﻿1875.] 
  Sea-bottom 
  procured 
  by 
  H.M.S. 
  ' 
  Challenger.' 
  241 
  

  

  here 
  (according 
  to 
  him) 
  has 
  a 
  depth 
  of 
  700 
  fathoms 
  ; 
  and 
  this 
  very 
  strik- 
  

   ing 
  example 
  of 
  want 
  of 
  conformity 
  between 
  the 
  surface-fauna 
  and 
  the 
  

   bottom-deposit 
  consequently 
  remains 
  to 
  be 
  accounted 
  for 
  on 
  his 
  hypo- 
  

   thesis. 
  

  

  The 
  other 
  of 
  Prof. 
  Wyville 
  Thomson's 
  principal 
  conclusions, 
  as 
  to 
  

   which 
  I 
  have 
  rather 
  a 
  suggestion 
  to 
  offer 
  than 
  an 
  objection 
  to 
  take, 
  

   relates 
  to 
  the 
  origin 
  of 
  the 
  " 
  red 
  clay 
  " 
  which 
  he 
  found 
  covering 
  large 
  

   areas 
  in 
  the 
  Atlantic, 
  and 
  met 
  with 
  also 
  between 
  Kerguelen's 
  Island 
  and 
  

   Melbourne. 
  Into 
  this 
  red 
  clay 
  he 
  describes 
  the 
  Globigerina-ooze 
  as 
  gra- 
  

   duating, 
  through 
  the 
  " 
  grey 
  ooze 
  " 
  ; 
  and 
  he 
  affirms 
  this 
  transition 
  to 
  be 
  

   essentially 
  dependent 
  on 
  the 
  depth 
  of 
  the 
  bottom. 
  " 
  Crossing," 
  he 
  says 
  

   " 
  from 
  these 
  shallower 
  regions 
  occupied 
  by 
  the 
  ooze 
  into 
  deeper 
  soundings, 
  

   we 
  find 
  universally 
  that 
  the 
  calcareous 
  formation 
  gradually 
  passes 
  into, 
  

   and 
  is 
  replaced 
  by, 
  an 
  extremely 
  pure 
  clay, 
  which 
  occupies, 
  speaking 
  

   generally, 
  all 
  depths 
  below 
  2500 
  fathoms, 
  and 
  consists 
  almost 
  entirely 
  of 
  

  

  a 
  silicate 
  of 
  the 
  red 
  oxide 
  of 
  iron 
  and 
  alumina 
  The 
  mean 
  

  

  maximum 
  depth 
  at 
  which 
  the 
  Globigerina-ooze 
  occurs, 
  may 
  be 
  taken 
  

   at 
  about 
  2250 
  fathoms 
  ; 
  the 
  mean 
  depth 
  at 
  which 
  we 
  find 
  the 
  trans- 
  

   ition 
  grey 
  ooze 
  is 
  2400 
  fathoms 
  ; 
  and 
  the 
  mean 
  depth 
  of 
  the 
  red-clay 
  

  

  soundings 
  is 
  about 
  2700 
  fathoms 
  We 
  were 
  at 
  length 
  

  

  able," 
  he 
  continues, 
  " 
  to 
  predict 
  the 
  nature 
  of 
  the 
  bottom 
  from 
  the 
  depth 
  of 
  

   the 
  soundings 
  with 
  absolute 
  certainty 
  for 
  the 
  Atlantic 
  and 
  the 
  Southern 
  

   Sea." 
  And 
  from 
  these 
  data 
  he 
  considers 
  it 
  an 
  indubitable 
  inference 
  

   " 
  that 
  the 
  red 
  clay 
  is 
  essentially 
  the 
  insoluble 
  residue, 
  the 
  ash, 
  as 
  it 
  were, 
  

   of 
  the 
  calcareous 
  organisms 
  w 
  T 
  hich 
  form 
  the 
  Globigerina-ooze 
  after 
  the 
  

   calcareous 
  matter 
  has 
  been 
  by 
  some 
  means 
  removed." 
  This 
  inference 
  he 
  

   considers 
  to 
  have 
  been 
  confirmed 
  by 
  the 
  analysis 
  of 
  several 
  samples 
  of 
  

   Globigerina-ooze, 
  " 
  always 
  with 
  the 
  result 
  that'a 
  small 
  proportion 
  of 
  a 
  red 
  

   sediment 
  remains, 
  which 
  possesses 
  all 
  the 
  characters 
  of 
  the 
  red 
  clay." 
  

   Prof. 
  "Wyville 
  Thomson 
  further 
  suggests 
  that 
  the 
  removal 
  of 
  the 
  calcare- 
  

   ous 
  matter 
  may 
  be 
  due 
  to 
  the 
  presence 
  of 
  an 
  excess 
  of 
  carbonic 
  acid 
  in 
  

   the 
  bottom-waters, 
  and 
  to 
  the 
  derivation 
  of 
  this 
  water 
  in 
  great 
  part 
  from 
  

   circumpolar 
  freshwater 
  ice, 
  so 
  that, 
  being 
  comparatively 
  free 
  from 
  car- 
  

   bonate 
  of 
  lime, 
  its 
  solvent 
  power 
  for 
  that 
  substance 
  is 
  greater 
  than 
  that 
  of 
  

   the 
  superjacent 
  waters 
  of 
  the 
  ocean. 
  He 
  might 
  have 
  added 
  probability 
  to 
  

   his 
  hypothesis 
  if 
  he 
  had 
  cited 
  the 
  observations 
  of 
  Mr. 
  Sorby 
  as 
  to 
  the 
  

   increase 
  of 
  solvent 
  power 
  for 
  carbonate 
  of 
  lime 
  possessed 
  by 
  water 
  under 
  

   greatly 
  augmented 
  pressure*. 
  

  

  Greatly 
  struck 
  with 
  the 
  ingenuity 
  of 
  this 
  hypothesis, 
  I 
  turned 
  to 
  Prof. 
  

   "Wyville 
  Thomson's 
  tabular 
  statement 
  of 
  the 
  facts 
  in 
  detail 
  ; 
  and 
  must 
  

   own 
  to 
  a 
  great 
  feeling 
  of 
  surprise 
  at 
  the 
  want 
  of 
  conformity 
  of 
  these 
  

   details 
  with 
  the 
  assertions 
  of 
  universality 
  and 
  certainty 
  of 
  prediction 
  

   which 
  I 
  have 
  italicized 
  in 
  the 
  above 
  extracts. 
  Thus 
  in 
  the 
  deepest 
  

   sounding 
  in 
  the 
  whole 
  Atlantic 
  (that 
  of 
  3875 
  fathoms, 
  taken 
  on 
  the 
  

   * 
  Proceedings 
  of 
  the 
  Royal 
  Society, 
  vol. 
  xii. 
  p. 
  538. 
  

  

  