﻿38 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  these 
  more 
  advanced 
  stages 
  are 
  usually 
  found 
  in 
  the 
  case 
  of 
  

   inclusions 
  away 
  from 
  the 
  near 
  vicinity 
  of 
  the 
  border. 
  

  

  We 
  have 
  not, 
  up 
  to 
  the 
  present 
  time, 
  definitely 
  classed 
  any 
  

   of 
  the 
  granites 
  of 
  northern 
  New 
  York 
  as 
  of 
  Laurentian 
  age. 
  Just 
  

   across 
  the 
  border 
  in 
  Canada 
  however, 
  where 
  the 
  rocks 
  are 
  identi- 
  

   cal, 
  this 
  term 
  is 
  definitely 
  applied 
  to 
  the 
  granite 
  gneiss 
  of 
  the 
  

   bathyliths 
  which 
  invaded 
  the 
  Grenville 
  series 
  from 
  beneath, 
  

   broke 
  it 
  up 
  into 
  disconnected 
  belts 
  and 
  patches 
  and 
  destroyed 
  

   all 
  trace 
  of 
  its 
  floor. 
  The 
  absolute 
  identity 
  of 
  the 
  rocks 
  and 
  their 
  

   relations, 
  leads 
  us 
  to 
  apply 
  the 
  name 
  here 
  to 
  the 
  granite 
  gneiss 
  

   bodies 
  with 
  much 
  confidence 
  in 
  the 
  wisdom 
  and 
  propriety 
  of 
  the 
  

   correlation. 
  Whether 
  these 
  Laurentian 
  granites 
  are 
  recognizable, 
  

   however, 
  over 
  any 
  considerable 
  part 
  of 
  the 
  Adirondack 
  

   region, 
  in 
  distinction 
  from 
  granites 
  of 
  later 
  date, 
  is 
  a 
  much 
  less 
  

   certain 
  matter, 
  though 
  we 
  believe 
  it 
  to 
  be 
  the 
  case. 
  It 
  is 
  thought 
  

   for 
  example 
  that 
  what 
  we 
  have 
  called 
  the 
  Saranac 
  gneiss 
  in 
  

   Clinton 
  county, 
  and 
  the 
  Long 
  Lake 
  gneiss 
  of 
  that 
  quadrangle, 
  

   are 
  in 
  all 
  probability 
  of 
  Laurentian 
  age. 
  

  

  Theresa 
  syenite. 
  This 
  comparatively 
  small 
  intrusive 
  mass 
  lies 
  

   to 
  the 
  southward 
  of 
  Theresa, 
  in 
  a 
  valley 
  floored 
  by 
  Precambric 
  

   rocks, 
  but 
  walled 
  in 
  by 
  Potsdam 
  on 
  all 
  sides 
  It 
  is 
  somewhat 
  

   less 
  than 
  2 
  miles 
  in 
  length 
  and 
  with 
  a 
  breadth 
  of 
  less 
  than 
  half 
  a 
  

   mile, 
  so 
  far 
  as 
  the 
  exposures 
  go 
  ; 
  at 
  the 
  south 
  it 
  may 
  have 
  greater 
  

   breadth 
  underneath 
  the 
  Potsdam. 
  

  

  The 
  general 
  rock 
  is 
  of 
  medium 
  coarseness 
  and 
  granitic 
  texture, 
  

   though 
  always 
  with 
  evidence 
  of 
  mashing 
  and 
  granulation, 
  and 
  

   of 
  gray 
  to 
  greenish 
  color. 
  Most 
  of 
  it 
  is 
  chiefly 
  made 
  up 
  of 
  feld- 
  

   spars. 
  It 
  resembles 
  in 
  high 
  degree 
  the 
  common 
  greenish, 
  augite 
  

   syenite 
  of 
  the 
  Adirondack 
  region, 
  is 
  unhesitatingly 
  classed 
  with 
  

   that, 
  and 
  is 
  the 
  only 
  representative 
  of 
  that 
  rock 
  type 
  within 
  the 
  

   mapped 
  area. 
  Like 
  it, 
  this 
  rock 
  is 
  quite 
  variable, 
  becoming- 
  red 
  

   and 
  granitic 
  looking 
  on 
  the 
  one 
  hand, 
  and 
  more 
  basic 
  with 
  

   increase 
  of 
  black 
  minerals 
  on 
  the 
  other. 
  Near 
  the 
  border 
  some 
  

   varieties 
  become 
  feebly 
  porphyritic. 
  

  

  Microperthitic 
  feldspar 
  is 
  always 
  the 
  chief 
  constituent 
  of 
  the. 
  

   rock. 
  Some 
  oHgoclase 
  is 
  always 
  present. 
  Quartz 
  varies 
  from 
  

   some 
  i^i 
  in 
  the 
  more 
  granitic, 
  red 
  varieties, 
  down 
  to 
  complete 
  

   absence. 
  Augite 
  is 
  the 
  most 
  prominent 
  black 
  mineral 
  in 
  the 
  

   ordinary 
  rock, 
  with 
  biotite 
  usually 
  and 
  hornblende 
  sometimes 
  

   sparingly 
  present; 
  magnetite, 
  apatite, 
  titanite 
  and 
  zircon 
  are 
  the 
  

   chief 
  accessories, 
  the 
  apatite 
  usually 
  quite 
  prominent, 
  another 
  

   feature 
  which 
  the 
  rock 
  has 
  in 
  common 
  with 
  the 
  general 
  Adiron- 
  

  

  