﻿Ray 
  — 
  Ages 
  of 
  Pleistocene 
  Deposits. 
  373 
  

  

  in 
  the 
  Miocene 
  and 
  the 
  Pliocene 
  ; 
  and 
  Dr. 
  Mark 
  Francis 
  

   finds 
  that 
  Brazos 
  river 
  is 
  now 
  washing 
  out 
  from 
  its 
  flood- 
  

   plain 
  or 
  from 
  deposits 
  underlying 
  it, 
  jaws 
  and 
  teeth 
  of 
  

   mastodons 
  of 
  the 
  same 
  genns. 
  

  

  At 
  the 
  same 
  time 
  that 
  such 
  channels 
  were 
  being 
  

   re-excavated 
  the 
  materials 
  might 
  have 
  been 
  dumped 
  at 
  

   the 
  lower 
  and 
  flatter 
  reaches 
  and 
  have 
  built 
  up 
  a 
  terrace- 
  

   like 
  plain. 
  

  

  In 
  this 
  connection 
  it 
  may 
  be 
  allowed 
  to 
  discuss 
  briefly 
  

   the 
  geological 
  age 
  of 
  the 
  Alachua 
  clays 
  in 
  Florida 
  and 
  the 
  

   Idaho 
  formation 
  in 
  Idaho 
  and 
  Oregon. 
  The 
  Alachua 
  

   clays 
  have 
  furnished 
  a 
  considerable 
  vertebrate 
  fauna, 
  

   and 
  have 
  been 
  assigned 
  to 
  the 
  Pliocene 
  apparently 
  by 
  

   nearly 
  all 
  who 
  have 
  written 
  about 
  them. 
  13 
  This 
  conclu- 
  

   sion 
  has 
  doubtless 
  been 
  forced 
  by 
  the 
  occurrence 
  in 
  those 
  

   clays 
  of 
  rhinoceroses 
  belonging 
  to 
  the 
  genera 
  Teleoceras 
  

   and 
  Aphelops, 
  camels 
  of 
  the 
  genus 
  Procamelus, 
  and 
  

   species 
  of 
  Hipparion, 
  all 
  of 
  which 
  genera 
  were 
  repre- 
  

   sented 
  in 
  the 
  Tertiary 
  by 
  numerous 
  species 
  ; 
  but 
  which 
  

   are 
  not 
  known, 
  with 
  the 
  exception 
  of 
  Hipparion, 
  in 
  

   deposits 
  acknowledged 
  generally 
  to 
  belong 
  to 
  the 
  Pleisto- 
  

   cene. 
  However, 
  the 
  Pleistocene 
  fauna 
  with 
  which 
  the 
  

   Alachuan 
  species 
  have 
  been 
  compared 
  is 
  that 
  which 
  is 
  

   found 
  in 
  the 
  so-called 
  Equus 
  beds 
  of 
  the 
  plains. 
  This 
  is 
  

   itself 
  to 
  be 
  regarded 
  as 
  equivalent 
  to 
  the 
  fauna 
  of 
  the 
  

   Aftonian 
  beds, 
  intercalated 
  between 
  the 
  first 
  and 
  the 
  

   second 
  drifts. 
  This 
  stage 
  was, 
  therefore, 
  preceded 
  by 
  

   another, 
  the 
  Nebraskan, 
  about 
  whose 
  vertebrate 
  animals 
  

   we 
  know 
  nothing 
  whatever. 
  This 
  stage 
  probably 
  occu- 
  

   pied 
  a 
  long 
  period 
  of 
  time. 
  Indeed, 
  Chamberlin 
  and 
  

   Salisbury 
  14 
  suggest 
  that 
  it 
  (the 
  "sub- 
  Aftonian") 
  may 
  

   have 
  been 
  as 
  long 
  as 
  all 
  the 
  rest 
  of 
  the 
  Pleistocene. 
  Inas- 
  

   much 
  as 
  a 
  considerable 
  number 
  of 
  genera 
  of 
  mammals 
  

   did 
  continue 
  on 
  into 
  the 
  Aftonian 
  Pleistocene 
  from 
  the 
  

   Pliocene 
  and 
  even 
  from 
  the 
  Miocene, 
  it 
  is 
  not 
  unreason- 
  

   able 
  to 
  expect 
  that 
  still 
  other 
  Tertiary 
  genera 
  will 
  be 
  met 
  

   with 
  in 
  deposits 
  that 
  were 
  laid 
  down 
  during 
  Nebraskan 
  

   times, 
  if 
  such 
  should 
  be 
  discovered. 
  Now 
  among 
  the 
  

   genera 
  which 
  continue 
  on 
  into 
  undisputed 
  Pliocene 
  

   deposits 
  are 
  those 
  found 
  in 
  the 
  Alachua 
  clays, 
  Teleoceras, 
  

  

  18 
  Dall, 
  U. 
  S. 
  Geol. 
  Surv., 
  Bull. 
  84, 
  p. 
  127 
  ; 
  Matson 
  and 
  Sanford, 
  Water- 
  

   supply 
  paper 
  319, 
  p. 
  142; 
  Sellards, 
  8th 
  Ann. 
  Eep. 
  Fla. 
  Geol. 
  Surv., 
  p. 
  93; 
  

   Merriam, 
  J. 
  C, 
  Bull. 
  Dept. 
  Geol. 
  Univ. 
  Calif., 
  vol. 
  10, 
  p. 
  439. 
  

  

  14 
  Geology, 
  vol. 
  3, 
  pp. 
  383, 
  414, 
  420. 
  

  

  