﻿540 
  

  

  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  a 
  transported 
  or 
  sedimentary 
  clay 
  which 
  has 
  been 
  washed 
  down 
  

   to 
  its 
  present 
  resting-place. 
  In 
  transit, 
  the 
  particles 
  have 
  been 
  

   ground 
  apart 
  naturally, 
  either 
  by 
  rubbing 
  against 
  one 
  another 
  or 
  

   between 
  the 
  white 
  quartz 
  pebbles 
  scattered 
  so 
  plentifully 
  through 
  

   the 
  clay. 
  

  

  These 
  two 
  clays 
  are 
  practically 
  identical 
  in 
  their 
  composition, 
  

   as 
  can 
  be 
  seen 
  from 
  the 
  two 
  following 
  analyses. 
  

  

  

  Edgar, 
  

   Fla. 
  

  

  Dillsboro, 
  

  

  N. 
  C. 
  

  

  SiOj 
  

  

  45.39 
  

   39.13 
  

   .46 
  

   .51 
  

   .29 
  

   .83 
  

   14.01 
  

  

  43.90 
  

  

  AloOs 
  

  

  40 
  . 
  ee 
  

  

  •'■^■^i^^S 
  • 
  

  

  FeA 
  

  

  CaO 
  

  

  .14 
  

  

  MffO 
  

  

  tr 
  

  

  Alk 
  

  

  H,0 
  

  

  .46 
  

   14.84 
  

  

  """^3^^ 
  

  

  

  

  100.61 
  

  

  100.00 
  

  

  Physically, 
  there 
  is 
  a 
  marked 
  difference, 
  the 
  Edgar 
  clay 
  being 
  

   decidedly 
  plastic, 
  the 
  Dillsboro 
  clay 
  being 
  very 
  lean. 
  This 
  plate 
  

   theory 
  would 
  suggest 
  therefore 
  that 
  plasticity 
  was 
  due 
  to 
  capil- 
  

   larity, 
  the 
  force 
  of 
  surface 
  tension 
  tending 
  to 
  hold 
  the 
  plates 
  

   together, 
  but 
  not 
  interfering 
  with 
  their 
  gliding 
  motion. 
  

  

  The 
  one 
  objection 
  to 
  explaining 
  plasticity 
  entirely 
  by 
  the 
  fore- 
  

   going 
  theory 
  rests 
  on 
  the 
  fact 
  that 
  not 
  all 
  minerals 
  occurring 
  in 
  

   clay 
  axe 
  scaly, 
  and 
  that 
  neither 
  scaly 
  kaolinite 
  nor 
  even 
  scaly 
  mica 
  

   predominates 
  in 
  all 
  clays. 
  

  

  Clays 
  may 
  be 
  said 
  to 
  have 
  two 
  classes 
  of 
  particles, 
  ^dz, 
  plastic 
  

   and 
  nonplastic, 
  the 
  latter 
  being 
  the 
  sandy 
  grains. 
  

  

  Olchewsky-^ 
  was 
  probably 
  the 
  first 
  to 
  suggest 
  that 
  the 
  plasticity 
  

   and 
  cohesion 
  of 
  a 
  clay 
  are 
  dependent 
  on 
  the 
  interlocking 
  of 
  the 
  clay 
  

   particles 
  and 
  kaolinite 
  plates, 
  and 
  in 
  this 
  connection 
  used 
  the 
  

   briquet 
  method 
  of 
  testing 
  the 
  plasticity, 
  or 
  rather 
  obtaining 
  a 
  

  

  ' 
  Topf. 
  u. 
  Zieg. 
  Zeit. 
  1882. 
  no. 
  29. 
  

  

  