﻿264 
  MISS 
  C. 
  A. 
  RAISIN 
  ON 
  THE 
  NATURE 
  AND 
  [May 
  1 
  897, 
  

  

  since 
  it 
  ma} 
  7- 
  be 
  presumed 
  that 
  no 
  one 
  would 
  maintain 
  a 
  horn- 
  

   blendic 
  origin 
  for 
  the 
  Lizard 
  serpentine. 
  1 
  

  

  A 
  colourless 
  hornblende 
  is 
  characteristic 
  of 
  various 
  masses 
  of 
  

   serpentine. 
  At 
  places 
  (as, 
  for 
  example, 
  Portsoy), 
  a 
  peculiar 
  amphi- 
  

   bolite 
  occurs 
  which 
  shows 
  an 
  almost 
  exact 
  similarity 
  in 
  microscopic 
  

   structure 
  to 
  that 
  of 
  the 
  Rauenthal 
  ; 
  and 
  in 
  rocks 
  from 
  Portsoy 
  and 
  

   the 
  Lizard 
  the 
  appearance 
  of 
  hornblende 
  undergoing 
  serpen 
  tiniza- 
  

   tion 
  is 
  exactly 
  represented. 
  The 
  garnetiferous 
  serpentine 
  from 
  

   Zoblitz 
  also 
  may 
  be 
  closely 
  compared 
  in 
  the 
  character 
  of 
  the 
  

   serpentinized 
  hornblende, 
  except 
  that 
  in 
  one 
  slide 
  I 
  found 
  that 
  the 
  

   amount 
  is 
  far 
  greater 
  than 
  is 
  usual 
  in 
  the 
  Rauenthal 
  serpentine 
  ; 
  

   but 
  in 
  others 
  the 
  hornblende-serpentine 
  formed 
  the 
  smaller 
  part 
  of 
  

   the 
  rock, 
  and 
  the 
  account 
  given 
  by 
  Lemberg 
  2 
  describes 
  the 
  serpen- 
  

   tine 
  as 
  originating 
  from 
  an 
  olivine-rock 
  containing 
  some 
  hornblende 
  

   and 
  garnets 
  or 
  their 
  chlorite-pseudomorphs. 
  Thus, 
  in 
  the 
  first 
  two 
  

   characteristics, 
  it 
  may 
  be 
  compared 
  with 
  that 
  of 
  the 
  Rauenthal. 
  

  

  The 
  characteristic 
  chlorite 
  is 
  not 
  peculiar 
  to 
  the 
  Rauenthal 
  

   serpentine, 
  for 
  it 
  was 
  identified 
  by 
  Prof. 
  Bonney 
  in 
  slices 
  from 
  the 
  

   Lizard. 
  Even 
  there 
  it 
  suggested 
  a 
  possible 
  bleaching 
  of 
  biotite. 
  3 
  

   On 
  examining 
  these 
  slices, 
  I 
  at 
  once 
  recognized 
  the 
  mineral 
  as 
  

   similar 
  to 
  that 
  in 
  the 
  Rauenthal 
  mass. 
  It 
  is 
  represented 
  also 
  at 
  

   Portsoy. 
  

  

  Mica 
  has 
  generally 
  been 
  described, 
  occurring 
  in 
  serpentines 
  or 
  

   peridotites, 
  as 
  akin 
  to 
  phlogopite, 
  and 
  this 
  seems 
  to 
  be 
  the 
  nature 
  of 
  

   the 
  mineral 
  from 
  which 
  the 
  chlorite 
  originated 
  in 
  the 
  Rauenthal 
  

   rock. 
  Thus 
  an 
  interesting 
  comparison 
  may 
  be 
  made 
  with 
  the 
  few 
  

   and 
  rare 
  mica-peridotites 
  which 
  have 
  been 
  described. 
  4 
  

  

  The 
  chemical 
  composition 
  of 
  the 
  Rauenthal 
  and 
  of 
  other 
  serpentines 
  

   shows 
  so 
  great 
  a 
  resemblance 
  that 
  it 
  would 
  be 
  difficult 
  to 
  suppose 
  

   that 
  they 
  had 
  originated 
  by 
  alteration 
  of 
  two 
  totally 
  different 
  rocks. 
  

