﻿OF 
  THE 
  BALTIC 
  PKOVINCES 
  OE 
  ETJSSIA. 
  515 
  

  

  the 
  map 
  as 
  well-marked 
  zones 
  stretching 
  in 
  a 
  direction 
  nearly 
  parallel 
  

   to 
  the 
  north 
  coast, 
  and 
  following 
  each 
  other 
  from 
  ~N. 
  to 
  S., 
  or 
  from 
  

   N.E. 
  to 
  S."W., 
  according 
  to 
  the 
  inclination 
  of 
  the 
  strata. 
  

  

  In 
  my 
  former 
  publication 
  on 
  our 
  Silurian 
  (' 
  Untersuchungen 
  iiber 
  

   die 
  silurische 
  Formation 
  von 
  Ehstland, 
  Nord-Livland 
  und 
  Oesel/ 
  

   Dorpat, 
  1858) 
  I 
  marked 
  only 
  the 
  zones 
  represented 
  on 
  the 
  map 
  of 
  

   the 
  plain 
  itself, 
  with 
  the 
  numbers 
  from 
  1 
  to 
  8, 
  leaving 
  the 
  lower 
  stages 
  

   (visible 
  only 
  in 
  the 
  cliffs) 
  without 
  a 
  corresponding 
  notation. 
  I 
  

   have 
  now 
  introduced 
  a 
  new 
  designation, 
  by 
  letters 
  from 
  A 
  to 
  K 
  ; 
  the 
  

   lowest 
  stages, 
  A 
  and 
  B, 
  in 
  most 
  parts 
  of 
  the 
  country, 
  however, 
  are 
  

   visible 
  only 
  in 
  the 
  northern 
  cliffs 
  and 
  in 
  corresponding 
  river- 
  

   sections. 
  

  

  In 
  the 
  northern 
  cliffs 
  the 
  superposition 
  of 
  the 
  stages 
  is 
  directly 
  

   observable, 
  and 
  also 
  in 
  some 
  of 
  the 
  zones 
  of 
  the 
  interior 
  ; 
  in 
  others 
  

   it 
  is 
  only 
  assumed, 
  but 
  may 
  be 
  actually 
  observed 
  in 
  neighbouring 
  

   Silurian 
  countries 
  where 
  the 
  same 
  arrangement 
  of 
  strata 
  occurs, 
  

   as, 
  for 
  instance, 
  in 
  Sweden 
  or 
  Norway. 
  The 
  stages 
  of 
  the 
  interior 
  

   all 
  consist 
  of 
  limestones 
  and 
  marls, 
  showing 
  thus 
  a 
  continuous 
  deve- 
  

   lopment 
  of 
  marine 
  life 
  from 
  the 
  beginning 
  of 
  the 
  Lower 
  Silurian 
  to 
  

   the 
  end 
  of 
  the 
  Upper, 
  without 
  any 
  remarkable 
  changes 
  of 
  physical 
  

   conditions. 
  The 
  zoological 
  character 
  of 
  each 
  zone 
  is 
  extremely 
  

   constant, 
  though 
  there 
  exist 
  very 
  close 
  relations 
  between 
  the 
  faunas 
  

   of 
  neighbouring 
  zones. 
  As 
  most 
  of 
  the 
  zones 
  stretch 
  over 
  a 
  large 
  

   area 
  as 
  long 
  and 
  narrow 
  nearly 
  parallel 
  bands, 
  the 
  before-mentioned 
  

   uniformity 
  of 
  their 
  faunas 
  affords 
  us 
  the 
  means 
  by 
  which 
  to 
  check 
  

   the 
  value 
  of 
  differences 
  between 
  allied 
  species 
  of 
  different 
  zones, 
  and 
  

   allows 
  us 
  to 
  study 
  at 
  the 
  same 
  time 
  the 
  variations 
  of 
  species 
  both 
  in 
  

   time 
  and 
  space. 
  

  

  Peincipal 
  Divisions. 
  

  

  Three 
  clear 
  principal 
  divisions 
  of 
  the 
  whole 
  series 
  can 
  be 
  distin- 
  

   guished, 
  the 
  same 
  as 
  everywhere, 
  but 
  most 
  nearly 
  allied 
  to 
  those 
  

   of 
  Sweden 
  ; 
  and 
  therefore 
  the 
  same 
  nomenclature 
  is 
  adopted 
  by 
  

   me 
  in 
  the 
  same 
  sense 
  as 
  used 
  in 
  Sweden 
  by 
  Linnarsson 
  and 
  

   others. 
  The 
  divisions 
  are: 
  — 
  (1) 
  the 
  Cambrian 
  or 
  Primordial 
  Si- 
  

   lurian 
  (stage 
  A) 
  = 
  Cambrian 
  of 
  Dr. 
  Hicks 
  ; 
  (2) 
  the 
  Lower 
  Silu- 
  

   rian 
  (stages 
  B-P), 
  nearly 
  equal 
  to 
  the 
  Ordovician 
  of 
  Lapworth 
  ; 
  

   and 
  (3) 
  the 
  Upper 
  Silurian 
  (stages 
  G-K), 
  the 
  Silurian 
  of 
  Sedgwick. 
  

   According 
  to 
  the 
  geological 
  conditions 
  of 
  our 
  country, 
  I 
  should 
  rather 
  

   prefer 
  to 
  regard 
  our 
  whole 
  series 
  of 
  strata 
  as 
  one 
  system, 
  the 
  Cam- 
  

   brian 
  being 
  only 
  a 
  part 
  of 
  it 
  — 
  because 
  all 
  the 
  strata 
  are 
  arranged 
  

   conformably, 
  and 
  the 
  whole 
  is 
  covered 
  unconformably 
  by 
  the 
  Devo- 
  

   nian, 
  the 
  connecting 
  lowest 
  Devonian 
  stages 
  being 
  altogether 
  un- 
  

   represented 
  with 
  us. 
  

  

  The 
  three 
  principal 
  divisions 
  are 
  easily 
  recognizable 
  with 
  us, 
  as 
  

   there 
  do 
  not 
  exist 
  any 
  connecting 
  links, 
  and 
  the 
  palseontological 
  

   breaks 
  are 
  very 
  clear 
  between 
  the 
  Cambrian 
  and 
  the 
  Lower 
  Silurian 
  

   as 
  well 
  as 
  between 
  the 
  latter 
  and 
  the 
  Upper 
  Silurian. 
  Our 
  so-called 
  

   Cambrian 
  is 
  entirely 
  formed 
  of 
  sandstone, 
  clay, 
  and 
  shale 
  ; 
  both 
  Silu- 
  

   rian 
  divisions 
  are 
  purely 
  limestones 
  and 
  marls, 
  with 
  very 
  insig- 
  

  

  