﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  6l 
  

  

  with 
  thinner 
  bedded 
  upper 
  portions 
  ; 
  where 
  deposited 
  on 
  sloping 
  

   surfaces 
  the 
  lower 
  portion 
  is 
  often 
  very 
  massive, 
  and 
  quite 
  ir- 
  

   regularly 
  bedded 
  with 
  a 
  rude 
  tendency 
  to 
  conform 
  to 
  the 
  surface 
  

   of 
  deposit 
  [pi. 
  II, 
  12]. 
  Cross-bedding 
  is 
  present 
  somewhat 
  but 
  

   in 
  by 
  no 
  means 
  prominent 
  development. 
  Ripple 
  marks, 
  however, 
  

   abound. 
  Much 
  of 
  the 
  silicious 
  cement 
  has 
  been 
  deposited 
  as 
  

   secondary 
  enlargement 
  of 
  the 
  original 
  quartz 
  grains, 
  the 
  slides 
  fur- 
  

   nishing 
  some 
  beautiful 
  examples 
  of 
  this. 
  

  

  Occasional 
  long, 
  cylindrical 
  concretions 
  (?) 
  of 
  a 
  telegraph 
  pole 
  

   type 
  appear 
  in 
  the 
  sandstone, 
  and 
  are 
  called 
  " 
  tree 
  trunks 
  " 
  by 
  the 
  

   populace. 
  As 
  seen 
  in 
  cross 
  section 
  on 
  rock 
  surfaces 
  they 
  appear 
  

   as 
  circular 
  portions 
  of 
  the 
  rock, 
  from 
  i 
  to 
  3 
  feet 
  in 
  diameter. 
  On 
  

   cliff 
  sides 
  they 
  are 
  long, 
  vertical 
  cylinders 
  of 
  sandstone. 
  There 
  

   is 
  no 
  perceptible 
  difference 
  in 
  composition 
  between 
  them 
  and 
  the 
  

   adjacent 
  rock, 
  but 
  in 
  every 
  case 
  the 
  two 
  are 
  sharply 
  separated 
  by 
  

   v/hat 
  may 
  be 
  for 
  convenience 
  styled 
  a 
  circular 
  joint. 
  No 
  tendency 
  

   to 
  taper 
  at 
  the 
  ends 
  was 
  noted, 
  but 
  the 
  actual 
  terminations 
  were 
  

   in 
  no 
  case 
  seen. 
  They 
  certainly 
  reach 
  a 
  length 
  of 
  20 
  feet 
  and 
  may 
  

   be 
  considerably 
  longer. 
  Unless 
  they 
  represent 
  a 
  type 
  of 
  concre- 
  

   tionary 
  structure, 
  we 
  are 
  wholly 
  at 
  a 
  loss 
  to 
  account 
  for 
  them. 
  

   If 
  so 
  they 
  certainly 
  are 
  an 
  unusual 
  type 
  both 
  because 
  of 
  size 
  and 
  

   shape, 
  and 
  because 
  of 
  having 
  the 
  same 
  composition 
  as 
  the 
  inclos- 
  

   ing 
  rock. 
  In 
  plate 
  13 
  is 
  shown 
  an 
  excellent 
  example 
  of 
  one 
  of 
  

   them, 
  in 
  the 
  Potsdam 
  sandstone 
  at 
  Rideau, 
  Ont., 
  seen 
  by 
  us 
  in 
  

   1908 
  under 
  Dr 
  Ami's 
  guidance. 
  This 
  has 
  been 
  already 
  described 
  

   by 
  the 
  Canadian 
  geologists, 
  and 
  is 
  here 
  introduced 
  because, 
  while 
  

   corresponding 
  precisely 
  to 
  the 
  New 
  York 
  examples, 
  it 
  furnishes 
  a 
  

   much 
  better 
  illustration 
  than 
  any 
  there 
  seen.^ 
  

  

  Only 
  at 
  the 
  base 
  and 
  the 
  summit 
  does 
  the 
  sandstone 
  vary 
  from 
  

   these 
  general 
  characters. 
  Basal 
  conglomerates 
  are 
  present 
  in 
  but 
  

   scant 
  amount, 
  with 
  small 
  thickness 
  and 
  patchy 
  distribution. 
  The 
  

   majority 
  of 
  contacts 
  show 
  only 
  a 
  few, 
  scattered 
  quartz 
  or 
  quartzite 
  

   pebbles 
  in 
  the 
  basal 
  layer 
  of 
  the 
  sandstone. 
  There 
  are, 
  however, 
  

   frequent 
  patches 
  of 
  coarse, 
  basal 
  conglomerates, 
  especially 
  on 
  the 
  

   Theresa 
  quadrangle. 
  They 
  seem 
  in 
  all 
  cases 
  to 
  occupy 
  local 
  hol- 
  

   lows 
  in 
  the 
  limestone 
  valley 
  floors, 
  and 
  to 
  occur 
  only 
  where 
  the 
  

   limestone 
  contained 
  thin 
  quartzite 
  bands, 
  or 
  granite 
  dikes. 
  The 
  

   pebbles 
  are 
  all 
  sizes 
  up 
  to 
  that 
  of 
  the 
  fist, 
  and 
  show 
  little 
  or 
  no 
  

   rounding 
  in 
  most 
  cases, 
  being 
  usually 
  very 
  angular. 
  They 
  con- 
  

   si.st 
  chiefly 
  of 
  quartzite 
  and 
  of 
  white 
  granite, 
  though 
  in 
  some 
  cases 
  

   pebbles 
  of 
  red, 
  quartzose 
  sandstone 
  also 
  occur. 
  The 
  cement 
  is 
  

  

  ^ 
  Ells, 
  R. 
  W. 
  Roy. 
  Soc. 
  Can. 
  Trans., 
  ser. 
  2, 
  v. 
  9, 
  § 
  4, 
  p. 
  103. 
  

  

  