﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  63 
  

  

  the 
  Grenville 
  limestone 
  were 
  filled 
  with 
  this 
  type 
  of 
  sandstone^ 
  and 
  

   it 
  occurs 
  frequently 
  as 
  pebbles 
  in 
  the 
  otherwise 
  basal 
  conglomer- 
  

   ates, 
  being 
  the 
  only 
  sort 
  of 
  sandstone 
  occurring 
  as 
  pebbles 
  in 
  such 
  

   situation. 
  The 
  thorough 
  induration 
  seems 
  certainly 
  to 
  have 
  taken 
  

   place 
  before 
  the 
  pebbles 
  were 
  formed. 
  There 
  seems 
  no 
  way 
  to 
  ac- 
  

   count 
  for 
  these 
  conditions 
  except 
  to 
  assume 
  that 
  there 
  was 
  an 
  

   earlier 
  deposit 
  of 
  sand 
  in 
  the 
  district, 
  likely 
  in 
  no 
  great 
  amount, 
  

   and 
  chiefly 
  in 
  the 
  Grenville 
  hollows, 
  deposition 
  ceased, 
  thorough 
  

   cementation 
  followed 
  and 
  then 
  erosion; 
  in 
  other 
  words 
  that 
  there 
  

   was 
  a 
  slight 
  amount 
  of 
  deposition 
  here 
  in 
  earlier 
  Potsdam 
  time, 
  

   separated 
  by 
  an 
  erosion 
  unconformity 
  from 
  the 
  bulk 
  of 
  the 
  forma- 
  

   tion. 
  

  

  Occasional 
  beds 
  of 
  black, 
  and 
  of 
  mottled 
  black 
  and 
  white 
  sand- 
  

   stone 
  appear 
  in 
  the 
  upper 
  part 
  of 
  the 
  formation. 
  The 
  coloring 
  

   matter 
  is 
  entirely 
  in 
  the 
  cement, 
  which 
  is 
  silicious, 
  and 
  is 
  wholly 
  

   discharged 
  at 
  a 
  low 
  red 
  heat, 
  hence 
  likely 
  organic. 
  

  

  In 
  the 
  uppermost 
  lo 
  to 
  15 
  feet 
  of 
  the 
  formation 
  calcareous 
  ce- 
  

   ment 
  reappears, 
  foreshadowing 
  the 
  change 
  which 
  gave 
  rise 
  to 
  the 
  

   overlying 
  dolomite 
  formation. 
  In 
  consequence 
  of 
  this 
  the 
  rock 
  

   weathers 
  easily 
  to 
  a 
  weakly 
  holding, 
  brownish 
  sand, 
  usually 
  mottled 
  

   with 
  spots 
  of 
  deeper 
  brown. 
  This 
  portion 
  is 
  mostly 
  thin 
  bedded 
  but 
  

   terminates 
  above 
  in 
  a 
  very 
  massive 
  layer, 
  2 
  feet 
  thick 
  or 
  more, 
  which 
  

   is 
  comparatively 
  resistant 
  owing 
  to 
  its 
  massiveness 
  ; 
  and 
  this 
  heavy, 
  

   brown 
  mottled 
  layer 
  often 
  full 
  of 
  small, 
  rounded 
  sand 
  concretions, 
  

   makes 
  a 
  convenient 
  summit 
  for 
  the 
  formation, 
  owing 
  to 
  its 
  rela- 
  

   tive 
  prominence. 
  The 
  first 
  layer 
  of 
  gray 
  dolomite 
  usuially 
  comes 
  in 
  

   directly 
  above, 
  and 
  if 
  not, 
  no 
  more 
  than 
  a 
  foot 
  or 
  two 
  of 
  sand- 
  

   stone 
  intervenes. 
  The 
  two 
  formations 
  grade 
  into 
  one 
  another, 
  so 
  

   that 
  any 
  line 
  of 
  subdivision 
  must 
  be 
  an 
  arbitrary 
  one. 
  We 
  have 
  

   drawn 
  it 
  at 
  the 
  base 
  of 
  the 
  first 
  dolomite 
  layer 
  to 
  appear, 
  and 
  this 
  

   closely 
  corresponds 
  with 
  the 
  summit 
  of 
  this 
  thick 
  sandstone. 
  There 
  

   is, 
  however, 
  some 
  reason 
  for 
  the 
  belief 
  that 
  the 
  base 
  of 
  the 
  upper, 
  

   calcareous 
  sandstones 
  should 
  be 
  made 
  the 
  division 
  line. 
  

  

  With 
  the 
  exception 
  of 
  the 
  long 
  trails 
  of 
  an 
  unknown 
  animal, 
  to 
  

   which 
  the 
  name 
  of 
  Climactichnites 
  has 
  been 
  given, 
  some 
  of 
  which 
  

   have 
  been 
  found 
  in 
  the 
  sandstone 
  i 
  mile 
  west 
  of 
  Theresa, 
  no 
  fossils 
  

   have 
  been 
  found 
  in 
  the 
  formation 
  in 
  this 
  district 
  except 
  in 
  these 
  

   upper, 
  calcareous 
  beds.^ 
  In 
  these 
  a 
  large 
  linguloid 
  shell 
  (iden- 
  

   tified 
  by 
  Ulrich 
  asLingulepis 
  acuminata) 
  is 
  quite 
  com- 
  

   mon, 
  and 
  passes 
  up 
  into 
  the 
  lower 
  beds 
  of 
  the 
  Theresa 
  formation. 
  

  

  iWoodworth, 
  J. 
  B. 
  N. 
  Y. 
  State 
  Pal. 
  Rep't 
  1902. 
  p. 
  959-66. 
  

  

  