﻿266 
  MISS 
  C. 
  A. 
  EAISIN 
  ON 
  THE 
  NATUEE 
  AND 
  [May 
  1 
  89 
  7, 
  

  

  Thus 
  a 
  serpentine 
  such 
  as 
  may 
  be 
  found 
  at 
  the 
  Lizard 
  exhibits 
  

   marked 
  likenesses 
  to 
  that 
  of 
  the 
  Eauenthal. 
  The 
  bastite 
  is 
  similar, 
  

   the 
  accessory 
  hornblende, 
  the 
  chlorite 
  (although 
  more 
  common 
  in 
  

   the 
  Eauenthal), 
  the 
  general 
  network 
  of 
  the 
  serpentine, 
  the 
  variability 
  

   in 
  the 
  composition, 
  and 
  the 
  occasional 
  banding 
  at 
  the 
  Lizard. 
  It 
  

   may 
  perhaps 
  be 
  said 
  that 
  in 
  the 
  Eauenthal 
  rock 
  the 
  olivine 
  is 
  a 
  less 
  

   ferruginous 
  variety, 
  and 
  the 
  mica 
  richer 
  in 
  iron 
  more 
  common. 
  

   But, 
  with 
  such 
  marked 
  likenesses, 
  how 
  could 
  a 
  different 
  origin 
  for 
  

   the 
  two 
  masses 
  be 
  at 
  all 
  probable 
  ? 
  

  

  VI. 
  Summary. 
  

  

  The 
  views 
  of 
  Herr 
  Weigand 
  on 
  the 
  Eauenthal 
  serpentine 
  are 
  

   briefly 
  as 
  follows 
  : 
  — 
  

  

  That 
  a 
  passage 
  can 
  be 
  traced, 
  from 
  the 
  dark 
  hornblendic 
  bands 
  

   of 
  the 
  gneiss 
  (by 
  increase 
  and 
  modification 
  of 
  the 
  hornblende) 
  to 
  

   the 
  pale 
  greenish 
  amphibolite, 
  and 
  from 
  the 
  amphibolite 
  (by 
  a 
  

   process 
  of 
  alteration) 
  to 
  the 
  serpentine. 
  

  

  That 
  the 
  chemical 
  changes 
  in 
  the 
  latter 
  process 
  can 
  be 
  explained, 
  

   if 
  we 
  assume 
  that 
  chlorite 
  is 
  formed 
  mainly 
  from 
  certain 
  constituents 
  

   of 
  the 
  hornblende. 
  

  

  That 
  by 
  microscopic 
  examination 
  a 
  hornblendic 
  structure 
  is 
  

   shown 
  throughout 
  the 
  serpentine. 
  

  

  Therefore, 
  that 
  the 
  serpentine 
  here 
  is 
  the 
  result 
  of 
  change, 
  not 
  

   of 
  an 
  igneous 
  peridotite, 
  as 
  in 
  neighbouring 
  localities, 
  but 
  of 
  part 
  

   of 
  the 
  gneissic 
  series. 
  

  

  The 
  evidence 
  opposed 
  to 
  this 
  conclusion 
  may 
  be 
  shortly 
  stated 
  : 
  — 
  

  

  (I) 
  That 
  in 
  the 
  field 
  we 
  can 
  trace 
  no 
  passage 
  from 
  gneiss 
  to 
  the 
  

   peculiar 
  amphibolite. 
  

  

  That 
  no 
  consideration 
  is 
  given 
  by 
  Herr 
  Weigand 
  to 
  the 
  general 
  

   difficulty 
  which 
  would 
  be 
  involved 
  by 
  a 
  peculiar 
  and 
  local 
  modifi- 
  

   cation 
  of 
  the 
  gneiss 
  such 
  as 
  is 
  to 
  be 
  found 
  nowhere 
  else 
  in 
  the 
  

   neighbourhood. 
  

  

  (II) 
  That 
  the 
  chemical 
  changes 
  of 
  amphibolite 
  to 
  serpentine 
  as 
  

   exhibited 
  in 
  his 
  analyses 
  cannot 
  be 
  fully 
  explained 
  : 
  and 
  that 
  the 
  

   chlorite 
  seems 
  more 
  probably 
  derived 
  from 
  an 
  original 
  mica. 
  

  

  (III) 
  That 
  on 
  microscopic 
  examination 
  the 
  hornblendic 
  structure 
  

   in 
  the 
  serpentine 
  is 
  seen 
  to 
  be 
  limited 
  to 
  certain 
  isolated 
  crystals 
  or 
  

   crystalline 
  layers 
  or 
  patches 
  of 
  original 
  hornblende, 
  and 
  that 
  the 
  

   greater 
  part 
  of 
  the 
  serpentine 
  appears 
  to 
  be 
  derived 
  from 
  olivine. 
  

   That 
  enstatite, 
  a 
  constituent 
  of 
  peridotites, 
  occurs 
  here. 
  That 
  some 
  

   iron 
  oxide, 
  minute 
  rutile, 
  and 
  perofskite 
  are 
  also 
  present. 
  

  

  (IV) 
  That 
  apparent 
  gradations 
  in 
  the 
  rock 
  are 
  connected 
  with 
  the 
  

   different 
  arrangements 
  of 
  hornblende, 
  chlorite 
  and 
  enstatite. 
  That 
  

   this 
  variation 
  (of 
  which 
  the 
  amphibolite 
  may 
  form 
  an 
  extreme 
  case) 
  

  

  vol. 
  xlviii. 
  1892, 
  p. 
  135) 
  and 
  the 
  gabbros 
  at. 
  the 
  Lizard 
  (ibid. 
  vol. 
  xlvii. 
  1891, 
  

   pp. 
  484-490). 
  Of. 
  ' 
  Brit. 
  Petrogr.,' 
  J. 
  J. 
  H. 
  Teall, 
  pi. 
  xliii. 
  fig. 
  2. 
  See 
  also 
  

   Report 
  on 
  Rocks 
  of 
  St. 
  Paul's 
  Island, 
  Renard, 
  Chall. 
  Exped. 
  Narrative, 
  vol. 
  ii. 
  

   App. 
  B, 
  fig. 
  2, 
  pp. 
  7, 
  14. 
  

  

  