﻿46 
  

  

  Prof. 
  C. 
  W, 
  Thomson 
  on 
  the 
  

  

  [Nov. 
  26, 
  

  

  clay. 
  Tlie 
  manganese 
  is 
  doubtless, 
  like 
  the 
  iron, 
  set 
  free 
  by 
  the 
  decompo- 
  

   sition 
  of 
  the 
  organic 
  bodies 
  and 
  tests. 
  It 
  is 
  known 
  to 
  exist 
  in 
  the 
  ash 
  

   of 
  some 
  Alga; 
  to 
  the 
  amount 
  of 
  4 
  per 
  cent. 
  

  

  The 
  interesting 
  question 
  now 
  arises 
  as 
  to 
  the 
  cause 
  and 
  method 
  of 
  the 
  

   removal 
  of 
  the 
  carbonate 
  of 
  lime 
  from 
  the 
  cretaceous 
  deposit 
  ; 
  and 
  on 
  this 
  

   matter 
  we 
  are 
  not 
  yet 
  in 
  a 
  position 
  to 
  form 
  any 
  definite 
  conclusion. 
  

  

  One 
  possible 
  explanation 
  is 
  sufficiently 
  obvious. 
  All 
  sea-water 
  contains 
  

   a 
  certain 
  proportion 
  of 
  free 
  carbonic 
  acid, 
  and 
  Mr. 
  Buchanan 
  believes 
  

   that 
  he 
  finds 
  it 
  rather 
  in 
  excess 
  in 
  bottom-water 
  from 
  great 
  depths. 
  At 
  

   all 
  events, 
  the 
  quantity 
  present 
  is 
  sufficient 
  to 
  convert 
  into 
  a 
  soluble 
  com- 
  

   pound, 
  and 
  thus 
  remove 
  a 
  considerable 
  amount 
  of 
  carbonate 
  of 
  lime. 
  If 
  the 
  

   balance 
  of 
  supply 
  be 
  very 
  delicately 
  adjusted, 
  it 
  is 
  just 
  conceivable 
  that 
  

   the 
  lime 
  in 
  the 
  shells, 
  in 
  its 
  fine 
  state 
  of 
  subdivision, 
  having 
  been 
  attacked 
  

   by 
  the 
  sea-water 
  from 
  the 
  moment 
  of 
  the 
  death 
  of 
  the 
  animal, 
  may 
  be 
  

   entirely 
  dissolved 
  during 
  its 
  retarded 
  passage 
  through 
  the 
  half 
  mile 
  or 
  so 
  

   of 
  water 
  of 
  increasing 
  density. 
  A 
  great 
  deal 
  of 
  the 
  bottom-water 
  in 
  these 
  

   deep 
  troughs 
  has 
  been 
  last 
  at 
  the 
  surface, 
  in 
  the 
  form 
  of 
  circumpolar 
  

   freshwater 
  ice 
  ; 
  and 
  though 
  fully 
  charged 
  with 
  carbonic 
  acid, 
  it 
  is 
  possible 
  

   that 
  it 
  may 
  be 
  comparatively 
  free 
  from 
  carbonate 
  of 
  lime, 
  and 
  that 
  its 
  

   solvent 
  power 
  may 
  thus 
  be 
  greater. 
  

  

  The 
  red 
  clay 
  or. 
  more 
  probably, 
  the 
  circumstances 
  which 
  lead 
  to 
  its 
  

   deposition 
  seem 
  on 
  the 
  whole 
  unfavourable 
  to 
  the 
  development 
  of 
  animal 
  

   life. 
  AVhere 
  it% 
  special 
  characters 
  are 
  most 
  marked, 
  no 
  animals 
  which 
  

   require 
  much 
  carbonate 
  of 
  lime 
  for 
  the 
  development 
  of 
  their 
  tissues 
  or 
  of 
  

   their 
  habitations 
  appear 
  to 
  exist. 
  Our 
  growing 
  experience 
  is, 
  that 
  although 
  

   animal 
  life 
  is 
  possible 
  at 
  all 
  depths, 
  after 
  a 
  certain 
  depth, 
  say 
  1500 
  

   fathoms, 
  its 
  abundance 
  diminishes. 
  This 
  would 
  seem 
  to 
  indicate 
  that 
  the 
  

   extreme 
  conditions 
  of 
  vast 
  depths 
  are 
  not 
  favourable 
  to 
  its 
  development; 
  

   and 
  one 
  might 
  well 
  imagine 
  that 
  the 
  number 
  of 
  shell-building 
  animals 
  

   might 
  decrease, 
  until 
  the 
  supply 
  of 
  lime 
  was 
  so 
  far 
  reduced 
  as 
  to 
  make 
  

   it 
  difficult 
  for 
  them 
  to 
  hold 
  their 
  own 
  against 
  the 
  solvent 
  power 
  of 
  the 
  

   water 
  of 
  the 
  sea 
  — 
  just 
  as 
  in 
  many 
  districts 
  where 
  there 
  is 
  little 
  lime, 
  the 
  

   shells 
  of 
  land 
  and 
  freshwater 
  mollusks 
  are 
  light 
  and 
  thin, 
  and 
  the 
  animals 
  

   themselves 
  are 
  stunted 
  and 
  scarce. 
  

  

  It 
  seems, 
  however, 
  that 
  neither 
  the 
  extreme 
  depth 
  at 
  which 
  the 
  red 
  

   clay 
  is 
  found, 
  nor 
  the 
  conditions 
  under 
  which 
  it 
  is 
  separated 
  and 
  laid 
  

   down, 
  are 
  sufficient 
  entirely 
  to 
  negative 
  the 
  existence 
  of 
  living 
  animals, 
  

   even 
  of 
  the 
  higher 
  invertebrate 
  orders. 
  In 
  several 
  of 
  the 
  hauls, 
  we 
  

   brought 
  up 
  Holothurids 
  of 
  considerable 
  size, 
  with 
  the 
  calcareous 
  neck- 
  

   rings 
  very 
  rudimentary, 
  and 
  either 
  no 
  calcareous 
  bodies 
  in 
  the 
  test, 
  or 
  a 
  

   mere 
  trace 
  of 
  such. 
  Xearly 
  every 
  haul 
  gave 
  us 
  delicate 
  branching 
  

   Bryozoa, 
  with 
  the 
  zooeeium 
  almost 
  membranous. 
  One 
  fortunate 
  cast, 
  

   about 
  150 
  miles 
  from 
  Sombrero, 
  brought 
  up, 
  from 
  a 
  depth 
  of 
  2975 
  fathoms, 
  

   very 
  well-marked 
  red 
  mud. 
  which 
  did 
  not 
  effervesce 
  with 
  hydrochloric 
  

   acid. 
  Entangled 
  in 
  the 
  dredge, 
  and 
  imbedded 
  in 
  the 
  mud. 
  were 
  many 
  of 
  

  

  