﻿86 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  southeastern 
  border 
  of 
  the 
  Adirondacks 
  and 
  in 
  the 
  outliers 
  at 
  

   Schroon 
  Lake 
  and 
  Wells 
  shows 
  that 
  the 
  Little 
  Falls 
  sea 
  extended 
  

   over 
  at 
  least 
  as 
  much 
  of 
  the 
  southern 
  Adirondacks 
  as 
  did 
  the 
  

   Potsdam-Theresa 
  seas. 
  In 
  the 
  Mohawk 
  valley 
  region 
  it 
  ex- 
  

   tended 
  considerably 
  farther 
  westward 
  overlapping 
  upon 
  the 
  Pre- 
  

   cambric 
  rock 
  to 
  the 
  southwest 
  corner 
  of 
  the 
  Wilmurt 
  quadrangle 
  

   where 
  the 
  dolomite 
  thins 
  out 
  to 
  disappearance. 
  From 
  this 
  point 
  

   northwestward 
  the 
  Precambric 
  rock 
  margin 
  shows 
  no 
  dolomite, 
  

   thus 
  proving 
  the 
  absence 
  of 
  the 
  Little 
  Falls 
  sea 
  there. 
  The 
  very 
  

   rapid 
  decrease 
  in 
  thickness 
  of 
  the 
  dolomite 
  from 
  four 
  hundred 
  

   feet 
  at 
  Little 
  Falls 
  to. 
  complete 
  disappearance 
  just 
  beyond 
  the 
  

   northern 
  boundary 
  of 
  the 
  Little 
  Falls 
  quadrangle 
  also 
  shows 
  the 
  

   limit 
  of 
  the 
  sea 
  in 
  that 
  district. 
  Accordingly 
  there 
  must 
  have 
  

   been 
  a 
  large 
  land 
  mass 
  in 
  the 
  southwestern 
  Adirondack 
  region. 
  

   The 
  very 
  presence 
  of 
  so 
  many 
  sand 
  grains 
  in 
  the 
  dolomite 
  (giv- 
  

   ing 
  rise 
  to 
  the 
  old 
  name 
  Calciferous 
  sandrock) 
  requires 
  that 
  it 
  

   was 
  deposited 
  comparatively 
  near 
  a 
  land 
  mass. 
  Thus 
  during 
  

   late 
  Little 
  Falls 
  time 
  the 
  eastern 
  portion 
  of 
  the 
  southern 
  Adiron- 
  

   dacks 
  was 
  submerged 
  while 
  the 
  western 
  portion 
  remained 
  dry 
  

   land, 
  the 
  shore 
  line 
  extending 
  from 
  the 
  southwest 
  corner 
  of 
  the 
  

   Wilmurt 
  quadrangle 
  most 
  probably 
  in 
  a 
  northeasterly 
  direction 
  

   through 
  the 
  southern 
  Adirondacks. 
  That 
  its 
  shore 
  line 
  was, 
  in 
  

   general, 
  a 
  little 
  farther 
  westward 
  than 
  that 
  of 
  the 
  Potsdam 
  sea 
  is 
  

   strongly 
  suggested 
  by 
  the 
  fact 
  that 
  all 
  the 
  Cambric 
  sediments 
  

   were 
  gradually 
  accumulated 
  in 
  a 
  downsinking 
  trough 
  occupying- 
  

   the 
  southeastern 
  Adirondack 
  area. 
  This 
  idea 
  of 
  a 
  gradual 
  west- 
  

   erly 
  encroachment 
  of 
  the 
  Cambric 
  sea 
  is 
  borne 
  out 
  by 
  the 
  follow- 
  

   ing 
  facts 
  : 
  The 
  thickness 
  of 
  the 
  Cambric 
  section 
  within 
  the 
  Sara- 
  

   toga 
  quadrangle 
  is 
  from 
  four 
  hundred 
  to 
  five 
  hundred 
  feet 
  ; 
  

   within 
  the 
  Broadalbin 
  quadrangle 
  near 
  Northville 
  four 
  hundred 
  

   to 
  four 
  hundred 
  and 
  lifty 
  feet 
  ; 
  and 
  at 
  Wells 
  about 
  two 
  hundred 
  

   feet. 
  This 
  rapid 
  decrease 
  in 
  thickness 
  of 
  two 
  hundred 
  feet 
  from 
  

   Northville 
  to 
  Wells 
  within 
  a 
  distance 
  of 
  fourteen 
  miles 
  shows 
  a 
  

   westward 
  to 
  northwestward 
  encroachment 
  of 
  the 
  Cambric 
  sea 
  

   and 
  that 
  the 
  downward 
  slope 
  of 
  the 
  surface 
  here 
  receiving 
  Cam- 
  

   bric 
  sediments 
  was 
  fourteen 
  feet 
  a 
  mile 
  toward 
  the 
  southeast. 
  

   According 
  to 
  Ulrich 
  and 
  Cushing 
  1 
  ' 
  6 
  there 
  is 
  a 
  distinct 
  strati- 
  

   graphic 
  break 
  represented 
  by 
  a 
  notable 
  erosion 
  unconformity 
  at 
  

   the 
  top 
  of 
  the 
  Little 
  Falls 
  dolomite. 
  Thus 
  all 
  available 
  evidence 
  

   supports 
  the 
  idea 
  that, 
  by 
  the 
  close 
  of 
  the 
  Cambric 
  period, 
  subsidence 
  

  

  16 
  Page 
  129. 
  

  

  