﻿PLIOCENE 
  PERIOD 
  IN 
  ENGLAND. 
  681 
  

  

  after 
  the 
  Thames-system 
  partings 
  had 
  emerged, 
  and 
  that 
  system 
  must 
  

   have 
  become 
  entirely 
  a 
  river-system, 
  if, 
  indeed, 
  this 
  condition 
  of 
  a 
  

   strait 
  did 
  not 
  even 
  endure 
  until 
  the 
  depression 
  of 
  Stage 
  VI. 
  Mr. 
  

   Maw 
  describes 
  the 
  gravel 
  of 
  the 
  Severn 
  valley 
  with 
  marine 
  Mollusca 
  

   as 
  extending 
  down 
  to 
  the 
  modern 
  river 
  alluvium 
  as 
  far 
  up 
  that 
  valley 
  

   as 
  Ironbridge 
  and 
  Shrewsbury* 
  ; 
  and 
  it 
  seems 
  to 
  me 
  that 
  this 
  may 
  be 
  

   the 
  result 
  of 
  the 
  state 
  of 
  things 
  just 
  mentioned, 
  for 
  the 
  Bristol-Channel 
  

   extremity 
  of 
  this 
  valley 
  must, 
  from 
  this 
  great 
  difference 
  in 
  the 
  depres- 
  

   sion, 
  have 
  become 
  land 
  nearly 
  as 
  soon 
  as 
  its 
  source 
  extremity, 
  which 
  

   is 
  now 
  some 
  hundreds 
  of 
  feet 
  higher 
  above 
  the 
  sea 
  than 
  the 
  Bristol 
  

   extremity. 
  In 
  the 
  case 
  of 
  the 
  principal 
  tributary 
  of 
  the 
  Severn, 
  the 
  

   Warwickshire 
  Avon, 
  this 
  was 
  different, 
  because 
  the 
  course 
  of 
  that 
  

   river 
  being 
  from 
  north-east 
  to 
  south-west, 
  the 
  depression 
  of 
  the 
  

   different 
  parts 
  of 
  its 
  valley 
  was 
  pretty 
  uniform 
  ; 
  so 
  that 
  in 
  emergence 
  

   it 
  passed 
  from 
  the 
  marine 
  to 
  the 
  estuarine 
  (see 
  Map 
  6), 
  and 
  from 
  

   that 
  to 
  the 
  fluviatile 
  condition 
  in 
  the 
  due 
  gradation 
  of 
  its 
  various 
  

   portions 
  ; 
  and 
  thus, 
  contrary 
  to 
  the 
  case 
  of 
  the 
  Severn, 
  the 
  gravels 
  

   of 
  the 
  Avon 
  at 
  the 
  lower 
  elevations 
  contain 
  freshwater 
  shells 
  and 
  

   mammalian 
  remains 
  f 
  . 
  

  

  The 
  phenomena 
  presented 
  by 
  the 
  gravels 
  of 
  the 
  Trent 
  system 
  must 
  

   be 
  complicated 
  by 
  causes 
  partly 
  similar 
  to, 
  and 
  partly 
  dissimilar 
  from, 
  

   those 
  affecting 
  the 
  gravels 
  of 
  the 
  Severn, 
  — 
  similar 
  in 
  that 
  the 
  valleys 
  

   of 
  the 
  westernmost 
  part 
  of 
  the 
  Trent 
  system, 
  from 
  their 
  contiguity 
  

   to 
  the 
  area 
  of 
  greatest 
  depression, 
  emerged 
  later 
  than 
  the 
  lower 
  or 
  

   north-eastern 
  part 
  of 
  that 
  system 
  ; 
  but 
  dissimilar 
  in 
  that 
  the 
  valleys 
  

   of 
  the 
  lower 
  part 
  of 
  that 
  system 
  continued 
  to 
  be 
  occupied 
  by 
  the 
  

   land 
  -ice 
  after 
  those 
  of 
  the 
  upper 
  part 
  had 
  ceased 
  to 
  be 
  so. 
  The 
  

   phenomena 
  of 
  the 
  Trent 
  system 
  subsequent 
  to 
  the 
  Chalky 
  Clay 
  

   therefore 
  require 
  an 
  examination 
  by 
  themselves, 
  which 
  I 
  have 
  not 
  

   the 
  materials 
  to 
  make, 
  but 
  which, 
  when 
  attempted, 
  should 
  be 
  made 
  

   with 
  due 
  regard 
  to 
  these 
  conditions. 
  

  

  I 
  must 
  here 
  break 
  the 
  thread 
  of 
  my 
  attempt 
  to 
  trace 
  the 
  progress 
  

   of 
  the 
  emergence 
  of 
  England, 
  by 
  some 
  further 
  remarks 
  on 
  the 
  phe- 
  

   nomena 
  connected 
  with 
  the 
  submergence, 
  which 
  are 
  necessary 
  in 
  

   order 
  to 
  enable 
  me 
  to 
  place 
  before 
  geologists 
  properly 
  those 
  views 
  

   concerning 
  the 
  whole 
  chain 
  of 
  events 
  embraced 
  by 
  this 
  memoir 
  to 
  

   which 
  my 
  study 
  of 
  the 
  subject 
  has 
  led 
  me. 
  

  

  In 
  tracing 
  the 
  evidences 
  of 
  submergence 
  during 
  Stage 
  II., 
  I 
  stated 
  

   that 
  the 
  gravel 
  (&') 
  shown 
  at 
  Caesar's 
  Camp, 
  in 
  fig. 
  II. 
  of 
  the 
  plate 
  

   to 
  the 
  first 
  part 
  of 
  this 
  memoir, 
  spreads 
  out 
  over 
  that 
  part 
  of 
  the 
  

   Chalk 
  plateau 
  of 
  North 
  B 
  ants 
  which 
  skirted 
  the 
  western 
  edge 
  of 
  the 
  

   Wealden 
  excavation. 
  I 
  have 
  ascertained 
  that 
  this 
  gravel 
  reaches 
  

   the 
  elevation 
  of 
  nearly 
  700 
  feet, 
  the 
  level 
  of 
  the 
  rails 
  in 
  Meadsted 
  

   Cutting 
  — 
  where 
  (mixed 
  with 
  loam, 
  and 
  containing 
  large 
  waterworn 
  

   flints) 
  it 
  crowns 
  the 
  parting 
  between 
  drainage 
  falling 
  to 
  the 
  South- 
  

   ampton 
  water 
  and 
  that 
  falling 
  into 
  the 
  Thames 
  (and 
  which 
  is 
  

   indicated 
  by 
  the 
  letters 
  A 
  P 
  on 
  the 
  continuation 
  of 
  Map 
  2) 
  — 
  being 
  

  

  * 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xx. 
  p. 
  130. 
  

  

  t 
  Ingram, 
  in 
  vol. 
  xxxv. 
  of 
  the 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  p. 
  678, 
  and 
  Lloyd, 
  

   in 
  vol. 
  xxvi. 
  p. 
  202. 
  

  

  Q. 
  J. 
  G. 
  S. 
  No. 
  152. 
  2 
  z 
  

  

  