﻿226 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [Mar. 
  9, 
  

  

  and 
  two 
  fours 
  vertically. 
  More 
  than 
  these 
  could 
  easily 
  be 
  col- 
  

   lected, 
  were 
  it 
  desirable. 
  M. 
  Ebray 
  furnishes 
  us, 
  from 
  Vespilliere 
  

   (Departement 
  Isere), 
  with 
  a 
  vertical 
  section, 
  passing 
  downwards 
  

   from 
  diluvium 
  to 
  Gneiss, 
  through 
  Jurassic, 
  Liassic, 
  and 
  Carboni- 
  

   ferous 
  strata, 
  where, 
  on 
  successive 
  floors, 
  at 
  least 
  ten 
  great 
  epochs 
  

   are 
  wanting 
  *. 
  

  

  M. 
  Thurmanf 
  gives 
  a 
  curious 
  but 
  not 
  a 
  unique 
  section, 
  which 
  was 
  

   brought 
  to 
  light 
  in 
  digging 
  a 
  well 
  near 
  Wietlisbach, 
  1100 
  feet 
  deep. 
  

   There 
  are 
  here 
  not 
  only 
  several 
  important 
  strata 
  missing 
  (Lias, 
  &c), 
  

   but 
  the 
  whole 
  mass 
  has 
  been 
  inverted. 
  It 
  is 
  an 
  overthrow 
  : 
  on 
  the 
  

   top 
  are 
  Keuper 
  Marls 
  and 
  Muschelkalk, 
  followed 
  downwards 
  by 
  the 
  

   Great 
  Oolite 
  and, 
  finally, 
  by 
  Oxford 
  Clay, 
  largely 
  developed. 
  

  

  3. 
  Inferences. 
  — 
  The 
  Laurentian, 
  Silurian, 
  Jurassic, 
  and 
  other 
  gaps 
  

   (naming 
  them 
  from 
  their 
  floors) 
  occur 
  on 
  the 
  same 
  horizon 
  in 
  various 
  

   parts 
  of 
  the 
  earth; 
  and, 
  those 
  of 
  each 
  series 
  being 
  approximately 
  

   synchronous, 
  though 
  wide 
  apart 
  in 
  solar 
  time 
  perhaps, 
  they 
  must 
  

   frequently 
  unite 
  with 
  neighbouring 
  gaps 
  (floors) 
  of 
  all 
  ages, 
  as 
  they 
  

   emerge 
  to 
  about 
  the 
  same 
  level. 
  The 
  site 
  of 
  each 
  is 
  always 
  passing 
  

   through 
  its 
  own 
  local 
  changes, 
  both 
  in 
  level 
  and 
  in 
  various 
  natural 
  

   processes. 
  

  

  The 
  duration 
  of 
  one 
  of 
  these 
  blanks, 
  as 
  we 
  have 
  seen, 
  varies 
  beyond 
  

   human 
  estimate. 
  We 
  cannot 
  comprehend 
  the 
  vastness 
  of 
  geological 
  

   time. 
  Where 
  a 
  blank 
  only 
  affects 
  a 
  few 
  beds 
  in 
  the 
  midst 
  of 
  an 
  epoch, 
  

   the 
  time 
  may 
  be 
  small 
  ; 
  and 
  this 
  occurs 
  perpetually 
  : 
  but 
  they 
  are 
  

   usually 
  long, 
  and 
  longest, 
  according 
  to 
  our 
  present 
  knowledge, 
  when 
  

   we 
  can 
  count 
  upwards 
  from 
  Laurentian 
  to 
  Quaternary; 
  though 
  the 
  

   time 
  must 
  be 
  very 
  great 
  when 
  it 
  endures 
  from 
  the 
  Silurian 
  to 
  the 
  

   Tertiary, 
  of 
  which 
  interval 
  we 
  have 
  four 
  examples. 
  In 
  sixteen 
  

   cases 
  the 
  Silurian 
  waited 
  open 
  to 
  the 
  sky 
  for 
  the 
  advent 
  of 
  the 
  

   Carboniferous 
  period, 
  and 
  was 
  the 
  base 
  of 
  forty-five 
  gaps 
  in 
  all, 
  as 
  

   just 
  stated. 
  

  

  The 
  duration 
  of 
  these 
  periods 
  of 
  suspension 
  or 
  denudation 
  is 
  best 
  

   measured, 
  though 
  only 
  relatively 
  and 
  remotely, 
  by 
  the 
  number 
  of 
  

   lost 
  epochs, 
  or 
  parts 
  of 
  epochs, 
  which 
  ought 
  to 
  have 
  been 
  between 
  

   the 
  floor 
  and 
  roof 
  ; 
  thus 
  Carboniferous 
  upon 
  Silurian 
  involves 
  far 
  

   less 
  unrepresented 
  time 
  than 
  Eocene 
  upon 
  Silurian. 
  

  

  When 
  the 
  floor 
  and 
  roof 
  of 
  proximate 
  epochs 
  are 
  conformable, 
  or 
  

   nearly 
  so, 
  and 
  when 
  their 
  uniting 
  surfaces 
  show 
  few 
  signs 
  of 
  surf- 
  

   action, 
  the 
  duration 
  of 
  the 
  gap 
  maybe 
  small 
  ; 
  but 
  it 
  may 
  be 
  considered 
  

   long 
  when 
  beds 
  normally 
  more 
  distant 
  from 
  each 
  other 
  meet, 
  when 
  

   there 
  is 
  some 
  discordance 
  of 
  position, 
  and 
  when 
  there 
  is 
  an 
  interspace, 
  

   with 
  fossils 
  ground 
  to 
  powder, 
  or 
  occupied 
  by 
  foreign 
  matters. 
  

  

  D'Orbigny 
  (Cours 
  de 
  Paleontologie, 
  vol. 
  i. 
  part 
  2. 
  p. 
  500) 
  gives 
  a 
  

   beautiful 
  example 
  of 
  this 
  in 
  the 
  littoral 
  deposits 
  of 
  the 
  Bathonian 
  and 
  

   Callovian 
  stages 
  of 
  the 
  Jurassic. 
  He 
  remarks, 
  " 
  We 
  have 
  seen 
  that 
  

   at 
  Colleville 
  and 
  its 
  vicinity 
  the 
  first-mentioned 
  beds 
  of 
  the 
  cliffs 
  of 
  

   that 
  coast 
  have 
  been 
  ground, 
  corroded, 
  polished 
  by 
  the 
  waters, 
  before 
  

   the 
  first 
  clay-beds 
  of 
  the 
  Callovian 
  were 
  laid 
  down. 
  To 
  look 
  at 
  that 
  

  

  * 
  Bull. 
  Soc. 
  Geol. 
  de 
  France, 
  2 
  e 
  serie, 
  vol. 
  xx. 
  p. 
  297. 
  

   t 
  Fourth 
  Letter 
  on 
  the 
  Jura. 
  

  

  