﻿1864.] 
  BIGSBY 
  MISSING 
  SEDIMENTARY 
  FORMATIONS. 
  225 
  

  

  their 
  early 
  date 
  ; 
  an 
  opportunity 
  being 
  thus 
  afforded 
  for 
  possible 
  or, 
  

   rather, 
  probable 
  coalescence 
  with 
  other 
  emerged 
  lands. 
  In 
  the 
  

   one 
  hundred 
  and 
  fifty 
  instances 
  of 
  gaps. 
  given 
  in 
  this 
  paper 
  (taken 
  

   indifferently), 
  forty-six 
  times 
  has 
  the 
  Silurian, 
  in 
  different 
  parts 
  of 
  

   the 
  world, 
  formed 
  the 
  floors 
  of 
  gaps, 
  which 
  have 
  extended 
  up 
  to 
  nine 
  

   different 
  epochs 
  ; 
  namely, 
  into 
  higher 
  portions 
  of 
  its 
  own 
  period 
  three 
  

   times, 
  into 
  Devonian 
  nine, 
  Carboniferous 
  thirty-one, 
  into 
  Trias 
  and 
  

   Lias 
  once 
  each, 
  into 
  Jurassic 
  once, 
  Cretaceous 
  four, 
  Eocene 
  twice, 
  

   and 
  up 
  to 
  Quaternary 
  four 
  times. 
  On 
  three 
  occasions 
  the 
  Silurian 
  

   rocks 
  have 
  become 
  the 
  roof 
  or 
  covering 
  to 
  lower 
  Palaeozoic 
  forma- 
  

   tions. 
  The 
  Silurian, 
  we 
  see, 
  has 
  to 
  do 
  with 
  more 
  than 
  one-third 
  of 
  

   all 
  the 
  instances 
  I 
  have 
  given, 
  and 
  must 
  have 
  had 
  a 
  wide 
  diffusion. 
  

  

  The 
  older 
  Palaeozoic 
  rocks 
  (including 
  .only 
  Laurentian 
  and 
  some 
  

   other 
  metamorphic 
  beds, 
  once 
  thought 
  azoic) 
  furnish 
  us 
  with 
  the 
  

   next 
  greatest 
  number 
  of 
  floors 
  — 
  twenty-five, 
  or 
  nearly 
  one 
  quarter 
  

   of 
  the 
  instances. 
  Here 
  the 
  epochs 
  reached 
  vertically 
  by 
  these 
  

   twenty-five 
  gaps, 
  without 
  intercalation 
  or 
  interference, 
  are 
  ten 
  : 
  

   namely, 
  Silurian, 
  Devonian, 
  Trias, 
  Lias, 
  Jurassic, 
  Neocomian, 
  Chalk, 
  

   Eocene, 
  Miocene, 
  and 
  Quaternary. 
  Most 
  of 
  these 
  blanks, 
  I 
  need 
  

   hardly 
  say, 
  are 
  of 
  incalculable 
  duration. 
  

  

  The 
  blanks 
  commencing 
  with 
  the 
  Carboniferous 
  formation 
  are 
  

   twenty-two, 
  or 
  about 
  one-seventh 
  of 
  our 
  one 
  hundred 
  and 
  fifty 
  cases. 
  

   They 
  range 
  upwards 
  into 
  seven 
  separate 
  epochs 
  in 
  separate 
  countries 
  

   — 
  to 
  the 
  Permian 
  and 
  Jurassic 
  six 
  times 
  each, 
  to 
  Upper 
  Greensand, 
  

   to 
  Lias, 
  and 
  to 
  Quaternary 
  once 
  each, 
  and 
  to 
  Chalk 
  five 
  times, 
  always 
  

   indicating 
  omissions 
  greater 
  or 
  less 
  in 
  number. 
  In 
  addition 
  to 
  its 
  

   importance 
  as 
  being 
  the 
  roof 
  of 
  the 
  great 
  Russian 
  Carbonifero- 
  

   jurassic 
  gap, 
  the 
  Jurassic 
  is 
  the 
  base 
  or 
  floor 
  of 
  ten 
  other 
  and 
  newer 
  

   sedimentary 
  absences. 
  Five 
  occur 
  in 
  the 
  midst 
  of 
  its 
  own 
  parts 
  or 
  

   stages, 
  two 
  extend 
  to 
  the 
  Chalk, 
  and 
  three 
  to 
  the 
  Tertiaries. 
  

  

  These 
  four 
  periods, 
  the 
  Laurentian, 
  &c, 
  Silurian, 
  Carboniferous, 
  

   and 
  Jurassic, 
  comprise 
  one 
  hundred 
  and 
  thirteen 
  — 
  more 
  than 
  three- 
  

   fourths 
  of 
  our 
  instances. 
  Since 
  these 
  one 
  hundred 
  and 
  fifty 
  are 
  mere 
  

   representatives 
  of 
  great 
  numbers 
  of 
  like 
  phenomena, 
  known, 
  indeed, 
  

   but 
  necessarily 
  unnoticed, 
  we 
  may 
  infer 
  that 
  they 
  are 
  periods 
  pre- 
  

   dominating 
  and 
  spread 
  largely 
  over 
  the 
  earth 
  ; 
  and 
  so 
  field-ob- 
  

   servers 
  tell 
  us. 
  

  

  The 
  Devonian 
  occurs 
  as 
  a 
  base 
  but 
  four 
  times 
  ; 
  that 
  is, 
  eight 
  to 
  a 
  

   gap 
  connected 
  with 
  Coal-measures, 
  thrice 
  with 
  Lias, 
  and 
  once 
  with 
  

   Miocene. 
  

  

  Other 
  epochs 
  still 
  more 
  rarely 
  form 
  floor 
  or 
  roof. 
  The 
  Upper 
  

   Mesozoic 
  and 
  Upper 
  Palaeozoic 
  seem 
  to 
  be 
  oftenest 
  in 
  connexion 
  

   with 
  gaps. 
  

  

  These 
  gaps 
  recur 
  again 
  and 
  again, 
  in 
  the 
  vertical 
  column 
  of 
  sedi- 
  

   ments, 
  upon 
  the 
  same 
  locality 
  or 
  base, 
  in 
  consequence 
  of 
  what 
  

   Thurman 
  has 
  formulated 
  as 
  the 
  " 
  recurrence 
  of 
  elevation 
  " 
  (repeated 
  

   disturbance, 
  in 
  simple 
  words), 
  a 
  fact 
  well 
  exemplified 
  by 
  M. 
  Favre 
  in 
  

   a 
  section 
  of 
  Mont 
  Saleve, 
  near 
  Geneva. 
  The 
  one 
  hundred 
  and 
  fifty 
  

   cases 
  I 
  have 
  described 
  introduce 
  us 
  to 
  two 
  separate 
  gaps 
  on 
  the 
  

   same 
  spot 
  ten 
  times 
  in 
  the 
  sedimentary 
  column, 
  to 
  two 
  threes 
  

  

  