﻿FROM 
  THE 
  RADIOLARIAN 
  MARLS 
  OF 
  EARBADOS. 
  647 
  

  

  the 
  slides 
  and 
  fully 
  endorses 
  the 
  view 
  that 
  the 
  rock 
  belongs 
  to 
  the 
  

   Eadiolarian 
  deposits, 
  while 
  he 
  has 
  further 
  shown 
  me 
  some 
  slides 
  of 
  

   the 
  Barbados 
  Eadiolarian 
  earth 
  in 
  his 
  own 
  collection, 
  which 
  prove 
  

   their 
  identity. 
  

  

  The 
  fossil 
  having 
  therefore 
  come 
  from 
  the 
  Eadiolarian 
  deposits, 
  it 
  

   is 
  necessary 
  for 
  the 
  purpose 
  of 
  this 
  paper 
  to 
  consider 
  the 
  evidence 
  

   for 
  the 
  age 
  of 
  the 
  beds, 
  and 
  to 
  see 
  what 
  light 
  this 
  fossil 
  throws 
  upon 
  

   the 
  question. 
  It 
  may 
  be 
  taken 
  that 
  the 
  Eadiolarian 
  deposits 
  are 
  of 
  

   later 
  date 
  than 
  and 
  not 
  interstratified 
  with 
  the 
  Scotland 
  formation, 
  

   and 
  the 
  age 
  is 
  therefore 
  between 
  that 
  of 
  the 
  latter 
  and 
  that 
  of 
  the 
  

   Coral 
  limestone. 
  jSTo 
  definite 
  answer 
  can 
  be 
  given 
  as 
  to 
  the 
  age 
  of 
  

   the 
  Scotland 
  formation 
  : 
  the 
  evidence 
  of 
  the 
  three 
  species 
  of 
  Mollusca 
  

   is 
  certainly 
  inadequate 
  to 
  prove 
  their 
  supposed 
  Miocene 
  age, 
  especially 
  

   as 
  the 
  species 
  are 
  admittedly 
  close 
  allies 
  of 
  Pliocene 
  forms. 
  With 
  

   the 
  Eadiolaria 
  the 
  case 
  is 
  no 
  better, 
  as 
  the 
  writers 
  on 
  this 
  group 
  

   (Butschli 
  *, 
  von 
  Zittel 
  f, 
  and 
  others) 
  have 
  accepted 
  Schomburgk's 
  and 
  

   Forbes's 
  opinion, 
  and 
  as 
  both 
  the 
  premisses 
  of 
  this 
  are 
  disputed, 
  it 
  is 
  

   hardly 
  safe 
  to 
  accept 
  the 
  conclusion. 
  Ehrenberg, 
  when 
  abandoning 
  J: 
  

   his 
  old 
  view 
  of 
  the 
  Mesozoic 
  age 
  of 
  the 
  Eadiolarian 
  deposits 
  in 
  

   deference 
  to 
  Forbes's 
  opinion, 
  referred 
  to 
  the 
  difficulty 
  of 
  separating 
  

   the 
  lower 
  Tertiary 
  beds 
  from 
  the 
  Chalk, 
  although 
  he 
  thought 
  this 
  

   would 
  be 
  accomplished 
  by 
  further 
  microscopical 
  research. 
  He 
  thus 
  

   showed 
  that 
  he 
  recognized 
  that 
  the 
  two 
  sets 
  of 
  deposits 
  were 
  quite 
  

   distinct. 
  

  

  Hackel 
  has, 
  however, 
  instituted 
  a 
  comparison 
  between 
  the 
  Eadio- 
  

   larian 
  fauna 
  of 
  the 
  Barbadian 
  deposits 
  and 
  that 
  of 
  the 
  recent 
  seas, 
  

   and 
  finding 
  that 
  only 
  about 
  25 
  per 
  cent, 
  are 
  common 
  to 
  the 
  two, 
  has 
  

   supported 
  the 
  Miocene 
  age 
  with 
  a 
  more 
  weighty 
  argument 
  §. 
  But 
  

   neither 
  is 
  this 
  at 
  all 
  conclusive 
  ; 
  the 
  living 
  Eadiolaria 
  have 
  hardly 
  

   been 
  sufficiently 
  well 
  worked 
  to 
  enable 
  any 
  such 
  proportion 
  to 
  be 
  

   of 
  the 
  value 
  that 
  would 
  belong 
  to 
  one 
  of 
  the 
  better-known 
  groups, 
  

   and 
  a 
  closer 
  search 
  would 
  doubtless 
  considerably 
  increase 
  the 
  number 
  

   of 
  forms 
  common 
  to 
  the 
  faunas. 
  The 
  value 
  of 
  the 
  species 
  of 
  Eadio- 
  

   laria 
  is 
  very 
  doubtful, 
  and, 
  moreover, 
  Eadiolaria 
  are 
  probably 
  of 
  no 
  

   more 
  value 
  than 
  Foraminifera 
  in 
  the 
  correlation 
  of 
  deposits. 
  

   Echinoids, 
  on 
  the 
  other 
  hand, 
  have 
  always 
  been 
  regarded 
  as 
  of 
  special 
  

   value 
  as 
  time 
  guides, 
  and 
  the 
  evidence 
  of 
  one 
  Echinoid 
  is 
  worth 
  that 
  

   of 
  many 
  Eadiolaria. 
  Cystechinus 
  crassus 
  is 
  unquestionably 
  closely 
  

   allied 
  to 
  the 
  living 
  species 
  of 
  the 
  same 
  genus, 
  and 
  although 
  deep-sea 
  

   forms 
  may 
  be 
  very 
  conservative, 
  it 
  certainly 
  seems 
  to 
  show 
  that 
  the 
  

   beds 
  are 
  of 
  comparatively 
  recent 
  date, 
  either 
  Pliocene 
  or 
  Pleistocene. 
  

  

  * 
  O. 
  Butschli, 
  " 
  Protozoa," 
  Bronn's 
  Klassen 
  imd 
  Ordnungen 
  des 
  Thierreichs, 
  

   Bd. 
  i. 
  1882, 
  pp. 
  476-8. 
  

  

  t 
  K. 
  von 
  Zittel, 
  Palaozoologie, 
  Bd. 
  i. 
  (Munchen, 
  1879), 
  p. 
  118. 
  

  

  I 
  Ehrenberg, 
  " 
  Portzetzung 
  der 
  mikrogeologischen 
  Studien 
  als 
  Gesammt- 
  

   Uebersicht 
  der 
  mikroskopischen 
  Palaontologie 
  gleichartig 
  analysirter 
  Gebirgs- 
  

   arten 
  derErde, 
  mitspeeiellerRucksicht 
  auf 
  den 
  Polycvstinen-Mergel 
  von 
  Barba- 
  

   dos," 
  Abh. 
  d. 
  k. 
  Akad. 
  Wissensch. 
  Berlin, 
  1875 
  (1876), 
  p. 
  114. 
  

  

  § 
  E. 
  Hackel, 
  " 
  Keport 
  on 
  the 
  Badiolaria 
  collected 
  by 
  H.M.S. 
  ' 
  Challenger 
  ' 
  

   during 
  the 
  years 
  1873-6," 
  ' 
  Challenger 
  ' 
  Reports, 
  Zool. 
  vol. 
  xviii. 
  pt. 
  1 
  (London, 
  

   1887), 
  p. 
  clxxv. 
  

  

  