﻿244 
  On 
  the 
  Sea-bottom 
  procured 
  by 
  H. 
  M.S. 
  'Challenger.' 
  [Feb. 
  4>, 
  

  

  although 
  its 
  state 
  of 
  aggregation 
  is 
  different. 
  And 
  if 
  this 
  was 
  their 
  real 
  

   origin, 
  I 
  should 
  be 
  disposed 
  to 
  extend 
  the 
  same 
  view 
  to 
  the 
  red 
  clay 
  of 
  

   the 
  ' 
  Challenger 
  ' 
  soundings 
  ; 
  for 
  a 
  strong 
  a 
  priori 
  improbability 
  in 
  the 
  

   supposition 
  that 
  this 
  is 
  the 
  " 
  ash 
  " 
  of 
  the 
  shells 
  themselves 
  is 
  created 
  by 
  

   the 
  fact 
  that 
  we 
  have 
  no 
  knowledge 
  (so 
  far 
  as 
  I 
  am 
  aware) 
  of 
  the 
  pre- 
  

   sence 
  of 
  any 
  such 
  ash 
  in 
  calcareous 
  organisms 
  of 
  similar 
  grade. 
  It 
  is 
  

   certainly 
  not 
  proved 
  by 
  the 
  analyses 
  of 
  Globigerina-ooze 
  quoted 
  by 
  Prof. 
  

   Wyville 
  Thomson 
  ; 
  since 
  this 
  (supposing 
  it 
  to 
  be 
  free 
  from 
  any 
  extrane- 
  

   ous 
  admixture) 
  may 
  have 
  contained 
  many 
  shells 
  partially 
  or 
  completely 
  

   filled 
  with 
  such 
  deposit. 
  The 
  only 
  analysis 
  that 
  could 
  prove 
  it 
  would 
  

   be 
  that 
  either 
  of 
  shells 
  of 
  floating 
  Globigerince, 
  which 
  may 
  be 
  presumed 
  

   to 
  be 
  alive, 
  or 
  of 
  those 
  found 
  in 
  the 
  surface-layer 
  of 
  the 
  Globigerina-ooze, 
  

   which 
  (whether 
  living 
  or 
  dead) 
  have 
  their 
  chambers 
  filled 
  with 
  sarcode. 
  

  

  I 
  submit, 
  then, 
  that 
  if 
  the 
  red 
  clay 
  is 
  (as 
  I 
  am 
  disposed 
  to 
  believe) 
  a 
  

   derivative 
  of 
  the 
  Globigerina-ooze, 
  its 
  production 
  is 
  more 
  probably 
  due 
  to 
  

   a 
  post 
  mortem 
  deposit 
  in 
  the 
  chambers 
  of 
  the 
  Foraminif 
  era 
  than 
  to 
  the 
  

   appropriation 
  of 
  its 
  material 
  by 
  the 
  living 
  animals 
  in 
  the 
  formation 
  of 
  

   their 
  shells. 
  That 
  deposit 
  may 
  have 
  had 
  the 
  character, 
  in 
  the 
  first 
  in- 
  

   stance, 
  of 
  either 
  the 
  green 
  or 
  the 
  ochreous 
  silicate 
  of 
  alumina 
  and 
  iron, 
  

   which 
  constitutes 
  the 
  material 
  of 
  the 
  internal 
  casts, 
  and 
  may 
  have 
  been 
  

   subsequently 
  changed 
  in 
  its 
  character 
  by 
  a 
  metamorphic 
  action 
  analogous 
  

   to 
  that 
  which 
  changes 
  felspar 
  into 
  clay. 
  That 
  the 
  presence 
  of 
  an 
  excess 
  

   of 
  carbonic 
  acid 
  would 
  have 
  an 
  important 
  share 
  in 
  such 
  a 
  metamorphosis 
  

   appears 
  from 
  the 
  fact, 
  long 
  since 
  brought 
  into 
  notice 
  by 
  Sir 
  Charles 
  Lyell*, 
  

   of 
  the 
  disintegration 
  of 
  the 
  granite 
  in 
  Auvergne 
  and 
  of 
  the 
  gneiss 
  in 
  the 
  

   alluvial 
  plains 
  of 
  the 
  Po 
  where 
  subject 
  to 
  its 
  influence. 
  And 
  the 
  same 
  

   agency 
  (especially 
  when 
  operating 
  under 
  great 
  pressure) 
  would 
  be 
  fully 
  

   competent 
  to 
  effect 
  the 
  removal 
  of 
  the 
  calcareous 
  shells, 
  as 
  was 
  distinctly 
  

   pointed 
  out 
  nearly 
  thirty 
  years 
  ago 
  by 
  Prof. 
  W. 
  C. 
  "Williamson 
  in 
  his 
  clas- 
  

   sical 
  Memoir 
  on 
  the 
  Microscopic 
  Organisms 
  of 
  the 
  Levant 
  Mudt. 
  This 
  

   seems 
  to 
  me 
  the 
  most 
  probable 
  mode 
  of 
  accounting 
  for 
  their 
  disappear- 
  

   ance 
  from 
  a 
  deep-sea 
  deposit, 
  where 
  no 
  mechanical 
  cause 
  can 
  be 
  invoked. 
  

   But 
  in 
  shallower 
  waters, 
  where 
  the 
  same 
  excess 
  of 
  carbonic 
  acid 
  does 
  not 
  

   exist, 
  and 
  the 
  aid 
  of 
  pressure 
  is 
  wanting, 
  but 
  where 
  a 
  movement 
  of 
  water 
  

   over 
  the 
  bottom 
  is 
  produced 
  by 
  tides 
  and 
  currents, 
  I 
  am 
  disposed 
  rather 
  

   to 
  attribute 
  the 
  disappearance 
  of 
  the 
  shells 
  to 
  mechanical 
  abrasion, 
  

   having 
  noticed, 
  in 
  Capt. 
  Spratt's 
  iEgean 
  dredgings, 
  that 
  many 
  of 
  the 
  

   shells 
  were 
  worn 
  so 
  thin 
  that 
  the 
  coloured 
  mineral 
  deposit 
  in 
  their 
  in- 
  

   terior 
  could 
  be 
  seen 
  through 
  them 
  — 
  which 
  was, 
  in 
  fact, 
  what 
  first 
  drew 
  

   my 
  attention 
  to 
  its 
  presence. 
  This 
  is 
  the 
  explanation 
  I 
  should 
  be 
  dis- 
  

   posed 
  to 
  give 
  of 
  the 
  disappearance 
  of 
  the 
  shells 
  from 
  the 
  green 
  sand 
  

   brought 
  up 
  by 
  the 
  ' 
  Challenger' 
  in 
  the 
  course 
  of 
  the 
  Agulhas 
  Current 
  ; 
  but 
  

   whether 
  it 
  was 
  mechanical 
  abrasion 
  or 
  chemical 
  solution 
  that 
  removed 
  

   * 
  Principles 
  of 
  Geology, 
  11th 
  ed., 
  vol. 
  i. 
  p. 
  409. 
  

  

  t 
  Memoirs 
  of 
  the 
  Literary 
  and 
  Philosophical 
  Society 
  of 
  Manchester, 
  vol. 
  viii. 
  p. 
  98. 
  

  

  