﻿CLAYS 
  OF 
  ^'EW 
  YORK 
  

  

  509 
  

  

  metallic 
  scales, 
  or 
  as 
  a 
  superficial 
  coating 
  on 
  otlier 
  mineral 
  grains. 
  

   It 
  dissolves 
  quietly 
  in 
  muriatic 
  acid. 
  Iron 
  may 
  also 
  occur 
  in 
  clay 
  as 
  

   a 
  constituent 
  element 
  of 
  other 
  minerals, 
  and 
  indeed 
  the 
  effect 
  which 
  

   it 
  produces 
  is 
  dependent 
  not 
  so 
  much 
  on 
  the 
  actual 
  amount 
  of 
  iron 
  

   oxid 
  present 
  as 
  on 
  its 
  condition, 
  according 
  as 
  it 
  is 
  combined 
  with 
  

   silica, 
  carbonic 
  acid 
  or 
  some 
  other 
  acid. 
  

  

  Hornblende. 
  This 
  is 
  not 
  an 
  uncommon 
  constituent 
  of 
  clays, 
  and 
  

   when 
  present 
  is 
  generally 
  in 
  the 
  form 
  of 
  tiny 
  scales 
  or 
  flakes 
  of 
  a 
  

   dark 
  green 
  color, 
  sKowing 
  transparency 
  under 
  the 
  microscope 
  only 
  

   when 
  extremely 
  thin. 
  It 
  is 
  highly 
  probable 
  that 
  the 
  hornblende 
  

   does 
  not 
  remain 
  very 
  long 
  as 
  such, 
  for 
  it 
  decomposes 
  quite 
  easily, 
  

   yielding 
  hydrated 
  ferric 
  oxid 
  or 
  limonite. 
  

  

  Rutile 
  is 
  probably 
  of 
  widespread 
  occurrence 
  in 
  clays, 
  though 
  

   never 
  in 
  large 
  quantity. 
  It 
  occurs 
  mostly 
  in 
  the 
  form 
  of 
  bristle- 
  

   like 
  crystals. 
  JSTo 
  systematic 
  study 
  of 
  their 
  occurrence 
  in 
  clay 
  has 
  

   ever 
  been 
  taken 
  up. 
  The 
  writer 
  has 
  observed 
  them 
  in 
  some 
  of 
  

   the 
  Staten 
  Island 
  clays, 
  and 
  reference 
  has 
  been 
  made 
  to 
  them 
  from 
  

   time 
  to 
  time 
  by 
  other 
  writers. 
  {See 
  J. 
  J. 
  H. 
  TeaU. 
  Min. 
  mag. 
  

   7: 
  201; 
  G. 
  E. 
  Ladd. 
  Amer. 
  geol. 
  Ap. 
  1899) 
  

  

  Vanadiates, 
  though 
  not 
  as 
  common 
  in 
  clays, 
  may 
  cause 
  dis- 
  

   coloration. 
  In 
  Germany 
  they 
  have 
  been 
  found 
  in 
  clays 
  associated 
  

   with 
  the 
  lignites, 
  and 
  also 
  in 
  some 
  fire 
  clays, 
  but 
  in 
  this 
  country, 
  

   so 
  far 
  as 
  the 
  writer 
  is 
  aware, 
  they 
  have 
  never 
  been 
  investigated. 
  

   Clays 
  containing 
  soluble 
  vanadiates, 
  if 
  not 
  burned 
  at 
  a 
  sufficiently 
  

   high 
  temperature, 
  will 
  show 
  on 
  the 
  surface 
  of 
  the 
  ware 
  a 
  green 
  

   discoloration, 
  which, 
  though 
  it 
  can 
  be 
  washed 
  off 
  with 
  water, 
  will 
  

   continue 
  to 
  return 
  as 
  long 
  as 
  any 
  of 
  the 
  salt 
  is 
  left 
  in 
  the 
  brick. 
  

   Vanadiates 
  may 
  be 
  rendered 
  insoluble 
  by 
  burning 
  the 
  clay 
  to 
  a 
  

   point 
  of 
  vitrification. 
  (Soger's 
  Ges. 
  ScJirift. 
  p. 
  301) 
  

  

  Other 
  minerals 
  may 
  occur 
  in 
  clays, 
  such 
  as 
  magnetite, 
  titanite 
  

   etc., 
  but 
  the 
  quantity 
  is 
  small. 
  

  

  Organic 
  remains. 
  These 
  consist 
  of 
  bituminous 
  matter, 
  roots, 
  

   amber 
  and 
  other 
  substances, 
  which 
  volatilize 
  on 
  ignition. 
  

  

  