﻿260 
  MISS 
  C. 
  A. 
  RAISIN 
  ON 
  THE 
  NATURE 
  AND 
  [May 
  1 
  89 
  7, 
  

  

  recognized 
  in 
  the 
  serpentine, 
  and 
  augite 
  occurs 
  in 
  one 
  part 
  of 
  the 
  

   amphibolite. 
  

  

  There 
  seems 
  only 
  one 
  possible 
  explanation 
  — 
  since 
  the 
  hypothesis 
  

   of 
  a 
  modified 
  gneiss 
  is 
  not 
  alone 
  improbable 
  from 
  a 
  priori 
  reasons, 
  

   but 
  also 
  is 
  contradicted 
  by 
  field 
  evidence 
  and 
  by 
  microscopic 
  

   structure 
  — 
  namely, 
  that 
  the 
  serpentine 
  has 
  been 
  derived 
  from 
  a 
  

   peridotite, 
  i. 
  e. 
  from 
  an 
  igneous 
  rock. 
  The 
  inter] 
  amination 
  of 
  the 
  

   amphibolite, 
  its 
  boundary 
  ' 
  not 
  sharply 
  marked 
  off 
  ' 
  (as 
  was 
  described 
  

   by 
  Weigand), 
  the 
  ill-defined 
  hornbiendic 
  patches 
  and 
  streaks, 
  all 
  

   point 
  to 
  gradations 
  from 
  the 
  peridotite 
  to 
  the 
  amphibolite. 
  Similar 
  

   variability 
  also 
  is 
  shown 
  in 
  the 
  amount 
  and 
  arrangement 
  of 
  the 
  

   chlorite, 
  and 
  in 
  the 
  distribution 
  of 
  enstatite. 
  Thus 
  the 
  evidence 
  

   suggests 
  that 
  the 
  original 
  magma 
  was 
  somewhat 
  variable 
  (as 
  often 
  

   is 
  the 
  case, 
  especially 
  in 
  magmas 
  of 
  a 
  basic 
  character), 
  1 
  and 
  that 
  

   the 
  rock 
  formed 
  from 
  it 
  was 
  sometimes 
  an 
  oli 
  vine-en 
  statite 
  rock 
  

   (saxonite), 
  sometimes 
  a 
  hornblende-peridotite, 
  or 
  a 
  mica-peridotite, 
  

   or 
  even 
  a 
  hornblendite. 
  

  

  The 
  parallelism 
  of 
  the 
  structures 
  has, 
  however, 
  to 
  be 
  explained, 
  

   and 
  it 
  may 
  be 
  due 
  to 
  the 
  same 
  cause 
  which 
  has 
  developed 
  in 
  many 
  

   igneous 
  rocks 
  and 
  complexes 
  a 
  fluidal 
  banding 
  or 
  orientation. 
  The 
  

   mica-flakes 
  would 
  then 
  lie 
  in 
  the 
  direction 
  of 
  the 
  flow, 
  causing 
  a 
  

   platiness, 
  possibly 
  afterwards 
  further 
  developed 
  by 
  contraction, 
  and 
  

   the 
  hornblende-crystals 
  would 
  exhibit 
  a 
  similar 
  orientation. 
  The 
  

   arrangement 
  of 
  the 
  chlorite, 
  and 
  the 
  related 
  platy 
  structure 
  of 
  the 
  

   rock, 
  would 
  be 
  very 
  difficult 
  to 
  explain 
  on 
  Weigand's 
  hypothesis 
  as 
  

   to 
  the 
  origin 
  of 
  that 
  mineral. 
  It 
  is 
  impossible 
  to 
  appeal 
  to 
  pressure 
  

   as 
  a 
  cause 
  ; 
  the 
  whole 
  rock, 
  as 
  shown 
  in 
  both 
  the 
  serpentine 
  and 
  

   the 
  amphibolite, 
  evidently 
  is 
  generally 
  unmodified 
  by 
  any 
  such 
  

   mechanical 
  force. 
  

  

  At 
  places, 
  rather 
  ill-defined 
  large 
  patches 
  of 
  serpentine 
  and 
  of 
  

   amphibolite 
  are 
  found, 
  as 
  if 
  a 
  brecciation 
  had 
  occurred, 
  and 
  the 
  dis- 
  

   tinction 
  between 
  the 
  two 
  rocks 
  here 
  and 
  at 
  other 
  places 
  is 
  macro- 
  

   scopically 
  so 
  evident 
  that 
  it 
  suggests 
  the 
  possibility 
  of 
  magmas 
  

   somewhat 
  different 
  in 
  age. 
  The 
  gradations 
  and 
  intermixing, 
  

   however, 
  make 
  it 
  probable 
  that 
  this 
  distinction 
  originated 
  by 
  

   differentiation 
  of 
  a 
  single 
  magma, 
  but 
  whether 
  at 
  a 
  comparatively 
  

   late 
  epoch 
  after 
  the 
  intrusion 
  had 
  commenced, 
  or 
  whether 
  earlier, 
  

   it 
  does 
  not 
  seem 
  possible 
  to 
  prove. 
  Only 
  at 
  the 
  greater 
  depths, 
  

   separation 
  by 
  specific 
  gravity 
  on 
  Soret's 
  principle 
  might 
  have 
  

   acted, 
  causing 
  the 
  less 
  dense 
  part 
  of 
  the 
  magma, 
  which 
  solidified 
  as 
  

   amphibolite, 
  to 
  separate 
  from 
  the 
  heavier 
  part 
  ; 
  and 
  the 
  fragmental 
  

   appearance 
  just 
  mentioned 
  might 
  then 
  be 
  due 
  to 
  a 
  kind 
  of 
  flow- 
  

   brecciation. 
  This 
  pseudo-breccia 
  is 
  found 
  in 
  one 
  or 
  two 
  crags 
  

   towards 
  the 
  north-western 
  border 
  of 
  the 
  serpentine 
  massif. 
  In 
  

   this 
  direction 
  the 
  amphibolite 
  appears 
  to 
  be 
  more 
  developed, 
  not 
  

   because 
  it 
  is 
  due 
  to 
  metamorphosis 
  of 
  the 
  gneiss 
  (since 
  ser- 
  

   pentinized 
  hornbiendic 
  patches 
  and 
  streaks 
  occur, 
  almost 
  to 
  the 
  

  

  1 
  Cf. 
  J. 
  W. 
  Judd, 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xli. 
  (1885) 
  pp. 
  358, 
  390, 
  

   where 
  a 
  peridotite 
  is 
  shown 
  to 
  pass 
  gradually 
  into 
  a 
  picrite 
  or 
  other 
  minor 
  

   varieties, 
  and 
  even 
  into 
  gabbro 
  or 
  dolerite. 
  

  

  