﻿12 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  The 
  inference 
  as 
  to 
  their 
  origin 
  is 
  more 
  readily 
  apparent 
  in 
  the 
  case 
  

   of 
  the 
  limestones 
  and 
  schistose 
  types 
  than 
  in 
  reference 
  to 
  the 
  more 
  

   massive 
  gneisses, 
  for 
  which 
  the 
  field 
  evidence 
  alone 
  is 
  seldom 
  

   determinative. 
  

  

  Plutonic 
  igneous 
  masses 
  invaded 
  the 
  region 
  at 
  different 
  times 
  

   during 
  the 
  Precambric 
  period. 
  They 
  have 
  broken 
  up 
  the 
  sedi- 
  

   mentary 
  rocks 
  into 
  isolated 
  areas, 
  injected 
  them 
  with 
  their 
  materials 
  

   and 
  blended 
  with 
  them 
  along 
  the 
  contacts. 
  Subsequent 
  com- 
  

   pression 
  has 
  converted 
  them 
  into 
  gneisses 
  which 
  are 
  often 
  hard 
  to 
  

   distinguish 
  from 
  those 
  of 
  the 
  sedimentary 
  class. 
  A 
  later 
  manifes- 
  

   tation 
  of 
  igneous 
  activity 
  led 
  to 
  the 
  intrusion 
  of 
  dike 
  rocks. 
  

  

  While 
  a 
  great 
  part 
  of 
  the 
  crystallines 
  can 
  be 
  differentiated 
  into 
  

   the 
  two 
  classes 
  of 
  igneous 
  and 
  sedimentary 
  derivatives, 
  there 
  are 
  

   considerable 
  areas 
  of 
  gneisses 
  whose 
  origin 
  has 
  not 
  been 
  fully 
  estab- 
  

   lished. 
  Their 
  relationships 
  have 
  been 
  obscured 
  by 
  profound 
  altera- 
  

   tion, 
  leaving 
  little 
  evidence 
  as 
  to 
  their 
  original 
  nature. 
  It 
  is 
  in 
  

   connection 
  with 
  these 
  rocks 
  that 
  the 
  principal 
  stratigraphical 
  prob- 
  

   lems 
  remain 
  to 
  be 
  solved. 
  

  

  According 
  to 
  the 
  classification 
  generally 
  employed 
  for 
  Precambric 
  

   rocks, 
  the 
  sedimentary 
  gneisses 
  fall 
  within 
  the 
  Grenville 
  series. 
  

   If 
  any 
  rocks 
  exist 
  in 
  the 
  region 
  which 
  antedate 
  the 
  oldest 
  sediments 
  

   of 
  that 
  group, 
  they 
  are 
  probably 
  to 
  be 
  found 
  among 
  the 
  gneisses 
  

   previously 
  mentioned. 
  

  

  Sedimentary, 
  or 
  Grenville, 
  series. 
  So 
  far 
  as 
  known, 
  the 
  sedimentary- 
  

   derivatives 
  are 
  the 
  oldest 
  rocks 
  in 
  the 
  Adirondacks. 
  They 
  possess 
  

   much 
  similarity 
  in 
  their 
  development 
  and 
  individual 
  constitution 
  

   to 
  the 
  Grenville 
  series 
  of 
  Canada, 
  with 
  which 
  they 
  are 
  now 
  generally 
  

   correlated 
  as 
  the 
  nearest 
  equivalent 
  in 
  age. 
  They 
  are 
  believed 
  to 
  

   be 
  ancient 
  water 
  deposits 
  and 
  if 
  so 
  must 
  have 
  been 
  laid 
  down 
  upon 
  

   some 
  floor 
  of 
  still 
  older 
  rocks 
  that 
  have 
  not 
  yet 
  been 
  definitely 
  

   recognized. 
  Little 
  is 
  known 
  as 
  to 
  the 
  thickness 
  of 
  the 
  series, 
  though 
  

   from 
  the 
  facts 
  of 
  their 
  distribution 
  it 
  is 
  concluded 
  that 
  they 
  must 
  

   have 
  been 
  originally 
  very 
  thick. 
  The 
  variation 
  in 
  composition, 
  

   from 
  original 
  calcareous 
  and 
  magnesian 
  deposits 
  to 
  shales 
  and 
  sand- 
  

   stones 
  and 
  probably 
  coarse 
  conglomerates, 
  as 
  well, 
  is 
  such 
  that 
  it 
  

   can 
  be 
  explained 
  only 
  by 
  wide-reaching 
  changes 
  in 
  the 
  processes 
  

   of 
  accumulation 
  that 
  require 
  long 
  lapses 
  of 
  time. 
  Neither 
  the 
  base 
  

   nor 
  the 
  top 
  of 
  the 
  series 
  has 
  been 
  identified. 
  

  

  Limestone. 
  The 
  limestones 
  have 
  the 
  crystalline 
  texture 
  of 
  marbles 
  , 
  

   they 
  range 
  from 
  nearly 
  pure 
  lime 
  carbonates 
  to 
  magnesian 
  lime- 
  

   stones 
  and 
  dolomites. 
  They 
  are 
  always 
  impregnated 
  by 
  foreign 
  

   minerals 
  that 
  have 
  been 
  formed 
  out 
  of 
  the 
  carbonates 
  and 
  the 
  

  

  