﻿S8 
  

  

  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  of 
  the 
  sandstone 
  base 
  is 
  exposed, 
  owing 
  to 
  solution 
  of 
  the 
  limestone 
  

   beneath. 
  A 
  sketch 
  of 
  the 
  relations 
  here 
  is 
  given 
  in 
  figure 
  i, 
  the 
  

  

  Fxg. 
  I 
  Potsdam 
  contact 
  on 
  Grenville 
  limestone, 
  just 
  

   north 
  of 
  lower 
  bridge 
  at 
  Theresa, 
  showing 
  the 
  sloping 
  

   Grenville 
  hillside 
  on 
  which 
  deposition 
  took 
  place, 
  and 
  

   the 
  sand-filled 
  cracks 
  in 
  the 
  limestone. 
  

  

  arrow 
  showing 
  the 
  camera 
  position 
  for 
  plate 
  ii. 
  It 
  is 
  at 
  this 
  locality 
  

   that 
  the 
  best 
  examples 
  of 
  sand 
  extending 
  dov/n 
  into 
  widened 
  joint 
  

   cracks 
  in 
  the 
  Grenville 
  limestone 
  were 
  seen. 
  At 
  the 
  east 
  end 
  of 
  the 
  

   outlier 
  tlie 
  limestone 
  is 
  cut 
  out 
  by 
  granite 
  gneiss, 
  whose 
  summ.it 
  is 
  20 
  

   feet 
  above 
  the 
  top 
  of 
  the 
  sandstone, 
  hence 
  teniiinating 
  the 
  outlier 
  in 
  

   that 
  direction. 
  Of 
  course 
  the 
  full 
  original 
  thickness 
  of 
  the 
  sand- 
  

   stone 
  is 
  not 
  present 
  in 
  the 
  outlier, 
  but 
  only 
  the 
  mere 
  basal 
  portion, 
  

   and 
  formerly 
  the 
  sandstone 
  extended 
  over 
  the 
  granite 
  as 
  well. 
  

  

  Another 
  interesting 
  contact 
  occurs 
  along 
  the 
  Potsdam 
  front, 
  23^ 
  

   miles 
  northeast 
  of 
  Theresa. 
  From 
  a 
  previous 
  northeasterly 
  trend 
  

   the 
  front 
  here 
  turns 
  and 
  for 
  a 
  mile 
  and 
  more 
  runs 
  northwest 
  across 
  

   the 
  strike, 
  crossing 
  a 
  prominent 
  granite 
  ridge 
  and 
  then 
  dropping 
  70 
  

   feet 
  in 
  level 
  into 
  a 
  limestone 
  valley. 
  Near 
  the 
  turn 
  the 
  contact 
  

   sketched 
  in 
  figure 
  2 
  is 
  shown. 
  A 
  low 
  knob 
  of 
  ferruginous, 
  quartz 
  

   schist 
  projects 
  upward 
  into 
  the 
  Potsdam 
  to 
  the 
  amount 
  of 
  20 
  feet. 
  

  

  

  Fig. 
  2 
  Potsdam 
  contact 
  on 
  Grenville 
  quartz 
  schist, 
  

   2^ 
  miles 
  northeast 
  of 
  Theresa. 
  The 
  much 
  contorted 
  

   and 
  steeply 
  dipping 
  schists 
  constitute 
  a 
  ridge 
  over 
  20 
  

   feet 
  high 
  around 
  which 
  the 
  Potsdam 
  was 
  deposited. 
  

  

  The 
  Potsdam 
  here 
  is 
  more 
  evenly 
  bedded 
  than 
  in 
  the 
  cases 
  described 
  

   at 
  Theresa, 
  the 
  bedding 
  abutting 
  squarely 
  against 
  the 
  sides 
  of 
  the 
  

   knob. 
  Its 
  small 
  size 
  as 
  compared 
  with 
  the 
  long 
  ridge 
  slopes 
  of 
  the 
  

   other 
  contacts 
  is 
  thought 
  to 
  be 
  the 
  chief 
  reason 
  for 
  this 
  difference. 
  

  

  