﻿48 
  On 
  the 
  c 
  Challenger 
  ' 
  Soundings 
  in 
  the 
  Southern 
  Sea. 
  [Nov. 
  26, 
  

  

  Heard 
  Islands, 
  the 
  tow 
  net, 
  dragging 
  a 
  few 
  fathoms 
  below 
  the 
  surface, 
  

   came 
  up 
  nearly 
  filled 
  with 
  a 
  pale 
  yellow 
  gelatinous 
  mass. 
  This 
  was 
  

   found 
  to 
  consist 
  entirely 
  of 
  Diatoms 
  of 
  the 
  same 
  species 
  as 
  that 
  found 
  at 
  

   the 
  bottom. 
  By 
  far 
  the 
  most 
  abundant 
  was 
  the 
  little 
  bundle 
  of 
  siliceous 
  rods 
  

   (PL 
  III. 
  fig. 
  5) 
  fastened 
  together 
  loosely 
  at 
  one 
  end, 
  separating 
  from 
  one 
  

   another 
  at 
  the 
  other 
  end, 
  and 
  the 
  whole 
  bundle 
  loosely 
  twisted 
  into 
  a 
  

   spindle. 
  The 
  rods 
  are 
  hollow, 
  and 
  contain 
  the 
  characteristic 
  endochrome 
  

   of 
  the 
  Diatomacece. 
  Like 
  the 
  " 
  Globigerina-ooze" 
  then, 
  which 
  it 
  succeeds 
  

   to 
  the 
  southward 
  in 
  a 
  band 
  apparently 
  of 
  no 
  great 
  width, 
  the 
  materials 
  

   of 
  this 
  siliceous 
  deposit 
  are 
  derived 
  entirely 
  from 
  the 
  surface 
  and 
  inter- 
  

   mediate 
  depths. 
  It 
  is 
  somewhat 
  singular 
  that 
  Diatoms 
  did 
  not 
  appear 
  to 
  

   be 
  in 
  such 
  large 
  numbers 
  on 
  the 
  surface 
  over 
  the 
  Diatom-ooze 
  as 
  they 
  

   were 
  a 
  little 
  further 
  north. 
  This 
  may 
  perhaps 
  be 
  accounted 
  for 
  by 
  our 
  

   not 
  having 
  struck 
  their 
  belt 
  of 
  depth 
  with 
  the 
  tow-net 
  ; 
  or 
  it 
  is 
  possible 
  

   that 
  when 
  we 
  found 
  it, 
  on 
  the 
  11th 
  of 
  February, 
  the 
  bottom 
  deposit 
  was 
  

   really 
  shifted 
  a 
  little 
  to 
  the 
  south 
  by 
  the 
  warm 
  current, 
  the 
  excessively 
  

   fine 
  flocculent 
  debris 
  of 
  the 
  Diatoms 
  taking 
  a 
  certain 
  time 
  to 
  sink. 
  The 
  

   belt 
  of 
  Diatom-ooze 
  is 
  certainly 
  a 
  little 
  further 
  to 
  the 
  southward 
  in 
  

   long. 
  80° 
  E. 
  in 
  the 
  path 
  of 
  the 
  reflux 
  of 
  the 
  Agulhas 
  current, 
  than 
  in 
  

   long. 
  108° 
  E. 
  

  

  AH 
  along 
  the 
  edge 
  of 
  the 
  ice 
  pack 
  — 
  everywhere 
  in 
  fact 
  to 
  the 
  south 
  

   of 
  the 
  two 
  stations, 
  that 
  of 
  the 
  11th 
  of 
  February, 
  on 
  our 
  southward 
  

   voyage, 
  and 
  that 
  of 
  the 
  3rd 
  of 
  March, 
  on 
  our 
  return, 
  we 
  brought 
  up 
  

   fine 
  sand 
  and 
  greyish 
  mud, 
  with 
  small 
  pebbles 
  of 
  quartz 
  and 
  felspar, 
  and 
  

   small 
  fragments 
  of 
  mica-slate, 
  chlorite-slate, 
  clay-slate, 
  gneiss, 
  and 
  

   granite. 
  This 
  deposit, 
  I 
  have 
  no 
  doubt, 
  was 
  derived 
  from 
  the 
  surface 
  

   like 
  the 
  others, 
  but, 
  in 
  this 
  case, 
  by' 
  the 
  melting 
  of 
  icebergs 
  and 
  the 
  

   precipitation 
  of 
  foreign 
  matter 
  contained 
  in 
  the 
  ice. 
  

  

  We 
  never 
  saw 
  any 
  trace 
  of 
  gravel 
  or 
  sand, 
  or 
  any 
  material 
  necessarily 
  

   derived 
  from 
  land, 
  on 
  an 
  iceberg. 
  Several 
  showed 
  vertical 
  or 
  irregular 
  

   fissures 
  filled 
  with 
  discoloured 
  ice 
  or 
  snow 
  ; 
  but, 
  when 
  looked 
  at 
  closely, 
  

   the 
  discoloration 
  proved 
  usually 
  to 
  be 
  very 
  slight, 
  and 
  the 
  effect, 
  at 
  a 
  

   distance, 
  was 
  usually 
  due 
  to 
  the 
  foreign 
  material 
  which 
  filled 
  the 
  fissure 
  

   reflecting 
  light 
  less 
  perfectly 
  than 
  the 
  general 
  surface 
  of 
  the 
  berg. 
  I 
  

   conceive 
  that 
  the 
  upper 
  part 
  of 
  one 
  of 
  these 
  great 
  tabular 
  southern 
  ice- 
  

   bergs, 
  including 
  by 
  far 
  the 
  greater 
  part 
  of 
  its 
  bulk, 
  and 
  culminating 
  in 
  

   the 
  portion 
  exposed 
  above 
  the 
  surface 
  of 
  the 
  sea, 
  was 
  formed 
  by 
  the 
  

   piling 
  up 
  of 
  successive 
  layers 
  of 
  snow 
  throughout 
  the 
  period, 
  amounting 
  

   perhaps 
  to 
  several 
  centuries, 
  during 
  which 
  the 
  ice-cap 
  was 
  slowly 
  forcing 
  

   itself 
  over 
  the 
  low 
  land 
  and 
  out 
  to 
  sea, 
  over 
  a 
  long 
  extent 
  of 
  gentle 
  slope, 
  

   until 
  it 
  reached 
  a 
  depth 
  considerably 
  above 
  200 
  fathoms, 
  when 
  the 
  lower 
  

   specific 
  weight 
  of 
  the 
  ice 
  caused 
  an 
  upward 
  strain, 
  which 
  at 
  length 
  over- 
  

   came 
  the 
  cohesion 
  of 
  the 
  mass, 
  and 
  portions 
  were 
  rent 
  off 
  and 
  floated 
  

   away. 
  If 
  this 
  be 
  the 
  true 
  history 
  of 
  the 
  formation 
  of 
  these 
  icebergs, 
  the 
  

   absence 
  of 
  all 
  land 
  debris 
  in 
  the 
  portion 
  exposed 
  above 
  the 
  surface 
  of 
  the 
  

  

  