﻿218 
  MR. 
  W. 
  P. 
  D. 
  STEBBING 
  ON 
  TWO 
  BOULDERS 
  OF 
  [May 
  1 
  897, 
  

  

  The 
  existence 
  of 
  these 
  extraneous 
  fragments 
  suggests 
  some 
  

   interesting 
  questions. 
  We 
  should 
  like 
  to 
  know 
  from 
  what 
  special 
  

   localities, 
  and 
  by 
  what 
  controlling 
  agencies, 
  such 
  foreign 
  substances 
  

   came 
  into 
  their 
  present 
  positions, 
  though 
  I 
  have 
  no 
  doubt 
  that 
  over 
  

   and 
  beyond 
  these 
  a 
  multitude 
  of 
  other 
  questions 
  might 
  be 
  raised. 
  

  

  With 
  respect 
  to 
  the 
  various 
  theories 
  that 
  have 
  been 
  mentioned, 
  

   so 
  far 
  as 
  I 
  may 
  venture 
  to 
  offer 
  an 
  opinion, 
  the 
  agency 
  of 
  berg-ice 
  

   does 
  not 
  appear 
  likely 
  to 
  have 
  come 
  into 
  play 
  in 
  the 
  movement 
  of 
  

   boulders 
  such 
  as 
  those 
  from 
  Betchworth. 
  

  

  Coast-ice 
  appears 
  to 
  have 
  been 
  the 
  probable 
  medium 
  of 
  con- 
  

   veyance. 
  The 
  same 
  explanation 
  is 
  applicable 
  to 
  such 
  a 
  case 
  as 
  that 
  

   of 
  the 
  Purley 
  boulder, 
  where 
  there 
  was 
  a 
  mass 
  of 
  stones 
  of 
  various 
  

   sizes 
  with 
  beach-sand, 
  and 
  also 
  to 
  the 
  Cambridge 
  specimens. 
  Some 
  

   of 
  the 
  latter 
  have 
  scratches 
  on 
  them, 
  which 
  in 
  a 
  few 
  cases 
  are 
  

   covered 
  by 
  Plicatulce 
  affixed 
  after 
  they 
  were 
  made. 
  The 
  scratches 
  

   were 
  very 
  likely 
  caused 
  by 
  the 
  grinding 
  up 
  and 
  down 
  of 
  the 
  ice 
  

   holding 
  them 
  on 
  the 
  shore 
  before 
  it 
  floated 
  off. 
  Shore-ice 
  has 
  

   occurred 
  on 
  the 
  East 
  coast 
  of 
  England, 
  and 
  is 
  known 
  to 
  have 
  

   carried 
  away 
  shingle 
  frozen 
  into 
  it. 
  Specimens 
  in 
  this 
  case 
  need 
  

   not 
  be 
  much 
  rolled, 
  as 
  fresh 
  material 
  is 
  nearly 
  always 
  being 
  added 
  

   from 
  the 
  foreshore 
  and 
  cliffs. 
  

  

  Another 
  very 
  probable 
  agency 
  would 
  be 
  the 
  entanglement 
  of 
  earth 
  

   and 
  stones 
  in 
  the 
  roots 
  of 
  trees. 
  The 
  mass 
  of 
  stones 
  mingled 
  with 
  

   what 
  looked 
  like 
  rotten 
  wood, 
  noticed 
  by 
  a 
  workman 
  in 
  a 
  Totternhoe 
  

   Stone 
  pit 
  at 
  Isleham, 
  and 
  recorded 
  by 
  Messrs. 
  Jukes-Browne 
  and 
  

   W. 
  Hill, 
  would 
  appear 
  to 
  have 
  been 
  so 
  transported. 
  Darwin, 
  in 
  his 
  

   ' 
  Journal 
  of 
  the 
  Voyage 
  of 
  the 
  Beagle, 
  ' 
  mentions 
  the 
  occurrence 
  of 
  

   a 
  piece 
  of 
  greenstone 
  on 
  a 
  coral-island 
  in 
  the 
  Indian 
  Ocean, 
  which 
  

   clearly 
  could 
  not 
  have 
  been 
  brought 
  there 
  by 
  any 
  other 
  agency. 
  

   Analogous 
  to 
  that 
  manner 
  of 
  conveyance 
  would 
  be 
  the 
  clinging 
  of 
  

   seaweed 
  to 
  stones 
  and 
  rock, 
  either 
  below 
  or 
  between 
  tide-marks. 
  

  

  Most 
  of 
  the 
  boulders 
  that 
  I 
  have 
  mentioned 
  would 
  exceed 
  the 
  

   weight 
  that 
  could 
  have 
  been 
  so 
  shifted, 
  but 
  not 
  so 
  the 
  granite- 
  

   fragments 
  in 
  the 
  Carboniferous 
  Limestone 
  near 
  Dublin, 
  which 
  

   Valentine 
  Ball 
  supposed 
  to 
  have 
  been 
  thus 
  distributed. 
  The 
  same 
  

   theory 
  would 
  also 
  explain 
  the 
  occurrence 
  of 
  some 
  of 
  the 
  various 
  

   small 
  pebbles 
  of 
  quartz, 
  etc., 
  in 
  the 
  Chalk. 
  

  

  It 
  may 
  be 
  thought 
  rather 
  fanciful 
  to 
  add 
  the 
  hypothesis, 
  suggested 
  

   by 
  one 
  enquirer, 
  of 
  marine 
  animals 
  as 
  such 
  carriers. 
  At 
  all 
  events, 
  

   that 
  would 
  be 
  compatible 
  only 
  with 
  the 
  transport 
  of 
  few 
  and 
  minute 
  

   pebbles. 
  1 
  

  

  The 
  mass 
  of 
  supposed 
  Mesozoic 
  coal 
  found 
  in 
  the 
  Chalk 
  near 
  

   Dover 
  may 
  very 
  well 
  have 
  been 
  transported 
  by 
  coast-ice, 
  being 
  

   gently 
  deposited 
  when 
  the 
  ice 
  melted. 
  

  

  As 
  for 
  extraneous 
  boulders, 
  they 
  seem 
  to 
  come 
  chiefly 
  from 
  the 
  

   Middle 
  Chalk 
  and 
  about 
  the 
  zone 
  of 
  Terebratulina 
  gracilis. 
  To 
  my 
  

   knowledge 
  only 
  three 
  specimens 
  of 
  granite 
  have 
  been 
  obtained 
  from 
  

   the 
  Chalk, 
  namely 
  the 
  Purley 
  boulder 
  and 
  these 
  two 
  Betchworth 
  

  

  1 
  For 
  a 
  recent 
  instance 
  of 
  this 
  kind, 
  in 
  which 
  penguins 
  and 
  fur-seals 
  are 
  the 
  

   carriers, 
  see 
  the 
  Challenger 
  Reports, 
  Zoology, 
  vol. 
  ii. 
  (1881), 
  Birds, 
  p. 
  126. 
  

  

  