﻿1864.] 
  DUNCAN 
  WEST 
  INDIAN 
  CORALS. 
  363 
  

  

  also 
  common 
  in 
  all 
  the 
  coral-formations, 
  occurs 
  amongst 
  the 
  Pacific 
  

   and 
  "West 
  Indian 
  reefs 
  ; 
  and 
  the 
  dense 
  limestone 
  described 
  by- 
  

   Darwin 
  and 
  other 
  observers 
  is 
  produced 
  wherever 
  there 
  is 
  much 
  

   coral 
  -detritus, 
  and 
  it 
  is 
  not 
  to 
  be 
  distinguished 
  from 
  infinitely 
  

   o?der 
  limestone-rock. 
  The 
  common 
  recent 
  saccharoid 
  cast 
  is 
  formed 
  

   by 
  the 
  hardening 
  of 
  the 
  calcareous 
  infiltrations 
  of 
  the 
  interstices 
  

   of 
  the 
  corals, 
  and 
  by 
  the 
  subsequent 
  disintegration 
  and 
  solution 
  

   of 
  the 
  hard 
  parts 
  ;- 
  it 
  is 
  a 
  form 
  of 
  cast 
  constantly 
  seen 
  either 
  in 
  

   the 
  calcareous 
  or 
  siliceous 
  form 
  of 
  mineralization. 
  The 
  considera- 
  

   tion 
  of 
  these 
  post-mortem 
  changes 
  and 
  prefossil 
  accidents, 
  which 
  

   are 
  now 
  occurring, 
  thus 
  brings 
  many 
  of 
  the 
  structural 
  peculiarities 
  

   of 
  fossil 
  corals 
  within 
  our 
  comprehension 
  ; 
  some 
  of 
  these 
  changes 
  

   are 
  perfectly 
  represented 
  in 
  the 
  fossil 
  condition, 
  and 
  others 
  are 
  

   supposed 
  to 
  influence 
  the 
  gradual 
  transposition 
  of 
  elements, 
  or 
  the 
  

   molecular 
  alteration 
  of 
  the 
  original 
  salts, 
  which 
  occur 
  during 
  the 
  

   lapse 
  of 
  ages. 
  There 
  are 
  then, 
  as 
  data 
  for 
  our 
  guidance 
  in 
  the 
  ap- 
  

   preciation 
  of 
  such 
  fossil 
  changes, 
  post-mortem 
  and 
  prefossil 
  acci- 
  

   dents 
  and 
  chemical 
  changes, 
  various 
  media, 
  which 
  include 
  the 
  

   organism, 
  and 
  which 
  have 
  various 
  chemical 
  changes 
  constantly 
  

   progressing 
  in 
  their 
  mass, 
  an 
  aerated 
  sea 
  containing 
  various 
  mi- 
  

   nerals 
  and 
  salts 
  in 
  solution, 
  varying 
  temperatures, 
  time, 
  oscillations 
  

   of 
  level, 
  and 
  alterations 
  in 
  the 
  fossilizing 
  materials, 
  drainage, 
  and 
  

   pressure. 
  

  

  § 
  III. 
  Table 
  of 
  the 
  Forms 
  oe 
  Mineralization. 
  

  

  1. 
  Calcareous 
  2 
  varieties. 
  

  

  2. 
  Siliceous 
  4 
  „ 
  

  

  3. 
  Siliceous 
  and 
  crystalline 
  2 
  ,, 
  

  

  4. 
  Siliceous 
  and 
  destructive 
  4 
  „ 
  

  

  5. 
  Siliceous 
  cast 
  2 
  „ 
  

  

  6. 
  Calcareo-siliceous 
  5 
  „ 
  

  

  7. 
  Calcareo-siliceous 
  and 
  destructive 
  3 
  „ 
  

  

  8. 
  Calcareo-siliceous 
  cast 
  3 
  „ 
  

  

  § 
  IY. 
  Description 
  of 
  the 
  Forms 
  and 
  Varieties 
  *. 
  

  

  1. 
  Calcareous. 
  — 
  The 
  sclerenchyma 
  is 
  more 
  or 
  less 
  perfect; 
  it 
  con- 
  

   sists 
  of 
  the 
  usual 
  coral-salts, 
  but 
  it 
  is 
  very 
  indurated. 
  The 
  inter- 
  

  

  * 
  The 
  specimens 
  of 
  these 
  forms 
  of 
  mineralization 
  are 
  amongst 
  the 
  fossil 
  West 
  

   Indian 
  Corals 
  in 
  the 
  Geological 
  Society's 
  Museum 
  ; 
  they 
  are 
  numbered 
  as 
  follows. 
  

   It 
  is 
  necessary 
  to 
  observe 
  that 
  certain 
  specimens 
  may 
  illustrate 
  more 
  than 
  one 
  

   form 
  at 
  once, 
  and 
  that 
  all 
  the 
  fossil 
  corals 
  are 
  not 
  marked. 
  

   Forms 
  — 
  Siliceous, 
  nos. 
  1, 
  2, 
  3, 
  4. 
  

  

  „ 
  Siliceous 
  and 
  crystalline, 
  nos. 
  5, 
  6, 
  7, 
  8, 
  9, 
  19. 
  

  

  ,, 
  Siliceous 
  casts, 
  no. 
  20. 
  

  

  „ 
  Siliceous 
  and 
  destructive, 
  nos. 
  10, 
  11, 
  12, 
  13, 
  14, 
  15, 
  16, 
  17, 
  18. 
  

  

  ,, 
  Calcareous, 
  no. 
  21. 
  

  

  „ 
  Calcareo-siliceous, 
  nos. 
  22, 
  23, 
  24, 
  25, 
  26, 
  27. 
  

  

  „ 
  Calcareo-siliceous 
  and 
  destructive, 
  nos. 
  28, 
  29. 
  

  

  „ 
  Calcareo-siliceous 
  casts, 
  nos. 
  30, 
  31. 
  

  

  ,, 
  Deformed 
  calices 
  fossilized, 
  no. 
  32. 
  

  

  „ 
  Indurated 
  and 
  rolled 
  recent 
  fossils, 
  nos. 
  34, 
  35, 
  36, 
  37, 
  38. 
  

  

  „ 
  Softened 
  recent 
  coral 
  with 
  dry 
  polype-tissues, 
  no. 
  39. 
  

  

  