﻿256 
  MISS 
  C. 
  A. 
  RAISIN 
  ON 
  THE 
  NATURE 
  AND 
  [May 
  1 
  89 
  J, 
  

  

  the 
  regularity 
  in 
  its 
  arrangement. 
  If 
  there 
  be 
  any 
  difference 
  in 
  this 
  

   respect 
  from 
  other 
  serpentines, 
  there 
  is 
  a 
  far 
  greater 
  difference 
  

   between 
  it 
  and 
  the 
  changed 
  hornblende. 
  1 
  Moreover, 
  in 
  the 
  olivine 
  

   of 
  various 
  rocks 
  there 
  is 
  a 
  marked 
  difference 
  in 
  the 
  amount 
  of 
  

   internal 
  structure 
  which 
  it 
  exhibits. 
  While 
  in 
  many 
  crystals 
  no 
  

   cleavage 
  and 
  only 
  irregular 
  cracks 
  are 
  seen, 
  in 
  others 
  straight 
  

   parallel 
  lines 
  of 
  cleavage 
  are 
  well 
  developed. 
  Perhaps 
  no 
  better 
  

   examples 
  of 
  the 
  latter 
  character 
  can 
  be 
  found 
  than 
  in 
  certain 
  euly- 
  

   sites. 
  2 
  If, 
  however, 
  we 
  examine 
  for 
  comparison 
  other 
  serpentines, 
  

   we 
  find 
  in 
  many 
  that 
  bands 
  equally 
  straight 
  form 
  the 
  network; 
  

   and 
  the 
  structure 
  of 
  the 
  strings 
  in 
  the 
  Kauenthal 
  rock 
  was 
  stated, 
  

   by 
  Prof. 
  Bonney 
  to 
  ' 
  agree 
  perfectly 
  with 
  those 
  in 
  a 
  normal 
  

   serpentine.' 
  3 
  

  

  (3) 
  In 
  the 
  mode 
  of 
  development 
  of 
  the 
  chrysotile, 
  Herr 
  Weigand 
  

   sees 
  evidence 
  of 
  the 
  hornblendic 
  origin 
  of 
  the 
  rock. 
  The 
  fibrous 
  

   aggregates, 
  however, 
  in 
  some 
  of 
  these 
  slides 
  have 
  not 
  a 
  regular 
  

   arrangement, 
  but 
  form 
  a 
  matted 
  mass. 
  Again 
  in 
  other 
  rocks, 
  

   parallel 
  sets 
  of 
  fibres 
  can 
  be 
  found 
  beginning 
  to 
  develop 
  from 
  

   olivine. 
  Thus 
  the 
  fibrous 
  serpentine 
  may 
  in 
  some 
  cases 
  have 
  origi- 
  

   nated 
  by 
  alteration 
  of 
  hornblende, 
  but 
  there 
  seems 
  no 
  evidence 
  that 
  

   this 
  derivation 
  is 
  a 
  necessity 
  ; 
  on 
  the 
  contrary, 
  a 
  development 
  from 
  

   olivine 
  can 
  sometimes 
  be 
  traced. 
  

  

  (4) 
  Specific 
  Gravity 
  and 
  Hardness. 
  

  

  I 
  have 
  tested 
  four 
  specimens 
  of 
  the 
  Kauenthal 
  serpentine, 
  and 
  

   have 
  found 
  in 
  them 
  a 
  specific 
  gravity 
  varying 
  between 
  2*53 
  and 
  

   2-62. 
  These 
  results 
  differ 
  little 
  from 
  those 
  given 
  by 
  the 
  Bonhomme 
  

   (an 
  admitted 
  olivine-serpentine), 
  4 
  or 
  by 
  similar 
  rock 
  elsewhere. 
  

   A 
  specimen 
  of 
  the 
  amphibolite 
  (chosen 
  to 
  include 
  as 
  little 
  foreign 
  

   admixture 
  as 
  possible) 
  gave 
  a 
  specific 
  gravity 
  of 
  2*828. 
  

  

  Herr 
  Weigand 
  further 
  states 
  that 
  the 
  serpentine 
  of 
  the 
  Kauenthal 
  

   is 
  distinguished 
  by 
  its 
  greater 
  softness 
  (op. 
  cit. 
  p. 
  197). 
  I 
  find 
  

   that 
  the 
  degree 
  of 
  hardness 
  in 
  certain 
  type-specimens 
  is 
  nearly 
  4*0, 
  

   while 
  that 
  given 
  by 
  the 
  • 
  olivine-serpentiue 
  ' 
  (Bonhomme) 
  is 
  only 
  

   about 
  3-0. 
  

  

  1 
  The 
  serpentine-bands 
  in 
  the 
  network 
  of 
  an 
  olivine-serpentine 
  seem 
  broader 
  

   than 
  those 
  along 
  the 
  cleavages 
  in 
  hornblende. 
  Further, 
  in 
  those 
  slides 
  which 
  

   are 
  cut 
  across 
  the 
  structure-planes 
  of 
  the 
  rock, 
  a 
  fair 
  proportion 
  of 
  the 
  recog- 
  

   nizable 
  hornblende- 
  crystals 
  show 
  the 
  lattice-structure. 
  But 
  if 
  there 
  be 
  any 
  

   marked 
  regularity 
  in 
  the 
  serpentine, 
  the 
  parallelepipeds 
  mentioned 
  by 
  Weigand 
  

   are 
  mostly 
  rectangular. 
  

  

  2 
  It 
  becomes 
  a 
  question 
  whether 
  the 
  mode 
  of 
  origin 
  of 
  such 
  a 
  rock 
  may 
  not 
  

   be 
  related 
  to 
  the 
  more 
  perfect 
  cleavage 
  of 
  the 
  mineral. 
  If 
  we 
  could 
  connect 
  the 
  

   cause 
  of 
  this 
  structure 
  with 
  the 
  flow 
  of 
  the 
  original 
  magma 
  of 
  the 
  eulysite 
  (a 
  

   character 
  which 
  seems 
  indicated 
  in 
  the 
  rock), 
  this 
  might 
  have 
  an 
  interesting 
  

   significance 
  in 
  connexion 
  with 
  structures 
  in 
  the 
  Rauenthal 
  serpentine. 
  

  

  3 
  Geol. 
  Mag. 
  1887, 
  p. 
  68. 
  

  

  4 
  Herr 
  Weigand 
  gives 
  2 
  - 
  713 
  for 
  the 
  freshest 
  rock 
  and 
  2*609 
  for 
  one 
  more 
  

   decomposed 
  (op. 
  cit. 
  p. 
  189). 
  I 
  obtained, 
  for 
  3 
  specimens, 
  2-671, 
  2-622, 
  and 
  2*52 
  

   respectively 
  ; 
  but 
  the 
  rock 
  is 
  so 
  variable 
  that 
  differences 
  are 
  easily 
  explained. 
  

  

  For 
  Lizard 
  serpentines, 
  see 
  Quart. 
  Journ. 
  Geol 
  Soc. 
  vol. 
  xlvii. 
  (1891) 
  p. 
  466. 
  

   Sp. 
  gr. 
  from 
  2-545 
  to 
  277 
  for 
  8 
  specimens 
  ; 
  one 
  other 
  had 
  a 
  sp. 
  gr. 
  of 
  2*85. 
  

  

  