﻿[13] 
  ON 
  DEEP-SEA 
  DEPOSITS. 
  771 
  

  

  Such 
  is 
  a 
  rapid 
  view 
  of 
  the 
  deposits 
  found 
  in 
  the 
  deeper 
  waters 
  of 
  

   the 
  littoral 
  zones, 
  where 
  the 
  debris 
  from 
  the 
  neighboring 
  land 
  plays 
  the 
  

   most 
  important 
  part 
  in 
  the 
  formation 
  of 
  muds 
  and 
  sands. 
  

  

  When, 
  however, 
  we 
  pass 
  beyond 
  a 
  distance 
  of 
  about 
  2(30 
  miles 
  from 
  

   laud, 
  we 
  find 
  that 
  the 
  deposits 
  are 
  characterized 
  by 
  the 
  great 
  abun- 
  

   dance 
  of 
  fragmentary 
  volcanic 
  materials 
  which 
  have 
  usually 
  undergone 
  

   great 
  alteration, 
  and 
  by 
  the 
  enormous 
  abundance 
  of 
  the 
  shells 
  and 
  

   skeletons 
  of 
  minute 
  pelagic 
  organisms 
  which 
  have 
  fallen 
  to 
  the 
  bottom 
  

   from 
  the 
  surface 
  waters. 
  These 
  true 
  deep-sea 
  deposits 
  may 
  be 
  divided 
  

   into 
  those 
  in 
  which 
  the 
  organic 
  elements 
  predominate, 
  and 
  those 
  in 
  

   which 
  the 
  mineral 
  constituents 
  play 
  the 
  chief 
  part. 
  We 
  shall 
  commence 
  

   with 
  the 
  former. 
  

  

  Globigerina 
  ooze. 
  — 
  We 
  designate 
  by 
  this 
  name 
  all 
  those 
  truly 
  

   pelagic 
  deposits 
  containing 
  over 
  40 
  per 
  cent, 
  of 
  carbonate 
  of 
  lime, 
  which 
  

   consists 
  principally 
  of 
  the 
  dead 
  shells 
  of 
  pelagic 
  Foraminifera, 
  Globige- 
  

   rina, 
  Orbulina, 
  Pulvinulina, 
  Pullenia, 
  Sphceroidina, 
  &c. 
  In 
  some 
  local- 
  

   ities 
  this 
  deposit 
  contains 
  95 
  per 
  cent, 
  of 
  carbonate 
  of 
  lime. 
  The 
  color 
  

   is 
  milky 
  white, 
  yellow, 
  brown, 
  or 
  rose, 
  the 
  varieties 
  of 
  color 
  depending 
  

   principally 
  on 
  the 
  relative 
  abundance 
  in 
  the 
  deposit 
  of 
  the 
  oxides 
  

   of 
  iron 
  and 
  manganese. 
  This 
  ooze 
  is 
  fine 
  grained 
  ; 
  in 
  the 
  tropics 
  some 
  

   of 
  the 
  Foraminifera 
  shells 
  are 
  microscopic. 
  When 
  dried 
  it 
  is 
  pulver- 
  

   ulent. 
  Analyses 
  show 
  that 
  the 
  sediment 
  contains, 
  in 
  addition 
  to 
  car- 
  

   bonate 
  of 
  lime, 
  phosphate 
  and 
  sulphate 
  of 
  lime, 
  carbonate 
  or 
  magne- 
  

   sia, 
  oxides 
  of 
  iron 
  and 
  manganese, 
  and 
  argillaceous 
  matters. 
  The 
  resi- 
  

   due 
  is 
  of 
  a 
  reddish 
  brown 
  tinge. 
  Lapilli, 
  pumice, 
  and 
  glassy 
  fragments 
  

   often 
  altered 
  into 
  palagonite, 
  seem 
  always 
  to 
  be 
  present, 
  and 
  are 
  fre- 
  

   quent^ 
  very 
  abundant. 
  The 
  mineral 
  p 
  articles 
  are 
  generally 
  angular, 
  

   and 
  rarely 
  exceed 
  0.08 
  mm 
  in 
  diameter 
  ; 
  monoclinic 
  and 
  triclinic 
  feld- 
  

   spars, 
  augite, 
  olivine, 
  hornblende, 
  and 
  magnetite 
  are 
  the 
  most 
  frequent. 
  

   When 
  quartz 
  is 
  present 
  it 
  is 
  in 
  the 
  form 
  of 
  minute, 
  rounded, 
  probably 
  

   wind-borne 
  grains, 
  often 
  partially 
  covered 
  with 
  oxide 
  of 
  iron. 
  More 
  

   rarely 
  we 
  have 
  white 
  and 
  black 
  mica, 
  bronzite, 
  actinolite, 
  chromite, 
  

   glauconite, 
  and 
  cosmic 
  dust. 
  Siliceous 
  organisms 
  are 
  probably 
  never 
  

   absent, 
  sometimes 
  forming 
  20 
  per 
  cent, 
  of 
  the 
  deposit, 
  at 
  other 
  times 
  

   only 
  recognizable 
  after 
  careful 
  microscopic 
  examination. 
  In 
  some 
  re- 
  

   gions 
  the 
  frustules 
  of 
  Diatoms 
  predominate, 
  in 
  others 
  the 
  skeletons 
  of 
  

   liadiolarians. 
  

  

  The 
  fine 
  washings, 
  viewed 
  with 
  the 
  microscope, 
  are 
  not 
  homogeneous. 
  

   The 
  greater 
  part 
  consists 
  of 
  argillaceous 
  matter 
  colored 
  by 
  the 
  oxides 
  

   of 
  manganese. 
  Mixed 
  with 
  this, 
  we 
  distinguish 
  fragments 
  of 
  minerals 
  

   with 
  a 
  diameter 
  less 
  than 
  0.05 
  mm 
  , 
  and 
  minute 
  particles 
  of 
  pumice 
  can 
  

   nearly 
  always 
  be 
  detected. 
  Fragments 
  of 
  Eadiolarians, 
  Diatoms, 
  and 
  

   siliceous 
  spicules 
  can 
  always 
  be 
  recognized, 
  and 
  arc 
  sometimes 
  very 
  

   abundant. 
  

  

  Fteropod 
  ooze. 
  — 
  This 
  deposit 
  differs 
  in 
  no 
  way 
  from 
  a 
  Globige- 
  

   rina 
  ooze 
  except 
  in 
  the 
  presence 
  of 
  a 
  greater 
  number 
  and 
  variety 
  of 
  

  

  