﻿72 
  PROCEEDINGS 
  OP 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  found, 
  fairly 
  comparable 
  to 
  the 
  distinction 
  between 
  Eocene 
  and 
  

   Cretaceous 
  life. 
  Comparison 
  of 
  the 
  recent 
  forms 
  with 
  Miocene 
  

   types 
  would 
  show 
  a 
  distiuct, 
  but 
  less 
  well-marked, 
  difference, 
  and 
  

   if 
  recent 
  and 
  Pliocene 
  faunas 
  were 
  compared, 
  the 
  distinction 
  would 
  

   be 
  still 
  smaller 
  ; 
  but 
  all 
  the 
  newer 
  Tertiarics. 
  commencing 
  with 
  the 
  

   Miocene, 
  form 
  but 
  one 
  period 
  with 
  recent 
  times, 
  if 
  the 
  marine 
  

   faunas 
  are 
  taken 
  as 
  the 
  test; 
  and 
  it 
  may 
  be 
  doubted 
  whether 
  the 
  

   Pliocene 
  could 
  even 
  be 
  separated 
  as 
  a 
  different 
  geological 
  age 
  from 
  

   the 
  Recent. 
  

  

  So 
  far 
  I 
  have 
  merely 
  ventured 
  to 
  express 
  a 
  different 
  opinion 
  from 
  

   Professor 
  Hughes. 
  But 
  on 
  one 
  point 
  I 
  think 
  he 
  is 
  mistaken, 
  and 
  

   it 
  is 
  very 
  important 
  to 
  call 
  attention 
  to 
  the 
  mistake, 
  because 
  the 
  

   idea 
  expressed 
  may 
  be 
  widely 
  spread 
  amongst 
  geologists. 
  Professor 
  

   Hughes 
  says 
  that 
  " 
  we 
  are 
  every 
  day 
  reminded 
  by 
  the 
  work 
  of 
  

   specialists 
  that 
  the 
  result 
  of 
  applying 
  the 
  botanical 
  measure 
  often 
  

   differs 
  considerably 
  from 
  that 
  obtained 
  in 
  the 
  present 
  state 
  of 
  our 
  

   knowledge 
  from 
  a 
  consideration 
  of 
  the 
  included 
  animal 
  remains 
  .... 
  

   This 
  does 
  not 
  destroy 
  cur 
  confidence 
  in 
  the 
  value 
  of 
  palaeontological 
  

   evidence. 
  We 
  have 
  no 
  doubt 
  that 
  when 
  all 
  the 
  fossil 
  evidence, 
  

   botanical 
  and 
  zoological, 
  has 
  been 
  adduced 
  it 
  will 
  be 
  consistent." 
  

  

  Xow 
  I 
  think 
  that 
  it 
  will 
  be 
  found 
  that 
  the 
  real 
  contrast 
  in 
  the 
  

   indication 
  of 
  palaeontological 
  age 
  is 
  not 
  between 
  botany 
  and 
  zoology, 
  

   but 
  between 
  land 
  or 
  freshwater 
  faunas 
  and 
  floras 
  on 
  the 
  one 
  hand, 
  

   and 
  marine 
  faunas 
  on 
  the 
  other. 
  So 
  far 
  as 
  is 
  known, 
  there 
  is 
  not 
  a 
  

   single 
  well-marked 
  case 
  of 
  the 
  inversion 
  of 
  marine 
  faunas, 
  the 
  only 
  

   instance 
  of 
  any 
  importance 
  ever 
  brought 
  forward, 
  that 
  of 
  Barrande's 
  

   colonies, 
  in 
  which 
  an 
  Upper 
  Silurian 
  fauna 
  was 
  supposed 
  to 
  occur 
  in 
  

   beds 
  intercalated 
  amongst 
  others 
  with 
  Lower 
  Silurian 
  types, 
  having, 
  

   I 
  believe, 
  been 
  conclusively 
  shown 
  to 
  be 
  founded 
  on 
  a 
  mistake 
  in 
  

   observation. 
  This 
  fact, 
  the 
  absence 
  of 
  all 
  evidence 
  of 
  inversion, 
  is 
  of 
  

   itself 
  a 
  proof 
  that 
  similarity 
  of 
  pelagic 
  forms 
  does 
  signify 
  practical 
  

   synchronism 
  ; 
  because 
  if 
  the 
  similarity 
  implied 
  difference 
  of 
  time 
  due 
  

   to 
  migration, 
  some 
  cases 
  of 
  inversion 
  must 
  occur*. 
  But 
  in 
  land 
  

   faunas 
  and 
  floras 
  cases 
  of 
  inversion 
  and 
  of 
  the 
  association 
  of 
  types 
  

   characteristic 
  of 
  different 
  epochs 
  and 
  even 
  periods 
  in 
  the 
  same 
  beds 
  

  

  * 
  This 
  may 
  be 
  shown 
  thus 
  : 
  let 
  there 
  be 
  two 
  areas, 
  one 
  inhabited 
  by 
  a 
  fauna 
  

   A, 
  the 
  other 
  by 
  another 
  fauna 
  B. 
  Xow 
  let 
  A 
  migrate 
  into 
  the 
  area 
  occupied 
  

   by 
  B, 
  and 
  vice 
  versa. 
  We 
  should 
  then 
  find 
  in 
  the 
  one 
  area 
  B 
  fauna 
  in 
  the 
  

   upper 
  bed, 
  A 
  in 
  the 
  lower 
  ; 
  in 
  the 
  other 
  area 
  A 
  in 
  the 
  upper, 
  B 
  in 
  the 
  lower. 
  

   Of 
  course 
  the 
  relations 
  would 
  in 
  all 
  probability 
  be 
  more 
  complicated, 
  but 
  the 
  

   results 
  would 
  be 
  the 
  same. 
  

  

  