﻿E. 
  E. 
  Call 
  — 
  Silicified 
  Woods 
  of 
  Eastern 
  Arkansas. 
  399 
  

  

  There 
  can 
  be 
  little 
  question, 
  therefore, 
  that 
  the 
  process 
  of 
  

   silicification 
  has 
  occurred, 
  in 
  some 
  cases 
  at 
  least, 
  since 
  these 
  

   masses 
  were 
  torn 
  from 
  the 
  underlying 
  beds 
  by 
  the 
  waters 
  

   which 
  deposited 
  the 
  sands 
  above 
  the 
  clays.* 
  As 
  ordinarily 
  

   understood 
  the 
  process 
  is 
  purely 
  a 
  chemical 
  one 
  and 
  perhaps 
  

   very 
  slow. 
  It 
  consists 
  in 
  the 
  replacement, 
  particle 
  by 
  particle, 
  

   of 
  the 
  carbon 
  of 
  the 
  lignite 
  by 
  silicic 
  acid, 
  or 
  silicon 
  dioxide. 
  

   It 
  is 
  by 
  no 
  means 
  essential 
  that 
  the 
  organic 
  matter 
  be 
  unchanged 
  

   when 
  the 
  process 
  begins. 
  If 
  the 
  belief 
  that 
  this 
  wood 
  repre- 
  

   sents 
  what 
  was 
  once 
  lignite 
  be 
  a 
  correct 
  one, 
  then 
  the 
  process 
  

   of 
  silicification 
  can 
  occur 
  in 
  the 
  case 
  of 
  organic 
  matter 
  which 
  

   has 
  already 
  undergone 
  a 
  partial 
  change. 
  

  

  Where 
  found 
  in 
  clays 
  in 
  a 
  silicified 
  condition, 
  it 
  has 
  probably 
  

   resulted 
  from 
  the 
  same 
  processes 
  that 
  are 
  seen 
  to 
  obtain 
  in 
  the 
  

   highly 
  siliceous 
  sands 
  or 
  gravels 
  which 
  overlie 
  them. 
  Though 
  

   the 
  impervious 
  nature 
  of 
  most 
  clays 
  renders 
  the 
  percolation 
  of 
  

   of 
  silica-charged 
  waters 
  a 
  matter 
  of 
  great 
  difficulty 
  such 
  perco- 
  

   lation 
  certainly 
  occurs 
  in 
  them. 
  The 
  silicified 
  masses 
  of 
  wood 
  

   are 
  often 
  far 
  too 
  large 
  to 
  have 
  been 
  removed 
  from 
  the 
  clays 
  

   and 
  deposited 
  in 
  the 
  overlying 
  gravels 
  by 
  an 
  ordinary 
  wave 
  or 
  

   current 
  action 
  for 
  they 
  sometimes 
  weigh 
  tons. 
  In 
  the 
  form 
  of 
  

   lignite 
  the 
  same 
  masses 
  could 
  have 
  been 
  transported 
  by 
  cur- 
  

   rents 
  but 
  since 
  very 
  large 
  pieces 
  have 
  been 
  rarely, 
  if 
  ever, 
  

   found 
  far 
  from 
  lignite 
  deposits 
  even 
  that 
  proposition 
  has 
  very 
  

   little 
  weight. 
  

  

  The 
  vertical 
  distribution 
  of 
  the 
  silicified 
  woods 
  of 
  the 
  Arkan- 
  

   sas 
  Tertiary 
  is 
  limited 
  by 
  the 
  line 
  of 
  contact 
  between 
  the 
  sands 
  

   and 
  clays 
  which 
  constitute 
  the 
  Arkansas 
  series. 
  Below 
  this 
  

   line 
  the 
  silicified 
  w 
  r 
  ood 
  never 
  occurs, 
  with 
  the 
  single 
  exception 
  

   above, 
  f 
  so 
  far 
  as 
  observations 
  have 
  yet 
  extended. 
  Above 
  it 
  no 
  

  

  *Dr. 
  R. 
  A. 
  F. 
  Penrose, 
  Jr. 
  (op 
  cit, 
  pp. 
  24, 
  26, 
  50, 
  et 
  seq.), 
  has 
  placed 
  on 
  record 
  

   the 
  numerous 
  occurrences 
  of 
  silicified 
  wood 
  in 
  the 
  Tertiary 
  of 
  Texas 
  ; 
  he 
  finds 
  it 
  

   in 
  both 
  sands 
  and 
  clays. 
  In 
  his 
  description 
  of 
  the 
  Sabine 
  River 
  beds 
  he 
  says 
  : 
  

   •• 
  Silicified 
  wood 
  is 
  of 
  very 
  frequent 
  occurrence 
  in 
  these 
  strata; 
  sometimes 
  occur- 
  

   ring 
  as 
  small 
  fragments 
  ; 
  and 
  at 
  other 
  times 
  as 
  large 
  trunks 
  of 
  trees. 
  On 
  the 
  

   Brazos 
  River, 
  in 
  the 
  northern 
  part 
  of 
  Milam 
  County, 
  was 
  seen 
  a 
  trunk 
  one 
  and 
  a 
  

   half 
  feet 
  in 
  diameter, 
  protruding 
  from 
  a 
  cJav 
  bed. 
  Ten 
  feet 
  of 
  it 
  were 
  exposed, 
  

   while 
  the 
  rest 
  was 
  imbedded 
  in 
  the 
  clay. 
  In 
  many 
  places 
  such 
  fragments 
  are 
  

   collected 
  in 
  great 
  quantities, 
  but 
  it 
  is 
  especially 
  plentiful 
  in 
  the 
  lower 
  part 
  of 
  the 
  

   Fayette 
  beds. 
  It 
  is 
  generally 
  dark 
  brown 
  or 
  black 
  inside, 
  and 
  weathers 
  gray 
  or 
  

   buff 
  color 
  on 
  the 
  outside. 
  Sometimes 
  it 
  occurs 
  partly 
  lignitized 
  and 
  partly 
  silici- 
  

   fied. 
  It 
  frequently 
  shows 
  shrinkage 
  cracks 
  which 
  are 
  filled 
  with 
  quartz 
  or 
  

   chalcedony, 
  and 
  are 
  often 
  lined 
  with 
  quartz 
  crystals." 
  

  

  In 
  this 
  case 
  stratification- 
  was 
  but 
  partial 
  or 
  was 
  still 
  in 
  progress 
  and 
  since 
  

   there 
  is 
  exposed 
  in 
  the 
  face 
  of 
  the 
  bluff 
  a 
  log 
  which 
  was 
  partially 
  lignitized 
  and 
  

   partly 
  silicified 
  it 
  proves 
  all 
  but 
  conclusively 
  that, 
  even 
  in 
  the 
  Texan 
  Tertiaries, 
  

   the 
  lignitic 
  precedes 
  the 
  siliceous 
  condition 
  of 
  these 
  woods. 
  

  

  fin 
  this 
  case 
  the 
  stumps 
  are 
  still 
  standing, 
  the 
  roots, 
  also 
  silicified, 
  ramifying 
  

   in 
  all 
  directions 
  in 
  Eocene 
  blue 
  clays. 
  Less 
  than 
  one 
  hundred 
  feet 
  east, 
  however, 
  

   the 
  line 
  of 
  contact 
  between 
  the 
  sand 
  beds 
  and 
  the 
  clays 
  was 
  disclosed 
  in 
  a 
  ver- 
  

   tical 
  cut 
  in 
  a 
  hillside. 
  This 
  line 
  was 
  at 
  or 
  near 
  the 
  elevation 
  of 
  the 
  stumps. 
  It 
  

  

  