﻿232 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [Mar. 
  9, 
  

  

  the 
  foregoing 
  pages 
  ; 
  and 
  still 
  more 
  forcibly 
  from 
  the 
  fact, 
  not 
  con- 
  

   fined 
  to 
  one 
  region, 
  that 
  1188 
  Palaeozoic 
  faults 
  (a 
  kindred 
  pheno- 
  

   menon), 
  each 
  half 
  a 
  mile, 
  3, 
  10, 
  20, 
  or 
  30 
  miles 
  long, 
  have 
  been 
  seen 
  

   by 
  the 
  officers 
  of 
  the 
  Geological 
  Survey 
  within 
  the 
  little 
  area 
  of 
  

   Wales, 
  and 
  striking 
  out 
  in 
  every 
  direction. 
  (See 
  Geological 
  Survey 
  

   Maps, 
  sheets 
  36, 
  37, 
  59, 
  60, 
  74, 
  75, 
  &c.) 
  

  

  2. 
  We 
  are 
  taught 
  by 
  missing 
  formations 
  that 
  there 
  always 
  have 
  

   been 
  areas 
  of 
  dry 
  land, 
  because 
  there 
  always 
  have 
  been 
  gaps, 
  and 
  

   much 
  alike 
  in 
  character 
  ; 
  some 
  of 
  the 
  most 
  distinct 
  and 
  protracted 
  of 
  

   these 
  are 
  Silurian, 
  a 
  formation 
  about 
  whose 
  emergence 
  anywhere 
  

   there 
  has 
  hitherto 
  been 
  some 
  uncertainty. 
  

  

  3. 
  They 
  yield 
  us, 
  in 
  the 
  vast 
  Laurentian 
  spaces, 
  European 
  and 
  

   American, 
  the 
  remarkable 
  spectacle 
  of 
  the 
  most 
  ancient 
  land 
  known, 
  

   witnessing, 
  itself 
  little 
  disturbed, 
  for 
  a 
  length 
  of 
  time 
  which 
  no 
  man 
  

   can 
  measure, 
  the 
  successive 
  immersions 
  and 
  emersions 
  going 
  on 
  

   around 
  them, 
  with 
  all 
  their 
  strange 
  and 
  beautiful 
  results. 
  Agassiz, 
  

   Logan, 
  and 
  others 
  have 
  recognized 
  the 
  greatness 
  of 
  this 
  fact. 
  

  

  4. 
  The 
  great 
  Eussian 
  double 
  gap, 
  where 
  the 
  Oxfordian 
  stage 
  (Ju- 
  

   rassic) 
  is 
  interposed, 
  more 
  or 
  less 
  directly 
  (and 
  midway), 
  between 
  

   the 
  widely 
  separated 
  formations, 
  Carboniferous 
  and 
  Cretaceous, 
  is 
  

   worthy 
  of 
  special 
  attention. 
  

  

  5. 
  Gaps 
  show 
  us 
  multitudinous 
  discontinuities 
  in 
  deposition 
  ; 
  

   seldom 
  from 
  faults, 
  fractures, 
  or 
  igneous 
  outbursts, 
  but 
  simply 
  from 
  

   oscillations 
  on 
  broad 
  bases, 
  accompanied 
  by 
  the 
  submarine 
  changes 
  

   which 
  we 
  detect 
  by 
  reference 
  to 
  the 
  laws 
  affecting 
  the 
  distribution 
  

   of 
  organic 
  life 
  and 
  the 
  nature 
  of 
  the 
  sediment. 
  

  

  6. 
  These 
  gaps 
  occasion 
  a 
  rearrangement 
  of 
  mineral 
  substances, 
  

   and 
  of 
  organic 
  existences, 
  in 
  favour 
  of 
  the 
  new 
  formation 
  in 
  the 
  act 
  

   of 
  being 
  deposited 
  in 
  the 
  vicinity, 
  as 
  well 
  as 
  that 
  change 
  of 
  general 
  

   conditions 
  which 
  must 
  follow 
  emergence. 
  

  

  7. 
  In 
  one 
  direction 
  they 
  are 
  useful 
  in 
  the 
  production 
  of 
  variety 
  ; 
  thus 
  

   preventing 
  that 
  monotony 
  to 
  which 
  nature 
  seems 
  always 
  opposed. 
  

  

  8. 
  In 
  another 
  direction 
  they 
  greatly 
  retard 
  the 
  multiplication 
  and 
  

   diffusion 
  of 
  life 
  by 
  converting 
  into 
  dry 
  land, 
  or 
  shallows, 
  many 
  wide 
  

   seas, 
  whose 
  shores 
  and 
  bottoms 
  are 
  the 
  peculiar 
  nurseries 
  of 
  marine 
  

   creatures. 
  

  

  9. 
  They 
  have 
  caused 
  great 
  destruction 
  of 
  life 
  by 
  disturbing 
  con- 
  

   ditions 
  then 
  existing, 
  such 
  as 
  pressure, 
  light, 
  heat, 
  currents, 
  and 
  

   the 
  like, 
  all 
  necessary 
  to 
  the 
  welfare 
  of 
  plants 
  and 
  animals. 
  In 
  the 
  

   disturbance 
  which 
  took 
  place 
  in 
  France 
  at 
  the 
  end 
  of 
  the 
  Liassic 
  

   stage 
  300 
  species 
  of 
  Radiata 
  and 
  Mollusca 
  perished 
  *. 
  

  

  10. 
  Being 
  extraordinarily 
  numerous, 
  they 
  lessen 
  the 
  importance 
  

   of 
  the 
  great 
  rule 
  of 
  gradation 
  from 
  stage 
  to 
  stage 
  in 
  the 
  sedimentary 
  

   column. 
  

  

  11. 
  At 
  these 
  gaps 
  there 
  is 
  perfect 
  independence, 
  a 
  thorough 
  

   severance, 
  of 
  the 
  two 
  contiguous 
  beds 
  or 
  formations. 
  Often 
  not 
  a 
  

   connecting 
  link 
  is 
  left, 
  the 
  floor 
  strewn 
  with 
  the 
  long-since 
  dead 
  

   being 
  merely 
  the 
  support 
  of 
  the 
  incumbent 
  mass, 
  and 
  nothing 
  more. 
  

   An 
  impassable 
  barrier 
  has 
  thus 
  been 
  formed 
  to 
  the 
  recurrence 
  or 
  

  

  * 
  D'Orbigny, 
  ' 
  Cours 
  de 
  Paleont.' 
  vol. 
  i. 
  2 
  e 
  partie, 
  p. 
  475. 
  

  

  