﻿PLIOCENE 
  PEKIOD 
  IN 
  ENGLAND. 
  079 
  

  

  Clay 
  " 
  under 
  it, 
  in 
  it, 
  and 
  on 
  it." 
  The 
  gravel 
  thus 
  having 
  " 
  the 
  clay 
  

   under 
  it 
  " 
  corresponds 
  to 
  that 
  which 
  is 
  shown 
  under 
  the 
  letter 
  e 
  in 
  

   fig. 
  VII., 
  and 
  owes 
  such 
  position 
  to 
  the 
  ice 
  in 
  the 
  channel 
  having 
  

   wholly 
  cut 
  out 
  c 
  of 
  this 
  memoir, 
  and 
  laid 
  down 
  the 
  morainic 
  clay 
  d 
  in 
  

   its 
  place. 
  This, 
  from 
  its 
  having 
  been 
  below 
  the 
  sea-level, 
  on 
  the 
  

   retreat 
  of 
  the 
  ice 
  in 
  the 
  channel 
  was 
  overflowed 
  by 
  the 
  sea, 
  and 
  

   so 
  received 
  a 
  deposit 
  of 
  gravel 
  (e) 
  upon 
  it. 
  The 
  gravel 
  with 
  " 
  the 
  

   clay 
  in 
  it 
  " 
  is 
  that 
  where 
  this 
  cutting-out 
  of 
  c 
  has 
  been 
  only 
  partial, 
  

   so 
  that, 
  while 
  the 
  morainic 
  clay 
  received 
  e 
  in 
  the 
  same 
  way 
  upon 
  it, 
  

   it 
  nevertheless 
  rested 
  upon 
  a 
  part 
  ofc; 
  while 
  the 
  gravel 
  "with 
  the 
  

   clay 
  on 
  it 
  " 
  is 
  the 
  normal 
  condition, 
  i. 
  e. 
  c. 
  In 
  the 
  part 
  of 
  the 
  Lea 
  

   channel 
  which 
  is 
  crossed 
  by 
  fig. 
  XXXIX. 
  the 
  ice 
  has 
  laid 
  its 
  mo- 
  

   raine 
  of 
  Chalky 
  Clay 
  (d) 
  on 
  the 
  islands 
  on 
  either 
  side 
  of 
  the 
  channel, 
  

   but 
  not 
  in 
  the 
  channel 
  itself; 
  so 
  that 
  the 
  gravel/, 
  which 
  -was 
  deposited 
  

   by 
  the 
  sea 
  after 
  the 
  retreat 
  of 
  the 
  ice, 
  lies 
  at 
  a 
  lower 
  level 
  than 
  any 
  

   part 
  of 
  the 
  moraine 
  here. 
  Where 
  this 
  morainic 
  clay 
  rests 
  on 
  the 
  

   gravel 
  c 
  about 
  Finchley 
  (nine 
  miles 
  south-west 
  of 
  fig. 
  XXXIX), 
  

   it 
  is 
  at 
  an 
  elevation 
  of 
  about 
  300 
  feet, 
  and 
  must, 
  as 
  in 
  the 
  case 
  of 
  

   the 
  islands 
  at 
  either 
  end 
  of 
  Prof. 
  Hughes's 
  section, 
  have 
  been 
  so 
  laid 
  

   terrestrially* 
  ; 
  for 
  as 
  this 
  is 
  at 
  least 
  100 
  feet 
  above 
  the 
  elevation 
  at 
  

   which 
  the 
  general 
  evidence 
  indicates 
  the 
  sea 
  having 
  stood 
  in 
  the 
  

   west 
  of 
  Sheet 
  1, 
  and 
  east 
  of 
  Sheet 
  2, 
  when 
  the 
  ice 
  retreated 
  from 
  

   there, 
  it 
  must 
  have 
  emerged 
  before 
  the 
  ice 
  reached 
  it, 
  being 
  at 
  the 
  

