﻿FELSITES 
  m 
  THE 
  BALA 
  GKOUP 
  OE 
  NOBTH 
  WALES. 
  297 
  

  

  why 
  all 
  apparently 
  similar 
  rocks 
  did 
  not 
  present 
  the 
  same 
  characters. 
  

   In 
  accounting 
  for 
  the 
  presence 
  of 
  a 
  structure, 
  he 
  could 
  not 
  undertake 
  

   to 
  explain 
  its 
  absence. 
  In 
  reply 
  to 
  Mr. 
  Hill 
  he 
  said 
  that 
  the 
  

   mimicry 
  of 
  foliation 
  could 
  only 
  deceive 
  the 
  unassisted 
  eye. 
  and 
  

   disappeared 
  when 
  the 
  microscope 
  was 
  applied 
  to 
  the 
  study 
  of 
  the 
  

   rocks. 
  

  

  