﻿40 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  tion 
  is 
  complete 
  and 
  the 
  serpentine 
  itself 
  is 
  disintegrating. 
  The 
  

   northeastern 
  outcrops 
  are 
  the 
  most 
  extensive 
  and 
  afford 
  the 
  most 
  

   information 
  concerning 
  the 
  origin 
  of 
  the 
  deposit. 
  The 
  northern- 
  

   most 
  outcrop 
  is 
  dark 
  green 
  in 
  color, 
  of 
  very 
  coarse 
  texture 
  and 
  has 
  

   been 
  derived 
  very 
  largely 
  from 
  bronzite, 
  small 
  quantities 
  of 
  which 
  

   still 
  remain. 
  Succeeding 
  this 
  to 
  the 
  south 
  is 
  a 
  massive 
  rock 
  con- 
  

   sisting 
  of 
  hornblende 
  and 
  garnet 
  covering 
  an 
  area 
  of 
  about 
  one 
  hun- 
  

   dred 
  and 
  fifty 
  square 
  feet; 
  followed 
  in 
  turn 
  by 
  more 
  of 
  the 
  coarse 
  

   serpentine 
  some 
  of 
  which 
  is 
  reddened 
  by 
  the 
  oxidation 
  of 
  its 
  iron 
  

   content. 
  For 
  one 
  hundred 
  and 
  fifty 
  feet 
  or 
  more, 
  the 
  rock 
  is 
  not 
  

   visible 
  and 
  then 
  succeeds 
  a 
  fine 
  grained, 
  light 
  green, 
  rather 
  porous 
  

   serpentine 
  mass 
  which 
  forms 
  a 
  small 
  promontory 
  near 
  the 
  middle 
  of 
  

   the 
  area. 
  This 
  is 
  overlain 
  with 
  a 
  semblance 
  of 
  stratification 
  which 
  

   does 
  not 
  harmonise 
  w4th 
  that 
  of 
  the 
  neighboring 
  gneisses, 
  by 
  a 
  red- 
  

   dish 
  serpentine 
  rock 
  containing 
  actinolite 
  in 
  various 
  stages 
  of 
  altera- 
  

   tion. 
  In 
  this 
  portion 
  of 
  the 
  deposit 
  are 
  thick 
  veins 
  of 
  deweylite 
  and 
  

   chalcedony 
  and 
  a 
  considerable 
  amount 
  of 
  crystalline 
  calcite. 
  In 
  the 
  

   opinion 
  of 
  the 
  writer 
  the 
  calcite 
  is 
  a 
  by-product 
  of 
  the 
  serpentiniza- 
  

   tion. 
  

  

  Microscopic 
  study 
  of 
  the 
  New 
  Rochelle 
  serpentine 
  suggests 
  that 
  

   it 
  is 
  chiefly 
  derived 
  from 
  amphibole 
  and 
  bronzite. 
  The 
  occurrence 
  

   of 
  fibrous 
  amphibole 
  and 
  bronzite 
  or 
  enstatite 
  in 
  connection 
  with 
  the 
  

   serpentine 
  of 
  this 
  locality 
  has 
  already 
  been 
  recorded 
  by 
  Prof. 
  Dana. 
  

   In 
  thin 
  sections 
  examined 
  by 
  the 
  writer, 
  crystals 
  of 
  bronzite 
  may 
  be 
  

   seen 
  in 
  which 
  serpentine 
  has 
  been 
  formed 
  along 
  the 
  transverse 
  

   crevices. 
  In 
  these 
  bronzite 
  crystals 
  are 
  found 
  also 
  irregular 
  masses 
  

   of 
  pleonast, 
  the 
  relations 
  of 
  which 
  to 
  the 
  surrounding 
  mass 
  suggest 
  

   that 
  they 
  are 
  of 
  secondary 
  origin. 
  (PI. 
  VI 
  I.) 
  

  

  Where 
  actinolite 
  has 
  been 
  the 
  source 
  of 
  the 
  serpentine' 
  the 
  un- 
  

   altered 
  mineral 
  verges 
  through 
  a 
  zone 
  of 
  brown, 
  partly 
  decomposed 
  

   material 
  into 
  the 
  finely 
  fibrous 
  serpentine 
  which 
  contains 
  a 
  very 
  large 
  

   proportion 
  of 
  minute 
  crystals 
  of 
  magnetite. 
  (PI. 
  VIII.) 
  

  

  The 
  chang^e 
  from 
  actinolite 
  into 
  serpentine 
  does 
  not 
  seem 
  to 
  be 
  so 
  

   direct 
  as 
  that 
  from 
  bronzite. 
  The 
  zone 
  of 
  discoloration 
  appears 
  to 
  

   represent 
  an 
  intermediate 
  sta^e 
  in 
  which 
  the 
  excess 
  of 
  iron 
  is 
  re- 
  

   moved 
  from 
  chemical 
  combination 
  with 
  the 
  silica 
  and 
  set 
  free. 
  

  

  