﻿680 
  SEABLES 
  V. 
  WOOD 
  ON 
  THE 
  NEWEE 
  

  

  necting 
  the 
  Thames 
  valley 
  with 
  the 
  greatly 
  expanded 
  Bristol 
  Channel, 
  

   as 
  shown 
  in 
  Map 
  6 
  (PL 
  XXVI.). 
  Over 
  this 
  parting 
  (which 
  is 
  Oxford 
  

   Clay) 
  a 
  considerable 
  accumulation 
  of 
  gravel 
  is 
  spread, 
  chiefly 
  composed 
  

   of 
  flint*, 
  though 
  it 
  is 
  distant 
  ten 
  miles 
  from 
  the 
  nearest 
  chalk, 
  and 
  

   none 
  of 
  the 
  brooks 
  around 
  it 
  flow 
  from 
  the 
  chalk 
  direction. 
  Upon 
  

   the 
  emergence 
  of 
  this 
  parting, 
  the 
  valleys 
  of 
  all 
  the 
  Thames 
  system 
  

   became 
  estuarine, 
  from 
  which, 
  as 
  emergence 
  proceeded, 
  they 
  became 
  

   fluviatile 
  ; 
  the 
  valley 
  of 
  the 
  Avon 
  of 
  "Wilts 
  and 
  Somerset 
  thus 
  divided 
  

   from 
  the 
  Thames 
  system, 
  and 
  that 
  of 
  the 
  Avon 
  of 
  Warwick, 
  Wor- 
  

   cester, 
  and 
  Gloucestershires, 
  which 
  is 
  divided 
  from 
  this 
  system 
  by 
  

   the 
  partings 
  whose 
  emergence 
  I 
  traced 
  in 
  the 
  first 
  part 
  of 
  this 
  memoir, 
  

   passing 
  through 
  a 
  similar 
  phase. 
  Owing, 
  however, 
  to 
  the 
  increments 
  

   of 
  depression 
  already 
  traced, 
  the 
  fall 
  of 
  the 
  Thames 
  system 
  was 
  

   flatter, 
  while 
  that 
  of 
  the 
  two 
  Avons 
  was 
  probably 
  steeper 
  than 
  now, 
  

   so 
  that 
  when 
  we 
  take 
  up 
  the 
  history 
  of 
  the 
  Thames 
  in 
  Stage 
  YI. 
  we 
  

   shall 
  find 
  that 
  the 
  mixture 
  of 
  its 
  fresh 
  water 
  with 
  the 
  salt 
  had 
  come 
  

   to 
  take 
  place 
  considerably 
  to 
  the 
  east 
  or 
  north-east 
  of 
  the 
  part 
  where 
  

   this 
  now 
  occurs, 
  and 
  so 
  that 
  the 
  rivers 
  of 
  Essex 
  entered 
  the 
  estuary 
  of 
  

   the 
  Thames 
  considerably 
  to 
  the 
  eastward 
  of 
  the 
  present 
  coast 
  of 
  that 
  

   county 
  when 
  the 
  time 
  at 
  which 
  that 
  stage 
  begins 
  had 
  arrived 
  ; 
  for 
  

   the 
  freshwater-beds 
  of 
  that 
  stage 
  on 
  the 
  Essex 
  coast 
  descend 
  below 
  

   the 
  present 
  sea-level. 
  

  

  In 
  the 
  case 
  of 
  the 
  main 
  valley 
  of 
  the 
  Severn 
  the 
  case 
  is 
  more 
  

   complex 
  ; 
  for 
  since 
  at 
  its 
  Bristol-Channel 
  extremity 
  the 
  evidences 
  of 
  

   submergence 
  cannot 
  be 
  satisfactorily 
  traced 
  beyond 
  750 
  feet, 
  they 
  

   must 
  have 
  been 
  500 
  feet 
  at 
  least 
  more 
  than 
  this 
  at 
  the 
  source 
  of 
  this 
  

