﻿68 
  PKOCEEDIXGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  taining 
  a 
  percentage 
  of 
  silica 
  on 
  the 
  artificial 
  limit 
  between 
  acid 
  

   and 
  basic 
  rocks 
  ; 
  but 
  all 
  difficulties 
  of 
  this 
  kind 
  increase 
  in 
  geome- 
  

   trical 
  ratio 
  with 
  the 
  numbers 
  of 
  groups 
  into 
  which 
  an 
  attempt 
  is 
  

   made 
  to 
  classify 
  the 
  various 
  rocks. 
  

  

  Whilst 
  thus 
  criticizing 
  some 
  of 
  the 
  details 
  of 
  the 
  map, 
  it 
  would 
  

   be 
  unfair 
  not 
  to 
  recognize 
  the 
  fact 
  that 
  the 
  Directors 
  have 
  worked 
  

   under 
  considerable 
  difficulties, 
  having, 
  in 
  fact, 
  been 
  obliged 
  to 
  act 
  

   very 
  largely 
  on 
  their 
  own 
  responsibility. 
  In 
  all 
  probability 
  no 
  

   map 
  of 
  Europe 
  would 
  have 
  been 
  produced 
  had 
  not 
  Prof. 
  Beyrich 
  

   and 
  Mr. 
  Hauchecorne 
  undertaken 
  the 
  direction 
  of 
  the 
  work, 
  and 
  all 
  

   geologists 
  owe 
  a 
  debt 
  of 
  gratitude 
  to 
  those 
  gentlemen. 
  Although 
  it 
  

   is 
  not 
  likely 
  that 
  this 
  map 
  will 
  determine 
  the 
  questions 
  of 
  colora- 
  

   tion 
  and 
  nomenclature, 
  it 
  will 
  doubtless 
  contribute 
  largely 
  to 
  their 
  

   being 
  settled. 
  

  

  3. 
  It 
  is 
  probable 
  that 
  the 
  published 
  accounts 
  of 
  the 
  different 
  

   meetings 
  of 
  the 
  Congress 
  form 
  the 
  most 
  important 
  contribution 
  made 
  

   by 
  it 
  to 
  Geological 
  Science. 
  The 
  Reports 
  from 
  the 
  various 
  National 
  

   Committees 
  are 
  naturally 
  very 
  unequal 
  in 
  importance, 
  but 
  many 
  of 
  

   them 
  are 
  excellent, 
  and 
  all 
  of 
  them 
  suggestive. 
  

  

  In 
  this 
  connexion 
  it 
  will 
  be, 
  I 
  hope, 
  not 
  impertinent 
  if 
  I 
  call 
  

   attention 
  to 
  the 
  British 
  Sub-Committees' 
  Beports. 
  In 
  the 
  Preface 
  

   these 
  Beports 
  are 
  held 
  up 
  as 
  a 
  model 
  on 
  which 
  those 
  of 
  other 
  

   countries 
  should 
  be 
  framed 
  and 
  it 
  is 
  claimed 
  that 
  " 
  the 
  greatest 
  

   advance 
  in 
  the 
  work 
  proposed 
  to 
  be 
  done 
  has, 
  so 
  far, 
  been 
  made 
  in 
  

   practical 
  England 
  " 
  A 
  claim 
  of 
  this 
  kind 
  invites 
  criticism, 
  and 
  as 
  

   the 
  writer 
  is 
  the 
  President 
  of 
  the 
  National 
  Committee, 
  and 
  there- 
  

   fore 
  the 
  representative 
  of 
  English 
  geology, 
  his 
  views 
  are 
  doubtless 
  

   those 
  of 
  many 
  British 
  geologists. 
  As 
  already 
  noticed, 
  these 
  Beports 
  

   contain 
  an 
  epitome 
  of 
  the 
  detailed 
  stratigraphy 
  of 
  the 
  British 
  Isles, 
  

   arranged 
  in 
  convenient 
  divisions, 
  the 
  Beport 
  on 
  each 
  division 
  being 
  

   written 
  by 
  one 
  or 
  two 
  authors. 
  The 
  history 
  of 
  the 
  various 
  names 
  

   employed 
  for 
  the 
  different 
  subdivisions 
  in 
  which 
  the 
  strata 
  were 
  

   classed 
  is 
  given, 
  and 
  the 
  views 
  of 
  the 
  principal 
  observers 
  as 
  to 
  the 
  

   correlation 
  and 
  classification 
  of 
  the 
  beds 
  in 
  various 
  parts 
  of 
  the 
  

   country 
  are 
  recorded. 
  There 
  is 
  naturally 
  some 
  inequality; 
  slight 
  

   differences 
  are, 
  however, 
  to 
  be 
  expected, 
  and 
  taking 
  the 
  work 
  as 
  a 
  

   whole, 
  there 
  appears 
  to 
  be 
  every 
  reason 
  to 
  believe 
  that 
  the 
  authors 
  

   have 
  carried 
  out 
  very 
  thoroughly 
  that 
  which 
  they 
  undertook, 
  viz. 
  to 
  

   give 
  the 
  history, 
  synonymy, 
  and 
  detailed 
  classification 
  of 
  British 
  

   sedimentary 
  rocks. 
  

  

  