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  MESSES. 
  A. 
  J. 
  JUKES-BKOWJTE 
  AXD 
  TV. 
  HILL 
  ON 
  COLLOID 
  

  

  showed 
  the 
  material 
  to 
  "be 
  such 
  as 
  is 
  usual 
  in 
  the 
  Chalk 
  Marl, 
  

   viz. 
  a 
  large 
  proportion 
  of 
  amorphous 
  calcareous 
  material 
  with 
  shelly 
  

   fragments, 
  Toraniiniferal 
  cells, 
  and 
  grains 
  of 
  glauconite 
  and 
  quartz 
  

   scattered 
  abundantly 
  throughout. 
  

  

  But 
  there 
  were 
  also 
  many 
  traces 
  of 
  sponge-structure, 
  a 
  fact 
  in 
  

   itself 
  somewhat 
  remarkable 
  ; 
  for 
  in 
  a 
  large 
  series 
  of 
  specimens 
  of 
  

   Chalk 
  Marl 
  to 
  the 
  eastward 
  the 
  occurrence 
  of 
  sponge-spicules 
  in 
  

   abundance 
  is 
  exceptional. 
  These 
  sponge-remains 
  were, 
  first, 
  the 
  

   shadowy 
  outlines 
  of 
  scattered 
  spicules, 
  and, 
  second, 
  a 
  section 
  of 
  the 
  

   spicular 
  mesh 
  of 
  a 
  Hexactinellid 
  * 
  sponge, 
  the 
  outline 
  of 
  which 
  was 
  

   fa'rly 
  well 
  defined 
  and 
  the 
  spicular 
  canals 
  faintly 
  visible. 
  

  

  Tne 
  material 
  of 
  the 
  scattered 
  spicules 
  had 
  a 
  finely 
  granular 
  ap- 
  

   pearance, 
  its 
  nature 
  being 
  hardly 
  determinable 
  in 
  the 
  sections: 
  

   that 
  of 
  the 
  Hexactinellid 
  appeared 
  to 
  be 
  silica 
  in 
  the 
  colloid 
  con- 
  

   dition, 
  which 
  presented 
  partly 
  a 
  confused 
  granular 
  structure 
  and 
  

   partly 
  that 
  of 
  the 
  incomplete 
  rings, 
  as 
  described 
  by 
  Dr. 
  Hinde 
  ; 
  

   with 
  polarized 
  light 
  the 
  result 
  was 
  negative. 
  Treating 
  a 
  portion 
  of 
  

   this 
  specimen 
  with 
  hydrochloric 
  acid 
  a 
  brisk 
  effervescence 
  ensued, 
  

   the 
  whole 
  being 
  reduced 
  to 
  powder. 
  The 
  residue 
  proved 
  to 
  be 
  fine 
  

   structureless 
  material, 
  quartz-sand, 
  grains 
  and 
  rod-like 
  fragments 
  of 
  

   glauconite, 
  detached 
  spicules 
  of 
  the 
  Monactinellid 
  and 
  Tetractinellid 
  

   type, 
  and 
  fragments 
  of 
  the 
  spicular 
  mesh 
  of 
  a 
  Hexactinellid 
  sponge, 
  

   further 
  examination 
  of 
  the 
  spicular 
  remains 
  showed 
  them 
  to 
  be 
  

   in 
  a 
  condition 
  similar 
  to 
  those 
  of 
  the 
  malmstone 
  described 
  by 
  Dr. 
  

   Hinde. 
  Tie 
  wed 
  by 
  reflected 
  light, 
  they 
  appear 
  white 
  and 
  smooth. 
  

   By 
  transmitted 
  light 
  they 
  present 
  a 
  granular 
  appearance, 
  their 
  out- 
  

   line 
  seems 
  irregularly 
  broken, 
  and 
  the 
  impression 
  created 
  is 
  that 
  of 
  

   a 
  slightly 
  rough 
  exterior 
  ; 
  their 
  spicular 
  walls 
  remained 
  neutral 
  

   with 
  polarized 
  light. 
  Their 
  canals 
  are 
  in 
  almost 
  all 
  cases 
  empty, 
  

   and 
  air-bubbles 
  can 
  be 
  seen 
  following 
  their 
  ramifications 
  ; 
  but 
  the 
  

   rod-like 
  fragments 
  of 
  glauconite 
  seen 
  in 
  the 
  residue 
  after 
  treatment 
  

   of 
  the 
  marl 
  with 
  acid 
  testify 
  that 
  in 
  some 
  cases 
  the 
  spicular 
  canal 
  

   is 
  filled 
  with 
  this 
  mineral. 
  

  

  Placing 
  the 
  residue 
  of 
  this 
  specimen 
  of 
  the 
  marl 
  in 
  a 
  strong 
  

   solution 
  of 
  caustic 
  potash 
  and 
  maintaining 
  a 
  heat 
  of 
  about 
  16u° 
  or 
  

   17'- 
  ,: 
  for 
  40 
  minutes, 
  the 
  whole 
  of 
  the 
  free 
  spicules 
  disappeared. 
  

   But 
  the 
  result 
  was 
  different 
  in 
  the 
  case 
  of 
  the 
  Hexactinellid 
  mesh. 
  

   Examining 
  a 
  portion 
  of 
  this 
  from 
  time 
  to 
  time, 
  the 
  granular 
  ap- 
  

   pearance 
  slowly 
  disappeared, 
  and 
  at 
  the 
  end 
  of 
  -40 
  minutes 
  the 
  mesh, 
  

   when 
  mounted 
  in 
  Canada 
  balsam, 
  while 
  still 
  retaining 
  its 
  form, 
  

   appeared 
  nearly 
  translucent 
  ; 
  viewed 
  with 
  polarized 
  light 
  the 
  silica 
  

   now 
  remaining 
  seemed 
  to 
  be 
  wholly 
  chalcedonic. 
  

  

  Dr. 
  Hinde, 
  who 
  has 
  very 
  kindly 
  examined 
  this 
  and 
  many 
  other 
  

   of 
  our 
  specimens, 
  writes, 
  " 
  solution 
  seems 
  only 
  to 
  have 
  taken 
  place 
  

   in 
  the 
  nodes 
  of 
  the 
  mesh 
  which 
  are 
  now 
  in 
  places 
  occupied 
  by 
  air- 
  

   bubbles."' 
  The 
  mesh, 
  therefore, 
  consisted 
  partly 
  of 
  colloid 
  and 
  

   partly 
  of 
  chalcedonic 
  silica. 
  

  

  It 
  appears 
  to 
  us 
  that 
  in 
  this 
  particular 
  specimen 
  of 
  the 
  Chalk 
  

  

  * 
  This 
  is 
  the 
  only 
  specimen 
  of 
  Chalk 
  Marl 
  tve 
  have 
  examined 
  vrhk-h 
  con- 
  

   tains 
  the 
  mesh 
  of 
  a 
  Hexactinellid 
  sponge. 
  

  

  