﻿526 
  MAJOR-GENERAL 
  C. 
  A. 
  M'MAHON 
  ON 
  THE 
  HORNBLENDE-SCHISTS 
  

  

  the 
  effects 
  it 
  has 
  produced. 
  Such 
  minerals 
  as 
  olivine, 
  enstatite, 
  and, 
  

   less 
  commonly, 
  augite 
  are, 
  indeed, 
  frequently 
  scored 
  with 
  the 
  canals 
  

   formed 
  by 
  the 
  aqueous 
  agents 
  of 
  decomposition 
  in 
  their 
  passage 
  

   through 
  them 
  ; 
  hut 
  we 
  can 
  seldom 
  trace 
  the 
  channels 
  through 
  which 
  

   they 
  gained 
  access 
  to 
  these 
  minerals. 
  The 
  Lizard 
  rocks, 
  however, 
  

   seem 
  to 
  have 
  been 
  so 
  completely 
  penetrated 
  by 
  heated 
  water 
  that 
  it 
  

   has 
  worn 
  numerous 
  canals 
  in 
  the 
  body 
  of 
  the 
  rocks 
  themselves 
  by 
  

   which 
  its 
  former 
  presence 
  may 
  be 
  directly 
  traced. 
  Channels 
  now 
  

   stopped 
  with 
  fibrous 
  or 
  amorphous 
  serpentine, 
  with 
  calcite, 
  chlorite, 
  

   steatite, 
  and 
  other 
  products 
  of 
  aqueous 
  action, 
  may 
  be 
  seen 
  wending 
  

   their 
  sinuous 
  course 
  in 
  all 
  directions, 
  here 
  widening 
  into 
  a 
  lake-like 
  

   expanse, 
  there 
  contracting 
  into 
  a 
  narrow 
  canal. 
  In 
  other 
  places 
  the 
  

   channels 
  through 
  which 
  the 
  liquid 
  that 
  effected 
  the 
  decomposition 
  

   of 
  the 
  felspars 
  sapped 
  its 
  way 
  may 
  be 
  distinctly 
  traced 
  by 
  the 
  

   fringing 
  lines 
  of 
  magnetite, 
  ferrite, 
  or 
  limonite, 
  left, 
  like 
  sea-weed 
  

   on 
  the 
  shore, 
  to 
  mark 
  the 
  margin 
  of 
  the 
  once 
  flowing 
  streams. 
  

   On 
  either 
  side 
  of 
  these 
  streams 
  we 
  may 
  also 
  observe 
  how 
  the 
  

   liquid 
  overflowed 
  its 
  banks 
  — 
  to 
  continue 
  the 
  metaphor 
  — 
  and 
  flooded 
  

   the 
  felspars 
  on 
  either 
  side, 
  converting 
  them 
  into 
  the 
  isotropic 
  sub- 
  

   stance 
  that 
  now 
  stops 
  the 
  canals 
  themselves. 
  The 
  following 
  illustra- 
  

   tions 
  (figs. 
  2, 
  3) 
  represent 
  one 
  of 
  these 
  canals. 
  The 
  left-hand 
  sketch 
  

   shows 
  the 
  canal 
  as 
  seen 
  in 
  ordinary 
  transmitted 
  light, 
  the 
  right- 
  

   hand 
  one 
  gives 
  the 
  same 
  canal 
  with 
  a 
  portion 
  of 
  the 
  surrounding 
  

   felspar 
  in 
  polarized 
  light. 
  

  

  Fig. 
  2. 
  — 
  Canal 
  in 
  Kg. 
  3. 
  — 
  Canal 
  under 
  Polarized 
  

  

  Hornblende-schist. 
  Light. 
  

  

  l 
  

  

  M 
  

  

  The 
  illustration 
  given 
  in 
  fig. 
  4 
  is 
  a 
  sketch 
  of 
  a 
  portion 
  of 
  one 
  of 
  the 
  

   meandering 
  streams 
  alluded 
  to 
  above. 
  The 
  lower 
  portion 
  of 
  a 
  large 
  

   lake-like 
  expanse 
  filled 
  with 
  serpentinous 
  matter 
  is 
  shown 
  at 
  e. 
  

   Below 
  this 
  the 
  main 
  stream 
  follows 
  a 
  winding 
  course 
  until 
  it 
  strikes 
  

   the 
  crack 
  c-d, 
  which 
  dies 
  out 
  at 
  d, 
  follows 
  it 
  for 
  a 
  little 
  distance 
  

   and 
  then 
  striking 
  off 
  from 
  it, 
  makes 
  its 
  way 
  into 
  another 
  lake, 
  the 
  

  

  