﻿472 
  

  

  ME. 
  J. 
  PAEEItfSON 
  ON 
  SOME 
  

  

  [Dec. 
  1897, 
  

  

  directions. 
  There 
  are 
  also 
  fine 
  quartz-veins, 
  which 
  have 
  probably 
  

   formed 
  the 
  means 
  of 
  supply 
  to 
  what 
  can 
  be 
  scarcely 
  other 
  than 
  a 
  

   vesicle. 
  

  

  It 
  must 
  be 
  understood 
  that 
  this 
  nodular 
  structure, 
  if 
  indeed 
  it 
  

   may 
  be 
  called 
  such, 
  occurs 
  only 
  in 
  one 
  or 
  two 
  specimens, 
  and 
  it 
  is 
  

   merely 
  the 
  suspicion 
  that 
  other 
  and 
  better 
  known 
  cases 
  are 
  due 
  to 
  

   the 
  same 
  causes 
  that 
  has 
  led 
  me 
  to 
  record 
  it 
  here. 
  

  

  Before 
  passing 
  on 
  to 
  consider 
  the 
  true 
  fragmental 
  rocks, 
  some 
  

   notice 
  must 
  be 
  taken 
  of 
  a 
  variety 
  having 
  an 
  appearance 
  in 
  the 
  field 
  

   strongly 
  suggestive 
  of 
  a 
  f 
  el 
  stone-agglomerate. 
  

  

  In 
  it 
  white 
  angular 
  or 
  subangular 
  fragments, 
  with 
  a 
  tendency 
  to 
  

   roughly 
  resemble 
  an 
  almond 
  in 
  shape, 
  of 
  an 
  average 
  length 
  of 
  \ 
  inch, 
  

   but 
  which 
  vary 
  considerably, 
  are 
  embedded 
  in 
  a 
  softish 
  black 
  

   or 
  green-black 
  matrix, 
  which 
  in 
  places 
  contains 
  foreign-looking 
  

   fragments, 
  the 
  whole 
  presenting 
  a 
  well-marked 
  type 
  of 
  some 
  

   constancy. 
  

  

  Rock 
  with 
  white 
  fragments 
  due 
  to 
  jlow-brecciation. 
  

  

  [The 
  clotted 
  portions 
  represent 
  the 
  soft 
  black 
  matrix.] 
  

  

  In 
  places 
  the 
  pieces 
  of 
  felstone 
  are 
  separated 
  by 
  a 
  space 
  consider- 
  

   able 
  in 
  proportion 
  to 
  their 
  bulk 
  ; 
  in 
  others 
  they 
  are 
  close 
  together, 
  

   and 
  the 
  appearance 
  is 
  then 
  suggestive 
  of 
  a 
  slight 
  cracking, 
  followed 
  

   by 
  a 
  forcing 
  apart 
  by 
  a 
  second 
  material. 
  

  

  It 
  is 
  evident 
  that 
  such 
  an 
  appearance 
  as 
  this 
  might 
  be 
  produced 
  

   by 
  a 
  brecciating 
  force 
  after 
  the 
  consolidation 
  of 
  the 
  rock, 
  subsequent 
  

   infiltration 
  giving 
  rise 
  to 
  the 
  black 
  matrix 
  in 
  which 
  the 
  fragments 
  

   are 
  set. 
  But 
  it 
  is 
  also 
  clear 
  that, 
  if 
  such 
  be 
  the 
  right 
  interpretation, 
  

   the 
  magnitude 
  of 
  the 
  force 
  capable 
  of 
  moving 
  neighbouring 
  pieces 
  

   of 
  rock 
  apart, 
  and 
  often 
  of 
  leaving 
  fragments 
  of 
  different 
  structure 
  

   in 
  close 
  proximity, 
  would 
  have 
  been 
  sufficient 
  to 
  leave 
  a 
  clear 
  

   impress, 
  at 
  all 
  events 
  microscopically. 
  Of 
  this, 
  however, 
  there 
  is 
  no 
  

   indication, 
  except 
  in 
  one 
  instance 
  of 
  a 
  brecciated 
  felspar; 
  if 
  other 
  

   cases 
  had 
  been 
  present 
  they 
  would 
  no 
  doubt 
  have 
  been 
  visible 
  ; 
  on 
  

   the 
  contrary 
  the 
  evidence 
  points 
  sometimes 
  the 
  other 
  way, 
  as 
  in 
  

  

  