﻿REPORT 
  OF 
  THE 
  DIRECTOR 
  4I 
  

  

  With 
  regard 
  to 
  the 
  genesis 
  of 
  the 
  minerals 
  from 
  which 
  this 
  serpen- 
  

   tine 
  is 
  derived 
  but 
  httle 
  can 
  be 
  predicted 
  ; 
  there 
  seem 
  to 
  be, 
  however, 
  

   some 
  reasons 
  for 
  not 
  considering 
  them 
  of 
  sedimentary 
  origin. 
  While 
  

   the 
  writer 
  does 
  not 
  question 
  the 
  formation 
  of 
  amphibole 
  and 
  bronzite 
  

   from 
  sedimentary 
  deposits, 
  the 
  evidence 
  of 
  such 
  origin 
  in 
  this 
  case 
  is 
  

   not 
  conclusive. 
  It 
  is 
  impossible 
  at 
  present 
  to 
  predicate 
  with 
  certainty 
  

   the 
  geological 
  character 
  of 
  the 
  primitive 
  rock. 
  The 
  outcrops 
  are 
  so 
  

   limited 
  in 
  extent 
  and 
  so 
  far 
  advanced 
  in 
  alteration 
  that 
  the 
  writer 
  has 
  

   found 
  no 
  clue 
  to 
  guide 
  him 
  in 
  his 
  investigation 
  of 
  this 
  point. 
  It 
  is 
  

   safe 
  to 
  say 
  however 
  that 
  the 
  primitive 
  rock 
  mass 
  was 
  different 
  from 
  

   any 
  now 
  known 
  in 
  an 
  unaltered 
  condition 
  in 
  this 
  terrane. 
  A 
  frag- 
  

   ment 
  of 
  bronzite 
  rock 
  was 
  found 
  by 
  Mr. 
  J. 
  I. 
  Northrup 
  in 
  the 
  debris 
  

   removed 
  from 
  one 
  of 
  the 
  shafts 
  of 
  the 
  new 
  Croton 
  Aqueduct 
  near 
  

   Tarrytown 
  and 
  this 
  may 
  have 
  been 
  a 
  part 
  of 
  such 
  rock 
  mass 
  as 
  that 
  

   which 
  gave 
  being 
  to 
  the 
  New 
  Rochelle 
  serpentine, 
  but 
  unfortunately 
  

   nothing 
  can 
  be 
  ascertained 
  concerning 
  its 
  source. 
  

  

  The 
  origin 
  of 
  the 
  deposits 
  from 
  which 
  this 
  serpentine 
  and 
  its 
  con- 
  

   geners 
  have 
  been 
  derived 
  remains 
  the 
  most 
  important 
  question 
  con- 
  

   nected 
  with 
  their 
  history, 
  and 
  unfortunately 
  we 
  can 
  only 
  reason 
  upon 
  

   analogy 
  in 
  discussing 
  it. 
  In 
  all 
  probability 
  the 
  magnesian 
  silicate 
  

   rocks 
  which 
  by 
  their 
  alteration 
  have 
  yielded 
  these 
  serpentines 
  were 
  

   similar 
  in 
  their 
  origin 
  to 
  the 
  amphibolites 
  and 
  pyroxenites 
  which 
  

   abound 
  in 
  Westchester 
  county. 
  In 
  modern 
  sedimentation 
  no 
  evidence 
  

   has 
  been 
  recorded 
  of 
  an 
  alteration 
  of 
  conditions 
  which 
  would 
  yield 
  

   in 
  small 
  quantity 
  a 
  deposit 
  having 
  the 
  composition 
  of 
  a 
  magnesian 
  

   silicate 
  when 
  immediately 
  before 
  and 
  after 
  it 
  the 
  sediment 
  was 
  chiefly 
  

   composed 
  of 
  silica 
  and 
  aluminous 
  silicates. 
  In 
  composition 
  the 
  am- 
  

   phibolite 
  and 
  pyroxenite 
  beds 
  of 
  the 
  Manhattan 
  Group 
  bear 
  the 
  same 
  

   relation 
  to 
  the 
  strata 
  which 
  enclose 
  them 
  as 
  the 
  intrusive 
  mass 
  of 
  the 
  

   Palisades 
  bears 
  to 
  the 
  beds 
  of 
  sandstone 
  and 
  arkose 
  between 
  which 
  it 
  

   is 
  now 
  included. 
  There 
  is 
  nothing 
  but 
  their 
  somewhat 
  foliated 
  con- 
  

   dition 
  to 
  suggest 
  that 
  they 
  are 
  of 
  sedimentary 
  origin 
  and 
  this 
  charac- 
  

   teristic 
  has 
  been 
  shown 
  to 
  result 
  frequently 
  from 
  dynamo-meta- 
  

   morphism. 
  

  

  The 
  former 
  hypothesis 
  that 
  serpentine 
  is 
  largely 
  derived 
  from 
  the 
  

   alteration 
  of 
  magnesian 
  limestone 
  or 
  dolomite 
  does 
  not 
  seem 
  to 
  be 
  

  

  