﻿1 
  6 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Within 
  the 
  belt 
  are 
  comprised 
  several 
  large 
  magnetite 
  deposits, 
  

   including 
  those 
  at 
  Lyon 
  Mountain 
  and 
  vicinity, 
  the 
  Arnold 
  hill 
  

   and 
  Palmer 
  hill 
  bodies, 
  and 
  a 
  number 
  of 
  smaller 
  ones. 
  Oppor- 
  

   tunity 
  has 
  been 
  afforded 
  the 
  writer 
  of 
  studying 
  the 
  gneisses 
  in 
  the 
  

   field 
  as 
  well 
  as 
  to 
  compare 
  them 
  with 
  the 
  rocks 
  of 
  other 
  mining 
  

   districts. 
  At 
  many 
  localities 
  within 
  the 
  belt 
  have 
  been 
  found 
  

   undoubted 
  representatives 
  of 
  the 
  igneous 
  rocks. 
  The 
  acid 
  gneisses 
  

   particularly 
  contain 
  cores 
  which 
  are 
  coarsely 
  textured, 
  even 
  por- 
  

   phyritic, 
  and 
  in 
  other 
  respects 
  are 
  analogous 
  to 
  the 
  characteristic. 
  

   Adirondack 
  granites; 
  the 
  coarse 
  phases 
  can 
  be 
  traced 
  at 
  times 
  by 
  

   gradation 
  into 
  fine 
  grained 
  gneissoid 
  rocks 
  which 
  are 
  evidently 
  

   only 
  crushed 
  portions 
  of 
  the 
  same 
  mass. 
  It 
  seems 
  probable 
  that 
  

   the 
  granitic 
  series 
  will 
  be 
  found 
  to 
  abound 
  throughout 
  the 
  belt, 
  

   yet 
  there 
  are 
  large 
  areas 
  of 
  gneiss 
  that 
  can 
  not 
  be 
  satisfactorily 
  

   correlated 
  on 
  the 
  basis 
  of 
  present 
  knowledge. 
  

  

  Igneous 
  intrusions. 
  The 
  plutonic 
  igneous 
  rocks 
  of 
  the 
  Adi- 
  

   rondacks 
  can 
  be 
  divided 
  into 
  four 
  great 
  groups, 
  viz: 
  anorthosite, 
  

   gabbro, 
  syenite 
  and 
  granite. 
  In 
  their 
  normal 
  development 
  the 
  

   individual 
  groups 
  are 
  well 
  contrasted 
  by 
  their 
  physical 
  appear- 
  

   ance, 
  as 
  well 
  as 
  by 
  the 
  peculiarities 
  of 
  their 
  chemical 
  and 
  mineral 
  

   composition. 
  They 
  are 
  all 
  connected, 
  however, 
  by 
  a 
  series 
  of 
  

   intermediate 
  rock 
  types, 
  presenting 
  a 
  variation 
  scarcely 
  inter- 
  

   rupted 
  from 
  the 
  acid 
  to 
  the 
  basic 
  members. 
  This 
  close 
  relation 
  

   between 
  the 
  groups 
  is 
  generally 
  recognized 
  to 
  be 
  an 
  original 
  feature, 
  

   due 
  to 
  a 
  common 
  derivation 
  from 
  a 
  continuous 
  magma 
  in 
  the 
  

   interior. 
  By 
  repeated 
  segmentation 
  and 
  intrusion 
  the 
  magma 
  

   has 
  given 
  rise 
  to 
  the 
  rock 
  series 
  now 
  existing 
  at 
  the 
  surface. 
  

  

  Anorthosite. 
  The 
  anorthosite 
  is 
  the 
  earliest 
  in 
  point 
  of 
  time 
  of 
  

   the 
  intrusions 
  mentioned. 
  Its 
  occurrence 
  in 
  the 
  Adirondacks 
  was 
  

   made 
  known 
  by 
  Professor 
  Emmons 
  who 
  described 
  it 
  under 
  the 
  

   name 
  of 
  hypersthene 
  rock. 
  That 
  he 
  recognized 
  its 
  igneous 
  nature 
  

   is 
  clearly 
  evidenced 
  by 
  the 
  fact 
  that 
  in 
  his 
  report 
  it 
  is 
  placed 
  among 
  

   the 
  unstratified 
  class 
  of 
  rocks, 
  though 
  the 
  name 
  he 
  used 
  has 
  given 
  

   way 
  to 
  the 
  more 
  appropriate 
  one 
  which 
  emphasizes 
  the 
  feldspathic 
  

   component. 
  Hypersthene 
  plays 
  a 
  very 
  subordinate 
  role 
  in 
  the 
  

   composition 
  of 
  the 
  Adirondack 
  anorthosite. 
  The 
  rock 
  forms 
  the 
  

   central 
  massive 
  of 
  highest 
  uplifts. 
  It 
  is 
  exposed 
  over 
  an 
  area 
  that 
  

   is 
  roughly 
  triangular 
  in 
  shape 
  with 
  its 
  base 
  on 
  the 
  north 
  along 
  the 
  

   Essex-Clinton 
  county 
  border, 
  extending 
  west 
  from 
  Lake 
  Cham- 
  

   plain 
  for 
  over 
  50 
  miles, 
  and 
  its 
  apex 
  in 
  southern 
  Essex 
  county 
  

   near 
  the 
  Warren 
  county 
  line. 
  The 
  area 
  probably 
  exceeds 
  1200 
  

   square 
  miles. 
  There 
  are 
  some 
  belts 
  of 
  gneisses 
  and 
  crystalline 
  

  

  