﻿GEOLOGIC 
  F0EMATI0N8 
  OF 
  NEW 
  YORK 
  145 
  

  

  In 
  the 
  northern 
  part 
  of 
  Lewis 
  county 
  the 
  Potsdam 
  sandstone, 
  

   in 
  a 
  few 
  small 
  exposures, 
  rests 
  unconformably 
  upon 
  the 
  Arch- 
  

   aean 
  terrane, 
  and 
  passes 
  above 
  into 
  the 
  Calciferous 
  formation. 
  

   It 
  extends 
  almost 
  continuously 
  through 
  Jefferson, 
  St 
  Lawrence, 
  

   Franklin 
  and 
  Clinton 
  counties, 
  and 
  appears 
  southward 
  in 
  the 
  

   Champlain 
  valley 
  in 
  irregular 
  outcrops. 
  

  

  The 
  Potsdam, 
  though 
  not 
  seen 
  distinctly 
  in 
  the 
  Mohawk 
  val- 
  

   ley 
  (where 
  its 
  place 
  between 
  the 
  Archaean 
  and 
  the 
  Calciferous 
  

   sand 
  rock 
  appears 
  to 
  be 
  vacant) 
  is 
  a 
  tiiick 
  mass 
  in 
  Pennsylvania, 
  

   and 
  is 
  known 
  northeastward 
  and 
  northwestward 
  over 
  a 
  great 
  

   area. 
  

  

  The 
  base 
  of 
  the 
  Potsdam 
  at 
  a 
  few 
  places 
  in 
  New 
  York 
  is 
  a 
  

   coarse 
  conglomerate 
  which 
  gradually 
  passes 
  upward 
  into 
  the 
  

   typical 
  sandstone. 
  

  

  Near 
  Whitehall, 
  Saratoga 
  and 
  Poughkeepsie, 
  the 
  Potsdam 
  

   horizon 
  is 
  represented 
  by 
  a 
  limestone 
  and 
  at 
  the 
  two 
  former 
  

   localities 
  it 
  passes 
  upward 
  into 
  the 
  Calciferous 
  formation 
  with- 
  

   out 
  marked 
  change 
  except 
  in 
  fauna. 
  

  

  The 
  characteristics 
  of 
  the 
  Cambrian 
  strata 
  lead 
  to 
  the 
  con- 
  

   clusion 
  that 
  the 
  sediments 
  were 
  accumulated 
  in 
  shallow 
  seas 
  

   near 
  the 
  shore 
  of 
  a 
  slowly 
  sinking 
  land. 
  As 
  the 
  water 
  slowly 
  

   encroached 
  upon 
  the 
  land 
  in 
  late 
  Middle 
  or 
  early 
  Upper 
  Cam- 
  

   brian 
  time, 
  deeper 
  water 
  gradually 
  covered 
  the 
  earlier 
  long- 
  

   shore 
  deposits, 
  and 
  finer 
  sediments 
  were 
  deposited 
  upon 
  them. 
  

   Toward 
  the 
  close 
  of 
  Cambrian 
  time 
  (Potsdam) 
  only 
  the 
  higher 
  

   parts 
  of 
  the 
  continent 
  were 
  above 
  the 
  sea. 
  At 
  this 
  time 
  the 
  

   Potsdam 
  sandstone 
  was 
  deposited 
  along 
  the 
  shores, 
  while 
  in 
  

   the 
  deeper 
  water 
  the 
  conditions 
  were 
  becoming 
  favorable 
  for 
  

   the 
  formation 
  of 
  the 
  great 
  beds 
  of 
  Silurian 
  limestone. 
  The 
  

   conglomerate 
  at 
  the 
  base 
  of 
  the 
  Potsdam, 
  grading 
  upwards 
  into 
  

   the 
  finer 
  sediments 
  of 
  the 
  sandstone, 
  indicates 
  the 
  deepening 
  of 
  

   the 
  water 
  along 
  the 
  shore 
  line 
  of 
  the 
  Cambrian 
  ocean. 
  

  

  At 
  their 
  greatest 
  development 
  in 
  Washington 
  county, 
  the 
  

   Cambrian 
  formations 
  have 
  a 
  total 
  thickness 
  of 
  10,000 
  or 
  12,000 
  

   feet. 
  

  

  