﻿770 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [12] 
  

  

  and 
  by 
  the 
  more 
  important 
  part 
  played 
  by 
  the 
  grains 
  of 
  glauconite, 
  

   ■which 
  chiefly 
  give 
  the 
  green 
  color 
  to 
  these 
  sands. 
  

  

  Bed 
  muds. 
  — 
  In 
  some 
  localities, 
  as 
  for 
  instance 
  off 
  the 
  Brazilian 
  coast 
  

   of 
  America, 
  the 
  deposits 
  differ 
  from 
  blue 
  muds 
  by 
  the 
  large 
  quantity 
  

   of 
  ochreous 
  matter 
  brought 
  down 
  by 
  the 
  rivers 
  and 
  deposited 
  along 
  

   the 
  coast. 
  The 
  ferruginous 
  particles 
  when 
  mixed 
  up 
  with 
  the 
  argilla- 
  

   ceous 
  matter 
  give 
  the 
  whole 
  deposit 
  a 
  reddish 
  color. 
  These 
  deposits, 
  

   rich 
  iu 
  iron 
  in 
  the 
  state 
  of 
  limonite, 
  do 
  not 
  appear 
  to 
  contain 
  any 
  traces 
  

   of 
  glauconite, 
  and 
  have 
  relatively 
  few 
  remains 
  of 
  siliceous 
  organisms- 
  

  

  Volcanic 
  muds 
  and 
  sands. 
  — 
  The 
  muds 
  and 
  sands 
  around 
  volcanic 
  

   islands 
  are 
  black 
  or 
  gray; 
  when 
  dried 
  they 
  are 
  rarely 
  coherent. 
  The 
  

   mineral 
  particles 
  are 
  generally 
  fragmentary, 
  and 
  consist 
  of 
  lapilli 
  of 
  the 
  

   basic 
  and 
  acid 
  series 
  of 
  modern 
  volcanic 
  rocks, 
  which 
  are 
  scoriaceous 
  or 
  

   compact 
  vitreous 
  or 
  crystalline, 
  and 
  usually 
  present 
  traces 
  of 
  alteration. 
  

   The 
  minerals 
  are 
  sometimes 
  isolated, 
  sometimes 
  surrounded 
  by 
  their 
  

   matrix, 
  and 
  consist 
  principally 
  of 
  plagioclases,sanadin, 
  amphibole, 
  pyr- 
  

   oxene, 
  biotite, 
  olivine, 
  and 
  magnetic 
  iron; 
  the 
  size 
  of 
  the 
  particles 
  

   diminishes 
  with 
  distance 
  from 
  the 
  shore, 
  but 
  the 
  mean 
  diameter 
  is 
  gen- 
  

   erally 
  0.5 
  mra 
  . 
  Glauconite 
  does 
  not 
  appear 
  to 
  be 
  present 
  in 
  these 
  de- 
  

   posits, 
  and 
  quartz 
  is 
  also 
  very 
  rare 
  or 
  absent. 
  The 
  fragments 
  of 
  shells 
  

   and 
  rocks 
  are 
  frequently 
  covered 
  with 
  a 
  coating 
  of 
  peroxide 
  of 
  manga- 
  

   nese. 
  Shells 
  of 
  calcareous 
  organisms 
  are 
  often 
  present 
  in 
  great 
  abun- 
  

   dance, 
  and 
  render 
  the 
  deposit 
  of 
  a 
  lighter 
  color. 
  The 
  remains 
  of 
  Diatoms 
  

   and 
  Eadiolarians 
  are 
  usually 
  present. 
  

  

  Coral 
  muds. 
  — 
  These 
  muds 
  frequently 
  contain 
  as 
  much 
  as 
  95 
  per 
  cent, 
  

   of 
  carbonate 
  of 
  lime, 
  which 
  consist 
  of 
  fragments 
  of 
  Corals, 
  calcare- 
  

   ous 
  Algae, 
  Foraminifera, 
  Serpulae. 
  Mollusks, 
  and 
  remains 
  of 
  other 
  lime- 
  

   secreting 
  organisms. 
  There 
  is 
  a 
  large 
  amount 
  of 
  amorphous 
  calcareous 
  

   matter, 
  which 
  gives 
  the 
  deposit 
  a 
  sticky 
  and 
  chalky 
  character. 
  The 
  

   particles 
  may 
  be 
  of 
  all 
  sizes, 
  according 
  to 
  the 
  distance 
  from 
  the 
  reefs, 
  

   the 
  mean 
  diameter 
  being 
  1 
  to 
  2 
  mm 
  , 
  but 
  occasionally 
  there 
  are 
  large 
  

   blocks 
  of 
  coral 
  and 
  large 
  calcareous 
  concretions 
  ; 
  the 
  particles 
  are 
  white 
  

   and 
  red. 
  Eemains 
  of 
  siliceous 
  organisms 
  seldom 
  make 
  up 
  over 
  2 
  or 
  3 
  

   per 
  cent, 
  of 
  a 
  typical 
  coral 
  mud. 
  The 
  residue 
  consists 
  usually 
  of 
  a 
  small 
  

   amount 
  of 
  argillaceous 
  matter, 
  with 
  a 
  few 
  fragments 
  of 
  feldspar 
  and 
  

   other 
  volcanic 
  minerals 
  ; 
  but 
  off 
  barrier 
  and 
  fringing 
  reefs 
  facing 
  con- 
  

   tinents 
  we 
  may 
  have 
  a 
  great 
  variety 
  of 
  rocks 
  and 
  minerals. 
  Beyond 
  a 
  

   depth 
  of 
  1,000 
  fathoms 
  off 
  coral 
  islands 
  the 
  debris 
  of 
  the 
  reefs 
  begins 
  to 
  

   diminish 
  and 
  the 
  remains 
  of 
  pelagic 
  organisms 
  to 
  increase; 
  the 
  deposit 
  

   becomes 
  more 
  argillaceous, 
  of 
  a 
  reddish 
  or 
  rose 
  color, 
  and 
  gradually 
  

   passes 
  into 
  a 
  Globigerina 
  ooze 
  or 
  red 
  clay. 
  Coral 
  sands 
  contain 
  much 
  

   less 
  amorphous 
  matter 
  than 
  coral 
  muds, 
  but 
  in 
  other 
  respects 
  they 
  are 
  

   similar, 
  the 
  sands 
  being 
  usually 
  found 
  nearer 
  the 
  reefs 
  and 
  in 
  shallower 
  

   water 
  than 
  the 
  muds, 
  except 
  inside 
  lagoons. 
  In 
  some 
  regions 
  the 
  re- 
  

   mains 
  of 
  calcareous 
  algae 
  predominate, 
  and 
  in 
  those 
  cases 
  the 
  name 
  

   coralline 
  mud 
  or 
  sand 
  is 
  employed 
  to 
  point 
  out 
  the 
  distinction. 
  

  

  