﻿OP 
  THE 
  -BALTIC 
  PROVINCES 
  OF 
  RUSSIA. 
  

  

  525 
  

  

  from 
  the 
  Lower 
  Silurian 
  ; 
  no 
  intermediate 
  group 
  like 
  the 
  English 
  

   Llandovery 
  can 
  be 
  recognized. 
  There 
  is 
  a 
  clear 
  break 
  with 
  us 
  in 
  the 
  

   development 
  of 
  organic 
  life, 
  notwithstanding 
  the 
  fact 
  that 
  the 
  phy- 
  

   sical 
  conditions 
  remain 
  the 
  same 
  : 
  for 
  the 
  Upper 
  Silurian 
  strata 
  con- 
  

   sist 
  of 
  limestones 
  and 
  marls, 
  like 
  those 
  of 
  the 
  Lower 
  Silurian. 
  At 
  

   many 
  places 
  with 
  us 
  the 
  lowest 
  Upper 
  Silurian, 
  stage 
  G, 
  is 
  observed 
  

   in 
  immediate 
  contact 
  with 
  the 
  highest 
  Lower 
  Silurian, 
  F; 
  but 
  nowhere 
  

   can 
  there 
  be 
  any 
  doubt 
  concerning 
  the 
  geological 
  age 
  of 
  these 
  un- 
  

   varying 
  deposits. 
  The 
  same 
  seems 
  to 
  be 
  the 
  case 
  in 
  Sweden. 
  The 
  

   island 
  of 
  Gothland 
  shows 
  a 
  very 
  full 
  series 
  of 
  the 
  Upper 
  Silurian, 
  

   but 
  the 
  Lower 
  Silurian 
  is 
  entirely 
  absent 
  on 
  that 
  island 
  : 
  while, 
  on 
  

   the 
  other 
  hand, 
  there 
  are 
  no 
  traces 
  of 
  the 
  Upper 
  Silurian 
  in 
  Oeland. 
  

   In 
  Dalecarlia, 
  as 
  before 
  mentioned, 
  the 
  relations 
  of 
  the 
  Lower 
  

   Silurian 
  Lejj 
  tama-hmestone 
  to 
  the 
  Lobiferus- 
  and 
  Retiolites- 
  

   Graptolithic 
  schists 
  are 
  not 
  yet 
  clearly 
  made 
  out. 
  In 
  Norway 
  the 
  

   upper 
  part 
  of 
  stage 
  5 
  of 
  Kjerulf, 
  described 
  as 
  being 
  visible 
  on 
  the 
  

   island 
  of 
  lEalmo, 
  belongs 
  to 
  our 
  Upper 
  Silurian, 
  and 
  the 
  lower 
  part 
  

   to 
  the 
  Lower 
  Silurian. 
  Kjerulf 
  did 
  not 
  separate 
  the 
  two 
  divisions 
  

   clearly 
  ; 
  but 
  to 
  me, 
  during 
  my 
  explorations 
  in 
  the 
  neighbourhood 
  of 
  

   Christiania, 
  it 
  seemed 
  easy 
  enough 
  to 
  trace 
  the 
  limit 
  between 
  the 
  

   Upper 
  and 
  the 
  Lower 
  Silurian, 
  the 
  line 
  of 
  division 
  between 
  them 
  

   answering 
  clearly 
  to 
  that 
  in 
  our 
  own 
  country. 
  Prof. 
  Brogger, 
  I 
  

   hope, 
  will 
  clear 
  up 
  all 
  remaining 
  difficulties. 
  

  

  The 
  Upper 
  Silurian 
  of 
  our 
  country 
  I 
  divide 
  into 
  four 
  stages, 
  G, 
  

   H, 
  I, 
  K, 
  exactly 
  corresponding 
  to 
  distinct 
  stages 
  or 
  zones 
  in 
  the 
  

   island 
  of 
  Gothland 
  and, 
  apparently, 
  also 
  to 
  distinct 
  stages 
  in 
  Norway, 
  

   near 
  Christiania. 
  Compared 
  with 
  England, 
  the 
  lower 
  stages 
  G 
  and 
  

   H 
  cannot 
  be 
  strictly 
  correlated 
  ; 
  but 
  the 
  upper 
  ones 
  (I 
  and 
  K) 
  I 
  

   regard 
  without 
  hesitation 
  as 
  corresponding 
  respectively 
  to 
  the 
  AVen- 
  

   lock 
  and 
  Ludlow 
  groups. 
  

  

  The 
  stages 
  G 
  and 
  H 
  are 
  nearly 
  allied 
  to 
  each 
  other 
  ; 
  both 
  of 
  them 
  

   are 
  characterized 
  by 
  peculiar 
  species 
  of 
  smooth 
  (not 
  ridged) 
  Penta- 
  

   meri, 
  the 
  former 
  by 
  P. 
  borealis, 
  Eichw., 
  the 
  latter 
  by 
  P. 
  esthonus, 
  

   Eichw. 
  Both 
  stages 
  together 
  may 
  correspond 
  also 
  to 
  the 
  American 
  

   Clinton 
  group. 
  As 
  to 
  the 
  fauna, 
  the 
  corals 
  and 
  Trilobites 
  are 
  nearly 
  

   the 
  same 
  in 
  both 
  groups, 
  the 
  common 
  Upper 
  Silurian 
  Trilobites, 
  

   Cab/mene 
  Blumenbachii, 
  Encrinurus 
  puactatus 
  and 
  Proetas 
  concinnus, 
  

   passing 
  unaltered 
  through 
  the 
  three 
  stages 
  G, 
  H, 
  and 
  I. 
  The 
  cha- 
  

   racteristic 
  fossils 
  of 
  the 
  different 
  Upper 
  Silurian 
  stages 
  are 
  the 
  

   Brachiopocla, 
  as 
  already 
  pointed 
  out 
  in 
  Gothland 
  by 
  Prof. 
  Lindstrom, 
  

   and 
  also 
  the 
  Leperditice, 
  as 
  I 
  endeavoured 
  to 
  prove 
  in 
  my 
  memoir 
  

   on 
  the 
  Silurian 
  Leperditice 
  of 
  Russia 
  and 
  neighbouring 
  countries 
  

   (St. 
  Petersburg, 
  1&73). 
  The 
  Gasteropoda 
  and 
  Acephala 
  of 
  the 
  

   stages 
  G 
  and 
  H 
  are 
  not 
  yet 
  fully 
  examined. 
  

  

  Stage 
  G. 
  Sab 
  stage 
  G 
  1, 
  Jorden 
  Beds. 
  

  

  The 
  stage 
  G 
  (zones 
  4 
  and 
  5 
  of 
  my 
  former 
  publications) 
  can 
  be 
  

   subdivided 
  into 
  three 
  substages. 
  The 
  first 
  of 
  these, 
  the 
  Jorden 
  

   zone, 
  G 
  I, 
  consists 
  of 
  thin 
  calcareous 
  flagstones 
  and 
  marls, 
  and 
  may 
  

  

  