﻿kxvi 
  PKOCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [May 
  1 
  897,- 
  

  

  Prof. 
  Hughes, 
  in 
  speaking 
  of 
  the 
  volcanic 
  rocks 
  near 
  Bangor, 
  

   says 
  (op. 
  tit., 
  p. 
  141) 
  : 
  — 
  ' 
  This 
  series 
  can 
  be 
  matched 
  almost 
  bed 
  for 
  

   bed 
  among 
  the 
  green 
  slates 
  and 
  porphyries 
  of 
  the 
  Lake 
  District, 
  and, 
  

   like 
  these, 
  may 
  be 
  referred 
  to 
  an 
  original 
  volcanic 
  origin 
  and 
  some 
  

   subsequent 
  metamorphism 
  ; 
  but 
  they 
  do 
  not 
  present 
  a 
  sequence 
  like 
  

   the 
  lowest 
  part 
  of 
  the 
  Cambrian, 
  among 
  which 
  we 
  find 
  no 
  beds 
  that 
  

   could 
  by 
  any 
  process 
  be 
  changed 
  into 
  the 
  alternating 
  agglomerates 
  

   and 
  ashes 
  of 
  the 
  Bangor 
  volcanic 
  series/ 
  In 
  conclusion 
  he 
  says 
  

   (p. 
  144) 
  : 
  — 
  ' 
  On 
  the 
  whole, 
  then, 
  it 
  seems 
  that 
  we 
  have 
  an 
  old 
  ' 
  

   volcanic 
  series 
  of 
  remarkably 
  persistent 
  character 
  in 
  North 
  and 
  South 
  

   Wales 
  (and 
  probably 
  we 
  shall 
  find, 
  beyond 
  the 
  borders, 
  that 
  sub- 
  

   divisions 
  can 
  be 
  made 
  out 
  in 
  it, 
  though 
  as 
  yet 
  no 
  break 
  has 
  been 
  

   proved 
  in 
  the 
  series), 
  and 
  that 
  the 
  base 
  of 
  the 
  Cambrian 
  consists 
  of 
  

   a 
  strong 
  conglomerate 
  and 
  grit, 
  between 
  which 
  and 
  the 
  underlying 
  

   series 
  there 
  is 
  great 
  probability 
  of 
  an 
  unconformity.' 
  

  

  In 
  his 
  important 
  paper 
  (Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxxv. 
  1879) 
  

   Prof. 
  Bonney, 
  after 
  pointing 
  out 
  that 
  the 
  quartz-felsites 
  of 
  Llyn 
  

   Padarn 
  and 
  Bangor 
  exhibited 
  every 
  indication 
  of 
  an 
  igneous 
  origin, 
  

   says 
  (p. 
  319), 
  'We 
  must 
  then 
  refuse 
  to 
  these 
  Caernarvonshire 
  

   porphyries 
  an 
  origin 
  different 
  from 
  that 
  of 
  other 
  igneous 
  rocks 
  of 
  

   similar 
  composition, 
  and 
  cease 
  to 
  quote 
  them 
  as 
  examples 
  of 
  what 
  

   extreme 
  metamorphism 
  can 
  effect,' 
  and 
  8 
  there 
  is 
  no 
  difference 
  of 
  

   any 
  importance, 
  so 
  far 
  as 
  I 
  can 
  see, 
  between 
  these 
  quartz-felsites 
  and 
  

   comparatively 
  modern 
  rhyolites 
  ; 
  and 
  if 
  I 
  could 
  prove 
  that 
  a 
  base 
  still 
  

   remained 
  undevitrified 
  I 
  would 
  give 
  them 
  the 
  latter 
  name. 
  That 
  

   they 
  were 
  rhyolites 
  in 
  pre-Cambrian 
  times 
  I 
  have 
  no 
  doubt.' 
  Some- 
  

   geologists 
  have 
  since 
  then 
  endeavoured 
  to 
  show 
  that 
  these 
  rocks 
  are 
  

   of 
  Cambrian 
  instead 
  of 
  pre-Cambrian 
  age 
  ; 
  but 
  the 
  further 
  evidence 
  

   brought 
  forward 
  in 
  papers 
  by 
  Prof. 
  Bonney 
  and 
  Miss 
  Eaisin 
  shows, 
  

   I 
  think, 
  conclusively 
  that 
  they 
  form 
  a 
  part 
  of 
  the 
  pre-Cambrian 
  

   volcanic 
  series 
  in 
  Caernarvonshire, 
  as 
  first 
  suggested 
  by 
  Prof. 
  Hughes 
  

   and 
  myself. 
  

  

  In 
  the 
  year 
  1878, 
  accompanied 
  by 
  Prof. 
  Torell, 
  Mr. 
  Tawney, 
  

   Prof. 
  M 
  C 
  K. 
  Hughes, 
  and 
  Dr. 
  Sterry 
  Hunt, 
  I 
  examined 
  several 
  other 
  

   areas 
  in 
  Caernarvonshire, 
  and 
  the 
  results 
  were 
  communicated 
  to 
  the 
  

   Geological 
  Society 
  on 
  Feb. 
  5th, 
  1879, 
  an 
  appendix 
  on 
  the 
  micro- 
  

   scopic 
  structure 
  of 
  some 
  of 
  the 
  rocks 
  being 
  added 
  by 
  Prof. 
  Bonney. 
  

   Of 
  many 
  of 
  the 
  rocks 
  there 
  referred 
  to 
  we 
  spoke 
  with 
  some 
  caution, 
  

   and 
  I 
  must 
  admit 
  that 
  some 
  of 
  these 
  have 
  since 
  been 
  shown 
  to* 
  

   be 
  of 
  later 
  date, 
  while 
  others 
  are 
  still 
  of 
  doubtful 
  age 
  ; 
  but 
  those 
  

   referred 
  to 
  as 
  occurring 
  in 
  the 
  neighbourhood 
  of 
  Glynllifon 
  and 
  

  

  