﻿REPORT 
  OF 
  THE 
  DIRECTOR 
  , 
  43 
  

  

  fourth 
  of 
  an 
  inch 
  thick. 
  As 
  in 
  this 
  case 
  only 
  a 
  small 
  portion 
  of 
  the 
  

   rock 
  had 
  by 
  its 
  decomposition 
  yielded 
  serpentine, 
  and 
  the 
  layer 
  ob- 
  

   served 
  by 
  the 
  writer 
  had 
  been 
  leached 
  out 
  of 
  the 
  rock, 
  it 
  is 
  reasonable 
  

   to 
  infer 
  that 
  a 
  considerable 
  depth 
  of 
  the 
  rock 
  might 
  since 
  the 
  

   glacial 
  epoch 
  have 
  been 
  changed 
  into 
  serpentine 
  had 
  all 
  of 
  its 
  

   minerals 
  yielded 
  that 
  alteration 
  product. 
  

  

  From 
  what 
  is 
  known 
  of 
  the 
  erosion 
  of 
  the 
  region 
  about 
  New 
  York 
  

   it 
  may 
  be 
  inferred 
  that 
  the 
  rock 
  mass 
  which 
  yielded 
  the 
  New 
  Rochelle 
  

   serpentine 
  was 
  exposed 
  to 
  the 
  action 
  of 
  atmospheric 
  agencies 
  not 
  

   earlier 
  than 
  the 
  Mesozoic 
  age. 
  

  

  THE 
  STATEN 
  ISLAND 
  SERPENTINE. 
  

  

  The 
  general 
  characteristics 
  and 
  extent 
  of 
  this 
  deposit 
  have 
  been 
  

   described 
  by 
  Dr. 
  N. 
  L. 
  Britton, 
  but 
  the 
  question 
  of 
  its 
  origin 
  is 
  not 
  

   entirely 
  settled. 
  Throughout 
  most 
  of 
  its 
  extent 
  this 
  area 
  has 
  suf- 
  

   fered 
  so 
  complete 
  an 
  alteration 
  as 
  to 
  yield 
  no 
  traces 
  of 
  the 
  mineral 
  

   from 
  which 
  it 
  was 
  derived. 
  Mr. 
  Gratacap 
  records 
  the 
  presence 
  of 
  

   traces 
  of 
  unaltered 
  hornblende 
  in 
  specimens 
  from 
  Bard 
  avenue 
  and 
  

   elsewhere. 
  In 
  a 
  well 
  boring 
  made 
  through 
  the 
  serpentine 
  some 
  

   fibrous 
  amphibole 
  or 
  actinolile 
  was 
  found 
  in 
  a 
  comparatively 
  unal- 
  

   tered 
  condition. 
  (Trans. 
  N. 
  Y. 
  Acad. 
  Sci., 
  Vol. 
  I, 
  p. 
  58.) 
  Dr. 
  A. 
  

   A. 
  Julien 
  (loc. 
  cit.) 
  states 
  that 
  he 
  has 
  found 
  traces 
  of 
  unaltered 
  

   hornblende 
  in 
  Staten 
  Island 
  serpentine. 
  

  

  In 
  none 
  of 
  the 
  material 
  which 
  the 
  writer 
  has 
  examined 
  has 
  he 
  

   found 
  unaltered 
  particles 
  of 
  the 
  primary 
  mineral, 
  but 
  there 
  is 
  fre- 
  

   quently 
  present 
  a 
  reticulate 
  structure 
  similar 
  to 
  that 
  which 
  Rosenbusck 
  

   has 
  described 
  and 
  illustrated 
  as 
  characteristic 
  of 
  serpentine 
  derived 
  from 
  

   olivine. 
  In 
  a 
  large 
  number 
  of 
  sections 
  examined 
  by 
  the 
  writer 
  the 
  

   " 
  lattice 
  structure 
  " 
  characteristic 
  of 
  serpentine 
  derived 
  from 
  horn- 
  

   blende 
  was 
  wanting, 
  the 
  angles 
  between 
  the 
  cracks 
  being 
  more 
  

   nearly 
  those 
  of 
  pyroxene 
  than 
  of 
  hornblende. 
  It 
  is 
  not 
  improbable 
  

   that 
  more 
  than 
  one 
  magnesian 
  silicate 
  has 
  contributed 
  to 
  its 
  origin. 
  

  

  In 
  the 
  process 
  of 
  alteration 
  limonite 
  and 
  free 
  silica 
  were 
  the 
  chief 
  

   by-products. 
  The 
  former 
  appears 
  in 
  the 
  once 
  extensive 
  bed 
  of 
  

   limonite 
  which 
  has 
  been 
  used 
  as 
  an 
  iron 
  ore, 
  and 
  the 
  latter 
  in 
  the 
  

   groups 
  of 
  quartz 
  crystals 
  which 
  so 
  frequently 
  occur 
  in 
  the 
  former. 
  

  

  