﻿AND 
  BANDED 
  CRYSTALLINE 
  ROCKS 
  OF 
  THE 
  LIZARD. 
  523 
  

  

  evidence 
  that 
  the 
  hornblende 
  is 
  a 
  secondary 
  product 
  after 
  augite 
  ; 
  for 
  

   the 
  conversion 
  of 
  the 
  one 
  into 
  the 
  other 
  may 
  be 
  distinctly 
  traced, 
  and 
  

   the 
  predominance 
  of 
  the 
  hornblende 
  in 
  some 
  zones, 
  more 
  than 
  in 
  

   others, 
  indicates 
  that 
  the 
  augite 
  was 
  converted 
  into 
  that 
  mineral 
  more 
  

   freely 
  along 
  certain 
  planes 
  than 
  in 
  the 
  spaces 
  between 
  them. 
  

  

  The 
  three 
  specimens 
  that 
  follow 
  in 
  the 
  list 
  were 
  taken 
  from 
  a 
  

   quarry 
  on 
  the 
  roadside, 
  between 
  the 
  Landewednack 
  Church 
  and 
  

   Church 
  Cove, 
  which 
  is 
  worked 
  for 
  road-metal. 
  The 
  rocks 
  here 
  are 
  

   quite 
  typical 
  hornblende-schists. 
  The 
  fourth 
  specimen 
  was 
  taken 
  

   from 
  the 
  landing-place 
  in 
  Church 
  Cove, 
  and 
  belongs 
  to 
  a 
  slightly 
  

   lower 
  horizon 
  than 
  the 
  rocks 
  in 
  the 
  quarry. 
  Under 
  the 
  microscope 
  

   these 
  four 
  specimens 
  are 
  seen 
  to 
  be 
  distinctly 
  foliated 
  rocks, 
  fels- 
  

   pathic 
  bands 
  alternating 
  with 
  bands 
  in 
  which 
  the 
  felspar 
  is 
  sub- 
  

   ordinate 
  to 
  hornblende. 
  The 
  remarkable 
  feature 
  in 
  these 
  slices 
  is 
  

   that 
  they 
  contain 
  an 
  abundance 
  of 
  augite, 
  the 
  latter 
  mineral 
  being 
  

   restricted 
  to 
  the 
  felspathic 
  bands. 
  

  

  The 
  pyroxene 
  in 
  the 
  above 
  specimens, 
  which 
  appears 
  to 
  belong 
  

   to 
  the 
  species 
  malacolite, 
  is 
  colourless 
  in 
  thin 
  sections, 
  but 
  it 
  has 
  a 
  

   faint 
  greenish 
  tint 
  in 
  thick 
  slices. 
  It 
  possesses 
  no 
  dichroism 
  ; 
  it 
  is 
  

   occasionally 
  traversed 
  by 
  little 
  canals 
  of 
  aqueous 
  origin 
  similar 
  to 
  

   those 
  so 
  commonly 
  seen 
  in 
  olivine 
  and 
  enstatite 
  ; 
  it 
  is 
  occasionally 
  

   idiomorphic, 
  and 
  still 
  more 
  frequently 
  exhibits 
  the 
  characteristic 
  

   cleavage-lines 
  of 
  augite. 
  The 
  sections 
  that 
  show 
  well-marked 
  

   cleavage-lines 
  intersecting 
  each 
  other 
  at 
  an 
  angle 
  within 
  two 
  or 
  

   three 
  degrees 
  of 
  90° 
  exhibit 
  interference- 
  figures 
  in 
  converging 
  

   polarized 
  light, 
  and 
  the 
  major 
  axis 
  of 
  elasticity 
  bisects 
  the 
  obtuse 
  

   angle 
  of 
  the 
  rhomb 
  formed 
  by 
  the 
  lines 
  of 
  prismatic 
  cleavage. 
  These 
  

   facts 
  show 
  that 
  the 
  mineral 
  is 
  augite 
  and 
  not 
  epidote. 
  The 
  following 
  

   sketch 
  of 
  a 
  crystal 
  taken 
  from 
  one 
  of 
  my 
  slices 
  will, 
  I 
  doubt 
  not, 
  be 
  

   recognized 
  by 
  petrological 
  microscopists 
  as 
  that 
  of 
  an 
  almost 
  typical 
  

   augite. 
  

  

  Fig. 
  1. 
  — 
  Section 
  of 
  an 
  Augite 
  Crystal 
  partially 
  surrounded 
  by 
  

   Hornblende. 
  

  

  In 
  case, 
  however, 
  any 
  doubt 
  should 
  linger 
  in 
  the 
  minds 
  of 
  those 
  

   who 
  have 
  not 
  had 
  an 
  opportunity 
  of 
  critically 
  examining 
  these 
  slices 
  

   regarding 
  the 
  presence 
  of 
  malacolite 
  in 
  them, 
  I 
  may 
  mention 
  that 
  

   I 
  showed 
  all 
  my 
  specimens 
  to 
  my 
  friend 
  Mr. 
  J. 
  J. 
  Harris 
  Teall, 
  F.G.S., 
  

   and 
  he 
  had 
  no 
  doubt 
  as 
  to 
  the 
  identification 
  of 
  this 
  mineral. 
  More- 
  

   over, 
  he 
  was 
  kind 
  enough 
  to 
  re-examine 
  some 
  of 
  his 
  own 
  specimens 
  

  

  