﻿[7] 
  ON 
  DEEP-SEA 
  DEPOSITS. 
  765 
  

  

  miles 
  from 
  the 
  coast. 
  Waves 
  and 
  currents 
  probably 
  bave 
  no 
  erosive 
  

   or 
  transporting 
  power 
  at 
  depths 
  greater 
  than 
  200 
  or 
  300 
  fathoms, 
  and 
  

   even 
  at 
  such 
  depths 
  it 
  is 
  necessary 
  that 
  there 
  should 
  be 
  some 
  local 
  and 
  

   special 
  conditions 
  in 
  order 
  that 
  the 
  agitated 
  water 
  may 
  produce 
  any 
  

   mechanical 
  effect. 
  However, 
  it 
  is 
  not 
  improbable 
  that, 
  by 
  a 
  peculiar 
  

   configuration 
  of 
  the 
  bottom 
  and 
  ridges 
  among 
  oceanic 
  islands, 
  the 
  de- 
  

   posit 
  on 
  a 
  ridge 
  may 
  be 
  disturbed 
  by 
  the 
  tidal 
  wave 
  even 
  at 
  1,000 
  

   fathoms 
  ; 
  and 
  this 
  may 
  be 
  the 
  cause 
  of 
  the 
  hard 
  ground 
  sometimes 
  

   met 
  with 
  in 
  such 
  positions. 
  By 
  observations 
  off 
  the 
  coast 
  of 
  France 
  it 
  

   has 
  been 
  shown 
  that 
  line 
  mud 
  is 
  at 
  times 
  disturbed 
  at 
  a 
  depth 
  of 
  150 
  

   fathoms; 
  but 
  while 
  admitting 
  that 
  this 
  is 
  the 
  case 
  on 
  exposed 
  coasts, 
  

   the 
  majority 
  of 
  observations 
  indicate 
  that 
  beyond 
  100 
  fathoms 
  it 
  is 
  an 
  

   oscillation 
  of 
  the 
  water, 
  rather 
  than 
  a 
  movement 
  capable 
  of 
  exerting 
  

   any 
  geological 
  action, 
  which 
  concerns 
  us 
  in 
  this 
  connection. 
  

  

  Although 
  the 
  great 
  oceanic 
  currents 
  have 
  no 
  direct 
  influence 
  upon 
  

   the 
  bottom, 
  yet 
  they 
  have 
  a 
  very 
  important 
  indirect 
  effect 
  upon 
  depos- 
  

   its, 
  because 
  the 
  organisms 
  which 
  live 
  in 
  the 
  warm 
  equatorial 
  currents 
  

   form 
  a 
  very 
  large 
  part 
  of 
  the 
  sediment 
  being 
  deposited 
  there, 
  and 
  this 
  

   in 
  consequence 
  differs 
  greatly 
  from 
  the 
  deposits 
  forming 
  in 
  regions 
  

   where 
  the 
  surface 
  water 
  is 
  colder. 
  In 
  the 
  same 
  way 
  a 
  high 
  or 
  low 
  spe- 
  

   cific 
  gravity 
  of 
  the 
  surface 
  water 
  has 
  an 
  important 
  beariug 
  on 
  the 
  

   animal 
  and 
  vegetable 
  life 
  of 
  the 
  ocean, 
  and 
  this 
  in 
  its 
  turn 
  affects 
  the 
  

   character 
  of 
  the 
  deposits. 
  

  

  . 
  The 
  thermometric 
  observations 
  of 
  the 
  Challenger 
  show 
  that 
  a 
  slow 
  

   movement 
  of 
  cold 
  water 
  must 
  take 
  place 
  in 
  all 
  the 
  greater 
  depths 
  of 
  the 
  

   oceau 
  from 
  the 
  poles, 
  but 
  particularly 
  from 
  the 
  southern 
  pole, 
  towards 
  

   the 
  equator. 
  It 
  could 
  be 
  shown 
  from 
  many 
  lines 
  of 
  argument 
  that 
  this 
  

   extremely 
  slow 
  massive 
  movement 
  of 
  the 
  water 
  can 
  have 
  no 
  direct 
  in- 
  

   fiueuce 
  on 
  the 
  distribution 
  of 
  marine 
  sediments. 
  

  

  Glaciers, 
  which 
  eventually 
  became 
  icebergs 
  that 
  are 
  carried 
  far 
  out 
  

   to 
  sea 
  by 
  currents, 
  transport 
  detrital 
  matter 
  from 
  the 
  land 
  to 
  the 
  

   ocean, 
  and 
  thus 
  modify 
  in 
  the 
  Arctic 
  and 
  Antarctic 
  regions 
  the 
  deposits 
  

   taking 
  place 
  in 
  the 
  regions 
  affected 
  by 
  them. 
  The 
  detritus 
  from 
  ice- 
  

   bergs 
  in 
  the 
  Atlantic 
  can 
  be 
  traced 
  as 
  far 
  south 
  as 
  latitude 
  36° 
  off 
  the 
  

   American 
  coast, 
  and 
  in 
  the 
  southern 
  hemisphere 
  as 
  far 
  north 
  as 
  lati- 
  

   tude 
  40°. 
  

  

  The 
  fact 
  that 
  sea 
  water 
  retains 
  fine 
  matter 
  in 
  suspension 
  for 
  a 
  much 
  

   shorter 
  time 
  than 
  fresh 
  water 
  should 
  be 
  referred 
  to 
  here 
  as 
  having 
  an 
  

   important 
  influence 
  in 
  limiting 
  the 
  distribution 
  of 
  fine 
  argillaceous 
  and 
  

   other 
  materials 
  borne 
  down 
  to 
  the 
  sea 
  by 
  rivers, 
  thus 
  giving 
  a 
  distinc- 
  

   tive 
  character 
  to 
  deposits 
  forming 
  near 
  land. 
  

  

  We 
  have 
  pointed 
  out 
  the 
  influence 
  of 
  the 
  temperature 
  and 
  salinity 
  

   upon 
  the 
  distribution 
  of 
  the 
  surface 
  organisms 
  whose 
  skeletons 
  form 
  a 
  

   large 
  part 
  of 
  some 
  oceanic 
  deposits, 
  and 
  may 
  state 
  also 
  that 
  the 
  bathy- 
  

   metrical 
  distribution 
  of 
  calcareous 
  organisms 
  is 
  influenced 
  by 
  the 
  

   chemical 
  action 
  of 
  sea 
  water. 
  We 
  will 
  return 
  to 
  these 
  influences 
  pres- 
  

  

  