﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  II9 
  

  

  Smyth. 
  ^ 
  The 
  numerous 
  dikes, 
  chiefly 
  of 
  granite, 
  which 
  every- 
  

   where 
  cut 
  the 
  Grenville 
  give 
  every 
  facihty 
  for 
  determining 
  their 
  

   presence. 
  They 
  are 
  in 
  great 
  number 
  but 
  for 
  the 
  most 
  part 
  of 
  

   very 
  trifling 
  displacement. 
  Similar 
  faulting 
  locally 
  in 
  the 
  

   Paleozoic 
  rocks 
  suggests 
  that 
  this 
  faulting 
  is 
  of 
  Paleozoic 
  date, 
  

   but 
  the 
  much 
  greater 
  number 
  of 
  faults 
  noted 
  in 
  the 
  older 
  rocks 
  

   indicates 
  some 
  Precambric 
  faulting 
  at 
  least, 
  and 
  of 
  this 
  there 
  is 
  

   direct 
  evidence 
  in 
  some 
  instances. 
  The 
  hand 
  specimen 
  shown 
  in 
  

   plate 
  5, 
  lower 
  figure, 
  presents 
  an 
  adequate 
  illustration. 
  The 
  rock 
  is 
  a 
  

   well 
  banded, 
  acid 
  Grenville 
  gneiss, 
  consisting 
  chiefly 
  of 
  feldspar 
  and 
  

   quartz 
  and 
  seems 
  certainly 
  a 
  sediment, 
  a 
  metamorphosed 
  shaly 
  sand- 
  

   stone. 
  The 
  bands 
  vary 
  in 
  color 
  from 
  a 
  light 
  reddish 
  to 
  a 
  black- 
  

   ish 
  red, 
  and 
  are 
  very 
  plain, 
  though 
  without 
  sufficient 
  contrast 
  to 
  

   photograph 
  -clearly. 
  They 
  are 
  parallel 
  to 
  the 
  bedding 
  and 
  seem 
  

   certainly 
  to 
  represent 
  original 
  lamination 
  in 
  the 
  rock. 
  Shearing 
  

   has 
  occurred, 
  with 
  development 
  of 
  fracture 
  cleavage, 
  principally 
  

   at 
  a 
  high 
  angle 
  with 
  the 
  bedding, 
  but 
  with 
  secondary 
  fractures 
  

   which 
  rudely 
  follow 
  it, 
  and 
  along 
  many 
  of 
  the 
  former 
  minute 
  

   slips 
  of 
  the 
  rock 
  have 
  taken 
  place. 
  These 
  old 
  cracks 
  are 
  now 
  

   solidly 
  welded 
  up 
  w4th 
  secondary 
  minerals, 
  black 
  in 
  color, 
  except 
  

   for 
  an 
  occasional, 
  shining 
  pyrite 
  crystal, 
  and 
  it 
  is 
  this 
  secondary 
  

   filling 
  which 
  furnishes 
  the 
  evidence 
  for 
  the 
  date 
  of 
  the 
  deforma- 
  

   tion 
  and 
  gives 
  the 
  chief 
  interest 
  to 
  the 
  rock. 
  Pyroxene, 
  horn- 
  

   blende 
  and 
  black 
  mica 
  (biotite), 
  stated 
  in 
  order 
  of 
  abundance, 
  

   are 
  the 
  minerals 
  composing 
  the 
  filling, 
  their 
  grain 
  somewhat 
  

   coarser 
  than 
  that 
  of 
  the 
  rock. 
  They 
  are 
  of 
  the 
  same 
  types 
  as 
  the 
  

   minerals 
  of 
  the 
  Grenville 
  green 
  schists. 
  They 
  argue 
  for 
  fairly 
  

   deep 
  seated 
  conditions 
  at 
  the 
  time 
  of 
  the 
  deformation. 
  The 
  

   fractures 
  show 
  that 
  the 
  rock 
  was 
  above 
  the 
  zone 
  of 
  flow, 
  but 
  the 
  

   minerals, 
  the 
  pyroxene 
  especially, 
  indicate 
  anamorphic 
  condi- 
  

   tions 
  and 
  point 
  to 
  deformation 
  in 
  the 
  lower 
  part 
  of 
  the 
  zone 
  of 
  

   fracture. 
  Such 
  faulting 
  seems 
  not 
  only 
  of 
  Precambric 
  date, 
  but 
  

   to 
  have 
  preceded 
  the 
  greater 
  part 
  of 
  the 
  long, 
  Precambric 
  erosion 
  

   interval. 
  Its 
  date 
  is 
  made 
  quite 
  certain 
  by 
  the 
  numerous 
  dikes 
  

   of 
  Picton 
  granite 
  which 
  cut 
  the 
  schists, 
  the 
  granite 
  being 
  younger 
  

   than 
  the 
  filling 
  of 
  the 
  shear 
  zones. 
  

  

  There 
  are 
  also 
  frequent 
  shear 
  zones 
  in 
  the 
  Precambric 
  rocks, 
  

   zones 
  of 
  no 
  great 
  breadth 
  but 
  of 
  considerable 
  linear 
  extent, 
  along 
  

   Avhich 
  the 
  rock 
  is 
  shattered 
  into 
  quite 
  small 
  blocks 
  by 
  a 
  multitude 
  

   of 
  close 
  spaced 
  joints, 
  and 
  along 
  which 
  some 
  faulting 
  has 
  cer- 
  

   tainly 
  taken 
  place, 
  small 
  slips 
  along 
  many 
  planes. 
  No 
  such 
  shear 
  

  

  IN. 
  Y. 
  State 
  Geol. 
  19th 
  An. 
  Rep't, 
  pi. 
  15. 
  

  

  