﻿1864.] 
  DUNCAN 
  WEST 
  INDIAN 
  COltALS. 
  361 
  

  

  ing 
  after 
  separation 
  from 
  the 
  reef, 
  and 
  by 
  the 
  ravages 
  of 
  Lithodomi 
  

   and 
  Parrot-fish 
  before 
  death. 
  

  

  2. 
  By 
  decomposition 
  of 
  the 
  soft 
  parts. 
  — 
  When 
  a 
  recently 
  dead 
  

   coral 
  retains 
  its 
  soft 
  parts 
  sufficiently 
  long 
  for 
  decomposition 
  to 
  set 
  

   in, 
  and 
  it 
  is 
  exposed 
  to 
  the 
  direct 
  rays 
  of 
  the 
  sun, 
  the 
  superficial 
  

   tissues 
  become 
  diffluent 
  and 
  foetid 
  : 
  if 
  the 
  decomposing 
  membranes 
  

   be 
  not 
  speedily 
  washed 
  off, 
  they 
  become 
  dry, 
  black, 
  and 
  hard 
  ; 
  but 
  

   if 
  the 
  tide, 
  or 
  accidental 
  moisture 
  of 
  any 
  kind, 
  remove 
  the 
  super- 
  

   ficial 
  and 
  wash 
  out 
  the 
  deep 
  decomposing 
  polype-tissue, 
  the 
  coral 
  

   is 
  but 
  little 
  affected 
  as 
  regards 
  the 
  condition 
  of 
  its 
  sclerenchyma. 
  

   Beneath 
  the 
  dry 
  blackened 
  membranes 
  the 
  sclerenchyma 
  appears 
  

   invariably 
  softer 
  than 
  during 
  life 
  ; 
  moreover, 
  where 
  stained, 
  it 
  crum- 
  

   bles, 
  and 
  to 
  a 
  certain 
  depth, 
  even 
  when 
  there 
  is 
  no 
  discoloration, 
  it 
  

   has 
  less 
  cohesion 
  and 
  a 
  different 
  fracture 
  than 
  formerly. 
  The 
  

   fracture 
  is 
  of 
  an 
  opaque, 
  saccharoid, 
  white 
  colour, 
  and 
  the 
  texture 
  is 
  

   more 
  or 
  less 
  chalky 
  and 
  granular 
  : 
  a 
  new 
  chemical 
  compound 
  exists 
  

   in 
  the 
  sclerenchyma, 
  and 
  is 
  the 
  result 
  of 
  the 
  action 
  of 
  phosphates 
  and 
  

   chlorides 
  upon 
  the 
  carbonates 
  of 
  lime 
  and 
  magnesia 
  of 
  the 
  living 
  coral. 
  

   Corals 
  thus 
  altered 
  are 
  very 
  destructible, 
  and 
  as 
  simple 
  subaerial 
  

   wear 
  and 
  tear 
  rub 
  off 
  their 
  minuter 
  structural 
  details, 
  so 
  more 
  

   powerful 
  influences 
  destroy 
  all 
  the 
  parts 
  which 
  offer 
  the 
  charac- 
  

   teristics 
  for 
  classification. 
  The 
  most 
  recently 
  formed 
  parts 
  of 
  the 
  

   sclerenchyma 
  of 
  corals 
  are 
  the 
  most 
  porous 
  and 
  the 
  most 
  in 
  contact 
  

   with 
  the 
  soft 
  parts 
  : 
  the 
  edges 
  of 
  the 
  septa 
  and 
  the 
  lateral 
  granules 
  

   of 
  their 
  lamina? 
  are, 
  for 
  this 
  reason, 
  the 
  details 
  most 
  readily 
  af- 
  

   fected 
  by 
  the 
  chemistry 
  of 
  decomposition, 
  and 
  deformed 
  calices, 
  with 
  

   bent 
  and 
  collapsed 
  margins, 
  are 
  commonly 
  seen 
  on 
  recently 
  decom- 
  

   posed 
  corallum-surfaces 
  ; 
  moreover 
  these 
  conditions 
  are 
  seen 
  in 
  the 
  

   fossil 
  state, 
  the 
  deformities 
  being 
  permanently 
  transmitted 
  by 
  sili- 
  

   ceous 
  transposition*. 
  The 
  decomposition 
  of 
  the 
  deeply 
  seated 
  tissues 
  

   in 
  tall 
  Astraeans, 
  and 
  other 
  corallites 
  with 
  long 
  tubes, 
  appears 
  to 
  

   be 
  very 
  destructive 
  to 
  the 
  sclerenchyma 
  in 
  the 
  immediate 
  neigh- 
  

   bourhood 
  ; 
  it 
  can 
  hardly 
  be 
  prevented 
  or 
  controlled 
  by 
  the 
  contact 
  

   of 
  moisture, 
  and 
  it 
  therefore 
  often 
  happens 
  that 
  a 
  large 
  mass 
  of 
  

   coral 
  may 
  be 
  very 
  perfect 
  in 
  its 
  calicular 
  details, 
  but 
  very 
  imperfect 
  

   lower 
  down. 
  This 
  condition 
  is 
  also 
  transmitted 
  in 
  the 
  fossil 
  state. 
  

  

  Induration 
  proceeds 
  in 
  the 
  sclerenchyma 
  which 
  has 
  been 
  out 
  of 
  

   the 
  range 
  of 
  decomposition 
  ; 
  and 
  all 
  the 
  cast-away 
  masses, 
  their 
  

   debris, 
  and 
  also 
  huge 
  masses 
  of 
  reefs, 
  elevated 
  during 
  the 
  frequent 
  

   changes 
  of 
  level 
  of 
  such 
  localities, 
  have 
  a 
  tendency 
  to 
  harden, 
  and, 
  

   when 
  in 
  contact, 
  to 
  form 
  limestones 
  or 
  coral 
  breccias 
  f 
  . 
  The 
  in- 
  

   fluence 
  of 
  the 
  wash 
  of 
  the 
  tide 
  or 
  of 
  spray 
  on 
  these 
  masses 
  must 
  

   be 
  remembered, 
  especially 
  as 
  the 
  sea 
  is 
  charged 
  with 
  atmospheric 
  

   air, 
  and 
  contains 
  both 
  silica 
  and 
  carbonate 
  of 
  lime 
  in 
  minute 
  quan- 
  

   tities, 
  as 
  well 
  as 
  siliceous 
  organisms. 
  

  

  3. 
  By 
  fracture 
  from 
  the 
  parent 
  mass. 
  — 
  When 
  a 
  living 
  coral 
  is 
  

   broken 
  from 
  its 
  base, 
  or 
  separated 
  from 
  its 
  parent 
  mass, 
  or 
  removed 
  

  

  * 
  See 
  deformed 
  calices 
  of 
  an 
  Astraa 
  from 
  Antigua, 
  Coll. 
  Geol. 
  Soc. 
  no. 
  32. 
  

   This 
  state 
  is 
  associated 
  with 
  the 
  formation 
  of 
  casts 
  and 
  destructive 
  silicification. 
  

   t 
  The 
  results 
  of 
  the 
  observations 
  of 
  Dana, 
  Darwin, 
  Jukes, 
  and 
  others. 
  

  

  