
  the 
  southern 
  and 
  south- 
  

   western 
  border 
  of 
  the 
  Adirondacks. 
  This 
  result 
  as 
  Gushing 
  says 
  

   " 
  seems 
  specially 
  important 
  in 
  view 
  of 
  the 
  fact 
  that 
  Professors 
  

   Kemp 
  and 
  Smyth, 
  and 
  the 
  writer 
  (Gushing) 
  also, 
  have 
  found 
  evi- 
  

   dence 
  to 
  show 
  that, 
  in 
  the 
  St 
  Lawrence 
  and 
  Ghamplain 
  valleys 
  and 
  

   vicinity, 
  the 
  surface 
  on 
  which 
  the 
  Potsdam 
  was 
  deposited 
  was 
  con- 
  

   siderably 
  more 
  uneven 
  than 
  this. 
  In 
  other 
  words, 
  the 
  surface 
  to 
  

   the 
  south 
  was 
  worn 
  down 
  to 
  a 
  nearer 
  approach 
  to 
  base 
  level 
  than 
  

   was 
  the 
  case 
  farther 
  north." 
  

  

  Slope 
  of 
  the 
  Precambric 
  surface 
  where 
  now 
  exposed 
  

  

  We 
  have 
  just 
  shown 
  that 
  the 
  Paleozoic 
  sediments 
  were 
  deposited 
  

   upon 
  a 
  very 
  smooth 
  Precambric 
  surface. 
  The 
  uneven 
  and 
  dissected 
  

   character 
  of 
  that 
  surface 
  where 
  now 
  exposed 
  is 
  due 
  almost 
  entirely 
  

   to 
  erosion 
  since 
  the 
  stripping 
  away 
  of 
  the 
  sediments. 
  A 
  fairly 
  good 
  

   idea 
  of 
  the 
  present 
  general 
  slope 
  of 
  this 
  surface 
  may 
  be 
  obtained 
  

   by 
  comparing 
  altitudes 
  at 
  various 
  points. 
  

  

  