﻿1874.] 
  ' 
  Challenger' 
  Soundings 
  in 
  the 
  Southern 
  Sea. 
  39 
  

  

  paratively 
  small 
  ; 
  and 
  to 
  this 
  circumstance 
  the 
  extreme 
  clearness 
  and 
  the 
  

   unusual 
  appearance 
  of 
  being 
  composed 
  of 
  Globigerince 
  alone 
  was 
  pro- 
  

   bably 
  mainly 
  due. 
  We 
  found 
  the 
  same 
  kind 
  of 
  ooze, 
  nearly 
  free 
  from 
  

   coccoliths 
  and 
  rhabdoliths, 
  in 
  what 
  may 
  be 
  considered 
  about 
  a 
  corre- 
  

   sponding 
  latitude 
  in 
  the 
  north, 
  to 
  the 
  west 
  of 
  Faroe. 
  

  

  Before 
  leaving 
  the 
  subject 
  of 
  the 
  modern 
  Chalk, 
  it 
  may 
  be 
  convenient 
  

   to 
  pass 
  on 
  to 
  stations 
  158, 
  159, 
  and 
  160, 
  on 
  March 
  7th, 
  10th, 
  and 
  13th, 
  

   on 
  our 
  return 
  voyage 
  from 
  the 
  ice. 
  The 
  first 
  two 
  of 
  these, 
  at 
  depths 
  

   of 
  1800 
  and 
  2150 
  fathoms 
  respectively, 
  are 
  marked 
  on 
  the 
  chart 
  " 
  Glo- 
  

   bigerina-ooze 
  ; 
  " 
  and 
  it 
  will 
  be 
  observed 
  that 
  these 
  soundings 
  nearly 
  corre- 
  

   spond 
  in 
  latitude 
  with 
  the 
  like 
  belt 
  which 
  we 
  crossed 
  going 
  southwards 
  ; 
  

   the 
  third 
  sounding, 
  at 
  a 
  depth 
  of 
  2600 
  fathoms, 
  is 
  marked 
  "red 
  clay." 
  

  

  According 
  to 
  our 
  present 
  experience, 
  the 
  deposit 
  of 
  " 
  Globigerina-ooze 
  " 
  

   is 
  limited 
  to 
  water 
  of 
  a 
  certain 
  depth, 
  the 
  extreme 
  limit 
  of 
  the 
  pure 
  

   characteristic 
  formation 
  being 
  placed 
  at 
  a 
  depth 
  of 
  somewhere 
  about 
  

   2250 
  fathoms. 
  Crossing 
  from 
  these 
  shallower 
  regions 
  occupied 
  by 
  the 
  

   ooze 
  into 
  deeper 
  soundings, 
  we 
  find 
  universally 
  that 
  the 
  calcareous 
  for- 
  

   mation 
  gradually 
  passes 
  into, 
  and 
  is 
  finally 
  replaced 
  by, 
  an 
  extremely 
  fine 
  

   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 
  transition 
  is 
  very 
  slow, 
  and 
  extends 
  over 
  several 
  

   hundred 
  fathoms 
  of 
  increasing 
  depth 
  ; 
  the 
  shells 
  gradually 
  lose 
  their 
  sharp- 
  

   ness 
  of 
  outline 
  and 
  assume 
  a 
  kind 
  of 
  " 
  rotten 
  " 
  look 
  and 
  a 
  brownish 
  

   colour, 
  and 
  become 
  more 
  and 
  more 
  mixed 
  with 
  a 
  fine 
  amorphous 
  red- 
  

   brown 
  powder, 
  which 
  increases 
  steadily 
  in 
  proportion 
  until 
  the 
  lime 
  has 
  

   almost 
  entirely 
  disappeared. 
  This 
  brown 
  matter 
  is 
  in 
  the 
  finest 
  possible 
  

   state 
  of 
  subdivision, 
  so 
  fine 
  that 
  when, 
  after 
  sifting 
  it 
  to 
  separate 
  any 
  

   organisms 
  it 
  might 
  contain, 
  we 
  put 
  it 
  into 
  jars 
  to 
  settle, 
  it 
  remained 
  for 
  

   days 
  in 
  suspension, 
  giving 
  the 
  water 
  very 
  much 
  the 
  appearance 
  and 
  

   colour 
  of 
  chocolate. 
  

  

  In 
  indicating 
  the 
  nature 
  of 
  the 
  bottom 
  on 
  the 
  charts, 
  we 
  came 
  from 
  

   experience, 
  and 
  without 
  any 
  theoretical 
  consideration, 
  to 
  use 
  three 
  terms 
  

   for 
  soundings 
  in 
  deep 
  water. 
  Two 
  of 
  these, 
  Grl. 
  oz. 
  and 
  r. 
  cl., 
  were 
  

   very 
  definite, 
  and 
  indicated 
  strongly 
  marked 
  formations, 
  with 
  apparently 
  

   but 
  few 
  characters 
  in 
  common 
  ; 
  but 
  we 
  frequently 
  got 
  soundings 
  which 
  we 
  

   could 
  not 
  exactly 
  call 
  either 
  " 
  Globigerina-ooze 
  " 
  or 
  " 
  red 
  clay;" 
  and 
  before 
  

   we 
  were 
  fully 
  aware 
  of 
  the 
  nature 
  of 
  these 
  we 
  were 
  in 
  the 
  habit 
  of 
  indi- 
  

   cating 
  them 
  as 
  " 
  grey 
  ooze 
  " 
  (gr. 
  oz.). 
  We 
  now 
  recognize 
  the 
  " 
  grey 
  

   ooze" 
  as 
  an 
  intermediate 
  stage 
  between 
  the 
  Globigerina-ooze 
  and 
  the 
  red 
  

   clay 
  ; 
  we 
  find 
  that, 
  on 
  one 
  side 
  as 
  it 
  were 
  of 
  an 
  ideal 
  line, 
  the 
  red 
  clay 
  

   contains 
  more 
  and 
  more 
  of 
  the 
  material 
  of 
  the 
  calcareous 
  ooze, 
  while, 
  

   on 
  the 
  other, 
  the 
  ooze 
  is 
  mixed 
  with 
  an 
  increasing 
  proportion 
  of 
  " 
  red 
  

   clay." 
  

  

  Although 
  we 
  have 
  met 
  with 
  the 
  same 
  phenomenon 
  so 
  frequently, 
  that 
  

   we 
  were 
  at 
  length 
  able 
  to 
  predict 
  the 
  nature 
  of 
  the 
  bottom 
  from 
  the 
  

  

  