﻿Vol. 
  53.] 
  ORIGIN 
  OF 
  THE 
  KAUENTHAL 
  SERPENTINE. 
  257 
  

  

  (5) 
  Presence 
  of 
  Chlorite. 
  

  

  One 
  striking 
  characteristic, 
  macroscopic 
  and 
  microscopic, 
  in 
  the 
  

   serpentine 
  is 
  the 
  presence 
  of 
  the 
  ' 
  silvery 
  scales,' 
  or 
  the 
  peculiar 
  

   chlorite 
  which 
  is 
  stated 
  to 
  be 
  one 
  of 
  the 
  essential 
  points 
  of 
  distinc- 
  

   tion. 
  It 
  depends, 
  however, 
  on 
  the 
  explanation 
  to 
  be 
  given 
  of 
  the 
  

   formation 
  of 
  this 
  chlorite 
  whether 
  it 
  can 
  be 
  used 
  as 
  an 
  argument 
  

   for 
  the 
  origin 
  of 
  the 
  rock 
  from 
  an 
  amphibolite. 
  It 
  was 
  not 
  at 
  first 
  

   easy 
  to 
  come 
  to 
  a 
  conclusion 
  on 
  this 
  point, 
  and 
  the 
  question 
  is 
  

   partly 
  connected 
  with 
  the 
  relation 
  of 
  the 
  rocks 
  in 
  chemical 
  

   composition. 
  

  

  In 
  the 
  supposed 
  chemical 
  change 
  of 
  a 
  hornblende-rock 
  to 
  serpen- 
  

   tine, 
  Weigand 
  points 
  out 
  that 
  there 
  would 
  be 
  a 
  decrease 
  of 
  silica, 
  

   a 
  proportional 
  increase 
  of 
  magnesia, 
  and 
  the 
  loss 
  of 
  most 
  of 
  the 
  

   lime 
  and 
  alumina. 
  For 
  the 
  latter 
  changes 
  he 
  offers 
  two 
  suggestions 
  : 
  

   the 
  first, 
  that 
  these 
  constituent 
  substances 
  induced 
  the 
  formation 
  of 
  

   the 
  chlorite 
  ; 
  the 
  second, 
  that 
  possibly 
  layers 
  might 
  occur 
  of 
  poorly 
  

   aluminous 
  hornblende. 
  1 
  Of 
  the 
  latter 
  suggestion 
  it 
  is 
  only 
  

   necessary 
  to 
  say 
  that 
  it 
  would 
  be 
  as 
  easy 
  to 
  demand 
  a 
  belief 
  in 
  

   layers 
  of 
  completely 
  non-aluminous 
  olivine, 
  which 
  would 
  grant 
  the 
  

   whole 
  contention. 
  The 
  former 
  suggestion 
  seems 
  necessary 
  to 
  Herr 
  

   Weigand's 
  hypothesis, 
  and 
  demands 
  the 
  acceptance 
  of 
  his 
  view 
  that 
  

   the 
  chlorite 
  is 
  a 
  new 
  formation. 
  But 
  all 
  that 
  can 
  be 
  established 
  on 
  

   this 
  point 
  is 
  that 
  the 
  extrusion 
  of 
  iron 
  oxide 
  and 
  the 
  general 
  

   affinities 
  of 
  the 
  mineral 
  suggest 
  its 
  being 
  in 
  a 
  secondary 
  or 
  modified 
  

   condition. 
  The 
  sharp 
  contours, 
  however, 
  and 
  the 
  general 
  parallelism 
  

   of 
  the 
  flakes, 
  to 
  both 
  of 
  which 
  facts 
  Weigand 
  refers 
  as 
  evidence, 
  2 
  

   are 
  surely 
  no 
  arguments 
  for 
  his 
  view. 
  If 
  the 
  chlorite 
  were 
  

   developed 
  in 
  the 
  alteration 
  of 
  hornblende 
  to 
  serpentine 
  (using 
  up 
  the 
  

   spare 
  alumina 
  and 
  possibly 
  lime), 
  3 
  it 
  would 
  be 
  likely 
  to 
  occur 
  inter- 
  

   locking 
  with 
  the 
  serpentine, 
  of 
  an 
  irregular 
  form, 
  and 
  with 
  a 
  less 
  

   uniform 
  arrangement, 
  as 
  is 
  usually 
  the 
  case 
  in 
  secondary 
  minerals. 
  

   Further, 
  we 
  find 
  the 
  chlorite 
  sharply 
  limited 
  at 
  its 
  junction 
  with 
  a 
  

   hornblende-crystal, 
  or 
  completely 
  embedded 
  in 
  an 
  enstatite, 
  as 
  if 
  it 
  

   represented 
  an 
  original 
  constituent 
  of 
  the 
  rock 
  ; 
  in 
  other 
  words, 
  it 
  

   seems 
  to 
  be 
  the 
  modification 
  of 
  a 
  mineral 
  with 
  a 
  definite 
  form. 
  

   Although 
  I 
  had 
  considered 
  in 
  the 
  field 
  the 
  question 
  of 
  its 
  develop- 
  

   ment, 
  and 
  even 
  had 
  tried 
  to 
  trace 
  a 
  connexion 
  with 
  more 
  than 
  one 
  

   occurrence 
  of 
  a 
  mica, 
  I 
  owe 
  to 
  Prof. 
  Bonney 
  the 
  suggestion 
  of 
  

   what 
  I 
  believe 
  to 
  be 
  the 
  correct 
  view, 
  reconciling 
  seemingly 
  con- 
  

   flicting 
  appearances 
  — 
  that 
  the 
  chlorite 
  probably 
  is 
  the 
  result 
  of 
  

   change 
  of 
  a 
  mica 
  akin 
  to 
  biotite 
  ; 
  if 
  so, 
  the 
  original 
  rock 
  must 
  have 
  

   been 
  related 
  to 
  a 
  mica-peridotite. 
  If 
  the 
  mica, 
  as 
  is 
  probable, 
  

   was 
  a 
  somewhat 
  ferruginous 
  variety, 
  then, 
  where 
  it 
  is 
  deficient, 
  

   the 
  presence 
  of 
  a 
  more 
  ferruginous 
  olivine 
  may 
  be 
  explained. 
  If 
  

  

  1 
  Op. 
  cit. 
  p. 
  202. 
  

  

  2 
  Ibid. 
  

  

  3 
  Herr 
  Weigand 
  notices 
  the 
  difficulty 
  of 
  the 
  lime, 
  and 
  makes 
  the 
  significant 
  

   remark 
  that 
  if 
  not 
  found 
  in 
  true 
  chlorite 
  in 
  such 
  large 
  proportions 
  it 
  is 
  not 
  

   unusual 
  in 
  the 
  mica 
  group 
  {op. 
  cit. 
  p. 
  200). 
  

  

  