﻿1864.] 
  BIGSBY 
  MISSING 
  SEDIMENTARY 
  FORMATIONS. 
  223 
  

  

  certain 
  distances; 
  and 
  therefore 
  denudation 
  must 
  have 
  been 
  both 
  

   common 
  and 
  extensive. 
  Its 
  enormous 
  and 
  wide-spread 
  effects 
  have 
  

   hitherto 
  not 
  been 
  sufficiently 
  noticed. 
  Masses 
  of 
  rock, 
  many 
  thou- 
  

   sands 
  of 
  feet 
  thick, 
  have 
  been 
  pared, 
  sliced 
  off, 
  and 
  then 
  swept 
  

   away 
  from 
  the 
  deposits 
  of 
  every 
  great 
  period 
  ; 
  so 
  that 
  the 
  earth's 
  

   surface 
  on 
  which 
  we 
  now 
  tread 
  is 
  not 
  that 
  which 
  was 
  inhabited 
  by 
  

   the 
  extinct 
  animals 
  of 
  bygone 
  ages. 
  It 
  has 
  been 
  raised 
  and 
  de- 
  

   pressed 
  many 
  times 
  even 
  since 
  the 
  Liassic 
  period 
  *. 
  

  

  As 
  Sir 
  Charles 
  Lyell 
  says 
  f 
  , 
  " 
  The 
  evidences 
  of 
  the 
  work 
  of 
  denu- 
  

   dation 
  are 
  defective, 
  because 
  it 
  is 
  the 
  nature 
  of 
  every 
  destroying 
  

   cause 
  to 
  obliterate 
  the 
  signs 
  of 
  its 
  own 
  agency." 
  But 
  this 
  remark 
  

   best 
  applies 
  to 
  extreme 
  cases. 
  

  

  The 
  most 
  material 
  of 
  these 
  indications 
  may 
  be 
  thus 
  summed 
  up 
  : 
  — 
  

   The 
  disappearance 
  of 
  a 
  stratum 
  may 
  be 
  attributed 
  to 
  denudation 
  

   when 
  its 
  place 
  is 
  occupied 
  by 
  patches 
  of 
  the 
  lost 
  stratum, 
  or 
  by 
  its 
  

   boulders, 
  grits, 
  or 
  sands, 
  especially 
  when 
  its 
  peculiar 
  organic 
  remains 
  

   remain 
  attached 
  ; 
  when 
  the 
  basement-bed, 
  burrowed 
  by 
  litho- 
  

   phagous 
  mollusks, 
  is 
  polished, 
  streaked, 
  and 
  guttered, 
  or 
  scooped 
  

   into 
  hollows, 
  often 
  very 
  deep 
  ; 
  when 
  the 
  lines 
  of 
  division 
  are 
  strong, 
  

   all 
  vestiges 
  of 
  transition 
  destroyed, 
  together 
  with 
  every 
  mark 
  of 
  

   intermixture 
  of 
  fossil 
  life. 
  

  

  M. 
  Hebert, 
  in 
  his 
  able 
  paper 
  on 
  the 
  " 
  Oscillations 
  of 
  the 
  North 
  of 
  

   France 
  during 
  the 
  Jurassic 
  Period 
  " 
  (Comptes 
  Rendus, 
  vol. 
  xliii.), 
  

   states 
  that 
  he 
  has 
  observed 
  on 
  the 
  surface 
  of 
  certain 
  strata, 
  and 
  

   especially 
  on 
  that 
  of 
  the 
  calcareous 
  beds, 
  marks 
  of 
  polish, 
  rubbing 
  

   and 
  excavation 
  by 
  water, 
  together 
  with 
  lithophagous 
  perforations 
  

   in 
  the 
  same 
  places, 
  and 
  often 
  collections 
  of 
  rolled 
  stones 
  scattered 
  

   about 
  — 
  the 
  clear 
  indications 
  of 
  emergence. 
  They 
  are 
  to 
  be 
  seen, 
  

