﻿REPORT 
  OF 
  THE 
  DIRECTOR 
  35 
  

  

  In 
  this 
  expression 
  of 
  doubt 
  as 
  to 
  the 
  igneous 
  origin 
  of 
  many 
  mag- 
  

   nesian 
  siHcate 
  rocks, 
  Dr. 
  Hunt 
  voices 
  the 
  sentiment 
  of 
  most 
  field 
  

   geologists 
  who 
  have 
  made 
  such 
  rock 
  masses 
  a 
  subject 
  of 
  study. 
  All 
  

   the 
  common 
  anhydrous 
  silicates 
  of 
  magnesia 
  are 
  found 
  to 
  occur 
  as 
  

   individual 
  rock 
  masses 
  or 
  as 
  constituents 
  of 
  them 
  in 
  the 
  stratified 
  

   crystalline 
  terranes. 
  In 
  the 
  opinion 
  that 
  anhydrous 
  and 
  hydrous 
  

   silicates 
  of 
  magnesia 
  are 
  simultaneously 
  developed 
  from 
  a 
  magne- 
  

   sian 
  sediment 
  or 
  magma, 
  Dr. 
  Hunt 
  seems 
  to 
  stand 
  alone 
  and 
  unfor- 
  

   tunately 
  for 
  those 
  who 
  would 
  give 
  due 
  weight 
  to 
  this 
  hypothesis, 
  

   does 
  not 
  advance 
  any 
  conclusive 
  arguments 
  in 
  its 
  behalf, 
  nor 
  does 
  

   he 
  record 
  any 
  observed 
  facts 
  in 
  connection 
  with 
  serpentine, 
  which" 
  

   make 
  it 
  apparent 
  that 
  this 
  mineral 
  is 
  ever 
  developed 
  simultaneously 
  

   with 
  olivine 
  or 
  any 
  other 
  anhydrous 
  magnesian 
  silicate. 
  Dr. 
  Hunt 
  

   alludes 
  to 
  the 
  studies 
  of 
  Scheerer 
  on 
  the 
  association 
  of 
  olivine 
  and 
  

   serpentine 
  at 
  Snarum, 
  in 
  Norway, 
  which 
  led 
  that 
  eminent 
  scientist 
  

   to 
  assert 
  his 
  belief 
  that 
  the 
  two 
  silicates, 
  hydrous 
  and 
  anhydrous, 
  

   were 
  formed 
  simultaneously, 
  because 
  the' 
  alleged 
  pseudomorphs 
  

   were, 
  in 
  many 
  cases, 
  enclosed 
  in 
  masses 
  of 
  chromite. 
  

  

  According 
  to 
  the 
  writer's 
  understanding 
  of 
  Prof. 
  Scheerer's 
  

   article,* 
  the 
  only 
  ground 
  for 
  rejecting 
  the 
  idea 
  of 
  pseudomorphism 
  

   was 
  that 
  if 
  the 
  crystals 
  of 
  serpentine 
  were 
  produced 
  by 
  the 
  hydration 
  

   of 
  pre-existing 
  olivine 
  an 
  increase 
  of 
  bulk 
  would 
  ensue 
  which 
  must 
  

   rend 
  apart 
  by 
  expansion, 
  the 
  matrix 
  of 
  the 
  altered 
  crystal, 
  many 
  of 
  

   the 
  pseudomorphs 
  being, 
  as 
  already 
  stated, 
  enclosed 
  in 
  masses 
  of 
  

   chromite 
  which 
  were 
  unfractured 
  and 
  conformed 
  exactly 
  to 
  the 
  sur- 
  

   face 
  of 
  the 
  included 
  crystal, 
  which 
  had 
  the 
  characteristic 
  form 
  of 
  

   olivine 
  though, 
  in 
  its 
  external 
  portion 
  at 
  least, 
  it 
  had 
  the 
  composition 
  

   of 
  a 
  serpentine. 
  

  

  If 
  this 
  was 
  Scheerer's 
  reason 
  for 
  rejecting 
  the 
  idea 
  of 
  the 
  pseudo- 
  

   morphism 
  of 
  the 
  olivine 
  into 
  serpentine, 
  his 
  objection 
  can 
  not 
  be 
  

   accepted 
  until 
  it 
  be 
  proven 
  that 
  the 
  chromite 
  masses 
  enclosing 
  the 
  

   serpentine 
  were 
  formed 
  before 
  the 
  latter. 
  As 
  chromite 
  masses 
  are 
  

   almost 
  exclusively 
  confined 
  to 
  serpentine 
  rocks 
  and 
  in 
  them, 
  accord- 
  

   ing 
  to 
  Tschermak, 
  are 
  formed 
  by 
  the 
  segregation 
  of 
  the 
  oxides 
  of 
  

   iron 
  and 
  chromium 
  which 
  are 
  set 
  free 
  in 
  the 
  decomposition 
  of 
  the 
  

  

  ♦ 
  Fogg. 
  Ann. 
  Vol. 
  LXVIII, 
  p. 
  319. 
  

  

  