﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  25 
  

  

  the 
  similarly 
  situated 
  inclusions 
  of 
  the 
  Grenville 
  rocks 
  them- 
  

   selves. 
  The 
  same 
  conditions 
  prevail 
  in 
  general 
  over 
  the 
  much 
  

   more 
  extensive 
  Precambric 
  areas 
  of 
  eastern 
  Canada. 
  Recently, 
  

   however, 
  Miller 
  and 
  Knight 
  have 
  announced 
  the 
  discovery, 
  in 
  

   central 
  Ontario, 
  of 
  a 
  basem.ent 
  to 
  the 
  Grenville 
  formation, 
  Gren- 
  

   ville 
  limestone 
  being 
  found 
  resting 
  on 
  an 
  ancient 
  lava 
  flow, 
  whose 
  

   surface 
  is 
  thought 
  to 
  show 
  signs 
  of 
  slight 
  previous 
  wear.^ 
  Miller 
  

   and 
  Knight 
  correlate 
  this 
  old 
  lava, 
  or 
  greenstone, 
  with 
  the 
  oldest 
  

   known 
  formation 
  of 
  the 
  upper 
  lake 
  region, 
  the 
  Keewatin, 
  which 
  

   consists 
  mainly 
  of 
  greenstones, 
  old 
  lava 
  flows 
  and 
  beds 
  of 
  frag- 
  

   mental 
  volcanic 
  materials. 
  There 
  are 
  present, 
  however, 
  some 
  

   associated 
  sediments, 
  and 
  Miller 
  and 
  Knight 
  regard 
  the 
  Grenville 
  

   as 
  of 
  Keewatin 
  age. 
  These 
  are 
  most 
  important 
  results 
  and 
  if 
  

   future 
  work 
  fully 
  establishes 
  these 
  correlations, 
  it 
  will 
  follow 
  

   that 
  the 
  Keewatin 
  has 
  steadily 
  increasing 
  sedimentary 
  content 
  

   and 
  less 
  and 
  less 
  volcanic 
  material 
  as 
  it 
  is 
  followed 
  eastward. 
  

   By 
  the 
  tim.e 
  New 
  York 
  is 
  reached 
  the 
  greenstones 
  have 
  entirely 
  

   disappeared, 
  so 
  far 
  as 
  is 
  known. 
  At 
  least 
  no 
  rocks 
  similar 
  to 
  

   them 
  have 
  ever 
  been 
  discovered 
  in 
  the 
  New 
  York 
  Precambric. 
  

   It 
  should 
  also 
  be 
  stated 
  that 
  Adams 
  is 
  not 
  disposed 
  to 
  accept 
  the 
  

   reference 
  of 
  the 
  Grenville 
  to 
  the 
  Keewatin 
  on 
  the 
  basis 
  of 
  the 
  

   evidence 
  yet 
  in 
  hand, 
  believing 
  a 
  reference 
  to 
  the 
  next 
  overlying 
  

   group, 
  the 
  Huronian, 
  to 
  be 
  more 
  probable.^ 
  

  

  However 
  this 
  may 
  be, 
  the 
  difficulty 
  of 
  accounting 
  for 
  the 
  dis- 
  

   appearance 
  of 
  the 
  old 
  floor 
  of 
  deposit 
  is 
  not 
  helped, 
  but 
  merely 
  

   pushed 
  a 
  stage 
  further 
  back. 
  Miller 
  and 
  Knight 
  speak 
  of 
  only 
  

   slight 
  erosion 
  of 
  the 
  old 
  lava 
  flow 
  prior 
  to 
  the 
  deposit 
  of 
  the 
  

   Grenville 
  limestone 
  upon 
  it. 
  It 
  is 
  of 
  course 
  possible 
  that 
  this 
  

   may 
  be 
  merely 
  an 
  interbedded 
  flow 
  of 
  Grenville 
  age 
  and 
  itself 
  

   rest 
  upon 
  other 
  Grenville 
  sediments. 
  But 
  in 
  any 
  case 
  these 
  

   Keewatin 
  lava 
  flows 
  and 
  fragmental 
  deposits 
  are 
  surface 
  deposits 
  

   and 
  require 
  the 
  presence 
  of 
  a 
  floor 
  on 
  which 
  they 
  were 
  laid 
  down 
  

   just 
  as 
  much 
  as 
  do 
  the 
  Grenville 
  sediments; 
  but 
  no 
  such 
  floor 
  

   to 
  the 
  Keewatin 
  is 
  known. 
  It 
  is 
  always 
  found 
  resting 
  on 
  Lauren- 
  

   tian 
  granite 
  gneisses 
  of 
  igneous 
  origin, 
  or 
  upon 
  yet 
  younger 
  

   igneous 
  rocks 
  which 
  invaded 
  it 
  from 
  beneath 
  in 
  molten 
  condition, 
  

   cut 
  it 
  to 
  pieces, 
  and 
  apparently 
  engulfed 
  and 
  assimilated 
  its 
  basal 
  

   portion 
  along 
  with 
  the 
  floor 
  upon 
  which 
  it 
  rested. 
  Precisely 
  

   these 
  same 
  conditions 
  prevail 
  in 
  general 
  in 
  respect 
  to 
  the 
  Gren- 
  

   ville 
  and 
  its 
  former 
  floor. 
  

  

  ^ 
  Bureau 
  of 
  Mines, 
  Ontario. 
  i6th 
  An. 
  Rep't, 
  pt 
  i, 
  p. 
  22-23. 
  

   2 
  Adams, 
  F. 
  D. 
  Jour. 
  Geol. 
  16 
  :634-35. 
  

  

  