﻿48 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Knob 
  mountain 
  a 
  brecciated 
  zone 
  occurs 
  bearing 
  nearly 
  in 
  line 
  

   with 
  the 
  cliffs. 
  

  

  The 
  syenite 
  is 
  exposed 
  in 
  force 
  northeast 
  of 
  Hammondville 
  in 
  

   the 
  vicinity 
  of 
  Overshot 
  and 
  Round 
  ponds. 
  It 
  has 
  the 
  anorthosite 
  

   on 
  the 
  west, 
  the 
  line 
  of 
  contact 
  following 
  just 
  west 
  of 
  the 
  road 
  

   toward 
  Dudley 
  pond. 
  A 
  tongue 
  of 
  syenite 
  extends 
  southward 
  

   from 
  this 
  area 
  into 
  the 
  sedimentary 
  gneisses 
  for 
  a 
  distance 
  of 
  a 
  

   mile 
  or 
  more. 
  

  

  The 
  stratigraphic 
  order 
  of 
  succession 
  for 
  the 
  sedimentary 
  rocks 
  

   is 
  stated 
  by 
  Dr 
  Ogilvie 
  to 
  be 
  hornblende 
  gneiss 
  at 
  the 
  base 
  and 
  

   limestone 
  above, 
  with 
  the 
  mica 
  schist 
  interbedded 
  in 
  both. 
  The 
  

   field 
  relations 
  do 
  not 
  indicate 
  any 
  unconformity 
  between 
  the 
  differ- 
  

   ent 
  members. 
  Concerning 
  the 
  relative 
  age 
  of 
  the 
  eruptives, 
  Dr 
  

   Ogilvie 
  states 
  that 
  the 
  anorthosite 
  is 
  probably 
  the 
  oldest 
  while 
  

   the 
  granite 
  and 
  syenite 
  are 
  nearly 
  of 
  the 
  same 
  period. 
  The 
  gabbro 
  

   was 
  the 
  last 
  to 
  be 
  intruded. 
  The 
  most 
  probable 
  order 
  is 
  anortho- 
  

   site, 
  syenite, 
  granite 
  and 
  gabbro. 
  

  

  The 
  stratigraphic 
  relations 
  of 
  the 
  Hammondville 
  gneiss 
  present 
  

   perhaps 
  the 
  most 
  difficult 
  problem 
  in 
  the 
  geology 
  of 
  the 
  district 
  

   and 
  one 
  that 
  is 
  of 
  special 
  interest 
  owing 
  to 
  its 
  bearing 
  upon 
  the 
  

   magnetite 
  deposits. 
  The 
  question 
  naturally 
  involves 
  the 
  origin 
  

   of 
  the 
  gneiss, 
  whether 
  this 
  is 
  to 
  be 
  considered 
  a 
  member 
  of 
  the 
  

   sedimentary 
  series 
  and 
  like 
  the 
  other 
  members 
  has 
  received 
  its 
  

   crystalline 
  character 
  by 
  metamorphism, 
  or 
  whether 
  it 
  represents 
  

   an 
  intrusive 
  of 
  which 
  the 
  original 
  igneous 
  features 
  have 
  been 
  

   obscured 
  through 
  crushing 
  and 
  possibly 
  a 
  partial 
  recrystallization. 
  

   The 
  evidence 
  obtained 
  from 
  a 
  study 
  of 
  thin 
  sections 
  of 
  the 
  gneiss 
  

   is 
  inconclusive. 
  As 
  has 
  been 
  previously 
  stated 
  the 
  mineralogy 
  

   differs 
  in 
  some 
  respects 
  from 
  that 
  of 
  typical 
  igneous 
  rocks 
  of 
  analo- 
  

   gous 
  composition, 
  though 
  the 
  differences 
  are 
  not 
  so 
  great 
  that 
  

   they 
  can 
  be 
  regarded 
  as 
  decisive. 
  Compared 
  with 
  the 
  class 
  of 
  

   igneous 
  rocks 
  most 
  closely 
  allied 
  in 
  composition, 
  that 
  is 
  the 
  diorites, 
  

   the 
  chief 
  points 
  of 
  contrast 
  are 
  in 
  the 
  proportions 
  of 
  quartz 
  and 
  

   ferromagnesian 
  minerals, 
  the 
  former 
  being 
  much 
  larger 
  and 
  the 
  

   latter 
  smaller 
  than 
  obtain 
  usually 
  in 
  diorites. 
  To 
  substantiate 
  

   these 
  inferences 
  chemical 
  analyses 
  of 
  the 
  gneiss 
  are 
  needed. 
  

  

  The 
  field 
  observations 
  of 
  Mr 
  Newman 
  and 
  the 
  writer 
  lend 
  some 
  

   support 
  to 
  the 
  view 
  that 
  the 
  gneiss 
  does 
  not 
  belong 
  to 
  the 
  intrusive 
  

   series, 
  or 
  at 
  least 
  is 
  not 
  contemporary 
  with 
  the 
  other 
  members 
  of 
  it. 
  

   The 
  granulation 
  and 
  intense 
  crushing 
  which 
  the 
  rock 
  has 
  under- 
  

   gone 
  is 
  not 
  common 
  in 
  the 
  same 
  degree 
  to 
  the 
  igneous 
  types 
  which 
  

   at 
  most 
  show 
  these 
  effects 
  in 
  limited 
  areas 
  or 
  zones 
  where 
  faulting 
  

  

  