﻿1864.] 
  DUNCAN 
  WEST 
  INDIAN 
  CORALS. 
  371 
  

  

  lime 
  and 
  granular 
  silica 
  ; 
  so 
  are 
  the 
  spaces 
  formerly 
  occupied 
  by 
  the 
  

   walls 
  and 
  exotheca. 
  

  

  Variety 
  3. 
  — 
  The 
  walls 
  remain, 
  and 
  consist 
  of 
  saccharoid 
  calcareo- 
  

   silica 
  ; 
  but 
  the 
  rest 
  of 
  the 
  sclerenchyma 
  is 
  deficient. 
  The 
  interspaces 
  

   are 
  empty, 
  and 
  are 
  encroached 
  upon 
  by 
  the 
  saccharoid 
  mineral. 
  

   Many 
  corallites 
  of 
  the 
  Barbadian 
  Astraeans 
  have 
  their 
  walls 
  and 
  

   coenenchyma 
  turned 
  into 
  saccharoid-looking 
  spar, 
  all 
  the 
  rest 
  being 
  

   deficient. 
  These 
  honeycombed-looking 
  masses 
  consist 
  of 
  semi- 
  

   crystalline 
  carbonate 
  of 
  lime, 
  with 
  much 
  silica 
  j 
  and 
  doubtless 
  much 
  

   of 
  the 
  destruction 
  of 
  details 
  was 
  prefossil, 
  for 
  the 
  species 
  has 
  very 
  

   delicate 
  septa 
  and 
  costae*. 
  

  

  8. 
  Calcareo 
  -siliceous 
  easts. 
  Variety 
  1. 
  — 
  The 
  sclerenchyma 
  is 
  de- 
  

   ficient 
  for 
  some 
  lines' 
  depth 
  from 
  the 
  calicular 
  surface, 
  but 
  is 
  present 
  

   elsewhere, 
  and 
  consists 
  of 
  carbonate 
  of 
  lime, 
  with 
  more 
  or 
  less 
  silica. 
  

   The 
  interspaces 
  are 
  filled 
  with 
  light 
  reddish-brown 
  silica 
  for 
  some 
  

   depth 
  below 
  the 
  former 
  calicular 
  margin 
  ; 
  but 
  below 
  the 
  spots 
  where 
  

   the 
  sclerenchyma 
  begins 
  to 
  be 
  seen 
  they 
  are 
  filled 
  with 
  dense 
  car- 
  

   bonate 
  of 
  lime, 
  which 
  is 
  of 
  a 
  light-brown 
  or 
  light-red 
  colour. 
  

  

  Variety 
  2. 
  — 
  A 
  few 
  septa 
  are 
  all 
  that 
  remains 
  of 
  the 
  sclerenchyma. 
  

   The 
  interspaces 
  are 
  filled 
  with 
  dense 
  carbonate 
  of 
  lime 
  : 
  this 
  salt 
  

   fills 
  up 
  the 
  reticulations 
  in 
  the 
  walls 
  of 
  perforate 
  corals, 
  and 
  is 
  more 
  

   or 
  less 
  mixed 
  with 
  silica, 
  and 
  varies 
  greatly 
  in 
  colour. 
  

  

  Variety 
  3. 
  — 
  The 
  columella 
  and 
  the 
  septal 
  ends 
  attached, 
  remain 
  

   alone 
  on 
  the 
  free 
  surface 
  of 
  the 
  corallum 
  ; 
  below, 
  all 
  the 
  scleren- 
  

   chyma 
  exists. 
  The 
  interseptal 
  loculi 
  are 
  filled 
  with 
  saccharoid 
  

   carbonate 
  of 
  lime 
  and 
  silica. 
  

  

  The 
  largest 
  casts 
  of 
  calices 
  as 
  yet 
  known 
  are 
  those 
  of 
  the 
  Astraeans 
  

   of 
  the 
  Marl 
  of 
  Antigua. 
  The 
  interspaces 
  are 
  seen 
  as 
  dense 
  light- 
  

   brown 
  silica 
  ; 
  the 
  septa, 
  calicular 
  walls, 
  and 
  costae 
  are 
  wanting 
  for 
  

   some 
  lines' 
  depth 
  f 
  ; 
  and 
  even 
  in 
  transverse 
  sections, 
  made 
  a 
  little 
  

   distance 
  below 
  the 
  surface, 
  the 
  filled 
  interseptal 
  loculi 
  are 
  distin- 
  

   guished 
  from 
  the 
  vacant 
  spaces 
  where 
  septa 
  have 
  once 
  been. 
  The 
  

   vacant 
  spaces 
  of 
  the 
  septa, 
  in 
  the 
  casts, 
  simulate 
  interseptal 
  loculi 
  ; 
  

   and 
  the 
  dense 
  silica 
  of 
  these, 
  which 
  is 
  free 
  from 
  carbonate 
  of 
  lime, 
  

   may 
  be 
  mistaken 
  for 
  septal 
  structure. 
  The 
  siliceous 
  interspaces 
  are 
  

   not 
  continued 
  down 
  far 
  into 
  the 
  corallum, 
  for 
  carbonate 
  of 
  lime 
  

   soon 
  exists 
  in 
  great 
  proportion 
  in 
  them 
  ; 
  and 
  where 
  the 
  silicification 
  

   of 
  these 
  interspaces 
  becomes 
  defective, 
  there 
  does 
  the 
  silicification 
  of 
  

   the 
  septa 
  begin 
  to 
  be 
  intense, 
  and 
  the 
  appearance 
  of 
  a 
  cast 
  then 
  

   ceases. 
  The 
  intensity 
  of 
  the 
  silicification 
  on 
  the 
  surface 
  is 
  very 
  

   evident 
  ; 
  and 
  that 
  there 
  was 
  infiltration 
  of 
  the 
  interseptal 
  loculi 
  by 
  

   carbonate 
  of 
  lime 
  and 
  other 
  salts 
  prior 
  to 
  the 
  loss 
  of 
  the 
  septa 
  is 
  

   so 
  also. 
  It 
  is 
  most 
  remarkable 
  that 
  the 
  whole 
  surface 
  of 
  a 
  large 
  

   corallum 
  should 
  be 
  covered 
  by 
  casts 
  of 
  its 
  calices, 
  and 
  that 
  the 
  

   sclerenchyma 
  should 
  be 
  deficient 
  for 
  some 
  depth 
  ; 
  and 
  it 
  is 
  difficult 
  

   of 
  explanation, 
  unless 
  the 
  prefossil 
  condition 
  of 
  the 
  coral 
  be 
  admitted 
  

   into 
  the 
  consideration 
  of 
  the 
  subject. 
  

  

  The 
  calicular 
  ends 
  of 
  rapidly 
  growing 
  corallites 
  are 
  more 
  delicate, 
  

  

  * 
  The 
  Trinidad 
  (St. 
  Croix) 
  corals 
  are 
  generally 
  found 
  thus 
  fossilized. 
  

   f 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xix. 
  pi. 
  xiii. 
  fig. 
  1 
  b. 
  

  

  