﻿CLAYS 
  OF 
  NEW 
  YOKK 
  539 
  

  

  Plasticity 
  

  

  This 
  property 
  pennits 
  the 
  clay 
  to 
  be 
  molded 
  intO' 
  any 
  desired 
  

   form 
  when 
  wet, 
  which 
  shape 
  it 
  retains 
  when 
  dry. 
  

  

  Just 
  what 
  the 
  cause 
  of 
  plasticity 
  is, 
  remains 
  to 
  be 
  proven 
  with 
  

   certainty. 
  We 
  find 
  this 
  property 
  best 
  developed 
  in 
  the 
  pasty 
  clay, 
  

   but 
  even 
  he^re 
  it 
  is 
  exceedingly 
  variable, 
  and 
  it 
  is 
  possible 
  to 
  col- 
  

   lect 
  a 
  series 
  of 
  samples 
  shomng 
  all 
  grades 
  of 
  transition 
  from 
  a 
  

   very 
  plastic 
  clay 
  to 
  a 
  mass 
  of 
  sand, 
  which 
  would 
  not 
  ordinarily 
  be 
  

   looked 
  on 
  as 
  plastic, 
  and 
  yet 
  does 
  possess 
  a 
  slight 
  amount 
  of 
  pasti- 
  

   ness 
  resembling 
  plasticity, 
  if 
  ground 
  very 
  fine. 
  We 
  can 
  not 
  say, 
  

   therefore, 
  that 
  plasticity 
  is 
  confined 
  tO' 
  clay, 
  but 
  simply 
  that 
  the 
  

   physical 
  conditions 
  existing 
  within 
  a 
  mass 
  of 
  clay 
  are 
  such 
  as 
  tend 
  

   to 
  produce 
  the 
  maximum 
  degree 
  of 
  tenacity, 
  the 
  highest 
  grade 
  of 
  

   plasticity. 
  

  

  Many 
  theories 
  have 
  been 
  advanced 
  to 
  explain 
  this 
  remarkable 
  

   property. 
  For 
  a 
  long 
  time 
  plasticity 
  was 
  supposed 
  to 
  be 
  directly 
  

   connected 
  with 
  the 
  hydrated 
  silicate 
  of 
  alumina, 
  or 
  kaolinite; 
  clays 
  

   high 
  in 
  kaolinite 
  were 
  said 
  to 
  be 
  very 
  plastic. 
  This 
  is 
  plainly 
  not 
  

   true, 
  as 
  any 
  series 
  of 
  clays 
  tested 
  will 
  demonstrate. 
  Pure 
  or 
  nearly 
  

   pure 
  kaolins 
  are 
  very 
  lean, 
  while 
  clays 
  low 
  in 
  kaolinite 
  may 
  be 
  

   highly 
  plastic. 
  

  

  Prof. 
  G. 
  H. 
  Cook-^ 
  considered 
  plasticity 
  to 
  be 
  due 
  to 
  a 
  plate 
  

   structure 
  present 
  in 
  the 
  clay, 
  the 
  plates 
  sliding 
  over 
  each 
  other 
  

   and 
  thus 
  permitting 
  mobility 
  in 
  the 
  mass 
  without 
  cracking. 
  He 
  

   fartlier 
  found 
  that 
  in 
  the 
  kaolins 
  the 
  plates 
  of 
  kaolinite 
  were 
  fre- 
  

   quently 
  collected 
  in 
  little 
  bunches, 
  and 
  that, 
  after 
  these 
  clays 
  were 
  

   rubbed 
  in 
  a 
  mortar, 
  in 
  order 
  to 
  tear 
  apart 
  the 
  plates, 
  they 
  showed 
  

   increased 
  plasticity. 
  

  

  There 
  seems 
  to 
  be 
  much 
  to 
  commend 
  this 
  theory 
  as 
  far 
  as 
  it 
  

   goes. 
  Compare 
  for 
  example 
  the 
  white 
  washed 
  kaolin 
  from 
  Dills- 
  

   boro, 
  ]Sr. 
  C, 
  with 
  the 
  washed, 
  white 
  plastic 
  clay 
  from 
  Edgar, 
  Fla., 
  

   the 
  one 
  a 
  residual 
  clay, 
  found 
  just 
  where 
  it 
  was 
  formed, 
  the 
  other 
  

  

  ^ 
  N. 
  J. 
  Geol. 
  sur. 
  1878. 
  Clays 
  of 
  New 
  Jersey. 
  

  

  