﻿AND 
  BANDED 
  CRYSTALLINE 
  ROCKS 
  OF 
  THE 
  LIZARD. 
  525 
  

  

  they 
  were 
  subjected 
  to 
  severe 
  crushing 
  * 
  Moreover, 
  it 
  is 
  evident 
  

   that 
  the 
  very 
  existence 
  of 
  cracks 
  and 
  fractures 
  shows 
  that 
  the 
  rocks 
  

   which 
  now 
  display 
  these 
  marks 
  of 
  strain 
  must 
  have 
  been 
  rigid 
  when 
  

   the 
  fractures 
  took 
  place, 
  and 
  their 
  continued 
  presence 
  demonstrates 
  

   that 
  the 
  dynamic 
  heat 
  developed 
  was 
  insufficient 
  to 
  induce 
  recrystal- 
  

   lization. 
  

  

  Whatever 
  may 
  be 
  said 
  of 
  other 
  rocks, 
  I 
  find 
  it 
  impossible 
  to 
  

   account 
  for 
  the 
  fine 
  banding 
  of 
  the 
  hornblende-schists 
  on 
  the 
  

   supposition 
  that 
  these 
  bands 
  were 
  produced 
  by 
  a 
  series 
  of 
  sliding 
  

   planes. 
  Not 
  only 
  would 
  the 
  regular 
  succession 
  and 
  alternation 
  of 
  

   these 
  thin 
  bands 
  present 
  a 
  serious 
  objection 
  to 
  the 
  acceptance 
  of 
  

   this 
  explanation, 
  but 
  it 
  is 
  obvious 
  that 
  the 
  shearing 
  of 
  a 
  solid 
  rock 
  

   into 
  such 
  extremely 
  thin 
  layers 
  would 
  have 
  developed 
  heat 
  sufficient 
  

   to 
  fuse 
  the 
  whole 
  mass, 
  in 
  which 
  case 
  it 
  would 
  have 
  lost 
  its 
  banded 
  

   structure 
  and 
  have 
  assumed 
  that 
  of 
  a 
  hornblende-granite. 
  The 
  

   stripes 
  are 
  so 
  sharply 
  defined 
  and 
  thin 
  that 
  several 
  of 
  them 
  can 
  be 
  

   seen 
  in 
  a 
  slice 
  mounted 
  on 
  an 
  ordinary 
  microscopic 
  slide. 
  The 
  

   supposition 
  that 
  these 
  bands 
  were 
  originally 
  thick 
  and 
  were 
  drawn 
  

   out 
  into 
  streaks 
  of 
  thread-like 
  thinness 
  by 
  stretching 
  is 
  not 
  sup- 
  

   ported 
  by 
  the 
  microscopic 
  evidence, 
  and 
  it 
  fails 
  to 
  explain 
  how 
  the 
  

   hornblende 
  segregated 
  into 
  a 
  series 
  of 
  parallel 
  zones. 
  The 
  felspars 
  

   that 
  make 
  up 
  the 
  base 
  of 
  the 
  rock 
  do 
  not 
  exhibit 
  in 
  their 
  orienta- 
  

   tion 
  or 
  shapes 
  the 
  marks 
  of 
  stretching 
  and 
  deformation 
  which 
  are 
  

   strikingly 
  displayed 
  in 
  some 
  of 
  the 
  foliated 
  gabbros 
  of 
  the 
  Lizard. 
  

   The 
  rock 
  is 
  not 
  composed 
  of 
  thin 
  shavings 
  of 
  two 
  or 
  more 
  different 
  

   rocks 
  ; 
  the 
  microscope 
  shows 
  that 
  there 
  is 
  no 
  difference 
  in 
  substance, 
  

   or 
  structure, 
  between 
  the 
  base 
  of 
  the 
  white 
  and 
  the 
  base 
  of 
  the 
  

   black 
  bands 
  ; 
  the 
  rock 
  seems 
  to 
  have 
  originally 
  been 
  a 
  homogeneous 
  

   one, 
  and 
  the 
  banding 
  to 
  have 
  been 
  produced 
  at 
  a 
  later 
  stage 
  in 
  its 
  

   history 
  by 
  the 
  segregation 
  of 
  the 
  hornblendic 
  element 
  in 
  planes 
  

   parallel 
  to 
  the 
  bedding. 
  The 
  main 
  question 
  seems 
  to 
  me 
  to 
  be, 
  

   How 
  has 
  this 
  segregation 
  of 
  hornblende 
  been 
  produced 
  ? 
  

  

  One 
  of 
  the 
  most 
  important 
  agents 
  in 
  bringing 
  about 
  the 
  banding 
  

   of 
  the 
  Lizard 
  hornblende-schists 
  appears 
  to 
  me 
  to 
  have 
  been 
  water. 
  

   The 
  rocks 
  themselves, 
  when 
  interrogated 
  with 
  the 
  aid 
  of 
  the 
  micro- 
  

   scope, 
  give 
  abundant 
  evidence 
  of 
  the 
  presence 
  and 
  action 
  of 
  water, 
  

   and 
  the 
  competence 
  of 
  this 
  agent, 
  aided 
  by 
  heat 
  and 
  pressure, 
  to 
  

   bring 
  about 
  great 
  mineralogical 
  and 
  structural 
  changes 
  can 
  hardly 
  

   be 
  doubted. 
  Indeed, 
  the 
  Lizard 
  rocks 
  have 
  been 
  penetrated 
  by 
  

   and 
  have 
  yielded 
  to 
  the 
  action 
  of 
  aqueous 
  influences 
  so 
  completely 
  

   that 
  they 
  may 
  almost 
  be 
  said 
  to 
  have 
  been 
  stewed 
  in 
  water. 
  The 
  

   Lizard 
  serpentine 
  which 
  covers 
  so 
  large 
  an 
  area, 
  and 
  which 
  still 
  

   bears 
  on 
  its 
  bosom 
  so 
  many 
  traces 
  of 
  the 
  potent 
  agent 
  that 
  reduced 
  

   this 
  ancient 
  peridotite 
  to 
  its 
  present 
  condition, 
  may 
  be 
  appealed 
  to 
  

   with 
  confidence 
  to 
  prove 
  the 
  truth 
  of 
  this 
  assertion. 
  

  

  Water 
  — 
  and 
  I 
  omit 
  for 
  brevity 
  sake 
  all 
  allusion 
  to 
  the 
  carbon 
  

  

  dioxide 
  and 
  other 
  chemical 
  reagents 
  with 
  which 
  it 
  is 
  usually 
  charged 
  

  

  — 
  appears 
  to 
  penetrate 
  rocks 
  through 
  such 
  fine 
  pores 
  that, 
  more 
  

  

  often 
  than 
  otherwise, 
  its 
  former 
  presence 
  can 
  only 
  be 
  inferred 
  from 
  

  

  * 
  See 
  also 
  Bonney, 
  ante. 
  

  

  