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  MAJOE-GENEBAL 
  C. 
  A. 
  M'MAHON 
  ON 
  THE 
  HOENBLEXDE-SCHTSTS 
  

  

  schists 
  of 
  the 
  Lizard, 
  it 
  would 
  prove 
  no 
  more 
  than 
  that 
  the 
  hornblende- 
  

   schists 
  are 
  of 
  great 
  geological 
  antiquity 
  (they 
  have 
  been 
  referred 
  to 
  

   the 
  Archaean 
  age 
  by 
  Professor 
  Bonney 
  *), 
  and 
  this 
  fact 
  would 
  not 
  

   stand 
  in 
  the 
  way 
  of 
  our 
  assigning 
  a 
  volcanic 
  origin 
  to 
  them. 
  

  

  Professor 
  Bonney, 
  in 
  his 
  second 
  paper, 
  " 
  On 
  the 
  Hornblendic 
  and 
  

   other 
  Schists 
  of 
  the 
  Lizard 
  District*' 
  t, 
  was 
  the 
  first 
  to 
  point 
  out 
  " 
  that 
  

   in 
  addition 
  to 
  the 
  ' 
  talco-micaceous 
  ' 
  schists 
  of 
  De 
  la 
  Beche 
  and 
  the 
  

   normal 
  hornblende-schists 
  there 
  is 
  a 
  third 
  group 
  " 
  (the 
  ' 
  granulitic 
  ') 
  

   which 
  was, 
  he 
  supposed, 
  " 
  deposited 
  by 
  rather 
  variable 
  currents 
  in 
  

   waters 
  of 
  no 
  very 
  great 
  depth 
  " 
  J. 
  

  

  In 
  his 
  annual 
  Address 
  as 
  President 
  of 
  the 
  Geological 
  Society, 
  in 
  

   1886, 
  Prof. 
  Bonney 
  gave 
  a 
  summary 
  of 
  his 
  conclusions 
  regarding 
  the 
  

   metamorphic 
  schists 
  of 
  the 
  Lizard, 
  part 
  of 
  which 
  it 
  is 
  desirable 
  to 
  

   to 
  quote 
  : 
  — 
  " 
  In 
  the 
  lowest 
  series 
  [viz. 
  the 
  micaceous] 
  bedding 
  is 
  

   indicated 
  by 
  distinct 
  mineral 
  changes 
  visible 
  to 
  the 
  eye 
  in 
  the 
  field, 
  

   and 
  fully 
  confirmed 
  by 
  microscopic 
  examination. 
  In 
  the 
  upper 
  

   series 
  [viz. 
  in 
  the 
  ' 
  granulitic 
  ' 
  group] 
  there 
  is 
  just 
  the 
  same 
  

   rapid 
  alternation 
  of 
  bands 
  widely 
  differing 
  in 
  mineral 
  character 
  

   that 
  I 
  have 
  described 
  in 
  the 
  melanite-schist 
  series 
  of 
  Yal 
  Piora. 
  

   Hence, 
  if 
  we 
  were 
  to 
  give 
  up 
  the 
  false-bedding 
  which 
  I 
  have 
  

   described 
  in 
  the 
  middle 
  group 
  [viz. 
  the 
  hornblende-schist 
  group] 
  

   (though, 
  after 
  careful 
  reconsideration, 
  I 
  feel 
  it 
  very 
  difficult 
  to 
  explain 
  

   this 
  as 
  the 
  result 
  of 
  mechanical 
  movements), 
  and 
  were 
  to 
  assume 
  the 
  

   whole 
  group 
  to 
  be 
  a 
  mass 
  of 
  crushed 
  dolerites 
  affected 
  by 
  mineral 
  

   changes 
  (which 
  a 
  part 
  may 
  very 
  well 
  be), 
  still 
  there 
  is, 
  above 
  and 
  

   below 
  this, 
  evidence 
  of 
  stratification. 
  Further, 
  even 
  if 
  we 
  reduce 
  

   the 
  apparent 
  bedding 
  throughout 
  to 
  gliding 
  planes, 
  and 
  suppose 
  the 
  

   whole 
  series 
  to 
  be 
  some 
  extraordinary 
  complication 
  of 
  mashed-up 
  

   igneous 
  and 
  sedimentary 
  rocks 
  (which 
  I 
  regard 
  as 
  most 
  improbable), 
  

   there 
  can, 
  even 
  then, 
  be 
  no 
  question 
  that 
  this 
  rolling 
  out, 
  this 
  meta- 
  

   morphism 
  of 
  the 
  most 
  exaggerated 
  kind, 
  is 
  anterior 
  to 
  the 
  intrusion 
  

   of 
  the 
  peridotite 
  (now 
  serpentine), 
  the 
  gabbro, 
  and 
  the 
  granite, 
  from 
  

   which 
  all 
  signs 
  of 
  crushing 
  (save 
  some 
  local 
  disturbance 
  near 
  a 
  fault) 
  

   are 
  absent 
  " 
  §. 
  

  

  Mr. 
  J. 
  J. 
  Harris 
  Teall, 
  P.G.S., 
  on 
  the 
  other 
  hand, 
  in 
  1887, 
  expressed 
  

   the 
  following 
  opinion 
  : 
  — 
  " 
  I 
  submit, 
  therefore, 
  that 
  the 
  rocks 
  of 
  the 
  

   Lizard 
  District 
  referred 
  to 
  in 
  this 
  communication 
  [J, 
  and 
  which 
  con- 
  

   stitute 
  the 
  greater 
  portion 
  of 
  Prof. 
  Bonney's 
  granulitic 
  series, 
  are 
  of 
  

   igneous 
  origin, 
  and 
  that 
  the 
  parallel 
  structure 
  which 
  characterizes 
  

   many 
  of 
  them 
  has 
  nothing 
  to 
  do 
  with 
  stratification 
  in 
  the 
  ordinary 
  

   sense 
  of 
  the 
  word, 
  but 
  is 
  a 
  consequence 
  of 
  the 
  deformation 
  to 
  which 
  

   the 
  original 
  rock-masses 
  have 
  been 
  subjected. 
  It 
  is 
  undoubtedly 
  

   true, 
  as 
  Prof. 
  Bonney 
  has 
  pointed 
  out, 
  that 
  many 
  of 
  the 
  rocks 
  are 
  

   largely 
  composed 
  of 
  broken 
  crystals, 
  and 
  may 
  be 
  said 
  therefore 
  to 
  

   possess 
  a 
  clastic 
  structure, 
  if 
  we 
  use 
  the 
  term 
  clastic 
  in 
  its 
  etymolo- 
  

  

  * 
  Quart. 
  Journ. 
  Geol. 
  Soc, 
  Ann. 
  Address, 
  1886, 
  vol. 
  xlii. 
  Proc. 
  p. 
  86. 
  

  

  + 
  Ibid. 
  vol. 
  xxxix. 
  p. 
  1. 
  

  

  I 
  Log. 
  cit. 
  pp. 
  2, 
  5. 
  

  

  § 
  Ibid. 
  vol. 
  xlii. 
  Proc. 
  p. 
  86. 
  

  

  |j 
  "On 
  the 
  origin 
  of 
  certain 
  Banded 
  Gneisses," 
  Geol. 
  Mag. 
  1887, 
  p. 
  491. 
  

  

  