   river, 
  because 
  the 
  head 
  of 
  one 
  of 
  its 
  upper 
  tributaries 
  (the 
  Perry, 
  in 
  

   the 
  S.E. 
  of 
  Sheet 
  74) 
  is 
  only 
  12 
  miles 
  south 
  of 
  Minera 
  Mountain, 
  

   on 
  which 
  Mr. 
  Mackintosh 
  has 
  found 
  the 
  gravel 
  (6') 
  with 
  marine 
  

   shells 
  at 
  1230, 
  and 
  without 
  shells 
  at 
  1350 
  feetf. 
  This 
  and 
  two 
  

   other 
  tributaries 
  of 
  the 
  Upper 
  Severn, 
  in 
  Sheet 
  73, 
  are 
  separated 
  

   from 
  the 
  drainage 
  flowing 
  by 
  the 
  Weaver 
  and 
  Dee 
  to 
  the 
  Irish 
  Sea 
  

   by 
  low 
  water-partings 
  of 
  about 
  300 
  feet 
  elevation. 
  It 
  is 
  evident 
  

   therefore 
  that 
  unless 
  a 
  more 
  complete 
  recovery 
  from 
  this 
  increment 
  

   of 
  depression 
  in 
  the 
  direction 
  of 
  North 
  Wales 
  and 
  Lancashire 
  had 
  

   taken 
  place, 
  when 
  the 
  partings 
  between 
  the 
  Thames 
  and 
  Severn 
  

   systems 
  emerged, 
  than 
  the 
  general 
  purview 
  of 
  the 
  case 
  appears 
  to 
  me 
  

   to 
  indicate, 
  the 
  valley 
  of 
  the 
  Severn 
  must 
  have 
  been 
  in 
  connection 
  

   with 
  that 
  of 
  the 
  Dee 
  and 
  Weaver, 
  and 
  Wales 
  have 
  been 
  completely 
  

   separated 
  from 
  England 
  by 
  the 
  strait 
  thus 
  constituted, 
  for 
  some 
  time 
  

  

  * 
  See 
  the 
  note 
  engraved 
  on 
  the 
  Geological-Survey 
  sheet 
  No. 
  34, 
  7 
  miles 
  S.S.W. 
  

   of 
  Cirencester. 
  The 
  flint-gravel 
  3^ 
  miles 
  east 
  of 
  this, 
  described 
  by 
  Lucy, 
  loc. 
  cit. 
  

   p. 
  35, 
  and 
  which 
  he 
  says 
  contains 
  mammalian 
  remains, 
  probably 
  represents 
  the 
  

   time 
  just 
  after 
  the 
  parting 
  had 
  emerged, 
  and 
  the 
  Swill 
  and 
  Minety 
  brooks 
  had 
  

   become 
  small 
  rivers 
  opening 
  into 
  the 
  estuary 
  of 
  the 
  Thames 
  and 
  Isis 
  ; 
  for 
  that 
  

   gravel 
  is 
  not 
  on 
  the 
  parting, 
  but 
  in 
  the 
  flat 
  valley 
  where 
  these 
  brooks 
  enter 
  the 
  

   Isis, 
  and 
  the 
  flint 
  of 
  which 
  it 
  is 
  composed 
  was 
  probably 
  derived 
  from 
  the 
  gravel 
  

   on 
  the 
  parting. 
  

  

  t 
  Quart. 
  Jo 
  urn. 
  Geol.Soe. 
  vol.xxxvii.p. 
  361. 
  Mr. 
  Mackintosh 
  states 
  that 
  gravel 
  

   as 
  much 
  rounded 
  as 
  that 
  in 
  which 
  shells 
  occurred 
  extends 
  up 
  to 
  1550 
  feet 
  

   (p. 
  368) 
  ; 
  but 
  I 
  do 
  not 
  at 
  present 
  see 
  sufficient 
  reason 
  for 
  thinking 
  thajt 
  the 
  sub- 
  

   mergence 
  reached 
  that 
  height. 
  

  

  

  