﻿42 
  . 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  the 
  Canadian 
  islands 
  to 
  the 
  mainland 
  and 
  thence 
  west 
  to 
  Kinsfs- 
  

   ton, 
  but 
  until 
  this 
  has 
  been 
  done 
  some 
  reserve 
  must 
  be 
  felt 
  in 
  

   making 
  the 
  correlation. 
  The 
  rock 
  near 
  Clayton 
  differs 
  in 
  con- 
  

   taining 
  no 
  quartz, 
  and 
  in 
  being 
  somewhat 
  more 
  mashed 
  than 
  

   the 
  generality 
  of 
  the 
  rock. 
  It 
  is 
  in 
  fact 
  an 
  acid 
  syenite 
  rather 
  

   than 
  a 
  granite. 
  Otherwise 
  the 
  two 
  are 
  exceedingly 
  alike, 
  and 
  

   since 
  the 
  granite 
  itself 
  is 
  low 
  in 
  silica 
  for 
  a 
  granite, 
  approaching 
  

   a 
  syenite 
  in 
  that 
  respect, 
  but 
  slight 
  variation 
  is 
  needed 
  to 
  cause 
  

   the 
  disappearance 
  of 
  the 
  quartz. 
  

  

  It 
  must 
  be 
  borne 
  in 
  mind, 
  in 
  inspecting 
  the 
  maps, 
  that 
  the 
  

   boundaries 
  drawn 
  between 
  the 
  Picton 
  granite 
  and 
  the 
  Laurentian 
  

   are 
  in 
  the 
  highest 
  degree 
  conventional. 
  They 
  are 
  of 
  the 
  same 
  

   vague 
  sort 
  as 
  those 
  between 
  the 
  Laurentian 
  and 
  Grenville, 
  but 
  

   even 
  more 
  vague 
  than 
  those 
  because 
  of 
  the 
  similarity 
  of 
  the 
  two 
  

   rocks. 
  The 
  fine 
  grained 
  dikes 
  of 
  the 
  Picton 
  are 
  exceedingly 
  like 
  

   the 
  acid 
  dikes 
  sent 
  out 
  from 
  the 
  Laurentian, 
  and 
  it 
  is 
  almost 
  an 
  

   impossible 
  matter 
  to 
  tell 
  which 
  rock 
  is 
  in 
  excess. 
  On 
  the 
  other 
  

   hand 
  the 
  maps 
  do 
  show 
  the 
  chief 
  areas 
  of 
  the 
  two 
  rocks, 
  bring 
  

   out 
  the 
  fact 
  that 
  the 
  one 
  is 
  younger 
  than 
  the 
  other, 
  and 
  show 
  

   their 
  relative 
  distribution 
  and 
  extent 
  as 
  accurately 
  as 
  possible 
  

   in 
  rocks 
  of 
  this 
  kind. 
  

  

  That 
  the 
  rock 
  is 
  the 
  youngest 
  of 
  the 
  intrusives 
  of 
  the 
  region 
  

   is 
  indicated 
  in 
  several 
  ways. 
  It 
  shows 
  less 
  sign 
  of 
  mashing 
  than 
  

   do 
  any 
  of 
  the 
  others, 
  that 
  is 
  its 
  unmashed 
  central 
  core 
  is 
  rela- 
  

   tively 
  much 
  larger. 
  Besides 
  its 
  abundant 
  inclusions 
  of 
  various 
  

   Grenville 
  rocks 
  it 
  contains 
  also 
  frequent 
  masses 
  of 
  granite 
  gneiss 
  

   of 
  Laurentian 
  type, 
  and 
  sends 
  abundant 
  dikes 
  into 
  similar 
  rock 
  

   where 
  bordered 
  by 
  it, 
  as 
  it 
  is 
  locally 
  on 
  both 
  Wellesley 
  and 
  

   Grindstone 
  islands 
  ; 
  and 
  also 
  it 
  contains 
  inclusions 
  of 
  an 
  augen 
  

   gneiss 
  which 
  is 
  absolutely 
  identical 
  in 
  character 
  with 
  the 
  rock 
  

   of 
  the 
  Alexandria 
  syenite. 
  Such 
  age 
  for 
  the 
  rock 
  then 
  seems 
  to 
  

   us 
  in 
  the 
  highest 
  degree 
  probable, 
  though 
  it 
  falls 
  somewhat 
  short 
  

   of 
  actual 
  demonstration. 
  

  

  Dikes 
  of 
  the 
  granite 
  are 
  thought 
  to 
  range 
  widely 
  in 
  the 
  rocks 
  

   east 
  and 
  south, 
  though 
  no 
  attempt 
  to 
  indicate 
  this 
  upon 
  the 
  

   areal 
  maps 
  has 
  been 
  made. 
  They 
  are 
  believed 
  to 
  be 
  numerously 
  

   present 
  in 
  the 
  green 
  schist 
  belts 
  of 
  the 
  western 
  part 
  of 
  the 
  

   Alexandria 
  quadrangle, 
  and 
  also 
  in 
  the 
  granite 
  gneiss 
  of 
  that 
  

   quadrangle. 
  Even 
  as 
  far 
  east 
  as 
  Alexandria 
  Bay 
  broad 
  dikes 
  of 
  

   acid, 
  usually 
  fine 
  grained, 
  granite 
  occur 
  abundantly, 
  cutting 
  the 
  

   granite 
  gneiss 
  all 
  to 
  pieces, 
  and 
  often 
  inclosing 
  sharp 
  inclusions 
  

   of 
  it. 
  We 
  have 
  never 
  seen 
  inclusions 
  of 
  this 
  type 
  held 
  abun- 
  

  

  