﻿28 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  schist, 
  which 
  lies 
  between 
  the 
  two 
  in 
  the 
  southeast 
  corner 
  of 
  the 
  

   Alexandria 
  sheet, 
  and 
  which 
  consists 
  of 
  alternating 
  bands 
  of 
  quart- 
  

   zite 
  and 
  various 
  schists 
  of 
  no 
  enormous 
  individual 
  thickness^ 
  but 
  

   which, 
  taken 
  together, 
  must 
  have 
  a 
  thickness 
  of 
  several 
  thousand 
  

   feet, 
  rests 
  upon 
  the 
  thick 
  limestone 
  and 
  is 
  the 
  youngest 
  portion 
  of 
  

   the 
  Grenville 
  exposed 
  within 
  the 
  map 
  limits. 
  To 
  the 
  north, 
  and 
  be- 
  

   neath 
  the 
  limestone 
  would 
  come 
  the 
  great 
  complex 
  of 
  green 
  schists 
  

   and 
  impure 
  greenish 
  limestones 
  which 
  there 
  occurs, 
  which 
  have 
  

   steep 
  dips 
  and 
  must 
  have 
  large 
  thickness, 
  at 
  least 
  as 
  great 
  as 
  the 
  

   two 
  previous 
  groups, 
  and 
  likely 
  greater. 
  Doubt 
  is 
  thrown, 
  hov/ever, 
  

   upon 
  this 
  interpretation 
  by 
  the 
  fact 
  that 
  the 
  rocks 
  which 
  follow 
  the 
  

   thick 
  limestone 
  to 
  the 
  south, 
  on 
  the 
  Theresa 
  sheet, 
  differ 
  consider- 
  

   ably 
  from 
  the 
  green 
  schist 
  series 
  which 
  follows 
  it 
  to 
  the 
  north 
  on 
  

   the 
  Alexandria 
  sheet, 
  and 
  yet 
  according 
  to 
  this 
  interpretation 
  the 
  

   two 
  should 
  be 
  identical, 
  representing 
  the 
  series 
  directly 
  beneath 
  

   the 
  thick 
  limestone. 
  Each 
  does 
  consist 
  of 
  schist, 
  calcareous 
  schist, 
  

   and 
  thin 
  limestone 
  bands, 
  with 
  an 
  occasional 
  thin 
  quartzite, 
  but 
  the 
  

   Theresa 
  rocks 
  are 
  not 
  of 
  this 
  distinct 
  green 
  schist 
  type. 
  A 
  possi- 
  

   ble 
  answer 
  to 
  this 
  objection 
  may 
  be 
  found 
  in 
  the 
  fact 
  that, 
  not- 
  

   withstanding 
  a 
  rather 
  intimate 
  acquaintance 
  with 
  the 
  Grenville 
  

   series 
  all 
  over 
  northern 
  New 
  York 
  and 
  in 
  parts 
  of 
  Canada, 
  the 
  

   writer 
  has 
  nowhere 
  else 
  seen 
  the 
  counterpart 
  of 
  this 
  green 
  schist 
  

   series. 
  It 
  is 
  in 
  rather 
  close 
  association 
  with 
  the 
  Picton 
  granite, 
  

   which 
  was 
  richly 
  supplied 
  with 
  mineralizing 
  agents, 
  and 
  is 
  every- 
  

   where 
  cut 
  with 
  numerous 
  dikes 
  from 
  this 
  granite, 
  so 
  that 
  its 
  pecu- 
  

   liar 
  characters 
  are 
  thought 
  to 
  be 
  largely, 
  or 
  wholly 
  attributable 
  to 
  

   this 
  contact 
  action, 
  and 
  thus 
  explained 
  as 
  due 
  to 
  these 
  local 
  condi- 
  

   tions. 
  If 
  this 
  be 
  not 
  the 
  explanation 
  there 
  seems 
  no 
  alternative 
  

   but 
  to 
  regard 
  the 
  two 
  thick 
  limestones 
  as 
  separate 
  beds, 
  thus 
  largely 
  

   increasing 
  the 
  thickness 
  of 
  the 
  section, 
  already 
  great. 
  If 
  the 
  struc- 
  

   ture 
  is 
  thus 
  correctly 
  interpreted, 
  a 
  thickness 
  of 
  at 
  least 
  20,000 
  feet 
  

   is 
  indicated 
  for 
  the 
  Grenville 
  of 
  the 
  district, 
  and 
  this 
  is 
  a 
  conser- 
  

   vative 
  estimate. 
  If 
  the 
  structure 
  is 
  not 
  synclinal 
  this 
  thickness 
  

   must 
  be 
  nearly 
  doubled. 
  

  

  This 
  matter 
  will 
  be 
  discussed 
  somewhat 
  more 
  in 
  detail 
  on 
  a 
  later 
  

   page. 
  The 
  purpose 
  here 
  is 
  simply 
  to 
  give 
  an 
  outline 
  of 
  the 
  sup- 
  

   posed 
  Grenville 
  succession 
  and 
  some 
  idea 
  of 
  the 
  great 
  thickness 
  

   of 
  the 
  series. 
  

  

  Limestones. 
  The 
  general 
  Grenville 
  limestone 
  of 
  the 
  district 
  is 
  

   a 
  coarsely 
  crystalline 
  and 
  quite 
  pure 
  white 
  marble, 
  only 
  sparingly 
  

   charged 
  with 
  other 
  minerals. 
  The 
  great 
  bulk 
  of 
  the 
  rock 
  of 
  the 
  

   thick 
  belt, 
  or 
  belts, 
  just 
  referred 
  to, 
  consists 
  of 
  %^ 
  or 
  upward 
  of 
  

  

  