﻿REPORT 
  OF 
  THE 
  DIRECTOR 
  igi2 
  85 
  

  

  through 
  the 
  village 
  of 
  St 
  Johnsville 
  in 
  the 
  Mohawk 
  valley. 
  Thus 
  

   we 
  are 
  certain 
  that 
  the 
  shallow 
  Potsdam 
  sea 
  overspread 
  prac- 
  

   tically 
  the 
  whole 
  southern 
  Adirondack 
  region 
  east 
  of 
  this 
  line 
  ex- 
  

   cept 
  for 
  a 
  few 
  local 
  knobs 
  or 
  ridges 
  of 
  hard 
  Precambric 
  rock 
  

   which 
  remained 
  above 
  the 
  sea 
  level. 
  A 
  fine 
  example 
  of 
  such 
  a 
  

   local 
  projection 
  above 
  the 
  Potsdam 
  sea 
  level 
  has 
  been 
  described 
  

   by 
  the 
  writer 
  10 
  in 
  his 
  report 
  on 
  the 
  Broadalbin 
  quadrangle. 
  That 
  

   the 
  Potsdam 
  shore 
  line 
  extended 
  a 
  short 
  but 
  unknown 
  distance 
  

   farther 
  west 
  than 
  Wells 
  and 
  North 
  River 
  is 
  certain 
  because 
  a 
  

   considerable 
  thickness 
  of 
  sandstone 
  is 
  still 
  represented 
  at 
  those 
  

   places. 
  This 
  conclusion 
  regarding 
  the 
  position 
  of 
  the 
  Potsdam 
  

   shore 
  line 
  is 
  in 
  harmony 
  with 
  the 
  statement 
  of 
  Ulrich 
  and 
  

   Cushing 
  ltJ 
  when 
  they 
  say 
  : 
  " 
  It 
  is 
  thought 
  that 
  along 
  the 
  Mo- 
  

   hawk 
  line 
  the 
  Potsdam 
  shore 
  had 
  a 
  southwesterly 
  trend 
  more 
  

   to 
  the 
  south 
  than 
  the 
  present 
  Precambric 
  margin, 
  the 
  two 
  

   meeting 
  at 
  an 
  angle 
  ; 
  east 
  of 
  the 
  meeting 
  point 
  the 
  Potsdam 
  ap- 
  

   pears 
  under 
  the 
  Little 
  Falls, 
  while 
  west 
  of 
  it 
  the 
  Potsdam 
  is 
  

   either 
  absent 
  or 
  erosion 
  has 
  not 
  yet 
  cut 
  down 
  to 
  it." 
  

  

  That 
  the 
  southwestern 
  Adirondacks 
  were 
  not 
  submerged 
  un- 
  

   der 
  the 
  Potsdam 
  sea 
  is 
  proved 
  by 
  the 
  complete 
  absence 
  of 
  the 
  

   sandstone 
  from 
  the 
  southwestern 
  border 
  ; 
  the 
  very 
  character 
  of 
  

   the 
  sediments 
  (sands 
  and 
  pebbles) 
  which 
  demands 
  nearness 
  to 
  a 
  

   mass 
  of 
  Precambric 
  rock 
  ; 
  and 
  the 
  negative 
  evidence 
  from 
  the 
  

   fact 
  that 
  no 
  outliers 
  of 
  Potsdam 
  have 
  ever 
  been 
  found 
  in 
  this 
  re- 
  

   gion. 
  The 
  Potsdam 
  sea 
  did 
  extend 
  up 
  the 
  St 
  Lawrence 
  valley 
  as 
  

   shown 
  by 
  the 
  presence 
  of 
  the 
  sandstone 
  there. 
  

  

  Thus 
  we 
  conclude 
  that 
  a 
  long, 
  low, 
  land 
  area 
  of 
  Precambric 
  

   rock 
  extended 
  in 
  a 
  northeast-southwest 
  direction 
  through 
  the 
  

   Adirondack 
  region, 
  and 
  that 
  this 
  height 
  of 
  land 
  in 
  Potsdam 
  time 
  

   had 
  almost 
  exactly 
  the 
  same 
  position 
  as 
  the 
  present 
  main 
  axis 
  of 
  

   elevation 
  of 
  the 
  mountains. 
  

  

  Since 
  the 
  Potsdam 
  sandstone 
  grades 
  into 
  the 
  succeeding, 
  alter- 
  

   nating 
  sandstone 
  and 
  dolomite 
  beds 
  of 
  the 
  Theresa 
  and 
  the 
  two 
  

   formations 
  have 
  almost 
  precisely 
  the 
  same 
  distribution, 
  we 
  are 
  

   safe 
  in 
  asserting 
  that 
  the 
  physical 
  geography 
  conditions 
  of 
  The- 
  

   resa 
  time 
  were 
  essentially 
  like 
  those 
  of 
  Potsdam 
  time 
  except 
  that 
  

   the 
  southeastern 
  Adirondacks 
  were 
  then 
  even 
  a 
  little 
  more 
  sub- 
  

   merged. 
  

  

  The 
  distribution 
  of 
  the 
  Little 
  Falls 
  dolomite 
  which 
  succeeds 
  

   the 
  Theresa 
  beds 
  without 
  unconformity 
  along 
  the 
  southern 
  and 
  

  

  10 
  Pages 
  51-52. 
  

   1<5 
  Page 
  139. 
  

  

  