﻿^l- 
  53*] 
  ORIGIN 
  OF 
  THE 
  RA.UENTHAL 
  SERPENTINE. 
  261 
  

  

  opposite 
  border 
  of 
  the 
  outcrop), 
  but 
  possibly 
  because 
  it 
  formed 
  here 
  

   the 
  lighter 
  upper 
  part 
  of 
  the 
  mass, 
  like 
  a 
  kind 
  of 
  scum. 
  

  

  Thus 
  I 
  believe 
  that 
  the 
  structural 
  and 
  mineralogical 
  characters 
  of 
  

   the 
  Rauenthal 
  serpentine 
  can 
  all 
  be 
  explained 
  by 
  the 
  intrusion 
  of 
  an 
  

   original 
  peridotite 
  -magma 
  x 
  somewhat 
  variable 
  in 
  its 
  composition, 
  

   and 
  that 
  they 
  do 
  not 
  require 
  the 
  hypothesis 
  of 
  an 
  origin 
  different 
  

   from 
  that 
  which 
  has 
  been 
  proved 
  for 
  most 
  serpentines. 
  

  

  IV. 
  Comparison 
  with 
  other 
  Serpentines 
  prom 
  the 
  Yosges. 
  

  

  In 
  order 
  to 
  test 
  more 
  fully 
  the 
  views 
  set 
  forth 
  above, 
  I 
  have 
  made 
  

   a 
  study 
  of 
  other 
  serpentines, 
  both 
  from 
  the 
  Vosges 
  and 
  from 
  more 
  

   distant 
  localities. 
  So 
  far 
  as 
  concerns 
  the 
  former, 
  before 
  comparing 
  

   them 
  with 
  the 
  Rauenthal 
  serpentine, 
  we 
  must 
  add 
  certain 
  types 
  of 
  

   rock 
  and 
  certain 
  mineral 
  constituents 
  to 
  those 
  described 
  by 
  Herr 
  

   "Weigand 
  ; 
  and 
  some 
  corrections 
  must 
  be 
  made 
  in 
  the 
  proportions 
  

   which 
  he 
  assigns 
  to 
  the 
  constituents. 
  

  

  1. 
  Thus 
  there 
  is 
  far 
  more 
  variation 
  in 
  each 
  mass 
  than 
  he 
  has 
  

   observed, 
  and 
  at 
  the 
  same 
  time 
  far 
  more 
  similarity 
  between 
  those 
  

   which 
  he 
  has 
  taken 
  as 
  different 
  masses. 
  The 
  Starkenbach 
  and 
  

   Bonhomme 
  serpentines 
  are 
  described 
  as 
  originating 
  from 
  separate 
  

   magmas, 
  2 
  but 
  parts 
  of 
  the 
  two 
  rocks 
  are 
  almost 
  identical. 
  The 
  

   Starkenbach 
  mass 
  is 
  stated 
  to 
  be 
  a 
  bronzite-serpentine 
  having 
  olivine 
  

   sometimes 
  up 
  to 
  as 
  much 
  as 
  25 
  per 
  cent. 
  3 
  While 
  one 
  of 
  my 
  

   specimens 
  agrees 
  fairly 
  well 
  with 
  this 
  description, 
  the 
  proportions 
  

   estimated 
  by 
  rough 
  calculation 
  in 
  the 
  slices 
  of 
  three 
  others 
  seem 
  to 
  

   give 
  — 
  in 
  two 
  of 
  them, 
  about 
  80 
  per 
  cent, 
  and 
  90 
  per 
  cent, 
  of 
  olivine 
  

   respectively, 
  in 
  another 
  about 
  50 
  per 
  cent, 
  of 
  augite. 
  The 
  Bonhomme 
  

   mass 
  is 
  described 
  as 
  an 
  olivine-serpentine, 
  and 
  therefore 
  distinct 
  

   from 
  that 
  of 
  Starkenbach. 
  As 
  we 
  have 
  just 
  seen, 
  parts 
  of 
  the 
  latter, 
  

   however, 
  are 
  formed 
  mainly 
  of 
  olivine, 
  and 
  it 
  is 
  acknowledged 
  that 
  

   in 
  the 
  former 
  variations 
  exist. 
  "Weigand 
  speaks 
  of 
  ' 
  only 
  a 
  few 
  

   small 
  flakes 
  of 
  hornblende 
  ' 
  being 
  accessory 
  * 
  (besides 
  picotite, 
  

   modified 
  'garnets/ 
  noble 
  erpentine, 
  and 
  iron 
  oxide), 
  but 
  this 
  

   hardly 
  describes 
  parts 
  of 
  the 
  rock 
  which 
  include 
  about 
  60 
  per 
  cent, 
  

   of 
  augite 
  and 
  hornblende. 
  

  

  2. 
  The 
  most 
  important 
  point, 
  however, 
  is 
  the 
  distinct 
  resemblance 
  

   of 
  the 
  Starkenbach 
  and 
  the 
  Bonhomme 
  masses 
  to 
  the 
  Rauenthal 
  

   rock, 
  since 
  both 
  these 
  are 
  admitted 
  by 
  Weigand 
  to 
  be 
  derived 
  from 
  

   forms 
  of 
  peridotite, 
  — 
  the 
  first 
  from 
  a 
  bronzite, 
  and 
  the 
  second 
  from 
  

   an 
  olivine 
  -rock. 
  5 
  

  

  (i) 
  Thus 
  one 
  slice 
  from 
  Starkenbach 
  is 
  from 
  a 
  rock 
  completely 
  

   serpentinized, 
  evidently 
  formed 
  from 
  two 
  minerals 
  — 
  enstatite 
  and 
  

   olivine. 
  The 
  enstatite 
  has 
  the 
  appearance 
  described 
  by 
  Weigand, 
  6 
  

   but 
  the 
  major 
  part 
  of 
  the 
  slide 
  consists 
  of 
  serpentine 
  undoubtedly 
  

  

  1 
  The 
  absence 
  of 
  intrusive 
  'dyke9 
  or 
  branching 
  veins' 
  seems 
  to 
  be 
  in 
  harmony 
  

   with 
  the 
  ' 
  usual 
  babit 
  of 
  peridotites 
  and 
  serpentines.' 
  See 
  T. 
  G. 
  Bonney, 
  Quart. 
  

   Jonrn. 
  G-eol. 
  Soc. 
  vol. 
  lii. 
  (1896) 
  p. 
  29. 
  

  

  2 
  B. 
  Weigand, 
  op. 
  cit. 
  p. 
  196. 
  3 
  Ibid. 
  p. 
  194. 
  

  

  4 
  Ibid. 
  p. 
  191. 
  5 
  Ibid. 
  pp. 
  191, 
  196. 
  6 
  Ibid. 
  p. 
  193. 
  

  

  