﻿[5] 
  ON 
  DEEP-SEA 
  DEPOSITS. 
  7G3 
  

  

  character 
  of 
  the 
  particles. 
  We 
  find 
  isolated 
  fragments 
  of 
  rocks 
  and 
  

   minerals 
  coming 
  from 
  crystalline 
  and 
  schisto-crystalline 
  series, 
  and 
  

   from 
  the 
  clastic 
  and 
  sedimentary 
  formations 
  ; 
  according 
  to 
  the 
  nature 
  

   of 
  the 
  nearest 
  coasts 
  they 
  belong 
  to 
  granite, 
  diorite, 
  diabase, 
  porphyry, 
  

   &c; 
  crystalline 
  schists, 
  ancient 
  limestones, 
  and 
  sedimentary 
  rocks 
  of 
  

   all 
  geological 
  ages, 
  with 
  the 
  minerals 
  which 
  come 
  from 
  their 
  disinte- 
  

   gration, 
  such 
  as 
  quartz, 
  monoclinic 
  and 
  triclinic 
  feldspars, 
  hornblende, 
  

   augite, 
  rhombic 
  pyroxene, 
  olivine, 
  muscovite, 
  biotite, 
  titanic 
  and 
  mag- 
  

   netic 
  iron, 
  tourmaline, 
  garnet, 
  epidote, 
  and 
  other 
  secondary 
  minerals. 
  

   The 
  trituration 
  and 
  decomposition 
  of 
  these 
  rocks 
  and 
  minerals 
  give 
  rise 
  

   to 
  materials 
  more 
  or 
  less 
  amorphous 
  and 
  without 
  distinctive 
  characters, 
  

   but 
  the 
  origin 
  of 
  which 
  is 
  indicated 
  by 
  association 
  with 
  the 
  rocks 
  and 
  

   minerals 
  just 
  mentioned. 
  

  

  Although 
  the 
  debris 
  of 
  continental 
  land 
  to 
  which 
  we 
  have 
  just 
  re- 
  

   ferred 
  plays 
  the 
  most 
  important 
  role 
  iu 
  the 
  immediate 
  vicinity 
  of 
  shores, 
  

   yet 
  our 
  researches 
  show 
  beyond 
  doubt 
  that 
  when 
  we 
  pass 
  out 
  towards 
  

   the 
  central 
  parts 
  of 
  the 
  great 
  ocean 
  basins, 
  the 
  debris 
  of 
  continental 
  

   rocks 
  gradually 
  disappears 
  from 
  the 
  deposits, 
  and 
  its 
  place 
  is 
  taken 
  by 
  

   materials 
  derived 
  from 
  modern 
  volcanic 
  rocks, 
  such 
  as 
  basalts, 
  trachytes, 
  

   angite-andesites, 
  and 
  vitreous 
  varieties 
  of 
  these 
  lithological 
  families, 
  

   for 
  instance, 
  pumice, 
  and 
  loose, 
  incoherent, 
  volcanic 
  particles 
  of 
  recent 
  

   eruptions, 
  with 
  their 
  characteristic 
  minerals. 
  All 
  these 
  mineral 
  sub- 
  

   stances 
  being 
  usually 
  extremely 
  fine 
  or 
  areolar 
  in 
  structure, 
  are 
  easily 
  

   attacked 
  by 
  the 
  sea 
  water 
  at 
  the 
  place 
  where 
  they 
  are 
  deposited. 
  This 
  

   chemical 
  action 
  brings 
  about 
  an 
  alteration 
  of 
  the 
  minerals 
  and 
  vitreous 
  

   fragments, 
  which 
  soon 
  passes 
  into 
  complete 
  decomposition, 
  and 
  in 
  

   special 
  circumstances 
  gives 
  rise 
  to 
  the 
  formation 
  of 
  secondary 
  products. 
  

   In 
  some 
  places 
  the 
  bottom 
  of 
  the 
  sea 
  is 
  covered 
  with 
  deposits 
  due 
  to 
  

   this 
  chemical 
  action, 
  principal 
  among 
  which 
  is 
  clayey 
  matter, 
  associ- 
  

   ated 
  with 
  which 
  there 
  are 
  often 
  concretions 
  composed 
  of 
  manganese 
  

   and 
  iron. 
  In 
  other 
  regions 
  the 
  reactions 
  which 
  result 
  in- 
  the 
  formation 
  

   of 
  argillaceous 
  matter 
  from 
  volcanic 
  products 
  give 
  rise 
  also 
  to 
  the 
  for- 
  

   mation 
  of 
  zeolites. 
  

  

  Among 
  other 
  products 
  arising 
  from 
  chemical 
  action, 
  probably 
  com- 
  

   bined 
  with 
  the 
  activity 
  of 
  organic 
  matter, 
  may 
  be 
  mentioned 
  the 
  for- 
  

   mation 
  of 
  glauconite 
  and 
  phosphatic 
  nodules, 
  with, 
  in 
  some 
  rare 
  and 
  

   doubtful 
  examples, 
  the 
  deposition 
  of 
  silica. 
  The 
  decomposition 
  of 
  the 
  

   tissues, 
  shells, 
  and 
  skeletons 
  of 
  organisms 
  adds 
  small 
  quantities 
  of 
  iron, 
  

   fluorine, 
  and 
  phosphoric 
  acid 
  to 
  the 
  inorganic 
  constituents 
  of 
  the 
  deep- 
  

   sea 
  deposits. 
  

  

  Finally, 
  we 
  must 
  mention 
  extra-terrestrial 
  substances 
  in 
  the 
  form 
  of 
  

   cosmic 
  dust. 
  

  

  We 
  now 
  pass 
  to 
  the 
  consideration 
  of 
  the 
  role 
  played 
  by 
  organisms 
  in 
  

   the 
  formation 
  of 
  marine 
  deposits. 
  Organisms 
  living 
  at 
  the 
  surface 
  of 
  

   the 
  ocean, 
  along 
  the 
  coasts, 
  and 
  at 
  the 
  bottom 
  of 
  the 
  sea 
  are 
  continu- 
  

   ally 
  extracting 
  the 
  lime, 
  magnesia, 
  and 
  silica 
  held 
  in 
  solutiou 
  in 
  sea 
  

  

  