﻿Vol. 
  53.] 
  GKANITE 
  EEOil 
  THE 
  MIDDLE 
  CHALK 
  OF 
  BETCHWOETH. 
  219 
  

  

  specimens. 
  Granite 
  seems 
  to 
  be 
  rare 
  in 
  the 
  Coal 
  Measures 
  also, 
  

   quartzite 
  being 
  by 
  far 
  the 
  commonest 
  rock 
  in 
  both 
  deposits. 
  

  

  One 
  of 
  the 
  Betchworth 
  specimens, 
  the 
  quartzite 
  in 
  the 
  Brighton 
  

   Museum, 
  and 
  most 
  of 
  the 
  Cambridge 
  boulders 
  have 
  shells, 
  etc., 
  still 
  

   affixed. 
  They 
  are 
  typical 
  Middle 
  Chalk 
  and 
  Cambridge 
  Greensand 
  

   forms, 
  and 
  evidently 
  grew 
  there 
  after 
  the 
  boulders 
  were 
  dropped 
  

   on 
  the 
  sea-bottom. 
  

  

  A 
  further 
  question 
  of 
  interest 
  in 
  relation 
  to 
  these 
  and 
  other 
  

   fragments 
  is 
  the 
  identification 
  of 
  the 
  places 
  whence 
  they 
  set 
  out. 
  

   Present 
  evidence 
  seems 
  to 
  point 
  to 
  the 
  north 
  as 
  the 
  starting-point 
  

   of 
  most 
  of 
  them 
  ; 
  but 
  there 
  is 
  no 
  certainty 
  about 
  the 
  particular 
  

   localities. 
  Godwin-Austen 
  supposed 
  the 
  Purley 
  boulder 
  to 
  have 
  

   come 
  from 
  Scandinavia, 
  which 
  also 
  appears 
  to 
  be 
  the 
  origin 
  of 
  many 
  

   of 
  the 
  Cambridge 
  Greensaud 
  fragments, 
  though 
  some 
  at 
  any 
  rate 
  

   may 
  be 
  presumed 
  to 
  have 
  originated 
  in 
  Scotland. 
  To 
  the 
  Scottish 
  

   Highlands 
  or, 
  in 
  Prof. 
  Bonney's 
  judgment, 
  more 
  probably 
  to 
  

   Scandinavia 
  may 
  be 
  assigned 
  also 
  the 
  birthplace 
  of 
  these 
  two 
  

   Betchworth 
  boulders. 
  

  

  PLATE 
  XV. 
  

  

  Reproduction 
  of 
  photographs 
  of 
  the 
  Betchworth 
  boulders, 
  | 
  nat. 
  size. 
  

  

  Discussion. 
  

  

  Prof. 
  Bonnet 
  said 
  that 
  these 
  rocks 
  showed 
  the 
  granular 
  structure 
  

   often 
  seen 
  in 
  rocks 
  of 
  Laurentian 
  type, 
  contained 
  microcline, 
  white 
  

   mica 
  slightly 
  bent 
  up, 
  and, 
  to 
  a 
  certain 
  extent, 
  a 
  mosaic 
  of 
  quartz. 
  

   The 
  felspar 
  in 
  the 
  Purley 
  boulder 
  was 
  more 
  idiomorphic. 
  He 
  

   thought 
  that 
  the 
  subject 
  had 
  been 
  very 
  clearly 
  and 
  well 
  brought 
  

   before 
  the 
  Society. 
  

  

  The 
  Peesident 
  remarked 
  that 
  Mr. 
  Stebbing 
  and 
  Prof. 
  Bonney 
  had 
  

   opened 
  out 
  a 
  question 
  of 
  great 
  interest. 
  Pew 
  probably 
  were 
  pre- 
  

   pared 
  to 
  admit 
  the 
  existence 
  of 
  a 
  glacial 
  period 
  in 
  the 
  heart 
  of 
  the 
  

   Cretaceous, 
  but 
  the 
  hypothesis 
  of 
  floating 
  ice 
  came 
  up 
  here. 
  Masses 
  

   so 
  transported 
  must 
  have 
  come 
  from 
  a 
  considerable 
  distance 
  : 
  there 
  

   was 
  indeed 
  room 
  for 
  much 
  imagination 
  and 
  much 
  discussion. 
  The 
  

   Author 
  had 
  mentioned 
  transport 
  by 
  marine 
  animals, 
  driftwood, 
  

   seaweed, 
  and 
  finally 
  ice 
  — 
  which 
  latter 
  appeared 
  to 
  be 
  the 
  most 
  

   reasonable. 
  

  

  Mr. 
  Si 
  rah 
  an 
  complimented 
  the 
  Author 
  on 
  his 
  careful 
  record 
  of 
  

   the 
  circumstances 
  under 
  which 
  these 
  boulders 
  had 
  been 
  found. 
  It 
  

   seemed 
  curious 
  that 
  such 
  foreign 
  bodies 
  were 
  not 
  found 
  more 
  

   frequently, 
  considering 
  how 
  vast 
  a 
  number 
  of 
  Chalk-exposures 
  

   occurred 
  throughout 
  the 
  country. 
  In 
  other 
  marine 
  formations, 
  

   moreover, 
  they 
  are 
  almost 
  unknown 
  — 
  possibly, 
  however, 
  in 
  con- 
  

   sequence 
  of 
  the 
  difficulty 
  of 
  detecting 
  them. 
  . 
  

  

  The 
  complete 
  rounding 
  of 
  many 
  of 
  the 
  boulders, 
  and 
  the 
  adhesion 
  

   to 
  them 
  of 
  Chalk 
  organisms, 
  pointed 
  to 
  their 
  derivation 
  from 
  a 
  

   shore 
  ; 
  and 
  this, 
  taken 
  in 
  connexion 
  with 
  the 
  large 
  size 
  of 
  some 
  

   of 
  them, 
  made 
  it 
  difficult 
  to 
  understand 
  that 
  they 
  had 
  been 
  floated 
  

  

  Q2 
  

  

  