﻿1864.] 
  DUNCAN 
  WEST 
  INDIAN 
  COKALS. 
  369 
  

  

  theca 
  ; 
  consequently 
  the 
  interseptal 
  loculi, 
  which, 
  are 
  filled 
  from 
  top 
  

   to 
  bottom 
  with 
  hard 
  silica 
  in 
  the 
  form 
  of 
  granules, 
  semitransparent 
  

   masses 
  of 
  more 
  or 
  less 
  darkly 
  coloured 
  chalcedony, 
  or 
  jasper, 
  re- 
  

   main 
  in 
  long 
  prisms, 
  slightly 
  separate. 
  The 
  septa 
  and 
  the 
  endotheca 
  

   are 
  wanting 
  in 
  one 
  variety 
  of 
  cast, 
  but 
  in 
  the 
  second 
  they 
  exist 
  

   more 
  or 
  less, 
  and 
  are 
  found 
  to 
  consist 
  of 
  a 
  silica 
  different 
  in 
  colour 
  

   from 
  the 
  rest. 
  

  

  A 
  very 
  likely 
  mistake 
  to 
  occur 
  in 
  the 
  diagnosis 
  of 
  some 
  casts, 
  

   where 
  the 
  calicular 
  surface 
  is 
  lost 
  and 
  a 
  transverse 
  section 
  of 
  the 
  

   mass 
  can 
  alone 
  be 
  had, 
  is 
  where 
  the 
  destruction 
  of 
  the 
  outer 
  third 
  

   of 
  the 
  septa 
  is 
  complete, 
  but 
  not 
  that 
  of 
  the 
  inner 
  third, 
  the 
  colu- 
  

   mella 
  remaining*. 
  In 
  these 
  instances, 
  the 
  outer 
  parts 
  of 
  the 
  inter- 
  

   septal 
  loculi 
  are 
  so 
  sharply 
  rounded 
  as 
  to 
  represent 
  a 
  costa, 
  and 
  to 
  

   cause 
  the 
  specimen 
  to 
  be 
  considered 
  an 
  Astrsean 
  instead 
  of 
  a 
  species 
  

   of 
  a 
  genus 
  without 
  costse. 
  The 
  casts 
  on 
  the 
  calicular 
  surfaces 
  are 
  

   easily 
  recognized 
  by 
  the 
  projection 
  instead 
  of 
  the 
  natural 
  depression 
  

   of 
  the 
  central 
  part 
  of 
  the 
  calices, 
  and 
  an 
  impression 
  taken 
  in 
  gutta 
  

   percha 
  yields 
  the 
  normal 
  appearance. 
  

  

  6. 
  Calcareo 
  -siliceous.- 
  — 
  Yariety 
  1. 
  The 
  sclerenchyma 
  is 
  perfect, 
  

   and 
  consists 
  of 
  the 
  usual 
  coral- 
  salts, 
  with 
  an 
  admixture 
  of 
  white 
  

   granular 
  silica. 
  The 
  interspaces 
  are 
  empty. 
  

  

  Yariety 
  2. 
  — 
  The 
  sclerenchyma 
  is 
  as 
  in 
  the 
  last 
  variety 
  ; 
  but 
  the 
  

   silica 
  exists 
  as 
  dark 
  granules 
  in 
  the 
  centre 
  of 
  the 
  septal 
  laminae. 
  

   The 
  interspaces 
  are 
  filled 
  with 
  dense, 
  granular, 
  light-brown, 
  light- 
  

   grey, 
  or 
  dark-brown 
  carbonate 
  of 
  lime. 
  

  

  Yariety 
  3. 
  — 
  The 
  sclerenchyma 
  is 
  more 
  or 
  less 
  perfect, 
  but 
  it 
  

   contains 
  more 
  silica 
  than 
  carbonate 
  of 
  lime, 
  and 
  the 
  silica 
  is 
  homo- 
  

   geneous, 
  semitransparent, 
  and 
  usually 
  dark 
  in 
  colour. 
  The 
  inter- 
  

   spaces 
  are 
  filled 
  as 
  in 
  the 
  last 
  variety 
  ; 
  but 
  much 
  granular 
  silica 
  

   exists 
  in 
  the 
  carbonate 
  of 
  lime. 
  

  

  Yariety 
  4. 
  — 
  The 
  sclerenchyma 
  is 
  as 
  in 
  the 
  last 
  variety 
  ; 
  but 
  the 
  

   colour 
  of 
  the 
  flint 
  is 
  an 
  opaque 
  cherty 
  white. 
  The 
  interspaces 
  are 
  

   filled 
  with 
  dark 
  carbonate 
  of 
  lime 
  and 
  a 
  little 
  silica 
  ; 
  but 
  many 
  

   corallites 
  are 
  empty, 
  and 
  some 
  endothecal 
  cells 
  alsof 
  . 
  

  

  Yariety 
  5. 
  — 
  The 
  sclerenchyma 
  is 
  as 
  in 
  the 
  third 
  variety 
  ; 
  but 
  in 
  

   many 
  specimens 
  the 
  silica 
  is 
  granular 
  and 
  very 
  brightly 
  coloured. 
  

   The 
  interspaces 
  are 
  filled 
  as 
  in 
  the 
  third 
  variety, 
  but 
  their 
  contents 
  

   are 
  often 
  brightly 
  coloured. 
  The 
  calcareo-siliceous 
  forms 
  of 
  mine- 
  

   ralization 
  are 
  very 
  common 
  in 
  all 
  the 
  raised 
  coral-formations 
  of 
  the 
  

   West 
  Indies, 
  except 
  in 
  the 
  Inclined 
  Beds 
  and 
  Chert 
  of 
  Antigua, 
  

   where 
  the 
  siliceous 
  form 
  alone 
  exists. 
  In 
  St. 
  Domingo 
  and 
  Jamaica 
  

   the 
  silicification 
  of 
  the 
  coral-salts 
  of 
  the 
  sclerenchyma, 
  and 
  of 
  the 
  

   infiltrated 
  carbonate 
  of 
  lime 
  of 
  the 
  interspaces 
  of 
  the 
  corals, 
  is 
  

   usually 
  more 
  or 
  less 
  incomplete. 
  In 
  the 
  Antiguan 
  Marl 
  also, 
  the 
  

   great 
  Astrseans 
  are 
  found 
  variously 
  affected 
  by 
  incomplete 
  silicifi- 
  

   cation 
  of 
  their 
  original 
  and 
  infiltrated 
  salts. 
  In 
  some 
  specimens 
  no 
  

   less 
  than 
  five 
  grades 
  of 
  this 
  form 
  of 
  fossilization 
  are 
  to 
  be 
  noticed, 
  

   in 
  others 
  but 
  one 
  ; 
  and 
  in 
  the 
  majority 
  there 
  are 
  usually 
  two 
  or 
  

  

  * 
  Stephanoccenia 
  tenuis, 
  nobis. 
  

  

  t 
  Quart. 
  Journ. 
  Greol. 
  Soc. 
  vol. 
  xix. 
  pi. 
  xiii. 
  fig. 
  5. 
  

  

  