﻿400 
  B. 
  E. 
  Call 
  — 
  Silicified 
  Woods 
  of 
  Eastern 
  Arkansas. 
  

  

  lignites 
  have 
  ever 
  been 
  found. 
  The 
  vertical 
  range 
  is 
  therefore 
  

   limited 
  by 
  the 
  thickness 
  of 
  the 
  sand 
  and 
  gravel 
  bed 
  which 
  is 
  

   commonly, 
  in 
  Arkansas, 
  between 
  fifty 
  and 
  eighty 
  feet. 
  

  

  There 
  is 
  a 
  marked 
  difference 
  in 
  the 
  vertical 
  range 
  of 
  this 
  

   fossil 
  in 
  the 
  Tertiary 
  of 
  Arkansas 
  and 
  the 
  Tertiary 
  of 
  California. 
  

   In 
  the 
  latter 
  State 
  the 
  vertical 
  range 
  is 
  often 
  many 
  hundreds, 
  

   even 
  several 
  thousands, 
  of 
  feet. 
  Whitney 
  says 
  :* 
  " 
  It 
  will 
  

   be 
  proper 
  to 
  add 
  to 
  some 
  of 
  the 
  most 
  important 
  facts 
  gathered 
  

   during 
  the 
  investigation 
  of 
  the 
  gravel 
  deposits 
  in 
  regard 
  to 
  

   the 
  mode 
  of 
  occurrence 
  of 
  the 
  fossil 
  plants 
  of 
  the 
  Pliocene 
  

   epoch. 
  The 
  vertical 
  range 
  of 
  these 
  has 
  been 
  alluded 
  to, 
  and 
  it 
  

   may 
  be 
  more 
  distinctly 
  stated 
  that 
  either 
  fossil 
  wood 
  or 
  leaves 
  

   have 
  been 
  found 
  at 
  every 
  elevation, 
  from 
  the 
  lowest 
  to 
  the 
  

   highest, 
  where 
  gravels 
  occur. 
  Even 
  as 
  high 
  as 
  Silver 
  Moun- 
  

   tain 
  City, 
  at 
  7,000 
  feet 
  of 
  elevation, 
  large 
  masses 
  of 
  fossil 
  wood 
  

   are 
  found 
  in 
  the 
  volcanic 
  deposits 
  ; 
  and 
  in 
  Plumas 
  county 
  the 
  

   same 
  occurrence 
  has 
  been 
  noted 
  on 
  several 
  of 
  the 
  highest 
  

   mountains 
  in 
  the 
  region, 
  as 
  Penman's 
  Peak 
  and 
  Clermont, 
  

  

  peaks 
  from 
  7,000 
  to 
  8,000 
  feet 
  high 
  Fragments 
  and 
  

  

  often 
  large 
  masses 
  of 
  wood 
  are 
  found, 
  both 
  in 
  the 
  gravels 
  

   and 
  the 
  associated 
  clayey 
  and 
  tufaceous 
  beds. 
  In 
  the 
  gravel 
  

   they 
  frequently 
  bear 
  the 
  marks 
  of 
  transportation 
  from 
  a 
  dis- 
  

   tance, 
  as 
  would 
  be 
  expected." 
  

  

  In 
  the 
  California 
  Tertiary 
  the 
  most 
  completely 
  silicified 
  and 
  

   best 
  preserved 
  specimens 
  of 
  wood 
  occur 
  in 
  connection 
  with 
  

   deposits 
  of 
  a 
  volcanic 
  character, 
  sometimes 
  a 
  rhyolitic 
  ash.f 
  It 
  

   is 
  suggested 
  by 
  Whitney 
  that 
  these 
  relationships 
  have 
  some- 
  

   thing 
  to 
  do 
  with 
  the 
  process 
  of 
  silicification. 
  For 
  that 
  region 
  

   Whitney 
  believes 
  that 
  not 
  only 
  were 
  the 
  woods 
  silicified 
  after 
  

   their 
  imbedding 
  in 
  white 
  pulverulent 
  volcanic 
  ash 
  but 
  u 
  the 
  

   lava 
  itself 
  exhibits 
  signs 
  of 
  having 
  been 
  acted 
  on 
  by 
  silicifying 
  

   agents 
  after 
  its 
  deposition." 
  That 
  the 
  greater 
  part 
  of 
  the 
  series 
  

   of 
  beds 
  included 
  in 
  the 
  gravel 
  formation 
  has 
  been 
  thoroughly 
  

   permeated 
  with 
  waters 
  holding 
  silica 
  in 
  solution 
  and 
  that 
  

   chemical 
  changes 
  induced 
  thereby 
  are 
  sufficient 
  to 
  explain 
  the 
  

   phenomena 
  appears 
  quite 
  probable. 
  The 
  relations 
  which 
  the 
  

   phenomena 
  sustain 
  to 
  the 
  facts 
  of 
  volcanism 
  so 
  abundant 
  in 
  that 
  

   region 
  are 
  set 
  forth 
  and 
  the 
  conclusion 
  is 
  drawn 
  that 
  that 
  rela- 
  

   tion 
  explains 
  silicification 
  in 
  these 
  woods. 
  In 
  California 
  it 
  

   becomes 
  a 
  subordinate 
  problem 
  under 
  volcanism. 
  

  

  The 
  chemical 
  processes 
  which 
  obtained 
  in 
  the 
  case 
  of 
  the 
  

   Arkansas 
  gravels 
  were 
  not 
  coordinate 
  with 
  those 
  of 
  California, 
  

  

  was 
  clear 
  that, 
  if 
  the 
  stumps 
  did 
  not 
  actually 
  project 
  into 
  the 
  overlying 
  sands, 
  they 
  

   were 
  but 
  a 
  short 
  distance 
  below 
  and 
  under 
  conditions 
  to 
  favor 
  silicificatiou 
  from 
  

   waters 
  percolating 
  through 
  the 
  clay 
  to 
  them. 
  

  

  * 
  Auriferous 
  Gravels 
  of 
  the 
  Sierra 
  Nevada, 
  pp. 
  235, 
  236. 
  See 
  also 
  this 
  Jour- 
  

   nal, 
  II, 
  vol. 
  xli, 
  p. 
  359. 
  1866. 
  

  

  fOp. 
  cit., 
  pp. 
  327-329. 
  

  

  