﻿PLTOCENE 
  PERIOD 
  IN 
  ENGLAND. 
  693 
  

  

  the 
  Cymia-formation 
  at 
  Grays 
  in 
  figs. 
  XXI. 
  and 
  XXII.* 
  In 
  

   this 
  connexion, 
  too, 
  the 
  generally 
  received 
  theory 
  of 
  the 
  cutting 
  

   down 
  of 
  valleys 
  by 
  the 
  rivers, 
  which 
  has 
  been 
  adopted 
  to 
  reconcile 
  

   the 
  evidences 
  of 
  the 
  former 
  width 
  over 
  which 
  a 
  river 
  extended 
  with 
  

   the 
  physical 
  difficulty 
  involved 
  in 
  the 
  presence 
  of 
  so 
  large 
  a 
  volume 
  

   of 
  fresh 
  water 
  in 
  the 
  valley, 
  as 
  these 
  evidences 
  would 
  otherwise 
  

   point 
  to, 
  should 
  be 
  dismissed 
  from 
  the 
  mind 
  ; 
  for 
  we 
  have 
  clear 
  

   evidence 
  that, 
  so 
  far 
  from 
  these 
  evidences 
  in 
  the 
  Thames 
  and 
  East- 
  

   Essex 
  valleys 
  being 
  connected 
  with 
  a 
  lowering 
  of 
  the 
  valley 
  by 
  

   river-excavation 
  accompanying 
  an 
  elevation 
  of 
  the 
  land, 
  they 
  are 
  

   connected 
  with 
  a 
  rise 
  of 
  the 
  river-level 
  due 
  to 
  a 
  general 
  depression 
  

   of 
  the 
  land 
  and 
  consequent 
  rise 
  of 
  the 
  sea-level. 
  

  

  From 
  the 
  same 
  cause 
  the 
  Wash 
  rivers, 
  Cam, 
  Great 
  Ouse, 
  Nen, 
  and 
  

   Welland, 
  when, 
  after 
  the 
  draining-off 
  of 
  the 
  great 
  volume 
  of 
  water 
  

   caused 
  by 
  their 
  being 
  dammed 
  up 
  by 
  the 
  ice, 
  these 
  rivers 
  came 
  into 
  

   existence, 
  had 
  a 
  flatter 
  fall, 
  and 
  mingled 
  with 
  the 
  sea 
  beyond 
  our 
  

   present 
  shore 
  : 
  the 
  sea-level 
  on 
  the 
  east 
  side 
  of 
  England 
  being 
  at 
  

   this 
  time 
  below 
  the 
  present. 
  

  

  The 
  channel 
  and 
  deposit 
  of 
  the 
  Thames 
  before 
  this 
  resubmergence 
  

   occurred 
  is 
  shown 
  by 
  the 
  bed 
  of 
  gravel 
  (No. 
  1 
  of 
  <f) 
  at 
  Grays, 
  

   which 
  is 
  confined 
  to 
  the 
  bottom 
  of 
  the 
  river-channel 
  which 
  occupied 
  

   the 
  site 
  of 
  the 
  Grays 
  brickfields 
  at 
  the 
  commencement 
  of 
  the 
  stage 
  

   under 
  consideration 
  (see 
  figs. 
  XXI. 
  & 
  XXII.); 
  and 
  its 
  dimensions, 
  

   even 
  when 
  we 
  allow 
  for 
  the 
  greater 
  distance 
  of 
  the 
  sea 
  than 
  now, 
  are 
  

   small. 
  This 
  river-channel 
  became 
  enlarged 
  by 
  the 
  depression 
  pre- 
  

   sently 
  traced, 
  so 
  that 
  the 
  beds 
  of 
  the 
  Ctyrenft-formation 
  there 
  which 
  

   succeeded 
  it, 
  and 
  are 
  numbered 
  2, 
  3, 
  and 
  4 
  in 
  the 
  figures, 
  are 
  

   mutually 
  transgressive. 
  At 
  Grays 
  there 
  is 
  a 
  shelf 
  of 
  chalk 
  between 
  

   this 
  original 
  channel 
  and 
  the 
  present 
  river, 
  so 
  that 
  the 
  channel 
  of 
  

   the 
  Cyrena-stage 
  was 
  different 
  from 
  that 
  at 
  present, 
  and 
  also 
  from 
  

   that 
  which 
  existed 
  during 
  the 
  gravel 
  g, 
  which, 
  so 
  far 
  as 
  can 
  be 
  seen, 
  

   appears 
  to 
  have 
  coincided 
  in 
  the 
  main 
  with 
  that 
  of 
  the 
  present 
  river, 
  

   though 
  in 
  a 
  more 
  expanded 
  state. 
  The 
  position 
  of 
  the 
  original 
  

   river-channel, 
  I 
  cannot 
  doubt, 
  was 
  shifted 
  by 
  the 
  disturbances 
  sub- 
  

   sequent 
  to 
  the 
  Ctymia-formation 
  presently 
  examined. 
  The 
  lines 
  

   of 
  figs. 
  XXI. 
  and 
  XXII. 
  show 
  the 
  position 
  of 
  the 
  #?/mw-formation 
  

   relatively 
  to 
  the 
  rivers 
  Thames 
  and 
  Darent, 
  as 
  well 
  as 
  to 
  the 
  gravel 
  

   (g) 
  described 
  in 
  Stage 
  VII. 
  

  

  Before 
  tracing 
  the 
  distribution 
  of 
  this 
  formation 
  I 
  may 
  observe 
  that, 
  

   as 
  has 
  been 
  long 
  known, 
  the 
  freshwater 
  parts 
  of 
  it 
  have 
  yielded 
  the 
  re- 
  

   mains 
  of 
  a 
  fauna, 
  both 
  mammalian 
  and 
  molluscan, 
  that 
  indicates 
  a 
  

   climate 
  different 
  from 
  that 
  which 
  must 
  have 
  prevailed 
  when 
  the 
  

   gravel 
  g 
  and 
  the 
  accumulations 
  of 
  most 
  of 
  the 
  caverns 
  were 
  formed. 
  

  

  * 
  I 
  have 
  taken 
  the 
  position 
  of 
  this 
  bottom 
  from 
  the 
  section 
  of 
  Mr. 
  Tylor 
  in 
  

   vol. 
  xxv. 
  of 
  the 
  Journal, 
  which 
  in 
  that 
  respect 
  agrees 
  with 
  my 
  own 
  observa- 
  

   tions 
  ; 
  but, 
  so 
  far 
  as 
  the 
  gravels 
  / 
  aadg 
  of 
  these 
  figures 
  are 
  concerned, 
  my 
  sections 
  

   differ 
  from 
  his, 
  that 
  gentleman 
  showing 
  them 
  as 
  one, 
  and 
  (so 
  far 
  as 
  I 
  can 
  follow 
  

   his 
  section) 
  as 
  wrapping 
  the 
  Cyrena-foxmation. 
  

  

  I 
  cannot, 
  however, 
  make 
  out 
  what 
  Mr. 
  Tylor 
  intends 
  to 
  represent 
  by 
  what 
  he 
  

   terms 
  "the 
  covering 
  bed 
  " 
  or 
  " 
  covering 
  gravel," 
  unless 
  it 
  be 
  the 
  bed* 
  y 
  of 
  this 
  

   memoir. 
  

  

  