﻿236 
  T. 
  M. 
  READE 
  ON 
  THE 
  CHALK-MASSES 
  

  

  beds 
  of 
  yielding 
  mud, 
  clay, 
  sand, 
  and 
  gravel. 
  If 
  such 
  ice-masses 
  

   with 
  their 
  burdens 
  sank 
  into 
  yielding 
  mud 
  vertically, 
  or 
  were 
  driven 
  

   into 
  it 
  by 
  lateral 
  pressure, 
  the 
  melting 
  of 
  the 
  ice 
  encircling 
  the 
  

   boulder 
  might 
  account 
  also 
  for 
  some 
  of 
  the 
  contortions 
  of 
  the 
  sur- 
  

   rounding 
  beds. 
  I 
  have 
  shown 
  that 
  the 
  drift 
  frequently 
  has 
  an 
  

   apparent 
  stratification 
  concentric 
  with 
  the 
  surface 
  of 
  the 
  boulder, 
  

   and 
  not 
  only 
  encircling, 
  but 
  frequently 
  penetrating 
  it. 
  

  

  The 
  enclosing 
  matrix 
  of 
  ice 
  as 
  it 
  gradually 
  melted 
  would 
  be 
  me- 
  

   chanically 
  replaced 
  by 
  particles 
  of 
  the 
  surrounding 
  drift; 
  and 
  in 
  

   this 
  way 
  it 
  is 
  quite 
  likely 
  that 
  the 
  concentric 
  foldings 
  of 
  the 
  drift 
  

   around 
  the 
  boulder 
  were 
  induced. 
  It 
  is 
  also 
  not 
  unlikely 
  that, 
  if 
  

   the 
  chalk-mass 
  were 
  fissured 
  ever 
  so 
  slightly 
  by 
  the 
  fall 
  or 
  deposition 
  

   on 
  an 
  uneven 
  bed, 
  percolation 
  of 
  water 
  would, 
  while 
  removing 
  the 
  

   chalk 
  in 
  the 
  walls 
  of 
  the 
  fissure, 
  introduce 
  at 
  the 
  same 
  time 
  fine 
  

   particles 
  of 
  drift, 
  and 
  so 
  produce 
  that 
  remarkable 
  interpenetration 
  of 
  

   the 
  chalk 
  with 
  laminated 
  drift 
  we 
  so 
  frequently 
  see, 
  as 
  well 
  as 
  

   assist 
  to 
  produce 
  in 
  these 
  separated 
  masses 
  rounded 
  contours 
  (see 
  

   fig. 
  8, 
  A, 
  B, 
  I), 
  E). 
  

  

  If 
  the 
  boulder 
  was 
  formed 
  and 
  conveyed 
  as 
  I 
  suggest, 
  the 
  chalk, 
  

   no 
  doubt, 
  at 
  the 
  time 
  would 
  be 
  frozen 
  hard 
  through 
  its 
  entire 
  

   substance. 
  The 
  gradual 
  thawing 
  of 
  it 
  would, 
  I 
  surmise, 
  while 
  pro- 
  

   ducing 
  a 
  sort 
  of 
  disintegration 
  of 
  the 
  particles, 
  render 
  it, 
  under 
  the 
  

   pressure 
  and 
  weight 
  of 
  drift 
  abovo, 
  partially 
  plastic. 
  In 
  this 
  way 
  

   we 
  may 
  account 
  for 
  the 
  bending 
  of 
  the 
  larger 
  masses 
  without 
  

   fracture, 
  as 
  is 
  often 
  shown 
  by 
  the 
  wavy 
  line 
  of 
  flints 
  they 
  contain. 
  

  

  It 
  was 
  my 
  good 
  fortune 
  to 
  see 
  a 
  mass 
  of 
  chalk 
  capped 
  with 
  drift 
  

   that 
  had 
  slipped 
  down 
  onto 
  the 
  shore. 
  Though 
  shattered, 
  it 
  pre- 
  

   served 
  its 
  form 
  ; 
  and 
  I 
  could 
  quite 
  believe 
  that 
  under 
  favourable 
  cir- 
  

   cumstances 
  it 
  might 
  again 
  be 
  consolidated 
  into 
  firm 
  chalk. 
  But 
  some 
  

   of 
  these 
  masses, 
  notably 
  the 
  one 
  shown 
  in 
  fig. 
  9, 
  are 
  of 
  such 
  extreme 
  

   tenuity 
  that 
  the 
  only 
  feasible 
  explanation 
  of 
  their 
  preservation 
  intact 
  

   appears 
  to 
  be 
  this 
  : 
  — 
  that, 
  after 
  deposition, 
  the 
  mass 
  has 
  been 
  exposed 
  

   on 
  the 
  upper 
  surface 
  to 
  the 
  action 
  of 
  the 
  sea, 
  which 
  has 
  thinned 
  it, 
  

   or 
  dressed 
  it 
  off, 
  into 
  the 
  shape 
  we 
  see, 
  before 
  the 
  drift 
  above 
  was 
  

   deposited 
  upon 
  it. 
  The 
  same 
  figure 
  seems 
  to 
  point 
  to 
  this 
  conclusion 
  ; 
  

   for 
  underneath 
  is 
  a 
  bed 
  of 
  closely 
  packed 
  shell-fragments, 
  and 
  above, 
  

   on 
  nearly 
  the 
  same 
  slope, 
  another. 
  I 
  can 
  see 
  no 
  escape 
  from 
  the 
  

   conclusion 
  that 
  the 
  upper 
  shell 
  bed 
  was 
  deposited 
  in 
  this 
  manner. 
  

   The 
  underlying 
  one 
  may 
  have 
  been 
  disturbed 
  by 
  the 
  deposition 
  of 
  

   the 
  boulder, 
  and 
  so 
  pushed 
  up 
  from 
  an 
  originally 
  more 
  level 
  plane 
  ; 
  

   and 
  the 
  contortions 
  of 
  the 
  sand 
  underneath 
  would 
  seem 
  to 
  point 
  to 
  

   this 
  disturbance 
  having 
  taken 
  place. 
  

  

  My 
  conclusions 
  may 
  therefore 
  be 
  summed 
  up 
  in 
  this 
  way 
  : 
  — 
  ■ 
  

  

  That 
  the 
  travelled 
  masses 
  were 
  derived 
  from 
  sea- 
  cliffs 
  ; 
  they 
  were 
  

   landslips 
  aided 
  by 
  the 
  penetration 
  of 
  water 
  forming 
  ice 
  intrusive, 
  in 
  

   fissures, 
  which 
  forced 
  and 
  quarried 
  them 
  from 
  the 
  parent 
  rocks. 
  

  

  That 
  water 
  issuing 
  from 
  subterranean 
  sources 
  accumulated 
  in 
  ice 
  

   round 
  the 
  fallen 
  masses, 
  and 
  then 
  was 
  united 
  and 
  frozen 
  into 
  the 
  

   shore-ice. 
  

  

  That 
  ice-floes 
  driven 
  onto 
  this 
  mass 
  would 
  often 
  get 
  frozen 
  into 
  

  

  