﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  3 
  1 
  

  

  mind 
  it 
  has 
  seemed 
  to 
  the 
  writer 
  as 
  though 
  the 
  weight 
  of 
  the 
  evi- 
  

   dence 
  were 
  in 
  favor 
  of 
  the 
  view 
  that 
  at 
  least 
  some 
  of 
  the 
  gray 
  and 
  

   bkie 
  limestone 
  was 
  representative 
  of 
  the 
  white 
  in 
  less 
  metamor- 
  

   phosed 
  condition, 
  and 
  if 
  some, 
  then 
  likely 
  all. 
  

  

  Nowhere 
  else 
  in 
  northern 
  New 
  York 
  has 
  the 
  writer 
  met 
  with 
  

   Grenville 
  limestone 
  of 
  this 
  fine 
  grained, 
  darker 
  colored 
  type. 
  A 
  

   comparison 
  is 
  at 
  once 
  suggested 
  with 
  the 
  district 
  in 
  Ontario 
  re- 
  

   cently 
  described 
  by 
  Adams 
  who 
  has 
  shown 
  that 
  a 
  similar, 
  though 
  

   better 
  marked 
  change 
  comes 
  over 
  the 
  Canadian 
  Grenville 
  limestone 
  

   when 
  followed 
  westward, 
  a 
  local 
  development 
  of 
  bluish 
  limestone 
  

   in 
  thin 
  bands 
  within 
  the 
  coarser 
  white 
  limestones.^ 
  The 
  evidence 
  

   seems 
  to 
  indicate 
  that 
  we 
  have 
  here 
  in 
  New 
  York 
  the 
  first 
  glimpses 
  

   of 
  a 
  similar 
  tendency. 
  

  

  The 
  consideration 
  of 
  the 
  contact 
  effects 
  which 
  the 
  various 
  igneous 
  

   rocks 
  have 
  had 
  upon 
  the 
  limestones 
  is 
  deferred 
  until 
  the 
  igneous 
  

   rocks 
  themselves 
  have 
  been 
  described. 
  

  

  Quartzites. 
  There 
  are 
  two 
  belts 
  of 
  ponderous 
  quartzites 
  in 
  the 
  

   region, 
  one 
  on 
  Wellesley 
  and 
  Grindstone 
  islands, 
  and 
  the 
  other 
  in 
  

   the 
  district 
  east 
  of 
  Redwood 
  (Alexandria 
  sheet). 
  In 
  both 
  cases 
  

   the 
  quartzite 
  is 
  interbanded 
  with 
  various 
  schists 
  and 
  amphibolites, 
  

   in 
  highly 
  folded 
  condition, 
  so 
  that 
  the 
  number 
  of 
  quartzite 
  beds 
  is 
  

   uncertain^ 
  and 
  whether 
  there 
  is 
  more 
  than 
  one 
  massive, 
  thick 
  quart- 
  

   zite 
  can 
  not 
  be 
  positively 
  stated. 
  There 
  is 
  certainly 
  a 
  considerable 
  

   number 
  of 
  thinner 
  bands. 
  Unless 
  our 
  interpretation 
  of 
  the 
  struc- 
  

   ture 
  is 
  wholly 
  at 
  fault, 
  these 
  two 
  belts 
  represent 
  lines 
  of 
  outcrop 
  

   of 
  the 
  same 
  geologic 
  horizon, 
  and 
  form 
  the 
  youngest 
  rocks 
  of 
  the 
  

   series 
  exposed 
  in 
  the 
  district. 
  In 
  addition 
  to 
  ^this 
  main 
  horizon 
  

   there 
  are 
  also 
  frequent 
  quartzite 
  bands 
  found 
  in 
  the 
  general 
  schist 
  

   series, 
  and 
  thin 
  bands 
  even 
  occur 
  at 
  times 
  with 
  the 
  limestones. 
  

   The 
  more 
  prominent 
  of 
  such 
  bands 
  are 
  indicated 
  upon 
  the 
  maps. 
  

  

  The 
  ponderous 
  quartzites 
  are 
  the 
  most 
  resistant 
  rocks 
  of 
  Pre- 
  

   cambric 
  age 
  in 
  the 
  region, 
  and 
  since 
  they 
  are 
  interbedded 
  with 
  

   schists 
  which 
  are 
  far 
  weaker, 
  the 
  districts 
  where 
  they 
  outcrop 
  are 
  

   quite 
  rugged 
  topographically, 
  as 
  Smyth 
  pointed 
  out 
  lo 
  years 
  ago. 
  

   The 
  quartzite 
  ridges 
  tower 
  abruptly 
  above 
  the 
  narrow 
  valleys 
  eaten 
  

   cut 
  along 
  the 
  schists. 
  

  

  Since 
  the 
  rock 
  is 
  an 
  altered 
  sandstone, 
  recrystallized 
  under 
  heat 
  

   and 
  pressure, 
  and 
  since 
  sandstones 
  often 
  range 
  in 
  composition 
  from 
  

   a 
  high 
  degree 
  of 
  purity 
  to 
  those 
  which 
  are 
  quite 
  impure, 
  either 
  

   shaly, 
  or 
  calcareous, 
  it 
  is 
  but 
  natural 
  to 
  find 
  much 
  variation 
  in 
  the 
  

   rock 
  from 
  place 
  to 
  place. 
  The 
  thick 
  bands 
  are 
  chiefly 
  constituted 
  

  

  ^ 
  Adams, 
  F. 
  D. 
  Jour. 
  Geol. 
  i6 
  -.62^-2^. 
  

  

  