﻿40 
  C. 
  Sckuchert—Heberts 
  Views 
  of 
  1857 
  

  

  The 
  limit 
  between 
  the 
  Trias 
  and 
  the 
  Lias 
  therefore 
  corresponds 
  

   to 
  a 
  maximum 
  of 
  elevation. 
  Our 
  countries 
  had 
  been 
  for 
  a 
  long 
  

   time 
  above 
  the 
  waters 
  of 
  the 
  sea, 
  and 
  when 
  the 
  latter 
  came 
  to 
  

   occupy 
  them 
  anew, 
  either 
  because 
  of 
  the 
  lapse 
  of 
  time 
  in 
  the 
  

   interval, 
  or 
  because 
  of 
  the 
  change 
  in 
  physical 
  conditions 
  which 
  

   was 
  the 
  result 
  of 
  the 
  new 
  order 
  of 
  things, 
  there 
  was 
  also 
  a 
  con- 
  

   siderable 
  change 
  in 
  the 
  fauna. 
  

  

  During 
  the 
  Cretaceous 
  epoch, 
  we 
  see 
  the 
  sea 
  again 
  advanc- 
  

   ing 
  more 
  and 
  more 
  into 
  the 
  Paris 
  basin, 
  the 
  JSTeocomian 
  strata 
  

   being 
  deposited 
  in 
  the 
  center 
  of 
  the 
  depression, 
  the 
  G-ault 
  ex- 
  

   ceeding 
  the 
  limits 
  of 
  that 
  stage 
  and 
  extending 
  toward 
  the 
  

   Meuse, 
  the 
  Ardennes, 
  Boulonnais, 
  Bra} 
  7 
  and 
  Normandy 
  — 
  

   points 
  that 
  were 
  previously 
  out 
  of 
  water, 
  although 
  remaining 
  

   a 
  part 
  of 
  the 
  Paris 
  basin 
  ; 
  the 
  chloritic 
  chalk 
  and 
  the 
  tuffa- 
  

   ceous 
  chalk 
  extend 
  much 
  further 
  and 
  so 
  show 
  that 
  up 
  to 
  this 
  

   time 
  the 
  waters 
  were 
  rising 
  constantly 
  along 
  the 
  shores 
  of 
  the 
  

   basin 
  and 
  that 
  they 
  ended 
  by 
  breaking 
  through 
  completely 
  

   toward 
  the 
  eastern 
  border. 
  The 
  land 
  was 
  therefore 
  more 
  and 
  

   more 
  depressed 
  during 
  all 
  this 
  part 
  of 
  the 
  Cretaceous 
  period. 
  

  

  The 
  study 
  of 
  the 
  movements 
  of 
  the 
  crust 
  is 
  useful 
  not 
  only 
  

   for 
  the 
  establishment 
  of 
  the 
  great 
  divisions 
  of 
  the 
  geological 
  

   classification, 
  i. 
  e., 
  the 
  terranes, 
  but 
  no 
  less 
  so 
  for 
  the 
  secondary 
  

   divisions 
  or 
  stages. 
  We 
  see, 
  in 
  fact, 
  that 
  it 
  is 
  natural 
  to 
  divide 
  

   the 
  Jurassic 
  terrane 
  into 
  two 
  corresponding 
  parts, 
  one 
  the 
  per- 
  

   iod 
  of 
  depression 
  which 
  includes 
  the 
  Lias, 
  the 
  Lower 
  and 
  the 
  

   Great 
  Oolite, 
  that 
  is, 
  the 
  Lower 
  Jurassic 
  terrane; 
  the 
  other 
  

   the 
  period 
  of 
  elevation, 
  which 
  is 
  composed 
  of 
  the 
  Oxford 
  clay, 
  

   the 
  Coral 
  Rag, 
  and 
  the 
  Kimmeridge 
  clay, 
  to 
  which 
  we 
  should 
  

   add 
  the 
  Portlandian 
  limestone, 
  that 
  is, 
  the 
  Upper 
  Jurassic 
  ter- 
  

   rane. 
  

  

  Our 
  two 
  periods 
  can 
  be 
  subdivided 
  very 
  clearly 
  with 
  the 
  aid 
  

   of 
  secondary 
  oscillations, 
  whose 
  duration, 
  although 
  very 
  short 
  

   in 
  comparison 
  with 
  that 
  of 
  the 
  great 
  oscillation, 
  was 
  never- 
  

   theless 
  immense 
  in 
  each 
  case. 
  We 
  have 
  proved 
  by 
  a 
  great 
  

   number 
  of 
  facts 
  that 
  the 
  limits 
  of 
  these 
  secondary 
  movements 
  

   coincide 
  exact!} 
  7 
  with 
  those 
  of 
  the 
  stages 
  fixed 
  by 
  the 
  most 
  

   certain 
  characters 
  borrowed 
  from 
  the 
  domain 
  of 
  stratigraphy 
  

   and 
  paleontology. 
  In 
  this 
  way 
  our 
  stages 
  are 
  distinguished 
  

   one 
  from 
  another 
  as 
  follows: 
  (1) 
  in 
  that 
  they 
  each 
  belong 
  to 
  a 
  

   different 
  secondary 
  oscillation, 
  separated 
  from 
  the 
  preceding 
  

   and 
  the 
  following 
  one 
  by 
  times 
  of 
  arrest 
  corresponding 
  to 
  an 
  

   emergence 
  of 
  the 
  land 
  and 
  consequently 
  to 
  a 
  break 
  in 
  sedimen- 
  

   tation 
  ; 
  (2) 
  in 
  that 
  the 
  line 
  of 
  contact 
  is 
  in 
  general 
  broken, 
  often 
  

   marked 
  by 
  denudation, 
  and 
  always 
  easy 
  to 
  recognize 
  when 
  one 
  

   includes 
  no 
  very 
  considerable 
  extent 
  of 
  terrane; 
  (3) 
  in 
  that 
  the 
  

   faunas 
  of 
  these 
  stages, 
  thus 
  limited, 
  differ 
  much 
  more 
  from 
  

   one 
  another 
  than 
  happens 
  in 
  any 
  other 
  method 
  of 
  classification. 
  

  

  