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  ANNIVERSARY 
  ADDRESS 
  OF 
  THE 
  PRESIDENT. 
  lxxV 
  

  

  Were 
  it 
  possible 
  to 
  obtain 
  evidence 
  of 
  the 
  forms 
  of 
  life 
  which 
  

   existed 
  when 
  the 
  earlier 
  pre-Cambrian 
  rocks 
  were 
  deposited, 
  it 
  

   is 
  probable 
  that 
  they 
  would 
  differ 
  materially 
  from 
  those 
  which 
  

   appeared 
  on 
  the 
  scene 
  when 
  the 
  Cambrian 
  seas 
  encroached 
  upon 
  

   this 
  land. 
  In 
  time 
  we 
  shall 
  doubtless 
  meet 
  with 
  better 
  evidence 
  

   of 
  the 
  faunas 
  of 
  the 
  pre-Cambrian 
  seas 
  than 
  we 
  have 
  hitherto 
  

   obtained 
  ; 
  but 
  I 
  fear 
  that 
  it 
  must 
  be 
  from 
  areas 
  which 
  were 
  less 
  

   subject 
  to 
  volcanic 
  and 
  other 
  disturbances 
  in 
  pre-Cambrian 
  times 
  

   than 
  these 
  Pembrokeshire 
  districts. 
  

  

  Caernarvonshire. 
  

  

  At 
  the 
  same 
  meeting 
  of 
  the 
  Society 
  (Dec. 
  5th, 
  1877) 
  as 
  that 
  at 
  

   which 
  the 
  volcanic 
  rocks 
  of 
  pre-Cambrian 
  age 
  in 
  Pembrokeshire 
  

   were 
  described 
  by 
  me, 
  I 
  communicated 
  a 
  paper 
  on 
  some 
  pre-Cambrian 
  

   rocks 
  in 
  Caernarvonshire 
  which 
  had 
  been 
  examined 
  by 
  Prof. 
  Hughes, 
  

   Mr. 
  Hudleston, 
  Mr. 
  Homfray, 
  and 
  myself 
  in 
  the 
  previous 
  summer. 
  

   As 
  in 
  the 
  St. 
  David's 
  paper, 
  I 
  was 
  indebted 
  to 
  Mr. 
  T. 
  Davies 
  for 
  

   very 
  valuable 
  petrological 
  notes. 
  Prof. 
  Hughes 
  also, 
  in 
  a 
  separate 
  

   paper, 
  1 
  gave 
  a 
  description 
  of 
  the 
  pre-Cambrian 
  rocks 
  near 
  Bangor 
  

   and 
  Caernarvon 
  which 
  was 
  accompanied 
  by 
  petrological 
  notes 
  from 
  

   Prof. 
  Bonney. 
  In 
  these 
  papers 
  it 
  was 
  shown 
  that 
  the 
  majority 
  of 
  

   the 
  pre-Cambrian 
  rocks 
  of 
  that 
  area 
  were 
  either 
  granitoid 
  rocks, 
  

   quartz-felsites, 
  or 
  other 
  rocks 
  of 
  igneous 
  origin, 
  and 
  that 
  the 
  Cam- 
  

   brian 
  conglomerates 
  which 
  rested 
  upon 
  them 
  were 
  mainly 
  derived 
  

   from 
  such 
  rocks. 
  At 
  p. 
  151 
  I 
  stated 
  that 
  in 
  the 
  ' 
  great 
  area 
  of 
  

   pre-Cambrian 
  rocks 
  extending 
  through 
  the 
  heart 
  of 
  Caernarvonshire 
  

   from 
  below 
  Tal-y-sarn 
  on 
  the 
  south 
  to 
  St. 
  Anne's 
  Chapel 
  near 
  

   Bethesda 
  on 
  the 
  north, 
  along 
  with 
  another 
  area 
  near 
  Caernarvon 
  

   and 
  Bangor 
  described 
  by 
  Prof. 
  Hughes, 
  are 
  undoubtedly 
  portions 
  

   still 
  remaining 
  of 
  the 
  old 
  pre-Cambrian 
  land 
  ; 
  and 
  in 
  them, 
  I 
  

   believe, 
  are 
  to 
  be 
  recognized 
  representatives 
  of 
  the 
  two 
  great 
  

   unconformable 
  series, 
  Dimetian 
  and 
  Pebidian, 
  so 
  well 
  shown 
  at 
  

   St. 
  David's. 
  With 
  the 
  former 
  of 
  these 
  I 
  would 
  associate 
  the 
  so-called 
  

   syenitic 
  ridge 
  (granitoid 
  rock) 
  at 
  Caernarvon 
  ; 
  and 
  with 
  the 
  latter 
  

   the 
  altered 
  beds 
  2 
  which 
  rest 
  directly 
  on 
  the 
  syenitic 
  ridge 
  towards 
  

   Bangor, 
  and 
  the 
  series 
  chiefly 
  described 
  in 
  this 
  paper 
  to 
  the 
  south 
  

   and 
  north 
  of 
  Llyn 
  Padarn 
  and 
  Moel 
  Tryfaen. 
  The 
  prevailing 
  

   characters 
  in 
  this 
  last 
  series 
  indicate 
  the 
  metamorphism 
  of 
  a 
  pre- 
  

   Cambrian 
  volcanic 
  group 
  of 
  ashes 
  and 
  breccias 
  rather 
  than 
  of 
  true 
  

   sedimentary 
  beds, 
  the 
  result 
  of 
  denudation 
  and 
  alteration 
  only.' 
  

  

  1 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxxiv. 
  (1878) 
  p. 
  137. 
  

  

  2 
  Now 
  considered 
  to 
  be 
  mainly 
  devitrifiecl 
  rhyolites. 
  

  

  