﻿OP 
  THE 
  BALTIC 
  PROVINCES 
  OF 
  RUSSIA. 
  519 
  

  

  sequence 
  of 
  a 
  lighter 
  green 
  than 
  the 
  sand. 
  Sometimes 
  the 
  limestone 
  

   is 
  of 
  a 
  reddish 
  tinge, 
  with 
  intercalated 
  dark-green 
  grains, 
  princi- 
  

   pally 
  in 
  the 
  lower 
  strata. 
  The 
  zoological 
  character 
  of 
  the 
  Silurian 
  

   fauna 
  seems 
  to 
  have 
  suddenly 
  changed 
  at 
  the 
  commencement 
  of 
  the 
  

   Limestone 
  period. 
  With 
  the 
  earliest 
  Limestone 
  bed 
  several 
  Trilo- 
  

   bites 
  appear. 
  The 
  most 
  characteristic 
  form 
  for 
  this 
  substage 
  is 
  

   Megalaspis 
  planilimbata, 
  Ang. 
  In 
  addition 
  there 
  are 
  found 
  other 
  

   Asaphidse, 
  and 
  Cheirurus 
  clavifrons, 
  Dalm. 
  The 
  predominating 
  Bra- 
  

   chiopoda 
  are 
  Porambonites 
  reticulatus, 
  Vsind.,Orthis 
  parva, 
  Pand.,0.&*?- 
  

   tensa, 
  Pand., 
  0. 
  callactis, 
  Dalm., 
  and 
  Orihisina 
  plana, 
  Pand. 
  Cephalo- 
  

   poda 
  and 
  Gasteropoda, 
  however, 
  are 
  wanting. 
  In 
  the 
  higher 
  strata 
  of 
  

   the 
  Glauconite 
  Limestone 
  the 
  glauconitic 
  grains 
  become 
  smaller, 
  and 
  

   the 
  limestone 
  becomes 
  softer 
  and 
  marly. 
  Here 
  is 
  the 
  true 
  horizon 
  of 
  

   the 
  well-known 
  Asaphus 
  expansus, 
  Dalm., 
  so 
  frequently 
  confounded 
  

   with 
  other 
  species 
  of 
  the 
  genus. 
  In 
  addition, 
  we 
  have 
  other 
  Asa- 
  

   phidae, 
  as 
  A. 
  angustifrons, 
  Dalm., 
  and 
  the 
  large 
  forms 
  A. 
  centron, 
  

   Leuchtbg., 
  and 
  acuticauda, 
  Ang. 
  ; 
  Cheirurus 
  claulfrons 
  becomes 
  more 
  

   frequent 
  ; 
  Phacops 
  (Pterygometopus) 
  sclerops, 
  Dalm., 
  and 
  the 
  first 
  

   representatives 
  of 
  lllcenus, 
  Lichas, 
  and 
  Ampysc 
  appear, 
  also 
  the 
  first 
  

   Cystidean 
  forms, 
  Glyptocystites 
  giganteus, 
  Leuchtbg., 
  and 
  Echinoencri- 
  

   nites 
  angulatus, 
  Pand. 
  Among 
  others 
  occur 
  the 
  first 
  Chaetetidae 
  and 
  

   Bolboporites 
  australis, 
  Pand. 
  This 
  upper 
  part 
  of 
  the 
  Glauconite 
  

   Limestone 
  is 
  more 
  richly 
  developed 
  on 
  the 
  lower 
  Wolchow 
  at 
  the 
  S.E. 
  

   end 
  of 
  Lake 
  Ladoga. 
  The 
  lower 
  part, 
  with 
  Megalaspis 
  plani- 
  

   limbata, 
  has 
  everywhere 
  the 
  same 
  aspect, 
  from 
  the 
  Wolchow 
  as 
  far 
  as 
  

   Baltischport 
  on 
  the 
  Gulf 
  of 
  Finland, 
  a 
  distance 
  of 
  more 
  than 
  300 
  

   English 
  miles. 
  

  

  B 
  3, 
  Orthoceratite 
  Limestone. 
  — 
  The 
  succeeding 
  stage, 
  B 
  3, 
  is 
  the 
  

   famous 
  Yaginaten- 
  or 
  Orthoceratite 
  Limestone. 
  It 
  has 
  a 
  relatively 
  

   small 
  thickness 
  with 
  us, 
  from 
  3 
  to 
  20 
  feet; 
  but 
  the 
  zoological 
  

   character 
  of 
  the 
  fauna 
  is 
  remarkably 
  constant, 
  not 
  only 
  here, 
  but 
  

   also 
  in 
  Scandinavia. 
  In 
  most 
  places 
  this 
  stage 
  consists 
  of 
  a 
  

   hard 
  grey 
  limestone, 
  and 
  is 
  crowded 
  with 
  the 
  well-known 
  Ortho- 
  

   ceratites 
  0. 
  communis 
  (duplex), 
  Wahlb., 
  and 
  0. 
  vaginata, 
  Schloth. 
  

   To 
  the 
  west 
  of 
  Iieval 
  it 
  gradually 
  passes 
  into 
  a 
  sandstone: 
  the 
  

   Orthoceratites 
  disappear 
  ; 
  but 
  the 
  other 
  characteristic 
  fossils 
  remain. 
  

   In 
  the 
  east 
  (for 
  example, 
  upon 
  the 
  Wolchow) 
  there 
  is 
  a 
  gradual 
  

   passage 
  from 
  the 
  upper 
  beds 
  of 
  the 
  Glauconite 
  Limestone 
  to 
  the 
  

   Vaginaten-Limestone 
  ; 
  but 
  in 
  Esthonia 
  we 
  commonly 
  find, 
  at 
  the 
  

   base 
  of 
  the 
  latter, 
  a 
  layer 
  of 
  about 
  2-3 
  feet 
  thickness, 
  filled 
  with 
  

   larger 
  or 
  smaller 
  concretions 
  of 
  phosphate 
  of 
  lime, 
  sometimes 
  

   assuming 
  a 
  pisolitic 
  character. 
  The 
  fauna 
  of 
  the 
  Orthoceratite 
  Lime- 
  

   stone 
  is 
  generally 
  well 
  known 
  both 
  with 
  us 
  and 
  in 
  Scandinavia. 
  

   Among 
  Trilobites 
  we 
  may 
  name 
  Phacops 
  sclerops 
  and 
  trigonocephalus, 
  

   Cheirurus 
  ornatus, 
  Dalm., 
  clavifrons, 
  Dalm., 
  and 
  affinis, 
  Ang., 
  

   Cybelebellatula, 
  Dalm., 
  Lichas 
  celorrhin, 
  Ang., 
  and 
  verrucosa, 
  Eichw. 
  

   (convexa, 
  Ang.), 
  Amphion 
  Fischeri, 
  Eichw., 
  lllcenus 
  Wahlenbergi, 
  

   Eichw., 
  Asaphus 
  heros, 
  Dalm., 
  Pcychopyge 
  globifrons, 
  Eichw., 
  Ampyx 
  

   nasutus, 
  &c. 
  Among 
  Cephalopoda 
  we 
  find, 
  in 
  addition 
  to 
  the 
  common 
  

   Orthoceratites, 
  Lituites 
  lamellosus, 
  His. 
  (convolvens 
  auct.), 
  L. 
  falcatus, 
  

  

  