﻿Yol. 
  53.] 
  SOME 
  OF 
  THE 
  GNEISSES 
  OE 
  ANGLESEY. 
  359 
  

  

  intrusion 
  of 
  the 
  district; 
  and 
  in 
  just 
  the 
  same 
  way 
  the 
  ' 
  halleflinta 
  ' 
  

   which 
  borders 
  the 
  exposed 
  edge 
  of 
  the 
  great 
  granitic 
  intrusion 
  of 
  

   the 
  centre 
  is 
  due 
  to 
  the 
  pressure 
  of 
  that 
  mass, 
  which 
  has 
  pounded 
  

   the 
  earlier 
  gneiss 
  into 
  the 
  minutest 
  fragments, 
  as 
  already 
  pointed 
  

   out 
  by 
  Prof. 
  Bonney 
  and 
  agreed 
  to 
  by 
  the 
  speaker. 
  If 
  we 
  were 
  to 
  

   regard 
  the 
  so-called 
  ' 
  felsite 
  ' 
  as 
  the 
  normal 
  rock 
  from 
  which 
  the 
  

   gneiss 
  had 
  been 
  derived, 
  it 
  would 
  be 
  very 
  remarkable 
  that 
  it 
  should 
  

   be 
  found 
  in 
  its 
  most 
  unaltered 
  condition 
  exactly 
  at 
  those 
  spots 
  

   where 
  it 
  must 
  have 
  been 
  subjected 
  to 
  the 
  greatest 
  amount 
  of 
  

   pressure. 
  The 
  origin 
  of 
  the 
  gneiss 
  appeared 
  to 
  the 
  speaker 
  to 
  be 
  

   still 
  an 
  entirely 
  open 
  question, 
  though 
  he 
  was 
  not 
  disposed 
  to 
  regard 
  

   it 
  as 
  igneous. 
  

  

  Mr. 
  Marr 
  did 
  not 
  quite 
  understand 
  how 
  the 
  occurrence 
  of 
  irre- 
  

   gular 
  blocks 
  of 
  dioritic 
  rock 
  in 
  the 
  gneiss 
  of 
  Llangaffo 
  proved 
  the 
  

   intrusive 
  origin 
  of 
  the 
  latter. 
  Judging 
  from 
  the 
  diagram, 
  he 
  could 
  

   well 
  imagine 
  that 
  the 
  dioritic 
  blocks 
  might 
  be 
  dissevered 
  portions 
  

   of 
  a 
  folded 
  dyke 
  of 
  diorite, 
  though 
  he 
  did 
  not 
  wish 
  to 
  press 
  this 
  

   explanation 
  as 
  the 
  correct 
  one. 
  

  

  