﻿292 
  PEOF. 
  J. 
  PEESTWICH 
  ON" 
  THE 
  OCCTJEEENCE 
  OF 
  

  

  Ightham 
  (Oldbury) 
  district. 
  Now 
  as 
  similar 
  subangular 
  fragments 
  

   of 
  ragstone 
  and 
  Oldbury 
  Stone 
  are 
  found 
  scattered, 
  in 
  places, 
  over 
  

   tbe 
  high 
  chalk 
  plateau 
  of 
  the 
  Ash 
  district, 
  the 
  inference 
  is 
  that 
  

   when 
  this 
  Lower-Greensend 
  debris 
  spread 
  over 
  this 
  area 
  a 
  con- 
  

   tinuous 
  plane 
  descended 
  from 
  the 
  high 
  range 
  of 
  the 
  Lower 
  Green- 
  

   sand 
  down 
  into 
  the 
  Thames 
  valley, 
  and 
  that 
  this 
  valley 
  has 
  since 
  

   that 
  period 
  undergone 
  denudation 
  to 
  the 
  depth 
  of 
  300 
  ft. 
  or 
  more, 
  

   and 
  the 
  tributary 
  valleys 
  in 
  proportion. 
  

  

  These 
  physiographical 
  changes 
  and 
  the 
  great 
  height 
  of 
  the 
  old 
  

   chalk 
  plateau, 
  with 
  its 
  " 
  red 
  clay 
  with 
  flints 
  " 
  and 
  " 
  southern 
  drift 
  " 
  

   high 
  above 
  the 
  valleys 
  containing 
  the 
  Postglacial 
  deposits, 
  point 
  

   to 
  the 
  great 
  antiquity 
  — 
  possibly 
  Preglacial 
  — 
  of 
  the 
  palaeolithic 
  

   implements 
  found 
  in 
  association 
  with 
  these 
  summit 
  drifts. 
  

  

  In 
  connexion 
  with 
  the 
  subject 
  of 
  all 
  these 
  drifts, 
  another 
  question 
  

   suggests 
  itself 
  by 
  the 
  manner 
  in 
  which 
  they 
  are 
  distributed. 
  They 
  

   are 
  not, 
  as 
  we 
  have 
  seen, 
  confined 
  to 
  the 
  lower 
  parts 
  or 
  river- 
  

   channels 
  of 
  the 
  valleys, 
  but 
  occur 
  in 
  them 
  at 
  all 
  heights 
  on 
  their 
  

   sides 
  and 
  on 
  the 
  adjacent 
  hills. 
  It 
  is 
  evident, 
  from 
  the 
  mass 
  of 
  

   material, 
  its 
  weight, 
  and 
  the 
  distances 
  to 
  which 
  it 
  has 
  been 
  carried, 
  

   that 
  the 
  agencies 
  by 
  which 
  its 
  distribution 
  was 
  effected 
  throughout 
  

   not 
  only 
  the 
  period 
  of 
  Postglacial 
  work, 
  but 
  throughout 
  the 
  whole 
  

   period 
  of 
  plain- 
  or 
  valley-excavation 
  — 
  whether 
  nuviatile, 
  marine, 
  or 
  

   glacial, 
  or 
  whether 
  during 
  Postglacial 
  or 
  antecedent 
  times 
  — 
  were 
  of 
  

   far 
  greater 
  power 
  than 
  those 
  operating 
  under 
  the 
  present 
  river 
  

   regime, 
  where 
  such 
  work 
  is 
  unknown. 
  Consequently 
  the 
  attempt 
  

   to 
  measure 
  or 
  to 
  infer 
  the 
  length 
  of 
  time 
  required 
  for 
  the 
  exca- 
  

   vation 
  of 
  these 
  valleys 
  (and 
  by 
  inference 
  of 
  all 
  the 
  outer 
  portion 
  of 
  the 
  

   Weald) 
  by 
  the 
  work 
  done 
  by 
  present 
  rivers, 
  which 
  possess 
  no 
  such 
  

   transporting 
  power, 
  cannot 
  but 
  lead 
  to 
  a 
  serious 
  misconception 
  of 
  

   the 
  antiquity 
  of 
  these 
  valley-systems, 
  and 
  prejudice 
  the 
  discussion 
  

   of 
  the 
  great 
  stratigraphical 
  problems 
  relating 
  to 
  the 
  antiquity 
  of 
  

   Man. 
  I 
  do 
  not 
  here 
  raise 
  the 
  question 
  of 
  the 
  mode 
  of 
  denudation, 
  

   which 
  has 
  been 
  largely 
  treated 
  of 
  by 
  Ramsay 
  * 
  and 
  Topley 
  t, 
  but 
  

   only 
  that 
  of 
  its 
  energy. 
  It 
  is 
  another 
  illustration 
  of 
  a 
  question 
  I 
  

   have 
  often 
  had 
  occasion 
  to 
  raise. 
  

  

  Although 
  this 
  inquiry 
  tends 
  to 
  carry 
  Man 
  further 
  back 
  geologically 
  

   than 
  is 
  generally 
  admitted 
  J, 
  I 
  would, 
  for 
  the 
  reasons 
  here 
  given 
  and 
  

   others 
  I 
  have 
  given 
  before 
  §, 
  so 
  close 
  up 
  the 
  time 
  required 
  for 
  the 
  ac- 
  

   complishment 
  of 
  these 
  great 
  physical 
  changes 
  that, 
  instead 
  of 
  calling 
  

   for 
  more 
  time, 
  I 
  believe 
  that 
  the 
  commonly 
  accepted 
  Crollian 
  chro- 
  

   nology 
  should 
  be 
  so 
  curtailed 
  that 
  the 
  age 
  of 
  Man 
  would 
  not 
  exceed, 
  

   or 
  possibly 
  not 
  equal, 
  that 
  now 
  claimed 
  for 
  him 
  on 
  that 
  hypothesis. 
  

  

  In 
  any 
  case 
  it 
  appears 
  to 
  me 
  certain 
  that 
  the 
  facts 
  described 
  

  

  * 
  ' 
  The 
  Physical 
  Geology 
  and 
  Geography 
  of 
  Great 
  Britain,' 
  3rd 
  edit. 
  pp. 
  

   336-346. 
  

  

  t 
  ' 
  The 
  Geology 
  of 
  the 
  Weald,' 
  Mem. 
  Geol. 
  Survey, 
  1875, 
  chapter 
  16. 
  

  

  | 
  Evidence 
  to 
  tbe 
  same 
  effect, 
  but 
  of 
  a 
  different 
  character, 
  has, 
  however, 
  been 
  

   brought 
  forward 
  by 
  several 
  geologists. 
  

  

  § 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xliii. 
  p. 
  393. 
  

  

  