﻿526 
  PROF. 
  P. 
  SCHMIDT 
  ON 
  THE 
  SILURIAN 
  STRATA 
  

  

  have 
  a 
  thickness 
  of 
  20 
  to 
  30 
  feet. 
  It 
  can 
  be 
  traced 
  along 
  the 
  northern 
  

   boundary 
  of 
  our 
  Upper 
  Silurian, 
  from 
  near 
  the 
  Peipus 
  Lake 
  at 
  Pastfer 
  

   as 
  far 
  as 
  the 
  island 
  of 
  Dago 
  ; 
  there 
  the 
  localities 
  Kallasto 
  and 
  Hel- 
  

   terma 
  belong 
  to 
  this 
  stage, 
  while 
  the 
  small 
  island 
  of 
  Wohhi 
  is 
  still 
  

   Lower 
  Silurian 
  (E 
  2). 
  The 
  characteristic 
  fossils 
  are 
  Leperditia 
  

   Hisingeri, 
  mihi, 
  Orihis 
  Davidsoni,YeTii., 
  Stropliomena 
  pecten, 
  Linn., 
  

   Leptoccelia 
  Duboisi, 
  Vern., 
  Bhynchonella 
  affinis, 
  Vera., 
  Dinobolus 
  

   Davidsoni, 
  Salt. 
  

  

  Substage 
  G 
  2, 
  Borealis 
  Bank. 
  

   The 
  next 
  substage, 
  G 
  2, 
  consists 
  almost 
  entirely 
  of 
  agglomerated 
  

   shells 
  of 
  Pentamerus 
  borealis, 
  Eichw. 
  It 
  forms 
  a 
  zone, 
  wider 
  in 
  

   the 
  east 
  and 
  narrower 
  in 
  the 
  west, 
  from 
  near 
  the 
  Peipus 
  as 
  far 
  as 
  

   Hapsal, 
  on 
  the 
  coast. 
  Its 
  thickness 
  amounts 
  to 
  40 
  feet. 
  Some 
  

   corals 
  are 
  mixed 
  with 
  the 
  Pentameri. 
  In 
  the 
  east 
  it 
  is 
  not 
  possible 
  

   to 
  find 
  both 
  valves 
  together 
  ; 
  but 
  in 
  the 
  west 
  the 
  shells 
  are 
  not 
  

   so 
  thickly 
  crowded, 
  but 
  not 
  more 
  than 
  a 
  few 
  wholly 
  preserved 
  speci- 
  

   mens 
  have 
  been 
  obtained. 
  In 
  the 
  island 
  of 
  Dago 
  the 
  Pentamerus 
  

   loses 
  its 
  predominant 
  character, 
  and 
  near 
  Kallasto 
  specimens 
  of 
  it 
  

   are 
  found 
  dispersed 
  among 
  corals 
  and 
  other 
  fossils 
  of 
  the 
  stage 
  G 
  1. 
  

  

  Substage 
  G 
  3, 
  Ratkull 
  Beds. 
  

  

  The 
  substage 
  G 
  3, 
  or 
  Raikiill 
  zone, 
  occupies 
  a 
  rather 
  large 
  zone 
  

   in 
  Northern 
  Livonia 
  and 
  South 
  Esthonia. 
  It 
  consists 
  of 
  coral 
  reefs 
  

   and 
  flagstones 
  ; 
  its 
  thickness 
  may 
  attain 
  perhaps 
  100 
  feet. 
  Most 
  

   fossils 
  are 
  the 
  same 
  as 
  in 
  Gl 
  ; 
  but 
  Leperditia 
  Hisingeri 
  becomes 
  scarcer, 
  

   and 
  is 
  replaced 
  by 
  L. 
  Keyserlingi, 
  mihi, 
  found 
  near 
  Raikiill, 
  the 
  

   estate 
  of 
  the 
  Count 
  A. 
  Keyserling, 
  at 
  which 
  place 
  the 
  zone 
  G 
  3 
  is 
  

   best 
  exposed. 
  Of 
  Trilobites, 
  besides 
  the 
  common 
  forms 
  mentioned 
  

   above, 
  we 
  may 
  name 
  Phacops 
  elegans, 
  Sars 
  & 
  Boeck 
  (characteristic 
  

   also 
  of 
  the 
  corresponding 
  stages 
  in 
  Scandinavia). 
  The 
  limestone 
  is 
  

   mostly 
  very 
  hard 
  and 
  often 
  dolomitic, 
  so 
  that 
  the 
  fossils 
  have 
  not 
  

   been 
  as 
  yet 
  studied 
  sufficiently. 
  

  

  Stage 
  H, 
  or 
  Pentamerus-esthonus 
  Zone. 
  

  

  The 
  stage 
  H 
  is 
  our 
  upper 
  Pentamerus-zoiie 
  (6 
  of 
  my 
  former 
  publi- 
  

   cations) 
  ; 
  it 
  occupies 
  also 
  a 
  large 
  area 
  south 
  of 
  G, 
  and 
  can 
  be 
  traced 
  

   from 
  Talkhof 
  near 
  Dorpat 
  to 
  the 
  west 
  end 
  of 
  Esthonia 
  near 
  Hap- 
  

   sal. 
  In 
  the 
  east, 
  dolomites 
  prevail 
  : 
  in 
  the 
  west, 
  grey 
  coral-lime- 
  

   stones 
  with 
  numerous 
  specimens 
  of 
  Pentamerus 
  esthonus, 
  Eichw. 
  

   The 
  specimens 
  are 
  not 
  so 
  crowded 
  together 
  as 
  in 
  the 
  Borealis-haiik 
  

   (G 
  2), 
  and 
  therefore 
  well 
  preserved 
  examples 
  are 
  not 
  scarce. 
  The 
  typi- 
  

   cal 
  Leperditia 
  of 
  this 
  stage 
  is 
  L. 
  abbreviata, 
  mihi 
  (formerly 
  regarded 
  

   by 
  me 
  as 
  a 
  variety 
  of 
  L. 
  Hisingeri, 
  mihi, 
  or 
  Schmidti, 
  Kolm.). 
  Of 
  

   other 
  fossils, 
  besides 
  numerous 
  corals, 
  such 
  as 
  Syringopora 
  bifurcata, 
  

   Lonsd., 
  Favosites 
  goilandicus, 
  and 
  at 
  least 
  five 
  species 
  of 
  Holy 
  sites 
  ,■ 
  

   there 
  occur 
  already 
  some 
  forms 
  of 
  the 
  next 
  stage 
  I: 
  — 
  Bumastes 
  

   barriensis, 
  Sil. 
  Syst., 
  Orihoceras 
  canaliculatum, 
  Sow., 
  Strophomena 
  

   euglypha, 
  Sow., 
  Spirifer 
  radiatus, 
  Sow., 
  and 
  the 
  typical 
  Atrypa 
  

   reticularis, 
  Linn. 
  

  

  