﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  9 
  

  

  New 
  York, 
  been 
  able 
  to 
  discover 
  anywhere 
  any 
  trace 
  of 
  the 
  

   older 
  rocks 
  which 
  formed 
  the 
  floor 
  upon 
  which 
  these 
  water-laid 
  

   sediments 
  were 
  deposited, 
  though 
  plainly, 
  with 
  such 
  an 
  origin, 
  

   they 
  must 
  originally 
  have 
  been 
  laid 
  down 
  on 
  some 
  such 
  floor 
  of 
  

   older 
  rocks. 
  It 
  follows 
  therefore 
  that 
  we 
  do 
  not 
  know 
  the 
  base 
  

   of 
  this 
  Grenville 
  series. 
  Neither 
  do 
  we 
  know 
  its 
  summit, 
  since 
  

   that 
  has 
  apparently 
  been 
  everywhere 
  removed 
  by 
  erosion. 
  

   Hence 
  we 
  can 
  not 
  know 
  its 
  thickness, 
  though 
  we 
  do 
  know 
  that 
  

   it 
  is 
  a 
  very 
  thick 
  rock 
  series, 
  several 
  thousands 
  of 
  feet 
  at 
  least. 
  

  

  Since 
  the 
  deposition 
  of 
  this 
  formation 
  it 
  has 
  undergone 
  many 
  

   changes. 
  The 
  rocks 
  have 
  been 
  greatly 
  compressed 
  and 
  intri- 
  

   cately 
  folded 
  and 
  plicated. 
  They 
  have 
  been 
  invaded 
  from 
  be- 
  

   neath 
  by 
  huge 
  masses 
  of 
  igneous 
  rocks, 
  which 
  have 
  broken 
  up 
  the 
  

   once 
  continuous 
  Grenville 
  formation 
  into 
  separate 
  and 
  discon- 
  

   nected 
  belts 
  and 
  patches, 
  have 
  probably 
  engulfed 
  and 
  digested 
  

   large 
  amounts 
  of 
  it, 
  and 
  are 
  likely 
  responsible 
  for 
  the 
  utter 
  dis- 
  

   appearance 
  of 
  the 
  old 
  flooi 
  on 
  which 
  the 
  formation 
  originally 
  

   rested. 
  As 
  a 
  result 
  of 
  this 
  mishandling 
  the 
  rocks 
  have 
  been 
  pro- 
  

   foundly 
  changed 
  in 
  character. 
  They 
  have 
  been 
  entirely 
  re- 
  

   crystallized, 
  with 
  complete 
  destruction 
  of 
  the 
  textures 
  which, 
  as 
  

   sediments, 
  they 
  originally 
  possessed, 
  and 
  with 
  the 
  production 
  of 
  

   a 
  foliation 
  cleavage, 
  or 
  schistosity, 
  due 
  to 
  a 
  banded 
  arrangement 
  

   of 
  the 
  minerals 
  formed 
  by 
  the 
  recrystallization. 
  In 
  addition 
  a 
  

   quantity 
  of 
  contact 
  rocks 
  has 
  been 
  produced 
  in 
  the 
  vicinity 
  of, 
  

   and 
  by 
  the 
  action 
  of, 
  the 
  igneous 
  rocks, 
  which 
  interact 
  with 
  the 
  

   others 
  to 
  produce 
  rocks 
  quite 
  different 
  from 
  either, 
  and 
  with 
  

   opportunities 
  for 
  manifold 
  variation, 
  with 
  variation 
  in 
  the 
  

   character 
  of 
  either 
  or 
  both 
  sets 
  of 
  the 
  original 
  rocks. 
  In 
  this 
  

   manner 
  many 
  rock 
  types 
  have 
  arisen, 
  often 
  of 
  puzzling 
  nature. 
  

  

  The 
  changes 
  which 
  have 
  been 
  produced 
  in 
  these 
  Grenville 
  rocks 
  

   are 
  of 
  such 
  nature 
  as 
  to 
  lead 
  to 
  the 
  confident 
  belief 
  that 
  they 
  took 
  

   place 
  at 
  some 
  considerable 
  depth 
  below 
  the 
  surface, 
  or 
  in 
  other 
  

   words 
  that 
  a 
  considerable 
  thickness 
  of 
  other 
  rocks 
  then 
  overlay 
  

   them, 
  a 
  rock 
  thickness 
  which 
  subsequently 
  disappeared 
  because 
  of 
  

   surface 
  wear 
  continued 
  through 
  long 
  ages. 
  

  

  Igneous 
  intrusions 
  

  

  As 
  has 
  been 
  implied 
  the 
  Grenville 
  sediments 
  are 
  the 
  most 
  ancient 
  

   rocks 
  of 
  which 
  we 
  have 
  definite 
  knowledge 
  in 
  northern 
  New 
  York. 
  

   Subsequent 
  to 
  their 
  formation 
  they 
  were 
  repeatedly 
  invaded 
  from 
  

   beneath 
  by 
  igneous 
  rocks 
  in 
  molten 
  condition. 
  In 
  the 
  immediate 
  

   district 
  the 
  bulk 
  of 
  this 
  igneous 
  rock 
  consisted 
  of 
  granite, 
  and 
  

  

  