﻿[19] 
  ON 
  DEEP-SEA 
  DEPOSITS. 
  777 
  

  

  zones, 
  at 
  depths 
  where 
  the 
  action 
  of 
  the 
  waves 
  is 
  not 
  felt, 
  and 
  at 
  points 
  

   to 
  which 
  the 
  terrigenous 
  materials 
  do 
  not 
  extend, 
  there 
  are 
  now 
  form- 
  

   ing 
  vast 
  accumulations 
  of 
  Globigerina 
  and 
  other 
  Pelagic 
  Foraminifera, 
  

   coccoliths, 
  rhabdoliths, 
  shells 
  of 
  pelagic 
  Mollusks, 
  and 
  remains 
  of 
  other 
  

   organisms. 
  These 
  deposits 
  may 
  perhaps 
  be 
  called 
  the 
  sediments 
  of 
  me- 
  

   dian 
  depths 
  and 
  of 
  warmer 
  zones, 
  because 
  they 
  diminish 
  in 
  great 
  depths 
  

   and 
  tend 
  to 
  disappear 
  towards 
  the 
  poles. 
  This 
  fact 
  is 
  evidently 
  in 
  

   relation 
  with 
  the 
  surface 
  temperature 
  of 
  the 
  ocean, 
  and 
  shows 
  that 
  

   pelagic 
  Foraminifera 
  and 
  Mollusks 
  live 
  in 
  the 
  superficial 
  waters 
  of 
  the 
  

   sea, 
  whence 
  their 
  dead 
  shells 
  fall 
  into 
  the 
  bottom. 
  Globigerina 
  ooze 
  

   is 
  not 
  found 
  in 
  inclosed 
  seas 
  nor 
  in 
  polar 
  latitudes. 
  In 
  the 
  south- 
  

   ern 
  hemisphere 
  it 
  has 
  not 
  been 
  met 
  with 
  beyond 
  the 
  fiftieth 
  parallel. 
  

   In 
  the 
  Atlantic 
  it 
  is 
  deposited 
  upon 
  the 
  bottom 
  at 
  a 
  very 
  high 
  lati- 
  

   tude 
  below 
  the 
  warm 
  waters 
  of 
  the 
  Gulf 
  Stream, 
  and 
  is 
  not 
  observed 
  

   under 
  the 
  cold 
  descending 
  polar 
  current 
  which 
  runs 
  south 
  in 
  the 
  same 
  

   latitude. 
  These 
  facts 
  are 
  readily 
  explained 
  if 
  we 
  admit 
  that 
  this 
  ooze 
  

   is 
  formed 
  chiefly 
  by 
  the 
  shells 
  of 
  surface 
  organisms 
  which 
  require 
  an 
  

   elevated 
  temperature 
  and 
  a 
  wide 
  expanse 
  of 
  sea. 
  But 
  as 
  long 
  as 
  the 
  

   conditions 
  of 
  the 
  surface 
  are 
  the 
  same 
  we 
  would 
  expect 
  the 
  deposits 
  at 
  

   the 
  bottom 
  also 
  to 
  remain 
  the 
  same. 
  In 
  showing 
  that 
  such 
  is 
  not 
  the 
  

   case 
  we 
  are 
  led 
  to 
  take 
  into 
  account 
  an 
  agent 
  which 
  is 
  in 
  direct 
  correla- 
  

   tion 
  with 
  the 
  depth. 
  We 
  may 
  regard 
  it 
  as 
  established 
  that 
  the 
  majority 
  

   of 
  the 
  calcareous 
  organisms 
  which 
  make 
  up 
  the 
  Globigerina 
  and 
  Ptero- 
  

   pod 
  oozes 
  live 
  in 
  the 
  surface 
  waters, 
  and 
  we 
  may 
  also 
  take 
  for 
  granted 
  

   that 
  there 
  is 
  always 
  a 
  specific 
  identity 
  between 
  the 
  calcareous 
  organisms 
  

   which 
  live 
  at 
  the 
  surface 
  and 
  the 
  shells 
  of 
  these 
  pelagic 
  creatures 
  found 
  

   at 
  the 
  bottom. 
  This 
  observation 
  will 
  permit 
  us 
  to 
  place 
  in 
  relation 
  the 
  

   organic 
  deposits 
  and 
  those 
  which 
  are 
  directly 
  or 
  indirectly 
  the 
  result 
  of 
  

   the 
  chemical 
  activity 
  of 
  the 
  ocean. 
  Globigerina 
  ooze 
  is 
  found 
  in 
  the 
  

   tropical 
  zone 
  at 
  depths 
  which 
  do 
  not 
  exceed 
  2,400 
  fathoms, 
  but 
  when 
  

   depths 
  of 
  3,000 
  fathoms 
  are 
  explored 
  in 
  this 
  zone 
  of 
  the 
  Atlantic 
  and 
  

   Pacific 
  there 
  is 
  found 
  an 
  argillaceous 
  deposit 
  without, 
  in 
  many 
  instances, 
  

   any 
  trace 
  of 
  calcareous 
  organisms. 
  When 
  we 
  descend 
  from 
  the 
  "• 
  sub- 
  

   marine 
  plateaus 
  " 
  to 
  depths 
  which 
  exceed 
  2,250 
  fathoms 
  the 
  Globigerina 
  

   ooze 
  gradually 
  disappears, 
  passing 
  into 
  a 
  grayish 
  marl, 
  and 
  finally 
  is 
  

   wholly 
  replaced 
  by 
  an 
  argillaceous 
  material, 
  which 
  covers 
  the 
  bottom 
  at 
  

   all 
  depths 
  greater 
  than 
  2,900 
  fathoms. 
  

  

  The 
  transition 
  between 
  the 
  calcareous 
  formations 
  and 
  the 
  argillaceous 
  

   ones 
  takes 
  place 
  by 
  almost 
  insensible 
  degrees. 
  The 
  thinner 
  and 
  more 
  

   delicate 
  shells 
  disappear 
  first. 
  The 
  thicker 
  and 
  larger 
  shells 
  lose 
  little 
  

   by 
  little 
  the 
  sharpness 
  of 
  their 
  contour 
  and 
  appear 
  to 
  undergo 
  a 
  pro- 
  

   found 
  alteration. 
  They 
  assume 
  a 
  brownish 
  color, 
  and 
  break 
  up 
  in 
  pro- 
  

   portion 
  as 
  the 
  calcareous 
  constituent 
  disappears. 
  The 
  red 
  clay 
  predomi- 
  

   nates 
  more 
  and 
  more 
  as 
  the 
  calcareous 
  element 
  diminishes 
  in 
  the 
  de- 
  

   posit. 
  

  

  