﻿Prof. 
  C. 
  W. 
  Thomson 
  on 
  the 
  

  

  [Nov. 
  26, 
  

  

  difficulty. 
  My 
  first 
  impression 
  was, 
  that 
  it 
  might 
  be 
  the 
  most 
  minutely 
  

   divided 
  material, 
  the 
  ultimate 
  sediment, 
  produced 
  by 
  the 
  disintegration 
  of 
  

   the 
  land, 
  by 
  rivers 
  and 
  by 
  the 
  action 
  of 
  the 
  sea 
  on 
  exposed 
  coasts, 
  and 
  

   held 
  in 
  suspension 
  and 
  distributed 
  by 
  ocean 
  currents, 
  and 
  only 
  making 
  

   itself 
  manifest 
  in 
  places 
  unoccupied 
  by 
  the 
  Globigerina-ooze. 
  Several 
  

   circumstances 
  seemed, 
  however, 
  to 
  negative 
  this 
  mode 
  of 
  origin. 
  The 
  

   formation 
  seemed 
  too 
  uniform 
  ; 
  whenever 
  we 
  met 
  with 
  it, 
  it 
  had 
  the 
  

   same 
  character, 
  and 
  it 
  only 
  varied 
  in 
  composition 
  in 
  containing 
  less 
  or 
  

   more 
  carbonate 
  of 
  lime. 
  

  

  Again, 
  we 
  were 
  gradually 
  becoming 
  more 
  and 
  more 
  convinced 
  that 
  all 
  

   the 
  important 
  elements 
  of 
  the 
  Globigerina-ooze 
  lived 
  on 
  the 
  surface 
  ; 
  and 
  

   it 
  seemed 
  evident 
  that, 
  so 
  long 
  as 
  the 
  conditions 
  on 
  the 
  surface 
  remained 
  

   the 
  same, 
  no 
  alteration 
  of 
  contour 
  at 
  the 
  bottom 
  could 
  possibly 
  pre- 
  

   vent 
  its 
  accumulation 
  ; 
  and 
  the 
  surface 
  conditions 
  in 
  the 
  Mid- 
  Atlantic 
  

   were 
  very 
  uniform, 
  a 
  moderate 
  current 
  of 
  a 
  very 
  equal 
  temperature 
  pass- 
  

   ing 
  continuously 
  over 
  elevations 
  and 
  depressions, 
  and 
  everywhere 
  yield- 
  

   ing 
  to 
  the 
  tow-net 
  the 
  ooze-forming 
  Foraminifera 
  in 
  the 
  same 
  proportion. 
  

   The 
  Mid- 
  Atlantic 
  swarms 
  with 
  pelagic 
  Mollusca 
  ; 
  and, 
  in 
  moderate 
  depths, 
  

   the 
  shells 
  of 
  these 
  are 
  constantly 
  mixed 
  with 
  the 
  Globigerina-ooze, 
  some- 
  

   times 
  in 
  number 
  sufficient 
  to 
  make 
  up 
  a 
  considerable 
  portion 
  of 
  its 
  bulk. 
  

   It 
  is 
  clear 
  that 
  these 
  shells 
  must 
  fall 
  in 
  equal 
  numbers 
  upon 
  the 
  red 
  clay 
  ; 
  

   but 
  scarcely 
  a 
  trace 
  of 
  one 
  of 
  them 
  is 
  ever 
  brought 
  up 
  by 
  the 
  dredge 
  on 
  

   the 
  red-clay 
  area. 
  It 
  might 
  be 
  possible 
  to 
  explain 
  the 
  absence 
  of 
  shell- 
  

   secreting 
  animals 
  living 
  on 
  the 
  bottom 
  by 
  the 
  supposition 
  that 
  the 
  

   nature 
  of 
  the 
  deposit 
  was 
  injurious 
  to 
  them; 
  but 
  then 
  the 
  idea 
  of 
  a 
  

   current 
  sufficiently 
  strong 
  to 
  sweep 
  them 
  away 
  is 
  negatived 
  by 
  the 
  

   extreme 
  fineness 
  of 
  the 
  sediment 
  which 
  is 
  being 
  laid 
  down 
  ; 
  the 
  absence 
  

   of 
  surface 
  shells 
  appears 
  to 
  be 
  intelligible 
  only 
  on 
  the 
  supposition 
  that 
  

   they 
  are 
  in 
  some 
  way 
  removed. 
  

  

  We 
  conclude, 
  therefore, 
  that 
  the 
  " 
  red 
  clay 
  " 
  is 
  not 
  an 
  additional 
  sub- 
  

   stance 
  introduced 
  from 
  without, 
  and 
  occupying 
  certain 
  depressed 
  regions 
  

   on 
  account 
  of 
  some 
  law 
  regulating 
  its 
  deposition 
  ; 
  but 
  that 
  it 
  is 
  produced 
  

   by 
  the 
  removal, 
  by 
  some 
  means 
  or 
  other, 
  over 
  these 
  areas, 
  of 
  the 
  carbonate 
  

   of 
  lime 
  which 
  forms 
  probably 
  about 
  98 
  per 
  cent, 
  of 
  the 
  material 
  of 
  the 
  

   Globigerina-ooze. 
  We 
  can 
  trace, 
  indeed, 
  every 
  successive 
  stage 
  in 
  the 
  

   removal 
  of 
  the 
  carbonate 
  of 
  lime 
  in 
  descending 
  the 
  slope 
  of 
  the 
  ridge 
  or 
  

   plateau 
  where 
  the 
  Globigerina-ooze 
  is 
  forming, 
  to 
  the 
  region 
  of 
  the 
  clay. 
  

   We 
  find, 
  first, 
  that 
  the 
  shells 
  of 
  pteropods 
  and 
  other 
  surface 
  Mollusca, 
  

   which 
  are 
  constantly 
  falling 
  on 
  the 
  bottom, 
  are 
  absent, 
  or 
  if 
  a 
  few 
  remain 
  

   they 
  are 
  brittle 
  and 
  yellow, 
  and 
  evidently 
  decaying 
  rapidly. 
  These 
  shells 
  

   of 
  Mollusca 
  decompose 
  more 
  easily, 
  and 
  disappear 
  sooner, 
  than 
  the 
  smaller 
  

   and 
  apparently 
  more 
  delicate 
  shells 
  of 
  Ehizopods. 
  The 
  smaller 
  Forami- 
  

   nifera 
  now 
  give 
  way 
  and 
  are 
  found 
  in 
  lessening 
  proportion 
  to 
  the 
  larger 
  ; 
  

   the 
  coccoliths 
  first 
  lose 
  their 
  thin 
  outer 
  border 
  and 
  then 
  disappear, 
  and 
  

   the 
  clubs 
  of 
  the 
  rhabdoliths 
  get 
  worn 
  out 
  of 
  shape 
  and 
  are 
  last 
  seen, 
  

  

  