﻿vol. 
  53.] 
  fauna 
  of 
  the 
  keisley 
  limestone. 
  103 
  

  

  Conditions 
  of 
  Deposition" 
  and 
  Okigin 
  of 
  the 
  Fauna 
  

   of 
  the 
  keisley 
  llmestone. 
  

  

  The 
  isolation 
  of 
  the 
  patch 
  of 
  limestone 
  at 
  Keisley 
  has 
  been 
  fully 
  

   emphasized, 
  but, 
  as 
  already 
  mentioned, 
  Marr 
  l 
  is 
  inclined 
  to 
  think 
  

   that 
  it 
  is 
  merely 
  a 
  very 
  local 
  development, 
  under 
  peculiar 
  and 
  very 
  

   restricted 
  conditions, 
  of 
  a 
  thin 
  limestone 
  underlying 
  the 
  Stauro- 
  

   cejphalus-Limestone. 
  A 
  white 
  horny 
  limestone 
  in 
  Skelgill, 
  and 
  a 
  

   similar 
  limestone 
  in 
  Swindale 
  Beck 
  may 
  be, 
  in 
  his 
  opinion, 
  the 
  

   attenuated 
  and 
  lithologically-different 
  representatives 
  of 
  the 
  Keisley 
  

   mass. 
  He 
  adduces 
  cases 
  in 
  other 
  districts 
  with 
  beds 
  of 
  various 
  ages 
  

   in 
  which 
  ' 
  reefs 
  ' 
  or 
  lenticular 
  masses 
  of 
  crystalline 
  limestone 
  occur 
  

   on 
  the 
  same 
  horizon 
  as 
  these 
  horny 
  limestones 
  and 
  in 
  close 
  con- 
  

   nexion 
  with 
  them. 
  Such 
  is 
  the 
  case 
  with 
  some 
  Devonian 
  lime- 
  

   stones 
  near 
  Torquay, 
  with 
  the 
  Konieprus 
  Limestone 
  (Ff2) 
  in 
  

   Bohemia, 
  with 
  the 
  Leiotama-Limestone 
  and 
  Klingkalk 
  of 
  Dalecarlia 
  

   (according 
  to 
  Nathorst 
  2 
  ), 
  with 
  the 
  ' 
  knoll-reefs 
  ' 
  described 
  by 
  

   Tiddeman, 
  3 
  of 
  Carboniferous 
  age, 
  south 
  of 
  the 
  Craven 
  fault 
  in 
  West 
  

   Yorkshire, 
  and 
  with, 
  some 
  Devonian 
  limestones 
  of 
  the 
  Ardennes. 
  

   In 
  all 
  these 
  instances 
  the 
  district 
  and 
  rocks 
  in 
  which 
  they 
  occur 
  

   have 
  suffered 
  great 
  disturbance. 
  

  

  With 
  regard 
  to 
  the 
  Keisley 
  Limestone, 
  I 
  am 
  inclined 
  to 
  think 
  

   that 
  we 
  may 
  be&t 
  explain 
  the 
  fact 
  that 
  it 
  is 
  not 
  palseontologically 
  

   represented 
  elsewhere 
  in 
  the 
  British 
  Isles, 
  except 
  at 
  Kildare, 
  by 
  

   supposing 
  that 
  a 
  wave 
  of 
  migration 
  started 
  from 
  the 
  Baltic 
  towards 
  

   the 
  close 
  of 
  Middle 
  Bala 
  times 
  ; 
  that 
  it 
  travelled 
  in 
  a 
  westerly 
  

   direction 
  over 
  Scandinavia, 
  the 
  North 
  of 
  England, 
  and 
  into 
  Ireland, 
  

   but 
  only 
  in 
  isolated 
  spots 
  — 
  such 
  as 
  are 
  now 
  found 
  in 
  Dalecarlia, 
  

   Keisley, 
  and 
  Kildare 
  — 
  did 
  the 
  fauna 
  which 
  it 
  bore 
  (namely, 
  the 
  

   fauna 
  of 
  Stage 
  F 
  of 
  Western 
  Russia) 
  find 
  the 
  conditions 
  suitable 
  for 
  

   its 
  settlement. 
  In 
  the 
  intervening 
  areas 
  it 
  was 
  unable 
  to 
  exist, 
  at 
  

   any 
  rate 
  in 
  its 
  entirety. 
  Many 
  of 
  the 
  species 
  of 
  the 
  fauna 
  of 
  the 
  

   seas 
  which 
  it 
  invaded 
  continued 
  to 
  flourish 
  alongside 
  of 
  it, 
  and 
  con- 
  

   tributed 
  their 
  remains 
  to 
  the 
  formation 
  of 
  the 
  limestone-patches. 
  

   On 
  the 
  surrounding 
  portions 
  of 
  the 
  sea-floor, 
  thin 
  horny 
  lime- 
  

   stone 
  accumulated 
  in 
  some 
  parts, 
  and 
  in 
  others 
  shales, 
  etc., 
  but 
  

   without 
  the 
  peculiar 
  fauna. 
  After 
  an 
  existence 
  of 
  brief 
  duration 
  in 
  

   these 
  isolated 
  outposts, 
  far 
  removed 
  from 
  its 
  original 
  home, 
  most 
  

   of 
  the 
  fauna 
  died 
  out, 
  mainly 
  owing 
  to 
  the 
  cessation 
  of 
  favourable 
  

   conditions, 
  but 
  partly 
  owing 
  to 
  the 
  immigration 
  of 
  the 
  new 
  fauna 
  

   of 
  the 
  Staurocephalus-zone. 
  It 
  left 
  but 
  few 
  descendants 
  behind 
  it. 
  

   The 
  facts 
  in 
  favour 
  of 
  the 
  view 
  that 
  the 
  existence 
  of 
  this 
  fauna 
  

   was 
  largely 
  conditional 
  on 
  the 
  physical 
  and 
  biological 
  environment 
  

   are 
  : 
  (1) 
  the 
  presence 
  of 
  numerous 
  specifically 
  -identical 
  forms, 
  

   although 
  the 
  localities 
  are 
  so 
  widely 
  separated 
  one 
  from 
  another 
  ; 
  

   (2) 
  the 
  absolute 
  limitation 
  of 
  many 
  of 
  these 
  forms 
  to 
  these 
  patches 
  

   of 
  limestone 
  ; 
  (3) 
  the 
  occurrence 
  of 
  blind 
  species 
  of 
  Illcenus 
  with 
  

  

  1 
  GeoL 
  Mag. 
  1892, 
  p. 
  97. 
  

  

  2 
  Geol. 
  Foren. 
  i 
  Stockholm 
  Forhandl. 
  no. 
  93, 
  vol. 
  vii. 
  (1884) 
  p. 
  559. 
  

  

  3 
  Rep. 
  Internat. 
  Geol. 
  Oongr. 
  1888, 
  pp. 
  319-322. 
  

  

  