﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  95 
  

  

  and 
  the 
  rocks 
  of 
  this 
  group 
  are 
  known 
  as 
  the 
  Stones 
  River 
  forma- 
  

   tion. 
  During 
  Chazy 
  time 
  the 
  depression 
  in 
  which 
  Stones 
  River 
  rocks 
  

   were 
  forming 
  was 
  encroaching 
  upon 
  northern 
  New 
  York 
  from 
  the 
  

   south 
  and 
  west, 
  and 
  by 
  the 
  close 
  of 
  the 
  middle 
  Chazy 
  this 
  depression 
  

   had 
  become 
  sufficiently 
  extensive 
  to 
  involve 
  our 
  district 
  here, 
  and 
  the 
  

   deposition 
  of 
  the 
  Pamelia 
  formation 
  commenced, 
  the 
  Pamelia 
  being 
  

   the 
  local 
  New 
  York 
  facies 
  of 
  the 
  Stones 
  River 
  formation, 
  and 
  repre- 
  

   senting 
  only 
  a 
  portion 
  of 
  its 
  upper 
  division. 
  The 
  tilting 
  of 
  our 
  dis- 
  

   trict 
  necessary 
  to 
  permit 
  of 
  this 
  invasion 
  from 
  the 
  southwest, 
  

   changed 
  its 
  former 
  easterly 
  inclination 
  to 
  a 
  southwesterly 
  one, 
  over 
  

   most 
  of 
  the 
  district; 
  but 
  apparently 
  this 
  change 
  of 
  slope 
  died 
  out 
  on 
  

   the 
  eastern 
  edge 
  of 
  the 
  Alexandria 
  sheet, 
  east 
  of 
  which 
  lay 
  the 
  land 
  

   area 
  which 
  separated 
  the 
  Pamelia 
  basin 
  from 
  the 
  Chazy 
  basin 
  ; 
  and 
  

   this 
  received 
  no 
  westerly 
  tilt, 
  but 
  chiefly 
  retained 
  its 
  old 
  slope 
  to 
  the 
  

   east. 
  This 
  in 
  our 
  view 
  is 
  the 
  origin 
  of 
  the 
  Frontenac 
  axis, 
  as 
  the 
  

   narrow 
  isthmus 
  of 
  Precambric 
  rocks 
  w^hich 
  connects 
  the 
  main 
  xA.di- 
  

   rondack 
  Precambric 
  mass 
  with 
  the 
  great 
  Canadian 
  area 
  of 
  these 
  

   rocks, 
  and 
  which 
  passes 
  through 
  our 
  district 
  here, 
  is 
  called. 
  It 
  

   simply 
  represents 
  an 
  axis 
  of 
  the 
  old 
  Precambric 
  floor 
  which 
  became 
  

   less 
  depressed 
  than 
  the 
  portions 
  of 
  the 
  floor 
  east 
  and 
  west 
  from 
  it. 
  

   The 
  Potsdam-Beekmantown-Chazy 
  depressions 
  sagged 
  the 
  district 
  to 
  

   the 
  east, 
  covering 
  it 
  with 
  steadily 
  increasing 
  thickness 
  of 
  their 
  de- 
  

   posits 
  in 
  that 
  direction; 
  the 
  PameHa 
  depression 
  sagged 
  the 
  district 
  

   to 
  the 
  west, 
  and 
  in 
  that 
  direction 
  the 
  overlying 
  deposits 
  steadily 
  in- 
  

   crease 
  in 
  thickness. 
  The 
  Frontenac 
  axis 
  is 
  the 
  pivotal 
  district 
  be- 
  

   tween 
  the 
  two, 
  where 
  sagging 
  was 
  least 
  and 
  deposit 
  thinnest. 
  Sub- 
  

   sequent 
  erosion 
  could 
  thus 
  wear 
  away 
  this 
  thin 
  cover 
  and 
  bring 
  the 
  

   Precambric 
  back 
  to 
  daylight, 
  along 
  this 
  line, 
  as 
  it 
  has 
  done, 
  while 
  yet 
  

   the 
  thicker 
  cover, 
  east 
  and 
  west, 
  in 
  part 
  remains. 
  

  

  According 
  to 
  Ulrich 
  the 
  Pamelia 
  formation 
  is 
  of 
  age 
  intermediate 
  

   between 
  the 
  middle 
  and 
  upper 
  Chazy 
  of 
  the 
  Champlain 
  valley, 
  but 
  

   little 
  sedimentation 
  having 
  taken 
  place 
  there 
  in 
  Pamelia 
  time; 
  in 
  

   other 
  words 
  while 
  this 
  region 
  was 
  subsiding 
  and 
  accumulating 
  de- 
  

   posit, 
  that 
  ceased 
  to 
  subside. 
  With 
  the 
  cessation 
  of 
  Pamelia 
  deposi- 
  

   tion 
  on 
  the 
  west, 
  resulting 
  in 
  the 
  -unconformity 
  between 
  the 
  Pamelia 
  

   and 
  Lowville, 
  deposition 
  was 
  renewed 
  on 
  the 
  east 
  and 
  the 
  upper 
  

   Chazy 
  was 
  laid 
  down. 
  In 
  like 
  manner 
  the 
  Lowville 
  formation 
  is 
  

   but 
  slightly 
  represented 
  in 
  the 
  Champlain 
  valley, 
  though 
  well 
  de- 
  

   veloped 
  here, 
  as 
  if, 
  with 
  renewed 
  subsidence 
  here 
  it 
  again 
  ceased 
  

   there. 
  Toward 
  the 
  close 
  of 
  the 
  Lowville, 
  uplift 
  occurred 
  on 
  the 
  

   northwest 
  giving 
  rise 
  to 
  the 
  unconformity 
  between 
  the 
  main 
  mass 
  of 
  

   the 
  Lowville 
  and 
  the 
  Leray 
  limestone. 
  At 
  the 
  same 
  time 
  depression 
  

  

  