﻿Vol. 
  53.] 
  ORIGIN 
  OF 
  THE 
  RATIENTHAL 
  SERPENTINE. 
  251 
  

  

  (4) 
  Relation 
  to 
  the 
  Granite. 
  

  

  I 
  traced 
  the 
  serpentine 
  upward, 
  passing 
  off 
  it 
  in 
  many 
  places 
  

   until 
  satisfied 
  that 
  I 
  was 
  on 
  the 
  granite 
  and 
  that 
  no 
  serpen- 
  ine 
  

   occurred 
  higher 
  up, 
  since 
  fallen 
  blocks 
  were 
  not 
  to 
  be 
  seen. 
  The 
  

   two 
  rocks 
  approach 
  most 
  closely 
  along 
  the 
  upper 
  course 
  of 
  the 
  

   streamlet 
  already 
  noticed, 
  especially 
  below 
  the 
  road 
  (<J) 
  and 
  above 
  

   the 
  little 
  path 
  (y). 
  Clambering 
  here 
  for 
  a 
  few 
  paces 
  at 
  several 
  

   spots 
  over 
  ground 
  covered 
  with 
  soil 
  and 
  plants, 
  I 
  passed 
  in 
  each 
  

   case 
  from 
  the 
  serpentine 
  to 
  fragments 
  and 
  blocks, 
  mostly 
  moss- 
  

   covered, 
  consisting 
  of 
  granite, 
  but 
  I 
  found 
  no 
  actual 
  junction. 
  

  

  II. 
  IEicroscopic 
  Details. 
  

  

  In 
  the 
  slides 
  of 
  rocks 
  from 
  the 
  Rauenthal 
  certain 
  distinct 
  minerals 
  

   can 
  be 
  identified. 
  For 
  very 
  many 
  details 
  about 
  these 
  we 
  may 
  

   briefly 
  recapitulate 
  the 
  descriptions 
  given 
  in 
  previous 
  articles 
  by 
  

   Herr 
  Weigand 
  1 
  and 
  by 
  Prof. 
  Bonney. 
  2 
  

  

  (1) 
  Chlorite. 
  

  

  The 
  shining 
  folia 
  visible 
  macroscopically 
  exhibit 
  water-clear 
  

   sections 
  which 
  extinguish 
  straight, 
  and 
  are 
  identified 
  as 
  chlorite 
  

   often 
  enclosing 
  extruded 
  iron 
  oxide. 
  In 
  addition, 
  they 
  sometimes 
  

   contain 
  spindle-shaped 
  crystals 
  of 
  another 
  mineral*, 
  3 
  probably 
  aggre- 
  

   gates 
  of 
  perofskite, 
  or 
  perhaps 
  in 
  some 
  cases 
  an 
  impure 
  sphene. 
  

   The 
  chlorite 
  is 
  associated 
  either 
  with 
  the 
  ordinary 
  serpentine 
  or 
  

   with 
  the 
  amphibolite 
  (PI. 
  XYII. 
  figs. 
  4, 
  6). 
  At 
  places 
  it 
  shows 
  in 
  

   polarized 
  light 
  transverse 
  bands 
  like 
  strain-shadows, 
  so 
  that 
  it 
  

   imitates 
  the 
  twinning 
  of 
  felspar, 
  and 
  has 
  almost 
  a 
  microcline 
  

   appearance. 
  4 
  

  

  (2) 
  Hornblende. 
  

  

  Clearly-marked 
  hornblende 
  occurs 
  within 
  the 
  serpentine, 
  in 
  longi- 
  

   tudinal 
  sections 
  with 
  rectilineal 
  structure 
  and 
  in 
  transverse 
  sections 
  

   with 
  lattice-work, 
  both 
  often 
  showing 
  partial 
  alteration, 
  as 
  described 
  

   by 
  the 
  above-named 
  authors 
  5 
  (PL 
  XYII. 
  fig. 
  2). 
  There 
  would 
  

   be 
  no 
  difference 
  of 
  opinion 
  that 
  such 
  crystals 
  are 
  undergoing 
  

   serpentinization, 
  and 
  that 
  these 
  serpentinized 
  parts 
  retain 
  the 
  

   characteristic 
  indication 
  of 
  hornblende-cleavages. 
  The 
  transverse 
  

   serpentinized 
  bars 
  may 
  be 
  somewhat 
  sinuous 
  and 
  fringed, 
  but 
  the 
  

   longitudinal 
  planes 
  extend 
  as 
  straight 
  boundaries 
  to 
  the 
  kernels 
  of 
  

  

  1 
  ' 
  Die 
  Serpentine 
  der 
  Vogesen,' 
  Jahrb. 
  d. 
  k.-k. 
  Geol. 
  Reichsanstalt, 
  toI. 
  xxv. 
  

   (1875) 
  p. 
  197. 
  

  

  2 
  'Note 
  on 
  Specimens 
  of 
  the 
  Rauenthal 
  Serpentine,' 
  Geol. 
  Mag 
  1887, 
  

   pp. 
  65-70. 
  

  

  3 
  The 
  * 
  indicates 
  a 
  mineral 
  not 
  mentioned 
  in 
  Weigand's 
  description. 
  

  

  4 
  I 
  found 
  in 
  another 
  slide 
  a 
  twinning 
  somewhat 
  resembling 
  the 
  above 
  in 
  a 
  

   mineral 
  which 
  I 
  believe 
  to 
  be 
  pyroxenic, 
  probably 
  enstatite. 
  Cf. 
  T. 
  G. 
  Bonuey, 
  

   Geol. 
  Mag. 
  1887, 
  pp. 
  239. 
  240. 
  

  

  • 
  5 
  Id. 
  ibid. 
  ; 
  also 
  J. 
  J. 
  H. 
  Teall, 
  ' 
  British 
  Petrography,' 
  1888, 
  p. 
  111. 
  

  

  