﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  57 
  

  

  Space 
  intervenes. 
  This 
  is 
  due 
  in 
  part 
  to 
  the 
  many 
  miles 
  of 
  Postdam 
  

   boundary 
  in 
  the 
  region 
  and 
  in 
  part 
  to 
  the 
  scanty 
  glacial 
  deposit 
  and 
  

   hence 
  abundant 
  rock 
  exposures. 
  ^lany 
  of 
  the 
  exposed 
  contacts 
  

   are 
  on 
  slopes, 
  and 
  on 
  limestone, 
  and 
  it 
  is 
  these 
  that 
  are 
  most 
  unusual 
  

   and 
  interesting. 
  

  

  Plate 
  8 
  shows 
  Mr 
  Eaton's 
  photographs 
  of 
  a 
  contact 
  on 
  quartz 
  

   schists, 
  I 
  mile 
  southeast 
  of 
  Redwood 
  on 
  the 
  Rossie 
  road, 
  a 
  contact 
  

   already 
  described 
  and 
  figured 
  by 
  Smyth. 
  The 
  contact 
  here 
  is 
  on 
  the 
  

   summit 
  of 
  a 
  ridge 
  of 
  quartzite, 
  hence 
  is 
  fairly 
  horizontal 
  where 
  

   photographed, 
  though 
  the 
  level 
  drops 
  away 
  on 
  each 
  side 
  at 
  no 
  great 
  

   distance. 
  

  

  Two 
  fine 
  examples 
  of 
  contacts 
  on 
  slopes 
  occur 
  within 
  the 
  limits 
  

   of 
  the 
  village 
  of 
  Theresa, 
  along 
  with 
  others 
  almost 
  as 
  good. 
  One 
  of 
  

   these 
  is 
  by 
  the 
  roadside 
  a 
  short 
  distance 
  west 
  of 
  the 
  upper 
  bridge. 
  

   A 
  high 
  Potsdam 
  clift 
  borders 
  the 
  roadway 
  for 
  a 
  few 
  rods, 
  with 
  the 
  

   base 
  of 
  the 
  formation 
  well 
  below 
  the 
  road 
  level. 
  At 
  the 
  west 
  end 
  

   the 
  base 
  comes 
  up 
  to 
  the 
  road 
  level, 
  the 
  clifif 
  sets 
  back 
  some 
  20 
  feet, 
  

   and 
  the 
  base 
  rises 
  sharply 
  to 
  from 
  12 
  to 
  15 
  feet 
  above 
  the 
  roadway, 
  

   exposing 
  impure 
  Grenville 
  limestone 
  underneath. 
  The 
  recess 
  faces 
  

   north, 
  and 
  is 
  beset 
  with 
  shade 
  of 
  trees 
  so 
  that 
  satisfactory 
  pho- 
  

   tography 
  is 
  difficult, 
  the 
  view 
  shown 
  in 
  plates 
  9, 
  10 
  being 
  unsatisfac- 
  

   tory. 
  The 
  surface 
  of 
  deposit 
  has 
  an 
  angle 
  of 
  slope 
  of 
  45° 
  or 
  more, 
  

   and 
  the 
  soluble 
  limestone 
  has 
  been 
  somewhat 
  eaten 
  away 
  from 
  

   beneath 
  the 
  sandstone, 
  so 
  that 
  several 
  square 
  yards 
  of 
  the 
  actual 
  

   basal 
  surface 
  are 
  exposed. 
  This 
  is 
  set 
  with 
  occasional 
  quartz 
  peb- 
  

   bles, 
  but 
  these 
  are 
  sparse, 
  and 
  except 
  for 
  them 
  the 
  rock 
  is 
  quite 
  like 
  

   that 
  above. 
  The 
  sandstone 
  is 
  very 
  massive 
  and 
  irregularly 
  bedded, 
  

   with 
  a 
  semblance 
  of 
  parallelism 
  to 
  the 
  floor 
  of 
  deposit 
  as 
  is 
  usual 
  

   with 
  the 
  basal 
  Potsdam 
  hereabout. 
  

  

  The 
  other 
  contact 
  mentioned 
  is 
  exposed 
  on 
  the 
  north 
  side 
  of 
  the 
  

   river 
  just 
  above 
  the 
  lower 
  bridge. 
  The 
  map 
  shows 
  a 
  small 
  Potsdam 
  

   outlier 
  there, 
  whose 
  narrow, 
  southwest 
  edge 
  appears 
  as 
  a 
  low 
  cliff 
  by 
  

   the 
  roadside 
  [pi. 
  11]. 
  The 
  ground 
  level 
  falls 
  toward 
  the 
  river 
  and 
  

   at 
  the 
  south 
  end 
  of 
  the 
  clifif 
  the 
  base 
  of 
  the 
  sandstone 
  is 
  exposed, 
  

   resting 
  on 
  Grenville 
  limestone 
  underneath. 
  Plate 
  10 
  is 
  a 
  photo- 
  

   graph 
  of 
  this 
  contact. 
  At 
  the 
  south 
  the 
  clifif 
  bears 
  sharply 
  away 
  

   from 
  the 
  road 
  and 
  by 
  turning 
  into 
  the 
  yard 
  of 
  the 
  first 
  house 
  to 
  the 
  

   south 
  a 
  fine 
  exposure 
  of 
  the 
  south 
  margin 
  of 
  the 
  outlier 
  is 
  obtained, 
  

   showing 
  the 
  Grenville 
  limestone 
  rapidly 
  rising 
  in 
  altitude 
  and 
  car- 
  

   rying 
  up 
  the 
  Potsdam 
  base 
  with 
  it. 
  The 
  limestone 
  surface 
  falls 
  not 
  

   only 
  to 
  the 
  west 
  but 
  also 
  to 
  the 
  north. 
  As 
  in 
  the 
  previous 
  case 
  a 
  part 
  

  

  