   One 
  of 
  the 
  Lizard 
  serpentines 
  most 
  closely 
  related 
  seems 
  to 
  be 
  

   that 
  from 
  near 
  Cadgwith, 
  of 
  dark 
  or 
  black 
  colour. 
  The 
  microscope- 
  

   slide 
  also 
  shows 
  marked 
  similarity, 
  and 
  exhibits 
  chlorite 
  as 
  well 
  

   as 
  some 
  hornblende. 
  It 
  may 
  be 
  convenient 
  to 
  place 
  side 
  by 
  side 
  the 
  

   analyses 
  of 
  the 
  two 
  rocks, 
  and 
  of 
  two 
  others, 
  which 
  are 
  interesting 
  

   for 
  comparison 
  : 
  — 
  

  

  1 
  Residual 
  olivine 
  has 
  been 
  described 
  at 
  several 
  localities, 
  such 
  as 
  Coverack, 
  

   Cam 
  Sparnack, 
  south 
  of 
  Kennacka, 
  and 
  others 
  on 
  the 
  western 
  coast. 
  

  

  2 
  Zeitschr. 
  d. 
  Deutsch. 
  geol. 
  Gesellsch. 
  vol. 
  xxvii. 
  (1875) 
  p. 
  531. 
  

  

  3 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xlvii. 
  (1891) 
  pp. 
  473, 
  474. 
  Cf. 
  slices 
  from 
  

   near 
  Cadgwith, 
  Porthalla, 
  and 
  other 
  places. 
  

  

  4 
  The 
  clustered 
  chlorite 
  in 
  some 
  specimens 
  apparently 
  has 
  a 
  similarity 
  to 
  the 
  

   occurrence 
  of 
  mica 
  in 
  the 
  mica-peridotite 
  from 
  Kentucky 
  described 
  by 
  J. 
  S. 
  

   Diller, 
  where 
  the 
  mica 
  ' 
  occurs 
  in 
  round 
  or 
  oblong 
  patches.' 
  It 
  is, 
  however, 
  

   more 
  abundant 
  than 
  it 
  would 
  have 
  been 
  in 
  the 
  Rauenthal 
  rock 
  and 
  ' 
  forms 
  the 
  

   groundwork.' 
  Within 
  the 
  scales 
  is 
  scattered 
  some 
  serpentine. 
  ' 
  The 
  biotite 
  is 
  

   occasionally 
  altered 
  to 
  chlorite,' 
  Am. 
  Journ. 
  jSci. 
  ser. 
  3, 
  vol. 
  xliv. 
  (1892) 
  p. 
  287. 
  

   The 
  similar 
  dyke 
  near 
  Ithaca, 
  N.Y., 
  is 
  described 
  by 
  J. 
  F. 
  Kemp 
  as 
  occurring 
  

   with 
  ' 
  the 
  characteristic 
  reddish 
  biotite 
  of 
  the 
  peridotites,' 
  Am. 
  Journ. 
  Sci. 
  

   ser. 
  3, 
  vol. 
  xlii. 
  (1891) 
  p. 
  411. 
  Cf. 
  also 
  a 
  dyke 
  in 
  Central 
  New 
  York, 
  ibid. 
  vol. 
  

   xliii. 
  (1892) 
  pp. 
  322-327, 
  C. 
  H. 
  Smyth 
  Jr. 
  ; 
  and 
  the 
  De 
  Witt 
  dyke, 
  ibid. 
  vol. 
  

   xlix. 
  (1895) 
  p. 
  458. 
  N. 
  H. 
  Darton 
  & 
  J. 
  F. 
  Kemp. 
  

  

  