﻿IN 
  THE 
  CONTORTED 
  DRIFT 
  OF 
  CROMEB. 
  233 
  

  

  quietly 
  deposited 
  in 
  water. 
  That 
  a 
  mass 
  of 
  this 
  shape 
  and 
  form 
  

   could 
  be 
  pushed 
  up, 
  enveloped 
  in 
  drift, 
  by 
  a 
  Scandinavian 
  or 
  any 
  

   other 
  ice-sheet, 
  and 
  preserve 
  its 
  continuity 
  undisturbed, 
  appears 
  

   to 
  me 
  to 
  be 
  all 
  but 
  inconceivable. 
  If, 
  then, 
  these 
  masses 
  were 
  

   detached 
  from 
  cliffs 
  (which, 
  as 
  I 
  have 
  shown, 
  their 
  form 
  and 
  the 
  

   nature 
  of 
  the 
  rock 
  of 
  which 
  they 
  are 
  composed 
  would 
  indicate), 
  and 
  if 
  

   they 
  have 
  been 
  floated 
  to 
  their 
  present 
  position, 
  it 
  follows 
  that 
  the 
  

   depth 
  of 
  water 
  in 
  which 
  they 
  were 
  rafted 
  off 
  cannot 
  have 
  been 
  

   very 
  great. 
  The 
  highest 
  point 
  of 
  the 
  Chalk 
  in 
  Norfolk 
  is 
  650 
  feet*. 
  

   The 
  highest 
  point 
  from 
  which 
  the 
  Marlstone 
  Eock-bed 
  masses 
  can 
  

   have 
  been 
  derived 
  is 
  from 
  700 
  to 
  800 
  feet. 
  

  

  The 
  extreme 
  limit 
  of 
  depth 
  of 
  water 
  could 
  therefore, 
  when 
  the 
  

   last 
  of 
  these 
  masses 
  were 
  quarried, 
  not 
  exceed 
  600 
  feet 
  above 
  the 
  

   present 
  sea-level. 
  But 
  we 
  must 
  not 
  lose 
  sight 
  of 
  the 
  fact 
  that 
  from 
  

   the 
  sea-level 
  the 
  Chalk 
  has 
  a 
  pretty 
  gradual 
  slope 
  upwards 
  from 
  east 
  

   to 
  west 
  ; 
  therefore 
  as 
  the 
  land 
  subsided 
  the 
  inshore 
  waters 
  would 
  in 
  

   all 
  cases 
  shallow 
  towards 
  the 
  cliff. 
  

  

  It 
  really 
  then 
  resolves 
  itself 
  into 
  a 
  question 
  of 
  " 
  launching 
  ;" 
  and 
  

   when 
  we 
  are 
  confronted 
  with 
  the 
  fact 
  that 
  a 
  mass 
  of 
  solid 
  chalk 
  

   in 
  some 
  cases 
  as 
  big 
  as 
  the 
  Great 
  Eastern 
  has 
  to 
  be 
  quarried 
  out 
  of 
  

   the 
  natural 
  bed 
  and 
  quietly 
  deposited 
  with 
  little 
  derangement 
  at 
  the 
  

   bottom 
  of 
  the 
  sea 
  or 
  on 
  the 
  nearest 
  submarine 
  bank, 
  it 
  forms 
  a 
  

   problem 
  for 
  solution 
  in 
  geological 
  engineering 
  of 
  a 
  very 
  interesting 
  

   nature. 
  

  

  It 
  is 
  easy 
  to 
  see, 
  in 
  the 
  case 
  of 
  strata 
  like 
  the 
  Marlstone 
  Eock-bed 
  

   resting 
  upon 
  strata 
  of 
  a 
  different 
  nature, 
  that 
  ordinary 
  landslips 
  would 
  

   detach 
  masses 
  from 
  the 
  parent 
  rock, 
  which 
  might 
  afterwards 
  be 
  

   conveyed 
  by 
  ice 
  to 
  a 
  distance. 
  But 
  with 
  regard 
  to 
  the 
  Chalk 
  the 
  

   case 
  is 
  rather 
  different. 
  The 
  masses 
  in 
  the 
  Norfolk 
  Drift 
  appear 
  to 
  

   be 
  homogeneous; 
  so 
  that 
  an 
  ordinary 
  landslip 
  hardly 
  meets 
  the 
  case. 
  

   We 
  know, 
  however, 
  that 
  the 
  Chalk 
  is 
  full 
  of 
  potholes 
  and 
  fissures 
  ; 
  

   and 
  any 
  crack 
  that 
  opened 
  in 
  the 
  top 
  of 
  a 
  cliff 
  might 
  be 
  opened 
  further 
  

   by 
  intrusive 
  ice. 
  Until 
  last 
  winter 
  I 
  never 
  realized 
  the 
  fact 
  that 
  

   ice 
  could 
  be 
  intrusive 
  ; 
  but 
  then 
  I 
  observed, 
  and 
  described 
  in 
  a 
  letter 
  

   to 
  'Nature,' 
  how 
  water 
  held 
  up 
  in 
  the 
  sandhills 
  and 
  percolating 
  

   therefrom 
  could 
  insinuate 
  itself 
  into 
  hard 
  peat 
  in 
  the 
  form 
  of 
  ice, 
  and 
  

   split 
  it 
  off 
  in 
  great 
  sheets, 
  one 
  of 
  these 
  I 
  measured 
  being 
  16 
  feet 
  

   long, 
  8 
  feet 
  wide, 
  and 
  8 
  inches 
  thick, 
  as 
  flat 
  as 
  a 
  flagstone, 
  and 
  

   containing 
  a 
  wedge 
  of 
  ice 
  throughout 
  its 
  whole 
  superficial 
  extent. 
  

   In 
  a 
  similar 
  manner 
  I 
  conceive 
  the 
  water 
  held 
  up 
  in 
  the 
  porous 
  chalk 
  

   would 
  insinuate 
  itself 
  into 
  any 
  latent 
  fissure 
  or 
  line 
  of 
  weakness 
  or 
  

   joint, 
  and, 
  gradually 
  increasing 
  by 
  percolation 
  and 
  by 
  water 
  from 
  

   melting 
  snow, 
  force 
  out 
  and 
  detach 
  masses 
  of 
  enormous 
  proportions 
  ; 
  

   also 
  such 
  streams 
  of 
  water 
  issuing 
  from 
  the 
  chalk 
  might 
  freeze 
  

   into 
  accumulated 
  masses 
  of 
  ice 
  about 
  the 
  detached 
  rock. 
  Pack 
  ice 
  

   driven 
  onto 
  the 
  shore 
  and 
  piled 
  up 
  over 
  and 
  around 
  it, 
  and 
  then 
  in 
  

   winter 
  frozen 
  into 
  a 
  sheet 
  or 
  ice-foot, 
  might 
  assist 
  the 
  accumulation 
  

   until 
  a 
  raft 
  were 
  formed 
  sufficient 
  to 
  float 
  off 
  boulders 
  of 
  the 
  largest 
  

  

  ■s 
  v 
  

  

  * 
  Penning, 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxxii. 
  p. 
  191. 
  

  

  *2 
  

  

  