﻿42 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  supported 
  by 
  recent 
  investigations. 
  In 
  the 
  literature 
  to 
  which 
  the 
  

   writer 
  has 
  access, 
  the 
  only 
  recorded 
  instance 
  of 
  such 
  derivation 
  is 
  

   that 
  of 
  a 
  pseudomorph 
  collected 
  from 
  the 
  Tilly 
  Foster 
  Mine, 
  the 
  form 
  

   and 
  structure 
  of 
  which 
  suggested 
  to 
  Prof. 
  J. 
  D. 
  Dana 
  that 
  it 
  had 
  been 
  

   derived 
  from 
  a 
  crystal 
  of 
  dolomite.* 
  Mr. 
  George 
  P. 
  Merrill 
  has 
  

   happily 
  suggested, 
  in 
  the 
  case 
  of 
  the 
  Montville 
  serpentine, 
  that 
  the 
  

   excess 
  of 
  silica 
  set 
  free 
  in 
  the 
  decomposition 
  of 
  the 
  diopside 
  has 
  to 
  

   some 
  extent 
  combined 
  with 
  the 
  magnesia 
  of 
  the 
  enclosing 
  dolomite 
  

   and 
  thus 
  formed 
  a 
  serpentine 
  in 
  addition 
  to 
  that 
  formed 
  by 
  the 
  altera- 
  

   tion 
  of 
  the 
  pyroxene. 
  It 
  is 
  evident 
  that 
  a 
  dolomitic 
  limestone 
  can 
  

   only 
  yield 
  serpentine 
  through 
  the 
  action 
  of 
  silicated 
  waters, 
  while 
  

   the 
  magnesia-iron 
  minerals 
  above 
  mentioned 
  will 
  yield 
  serpentine 
  

   under 
  the 
  influence 
  of 
  ordinary 
  atmospheric 
  waters. 
  

  

  In 
  the 
  present 
  opinion 
  of 
  the 
  writer 
  the 
  origin 
  of 
  the 
  New 
  Rochelle 
  

   serpentine 
  has 
  been 
  as 
  follows: 
  

  

  The 
  mica 
  schists 
  were 
  formed 
  by 
  sedimentation 
  and 
  meta- 
  

   morphism. 
  The 
  amphibolites 
  and 
  other 
  magnesian 
  silicate 
  

   rocks 
  were 
  intruded 
  and 
  by 
  subsequent 
  compression 
  at- 
  

   tained 
  their 
  foliated 
  structure. 
  Orographic 
  disturbance 
  subse- 
  

   quently 
  brought 
  the 
  strata 
  into 
  their 
  present 
  attitude 
  and 
  finally 
  

   erosion 
  removed 
  the 
  covering 
  of 
  mica 
  schist 
  and 
  laid 
  bare 
  the 
  trun- 
  

   cated 
  folds. 
  Atmospheric 
  waters 
  then 
  had 
  free 
  access 
  to 
  the 
  mag- 
  

   nesian 
  silicates 
  and 
  the 
  process 
  of 
  de-ferrugination 
  and 
  hydration 
  

   began 
  and 
  resulted 
  in 
  the 
  formation 
  of 
  the 
  serpentine. 
  The 
  excess 
  of 
  

   siHca 
  was 
  carried 
  off 
  and 
  deposited 
  in 
  the 
  form 
  of 
  chalcedony 
  of 
  

   which 
  large 
  masses 
  and 
  minute 
  veins 
  occur 
  in 
  the 
  deposit, 
  and 
  the 
  

   excess 
  of 
  iron 
  appears 
  as 
  magnetite 
  and 
  chromite, 
  while 
  according 
  to 
  

   the 
  combinations 
  into 
  which 
  the 
  magnesia 
  entered, 
  various 
  varieties 
  of 
  

   serpentine 
  were 
  formed, 
  together 
  with 
  magnesite, 
  talc 
  and 
  deweylite. 
  

  

  The 
  writer 
  is 
  not 
  disposed 
  to 
  attribute 
  any 
  very 
  great 
  geological 
  

   antiquity 
  to 
  the 
  serpentine. 
  Under 
  favorable 
  conditions 
  it 
  forms 
  

   quite 
  rapidly. 
  At 
  Stony 
  Point 
  on 
  the 
  Hudson 
  River, 
  the 
  writer 
  has 
  

   observed 
  a 
  surface 
  of 
  peridotite, 
  which 
  had 
  apparently 
  been 
  swept 
  

   clean 
  by 
  the 
  ice 
  sheet, 
  covered 
  by 
  a 
  layer 
  of 
  serpentine 
  about 
  onc^ 
  

  

  ♦Since 
  the 
  above 
  was 
  written 
  some 
  material 
  has 
  been 
  given 
  to 
  the 
  writer 
  by 
  Dr. 
  Hunt 
  of 
  the 
  

   Brooklyn 
  institute, 
  which 
  in 
  appearance 
  corroborates 
  Prof. 
  Dana'f 
  conclusion. 
  

  

  