﻿VoL 
  53-] 
  ANNIVERSARY 
  ADDRESS 
  OF 
  THE 
  PRESIDENT. 
  lxXVU 
  

  

  Craig-y-dinas, 
  and 
  described 
  as 
  breccias 
  and 
  felspathic 
  schistose 
  

   rocks, 
  etc., 
  are 
  undoubtedly 
  of 
  pre-Cambrian 
  age, 
  as 
  are 
  also 
  the 
  

   majority 
  of 
  the 
  schistose 
  rocks 
  in 
  the 
  Lleyn 
  Promontory. 
  1 
  

  

  As 
  illustrating 
  the 
  general 
  conclusions 
  arrived 
  at 
  by 
  us 
  at 
  that 
  

   time, 
  I 
  will 
  venture 
  to 
  quote 
  the 
  following 
  remarks 
  which 
  occur 
  in 
  

   the 
  paper 
  above 
  referred 
  to 
  (Quart. 
  Journ, 
  Geol. 
  Soc. 
  vol. 
  xxxv. 
  

   p. 
  300) 
  : 
  — 
  ' 
  This 
  condition 
  of 
  faulting 
  along 
  one 
  side 
  of 
  these 
  old 
  

   rocks, 
  with 
  the 
  entire 
  loss 
  of 
  the 
  succeeding 
  groups, 
  is 
  such 
  a 
  

   frequent 
  occurrence 
  that 
  it 
  seems 
  necessary 
  to 
  refer 
  specially 
  to 
  the 
  

   physical 
  conditions 
  or 
  probable 
  causes 
  which 
  produced 
  this 
  effect. 
  

   One 
  thing 
  which 
  has 
  become 
  particularly 
  evident 
  during 
  our 
  re- 
  

   searches 
  is 
  the 
  fact 
  that 
  all 
  bits 
  of 
  pre-Cambrian 
  rocks 
  which 
  have 
  

   been 
  included 
  in 
  succeeding 
  sediments 
  must 
  have 
  been 
  not 
  only 
  in 
  

   an 
  indurated 
  condition 
  when 
  broken 
  off 
  from 
  the 
  parent 
  rocks, 
  but, 
  

   moreover, 
  that 
  they 
  had 
  even 
  then 
  undergone 
  metamorphism, 
  and 
  

   the 
  more 
  slaty 
  ones 
  a 
  species 
  of 
  cleavage. 
  The 
  lowest 
  Cambrian 
  

   rocks 
  found 
  are 
  made 
  up 
  of 
  bits 
  and 
  pebbles 
  of 
  these 
  rocks, 
  and 
  so 
  

   like 
  are 
  they 
  frequently 
  to 
  the 
  solid 
  rocks 
  below 
  that 
  there 
  can 
  be 
  

   no 
  doubt 
  that 
  they 
  were 
  the 
  beach-pebbles 
  when 
  those 
  old 
  rocks 
  

   formed 
  coast-lines. 
  Now 
  these 
  old 
  rocks 
  must 
  have 
  undergone 
  

   gradual 
  depression 
  to 
  receive 
  the 
  subsequent 
  sediments; 
  and 
  as 
  

   this 
  depression 
  could 
  not 
  take 
  place 
  in 
  rigid 
  or 
  metamorphosed 
  

   rocks 
  without 
  producing 
  fractures, 
  we 
  have 
  at 
  once 
  one 
  cause 
  for 
  

   some 
  of 
  the 
  faults, 
  and 
  reasons 
  for 
  coast-lines 
  continuing 
  for 
  a 
  

   considerable 
  period 
  in 
  some 
  cases, 
  whilst 
  the 
  surrounding 
  areas 
  

   were 
  becoming 
  depressed 
  to 
  a 
  great 
  depth. 
  The 
  greatest 
  faults, 
  

   however, 
  and 
  those 
  which 
  we 
  have 
  most 
  frequently 
  to 
  deal 
  with, 
  

   are 
  those 
  which 
  occurred 
  after 
  the 
  succeeding 
  Cambrian 
  and 
  Silurian 
  

   sediments 
  were 
  deposited. 
  During 
  the 
  great 
  contractions 
  of 
  the 
  

   crust 
  in 
  Palaeozoic 
  time, 
  especially 
  towards 
  its 
  close, 
  the 
  rigid 
  pre- 
  

   Cambrian 
  crust 
  could 
  not 
  fold, 
  enormous 
  fractures 
  would 
  take 
  place 
  

   instead, 
  and 
  the 
  overlying 
  rocks 
  would 
  be 
  thrown 
  down. 
  In 
  some 
  

   cases, 
  as 
  found 
  here 
  and 
  at 
  other 
  places, 
  the 
  pre-Cambrian 
  would 
  

   be 
  brought 
  to 
  the 
  surface 
  along 
  one 
  edge 
  of 
  the 
  fracture, 
  and 
  its 
  

   other 
  edge 
  would 
  be 
  depressed 
  to 
  a 
  great 
  depth. 
  The 
  fault 
  in 
  

   Eamsey 
  Island, 
  at 
  St. 
  David's, 
  has 
  a 
  downthrow 
  of 
  over 
  16,000 
  feet, 
  

   and 
  I 
  think 
  the 
  one 
  here 
  can 
  hardly 
  be 
  less 
  — 
  that 
  is, 
  if 
  the 
  usual 
  

   sediments 
  found 
  in 
  other 
  areas 
  in 
  Caernarvonshire 
  were 
  ever 
  

   deposited 
  here, 
  and 
  there 
  seems 
  no 
  reason 
  to 
  suppose 
  that 
  they 
  

   were 
  not. 
  

   1 
  See 
  Miss 
  Eaisin's 
  paper, 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xlix. 
  (1893) 
  pp. 
  160, 
  163. 
  

  

  