﻿472 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  ranging 
  from 
  granite 
  to 
  gabbro, 
  and 
  these 
  give 
  place 
  farther 
  

   north 
  to 
  the 
  ordinary 
  gneisses 
  which 
  extend 
  several 
  miles. 
  

  

  On 
  the 
  south 
  the 
  limestone 
  is 
  bounded 
  by 
  a 
  belt 
  of 
  rock 
  whose 
  

   character 
  and 
  relation 
  to 
  the 
  limestone 
  and 
  gneisses 
  have 
  been 
  

   the 
  object 
  of 
  special 
  study. 
  

  

  This 
  rock 
  was 
  referred 
  to 
  by 
  Nason 
  a 
  several 
  years 
  ago 
  as 
  

   gabbro, 
  like 
  that 
  of 
  Essex 
  co., 
  and 
  is 
  probably 
  what 
  Van 
  

   Hise 
  and 
  Williams 
  6 
  classed 
  under 
  the 
  same 
  head. 
  A 
  more 
  de- 
  

   tailed 
  though 
  brief 
  account 
  of 
  it 
  was 
  given 
  by 
  the 
  writer 
  three 
  

   years 
  ago. 
  In 
  the 
  latter 
  description 
  the 
  name 
  gabbro 
  was 
  re- 
  

   tained, 
  on 
  account 
  of 
  its 
  previous 
  use 
  and 
  from 
  the 
  fact 
  that 
  

   portions 
  of 
  the 
  rock 
  were 
  found 
  to 
  consist 
  chiefly 
  of 
  plagioclase 
  

   and 
  pyroxene, 
  but 
  more 
  because 
  the 
  rock 
  was 
  regarded 
  as 
  an 
  out- 
  

   lying 
  portion 
  of 
  the 
  great 
  gabbro 
  masses 
  which 
  at 
  that 
  time 
  were 
  

   supposed 
  to 
  be 
  very 
  widespread 
  in 
  the 
  Adirondack 
  region. 
  

  

  But 
  in 
  using 
  the 
  term 
  gabbro 
  the 
  writer 
  was 
  careful 
  to 
  state 
  

   that 
  it 
  was 
  purely 
  provisional 
  and 
  based 
  upon 
  no 
  thorough 
  petro- 
  

   graphic 
  study, 
  the 
  discussion 
  in 
  which 
  it 
  was 
  employed 
  dealing 
  

   with 
  the 
  rock's 
  " 
  geologic 
  relationships 
  rather 
  than 
  its 
  petro- 
  

   graphic 
  affinities."** 
  It 
  was 
  also 
  pointed 
  out 
  that 
  the 
  rock 
  was 
  

   quite 
  variable 
  in 
  composition, 
  ranging 
  from 
  gabbro 
  to 
  augite- 
  

   syenite, 
  and 
  that 
  data 
  were 
  lacking 
  on 
  which 
  to 
  base 
  a 
  con- 
  

   clusion 
  as 
  to 
  the 
  relative 
  abundance 
  of 
  the 
  different 
  varieties. 
  

   In 
  subsequent 
  casual 
  references 
  to 
  the 
  rock 
  the 
  writer 
  has 
  always 
  

   accentuated 
  the 
  fact 
  that 
  its 
  petrographic 
  affinities 
  were 
  uncer- 
  

   tain, 
  but, 
  unfortunately 
  others 
  have 
  overlooked 
  this 
  qualification 
  

   and 
  so 
  far 
  as 
  it 
  has 
  been 
  mentioned 
  the 
  rock 
  has 
  been 
  classed 
  as 
  

   an 
  undoubted 
  gabbro. 
  

  

  So 
  far 
  as 
  the 
  work 
  planned 
  for 
  this 
  region 
  was 
  carried 
  out 
  *t 
  

   indicates 
  that 
  the 
  term 
  gabbro 
  should 
  not 
  be 
  retained 
  for 
  this 
  

   rock 
  as 
  a 
  whole 
  since 
  the 
  more 
  acid 
  augite-syenite 
  variety 
  forms 
  

   by 
  far 
  the 
  larger 
  part 
  of 
  the 
  mass. 
  

  

  a 
  Iron 
  bearing 
  rocks 
  of 
  the 
  Adirondacks, 
  American 
  geologist, 
  12:28. 
  

   6 
  Op. 
  cit. 
  

  

  a 
  Crystalline 
  limestones 
  and 
  associated 
  rocks 
  of 
  the 
  northwestern 
  Adirondack 
  region. 
  

   Bull. 
  geol. 
  soc. 
  6:271-82. 
  

   d 
  Op. 
  cit. 
  p. 
  271. 
  

  

  