   extreme 
  southern 
  limit 
  to 
  which 
  the 
  Chalky 
  Clay 
  extends. 
  In 
  other 
  

   places 
  where, 
  in 
  thus 
  previously 
  emerging 
  (as 
  e. 
  g. 
  in 
  fig. 
  XXXIX., 
  

   and 
  one 
  part 
  of 
  Prof. 
  Hughes's 
  section), 
  the 
  earlier 
  part 
  of 
  c 
  was 
  

   previously 
  washed 
  off, 
  the 
  morainic 
  clay 
  has 
  been 
  laid 
  down 
  terres- 
  

   trially 
  on 
  the 
  Eocene 
  or 
  Chalk. 
  The 
  gravel 
  of 
  the 
  higher 
  plain 
  is. 
  

   as 
  Prof. 
  Hughes 
  says, 
  marked 
  by 
  the 
  greater 
  abundance 
  of 
  quartz 
  and 
  

   quartzite 
  pebbles. 
  This 
  shows 
  its 
  affinity 
  to 
  the 
  gravel 
  of 
  greatest 
  

   submergence, 
  which, 
  in 
  the 
  westward 
  direction 
  especially, 
  is 
  con- 
  

   spicuous 
  for 
  the 
  abundance 
  in 
  it 
  of 
  those 
  pebbles 
  ; 
  while 
  the 
  gravel 
  

   of 
  the 
  lower 
  plain 
  is 
  conspicuous 
  by 
  the 
  abundance 
  in 
  it 
  of 
  the 
  

   debris 
  of 
  the 
  moraine 
  carried 
  into 
  the 
  channels 
  by 
  the 
  approaching 
  

   ice, 
  the 
  gravel 
  on 
  the 
  islands 
  (i. 
  e. 
  that 
  of 
  the 
  higher 
  plain) 
  having 
  

   emerged 
  before 
  the 
  ice 
  approached 
  near 
  enough 
  thus 
  to 
  change 
  the 
  

   character 
  of 
  its 
  constituent 
  material. 
  

  

  In 
  the 
  first 
  part 
  of 
  this 
  memoir 
  I 
  observed 
  that, 
  since 
  the 
  water- 
  

   parting 
  between 
  the 
  drainage 
  systems 
  of 
  the 
  Thames 
  and 
  Severn 
  by 
  

   way 
  of 
  the 
  Swill 
  brook 
  (a 
  tributary 
  of 
  the 
  Isis 
  in 
  Sheet 
  34) 
  and 
  the 
  

   Avon 
  of 
  Wilts 
  and 
  Somerset 
  is 
  about 
  150 
  feet 
  lower 
  than 
  that 
  by 
  

   way 
  of 
  the 
  Even 
  lode 
  and 
  Stour 
  in 
  Sheet 
  44 
  (over 
  which 
  the 
  red 
  

   chalk 
  carried 
  out 
  into 
  the 
  Severn 
  system 
  had 
  come 
  round 
  into 
  the 
  

   upper 
  part 
  of 
  the 
  Evenlode 
  valley), 
  it 
  must, 
  even 
  after 
  allowing 
  for 
  

   some 
  diminution 
  in 
  the 
  degree 
  of 
  submergence 
  in 
  that 
  direction, 
  have 
  

   emerged 
  later 
  ; 
  and 
  until 
  this 
  took 
  place 
  the 
  systems 
  of 
  the 
  Thames 
  

   and 
  Severn 
  must 
  have 
  been 
  connected 
  by 
  sea, 
  but 
  gradually 
  narrowing 
  

   from 
  the 
  broad 
  open 
  strait 
  shown 
  in 
  Map 
  2 
  (in 
  first 
  part 
  of 
  memoir) 
  

   until 
  the 
  valley 
  of 
  the 
  Swill 
  brook 
  became 
  part 
  of 
  a 
  narrow 
  strait 
  con- 
  

   * 
  See 
  note 
  to 
  explanation 
  of 
  maps 
  and 
  figures 
  at 
  end 
  of 
  memoir. 
  

  

  