﻿GEOLOGY 
  OF 
  THE 
  PORT 
  LEYDEN 
  QUADRANGLE 
  39 
  

  

  feet 
  of 
  mostly 
  sandstone. 
  Orton 
  refers 
  all 
  of 
  these 
  sandstones 
  to 
  

   the 
  Potsdam. 
  The 
  bottom 
  of 
  the 
  section 
  at 
  Stillwater 
  is 
  : 
  

  

  Feet 
  

  

  Dark 
  Trenton 
  370 
  

  

  Sand 
  and 
  shales 
  40 
  

  

  Sand, 
  green 
  and 
  white 
  25 
  

  

  Black 
  limestone 
  6 
  

  

  Red 
  and 
  white 
  sandstone, 
  calcareous 
  18 
  

  

  Precambric 
  struck 
  at 
  1697 
  

  

  Fossils 
  in 
  the 
  black 
  limestone 
  layer 
  prove 
  the 
  Upper 
  Cambric 
  

   (Potsdam) 
  age 
  of 
  the 
  deposit. 
  The 
  presence 
  of 
  this 
  Potsdam 
  in 
  

   Oswego 
  county 
  and 
  its 
  absence 
  along 
  the 
  Paleozoic-Precambric 
  

   boundary 
  to 
  the 
  eastward 
  on 
  the 
  Port 
  Leyden 
  sheet, 
  affords 
  con- 
  

   clusive 
  evidence 
  of 
  overlap. 
  

  

  Again, 
  we 
  have 
  a 
  strong 
  argument 
  in 
  favor 
  of 
  overlap 
  if 
  we 
  con- 
  

   sider 
  the 
  whole 
  thickness 
  of 
  sediments 
  between 
  the 
  top 
  of 
  the 
  Tren- 
  

   ton 
  and 
  the 
  Precambric. 
  Details 
  will 
  be 
  presented 
  later, 
  but 
  suffice 
  

   it 
  to 
  say 
  now 
  that 
  a 
  comparison 
  of 
  the 
  thickness 
  of 
  these 
  sediments 
  

   in 
  Oswego 
  county 
  with 
  those 
  near 
  Port 
  Leyden 
  shows 
  a 
  thinning 
  

   of 
  several 
  hundred 
  feet 
  in 
  passing 
  toward 
  the 
  latter 
  place. 
  Such 
  a 
  

   marked 
  diminution 
  in 
  thickness 
  toward 
  the 
  northeast 
  and 
  east 
  is 
  

   just 
  what 
  would 
  be 
  expected 
  in 
  the 
  case 
  of 
  overlap. 
  

  

  SURFACE 
  OF 
  THE 
  PRECAMBRIC 
  ROCKS 
  

   Smoothness 
  of 
  the 
  surface 
  which 
  received 
  Paleozoic 
  deposition 
  

  

  A 
  study 
  of 
  the 
  Paleozoic-Precambric 
  line 
  of 
  contact 
  gives 
  strong 
  

   evidence 
  in 
  favor 
  of 
  the 
  statement 
  that 
  the 
  sinking 
  surface 
  which 
  

   received 
  Paleozoic 
  sedimentation 
  must 
  have 
  been 
  w^orn 
  down 
  to 
  a 
  

   remarkably 
  smooth 
  condition 
  (peneplain). 
  Except 
  for 
  a 
  few 
  miles 
  

   near 
  the 
  southern 
  edge 
  of 
  the 
  map, 
  the 
  Paleozoic-Precambric 
  

   boundary 
  line 
  can 
  be 
  drawn 
  with 
  a 
  considerable 
  degree 
  of 
  accuracy. 
  

   A 
  glance 
  at 
  the 
  geologic 
  map 
  will 
  show 
  that 
  this 
  boundary 
  line 
  is 
  

   a 
  very 
  regular 
  one 
  which 
  at 
  no 
  point 
  shows 
  any 
  rapid 
  elevation 
  or 
  

   depression. 
  Such 
  a 
  regular 
  line 
  of 
  contact 
  is 
  precisely 
  what 
  one 
  

   would 
  expect 
  where 
  sediments 
  have 
  been 
  laid 
  down 
  upon 
  a 
  smooth 
  

   floor 
  and 
  then, 
  after 
  elevation, 
  have 
  been 
  stripped 
  off 
  rather 
  regu- 
  

   larly 
  by 
  erosion. 
  Even 
  a 
  comparatively 
  small 
  elevation 
  or 
  depres- 
  

   sion 
  along 
  the 
  contact 
  line 
  could 
  be 
  recognized. 
  At 
  several 
  points 
  

   where 
  the 
  actual 
  contact 
  is 
  exposed, 
  the 
  Precambric 
  floor 
  appears 
  

   to 
  be 
  smooth. 
  

  

  