   says 
  Hebert, 
  at 
  several 
  levels 
  ; 
  and 
  he 
  cites 
  in 
  particular 
  the 
  quarries 
  

   of 
  Meziers 
  and 
  the 
  Butte 
  Chaumitton 
  (Sarthe). 
  Among 
  other 
  like 
  

   facts, 
  D'Orbigny 
  gives 
  numerous 
  instances 
  of 
  the 
  occurrence 
  of 
  sand, 
  

   gravel, 
  boulders, 
  and 
  transported 
  mollusks 
  between 
  contiguous 
  for- 
  

   mations, 
  as 
  between 
  Miocene 
  and 
  Lias, 
  or 
  between 
  Neocomian 
  and 
  

   Chalk, 
  or 
  Upper 
  Greensand, 
  or 
  Chalk-marl 
  £. 
  

  

  The 
  thinner 
  the 
  lost 
  stratum, 
  the 
  sooner 
  it 
  is 
  gone. 
  Examples 
  of 
  

   these 
  statements 
  have 
  been 
  placed 
  in 
  the 
  foot-note 
  below 
  §. 
  In 
  North 
  

   America 
  two 
  very 
  instructive 
  instances 
  on 
  a 
  large 
  scale 
  occur, 
  in 
  which 
  

  

  * 
  Sir 
  Henry 
  De 
  la 
  Beche 
  is 
  our 
  great 
  authority 
  on 
  this 
  subject, 
  in 
  the 
  ad- 
  

   mirable 
  tliirty-seventh 
  chapter 
  of 
  his 
  ' 
  Geological 
  Observer 
  ;' 
  and 
  he 
  has 
  been 
  

   more 
  recently 
  followed, 
  with 
  practical 
  observations 
  of 
  great 
  importance, 
  by 
  Prof. 
  

   Ramsay, 
  in 
  the 
  first 
  volume 
  of 
  the 
  ' 
  Memoirs 
  of 
  the 
  Geological 
  Survey 
  of 
  Great 
  

   Britain,' 
  and 
  in 
  his 
  Presidential 
  Address 
  of 
  the 
  year 
  1863 
  to 
  this 
  Society. 
  

  

  t 
  'Principles,' 
  p. 
  154. 
  

  

  t 
  Cours 
  de 
  Paleontologie, 
  pp. 
  455, 
  640, 
  771, 
  783, 
  &c. 
  

  

  § 
  The 
  outliers 
  and 
  patches 
  at 
  Pradalis 
  and 
  Honrubio 
  in 
  Spain 
  : 
  Casiano 
  de 
  

   Prado, 
  Bull. 
  Soc. 
  Geol. 
  France, 
  2 
  e 
  serie, 
  vol. 
  xi. 
  p. 
  331. 
  At 
  Farringdon 
  : 
  Sharpe, 
  

   Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  x. 
  p. 
  182, 
  &c. 
  Scooping, 
  &c, 
  in 
  South 
  Staffordshire 
  : 
  

   Jukes, 
  South 
  Staff. 
  Coal-field, 
  p. 
  27. 
  In 
  the 
  Onondago 
  Salt-group 
  and 
  Delthyris 
  

   Shaly 
  Limestone 
  : 
  Hall 
  and 
  De 
  Verneuil, 
  Bull. 
  Soc. 
  Geol. 
  France, 
  2 
  e 
  serie, 
  vol. 
  iv. 
  

   p. 
  657. 
  The 
  change 
  from 
  Bird's-eye 
  to 
  Trenton 
  Limestone 
  (Lower 
  Silurian) 
  

   at 
  Fort 
  Plain, 
  &c, 
  in 
  the 
  Mohawk 
  Valley, 
  is 
  perfectly 
  abrupt, 
  and 
  the 
  fossils 
  

   distinct, 
  the 
  two 
  strata 
  being 
  in 
  contact. 
  

  

  