﻿740 
  SEAKLES 
  V. 
  WOOD 
  OX 
  THE 
  XEWEK 
  

  

  this 
  chalky 
  grit 
  to 
  a 
  greater 
  thickness 
  even 
  than 
  I 
  have 
  represented 
  

   in 
  fig. 
  I., 
  all 
  of 
  which, 
  towards 
  the 
  centre 
  of 
  the 
  valley, 
  was, 
  after 
  it 
  

   had 
  laid 
  the 
  Chalky 
  Clay 
  (d) 
  on 
  this 
  gravel 
  and 
  grit, 
  ploughed 
  out 
  

   by 
  the 
  ice 
  as 
  it 
  shrank 
  into 
  or 
  thickened 
  in 
  that 
  valley 
  as 
  emergence 
  

   proceeded. 
  

  

  This 
  chalk-grit 
  evidently 
  corresponds 
  to 
  the 
  band 
  of 
  marl 
  overlying 
  

   the 
  gravel 
  c 
  shown 
  in 
  fig. 
  X 
  A 
  ., 
  and 
  described 
  at 
  p. 
  488 
  of 
  the 
  first 
  

   part 
  of 
  this 
  memoir 
  ; 
  and 
  was 
  produced 
  by 
  the 
  washing 
  out 
  of 
  the 
  

   Chalky-Clay 
  mud-bank 
  by 
  the 
  ice-water 
  immediately 
  before 
  this 
  bank 
  

   was 
  precipitated 
  into 
  the 
  sea 
  along 
  the 
  shore. 
  

  

  I 
  have 
  also, 
  since 
  the 
  publication 
  of 
  the 
  first 
  part, 
  been 
  fortunate 
  

   in 
  discovering 
  a 
  section 
  disclosing 
  distinctly 
  the 
  behaviour 
  of 
  the 
  

   brickearth, 
  b 
  J, 
  to 
  the 
  sand 
  b 
  1 
  in 
  East 
  Suffolk. 
  This 
  is 
  at 
  Tudden- 
  

   harn, 
  three 
  miles 
  X.E. 
  of 
  Ipswich 
  ; 
  and 
  there 
  a 
  denuded 
  remnant 
  of 
  

   the 
  lower 
  part 
  of 
  this 
  brickearth, 
  about 
  8 
  feet 
  thick, 
  overlain 
  by 
  the 
  

   gravel 
  c 
  (just 
  as 
  it 
  is 
  shown 
  overlain 
  along 
  its 
  denuded 
  edge 
  by 
  this 
  

   gravel 
  in 
  fig. 
  I.), 
  passes 
  by 
  alternate 
  seams 
  of 
  brickearth 
  and 
  sand 
  

   into 
  the 
  sand 
  b 
  1, 
  which 
  underlies 
  it 
  in 
  a 
  thickness 
  of 
  about 
  15 
  feet, 
  

   and 
  rests 
  on 
  the 
  London 
  Clay, 
  the 
  Crag 
  having 
  either 
  never 
  

   existed 
  there 
  or 
  been 
  entirely 
  removed. 
  With 
  the 
  light 
  thus 
  

   thrown 
  upon 
  the 
  subject, 
  I 
  infer 
  that 
  the 
  break 
  in 
  the 
  great 
  sub- 
  

   sidence, 
  which 
  in 
  the 
  first 
  part 
  of 
  this 
  memoir 
  I 
  thought 
  might 
  be 
  

   indicated 
  by 
  the 
  unconformity 
  between 
  the 
  black 
  sandy 
  Till 
  at 
  

   Hasboro' 
  and 
  Bacton 
  cliffs 
  and 
  the 
  overlying 
  stratified 
  silt 
  and 
  clay, 
  

   did 
  not 
  take 
  place 
  ; 
  and 
  that 
  the 
  apparent 
  unconformity 
  must 
  arise 
  

   from 
  this 
  sandy 
  Till, 
  which 
  is 
  but 
  very 
  obscurely 
  stratified, 
  is 
  nearly 
  

   destitute 
  of 
  chalk 
  (while 
  the 
  stratified 
  silt 
  and 
  clay 
  is 
  full 
  of 
  it), 
  and 
  

   contains 
  fragments 
  and 
  worn 
  valves 
  of 
  the 
  commoner 
  shells 
  of 
  the 
  

   sand 
  hi. 
  being 
  a 
  rnorainic 
  reconstruction 
  of 
  those 
  sands 
  by 
  the 
  first 
  

   ice 
  which 
  reached 
  Norfolk, 
  soon 
  after 
  the 
  commencement 
  of 
  the 
  great 
  

   depression 
  submerged 
  this 
  shore 
  of 
  the 
  Crag 
  estuary, 
  and 
  which 
  pro- 
  

   bably 
  came 
  from 
  a 
  more 
  northerly 
  direction 
  than 
  that 
  which 
  gave 
  

   rise 
  to 
  the 
  main 
  mass 
  of 
  the 
  Cromer 
  Till, 
  which, 
  unlike 
  this 
  sandy 
  

   Till, 
  is 
  full 
  of 
  chalk-debris. 
  As 
  this 
  ice 
  by 
  its 
  retreat 
  before 
  

   increasing 
  submergence 
  uncovered 
  its 
  moraine, 
  the 
  sea 
  wore 
  those 
  

   hollows 
  in 
  its 
  surface 
  in 
  which 
  sands 
  are 
  bedded, 
  and 
  the 
  whole 
  then 
  

   became 
  covered 
  by 
  the 
  horizontal 
  and 
  highly 
  stratified 
  mud 
  full 
  of 
  

   chalk-debris 
  and 
  chalk-silt 
  which 
  spreads 
  evenly 
  over 
  this 
  uncon- 
  

   formable 
  surface, 
  and 
  probably 
  was 
  supplied 
  by 
  currents 
  from 
  the 
  

   ice 
  issuing 
  through 
  the 
  Humber, 
  of 
  which 
  the 
  clay 
  B 
  is 
  the 
  moraine. 
  

  

  The 
  shingly 
  sands, 
  bl, 
  at 
  Southwold, 
  immediately 
  beneath 
  the 
  

   moraine 
  at 
  the 
  north 
  end 
  of 
  the 
  cliff, 
  described 
  a 
  few 
  pages 
  back, 
  

   contain 
  a 
  seam 
  of 
  broken 
  shells, 
  which 
  was 
  also 
  exposed 
  in 
  the 
  

   railway-cutting 
  a 
  mile 
  or 
  so 
  inland. 
  

  

  The 
  species 
  are 
  exclusively 
  those 
  of 
  the 
  fluvio-marine 
  Crag, 
  and 
  

   were, 
  I 
  consider, 
  derived 
  from 
  it 
  when, 
  at 
  the 
  commencement 
  of 
  the 
  

   formation 
  of 
  these 
  sands, 
  that 
  Crag 
  and 
  the 
  Chillesford 
  Clay 
  formed 
  

   islands, 
  and 
  when 
  in 
  the 
  channels 
  around 
  these 
  islands 
  those 
  sands 
  

   were 
  first 
  bedded. 
  No 
  trace 
  of 
  the 
  characteristic 
  shell 
  of 
  the 
  lower 
  

   part 
  of 
  those 
  sands 
  in 
  Norfolk, 
  Tellina 
  balthica, 
  could 
  be 
  detected 
  in 
  

  

  