﻿^°1- 
  53-] 
  BOULDERS 
  FROM 
  THE 
  BETCHWORTH 
  CHALK. 
  213 
  

  

  15. 
  On 
  two 
  Boulders 
  of 
  Granite 
  from 
  the 
  Middle 
  Chalk 
  of 
  

   Betchworth, 
  Surrey. 
  By 
  W. 
  P. 
  D. 
  Stebbing, 
  Esq., 
  F.G.S. 
  

   (Bead 
  February 
  24th, 
  1897.) 
  

  

  [Plate 
  XV.] 
  

  

  Boulders 
  of 
  various 
  Palaeozoic 
  rocks, 
  other 
  than 
  mere 
  pebbles, 
  iu 
  

   the 
  Upper 
  Cretaceous 
  and 
  in 
  some 
  other 
  strata 
  have 
  at 
  different 
  

   times 
  been 
  described, 
  but 
  they 
  are 
  acknowledged 
  to 
  be 
  of 
  com- 
  

   paratively 
  rare 
  occurrence 
  in 
  rocks 
  of 
  Mesozoic 
  age. 
  It 
  may 
  be 
  of 
  

   interest 
  to 
  summarize 
  briefly 
  the 
  chief 
  finds 
  of 
  this 
  kind 
  which 
  

   have 
  been 
  made 
  up 
  to 
  the 
  present 
  in 
  this 
  country. 
  

  

  In 
  1827 
  Mantell 
  1 
  observed 
  that 
  ' 
  Iu 
  this 
  country 
  the 
  Chalk 
  

   very 
  rarely 
  contains 
  traces 
  of 
  older 
  deposits 
  : 
  the 
  only 
  instances 
  

   of 
  extraneous 
  rocks 
  that 
  have 
  come 
  under 
  my 
  observation 
  are 
  

   pebbles 
  of 
  quartz 
  and 
  some 
  fragments 
  of 
  green 
  schist.' 
  

  

  In 
  1850 
  Dixon 
  2 
  wrote 
  : 
  — 
  ' 
  Small 
  pebbles 
  and 
  large 
  rolled 
  frag- 
  

   ments 
  of 
  sandstone 
  and 
  quartz-rock 
  are 
  occasionally 
  discovered 
  in 
  

   the 
  centre 
  of 
  the 
  Upper 
  Chalk. 
  Mr. 
  Coombe 
  found 
  one 
  specimen, 
  

   weighing 
  near 
  14 
  lbs., 
  at 
  Houghton, 
  Sussex, 
  and 
  I 
  have 
  seen 
  others 
  

   from 
  the 
  same 
  pit 
  of 
  2 
  or 
  3 
  lbs. 
  weight. 
  Several 
  also 
  have 
  been 
  

   sent 
  me 
  by 
  Mr. 
  Catt 
  from 
  the 
  pits 
  near 
  Lewes.' 
  

  

  In 
  1857 
  the 
  well-known 
  Purley 
  boulder 
  was 
  found, 
  of 
  which 
  

   this 
  Society 
  is 
  fortunate 
  enough 
  to 
  possess 
  the 
  principal 
  remains. 
  

   R. 
  A. 
  C. 
  Godwin-Austen 
  in 
  vol. 
  xiv. 
  of 
  the 
  Quarterly 
  Journal, 
  p. 
  253, 
  

  

  says 
  ' 
  the 
  boulder 
  was 
  found 
  in 
  a 
  chalk 
  -pit 
  by 
  the 
  side 
  of 
  the 
  

  

  old 
  London 
  and 
  Brighton 
  road, 
  near 
  Purley 
  The 
  portion 
  of 
  

  

  the 
  Chalk-formation 
  in 
  which 
  the 
  pit 
  is 
  worked 
  is 
  the 
  lower 
  part 
  

   of 
  that 
  containing 
  flints.' 
  After 
  the 
  boulder 
  was 
  removed 
  there 
  

   were 
  found 
  associated 
  with 
  it 
  a 
  mass 
  of 
  fine, 
  waterworn, 
  siliceous 
  

   beach-sand, 
  evidently 
  derived 
  from 
  the 
  waste 
  of 
  a 
  coast-line 
  of 
  

   crystalline 
  rocks 
  ; 
  a 
  quantity 
  of 
  coarse 
  sand-like 
  material, 
  which 
  on 
  

   examination 
  proved 
  to 
  be 
  decomposed 
  rock 
  of 
  the 
  same 
  kind 
  as 
  the 
  

   boulder 
  ; 
  and 
  a 
  collection 
  of 
  blocks 
  of 
  smaller 
  dimensions, 
  also 
  

   waterworn. 
  Most 
  of 
  these 
  were 
  composed 
  of 
  a 
  peculiar 
  and 
  very 
  

   different 
  rock, 
  consisting 
  of 
  augite, 
  with 
  lath-shaped, 
  twinned 
  

   crystals 
  of 
  felspar 
  ; 
  but 
  some 
  were 
  of 
  greenstone. 
  The 
  largest 
  of 
  

   them 
  must 
  have 
  weighed 
  as 
  much 
  as 
  20 
  to 
  25 
  lbs, 
  ; 
  all 
  were 
  very 
  

   much 
  decomposed. 
  

  

  The 
  form 
  of 
  the 
  boulder 
  itself, 
  which 
  had 
  been 
  broken 
  up 
  by 
  the 
  

   workmen, 
  seems 
  to 
  have 
  been 
  roughly 
  egg-shaped, 
  and 
  it 
  was 
  

   evidently 
  a 
  rounded 
  waterworn 
  block 
  of 
  crystalline 
  granitoid 
  rock. 
  

   The 
  colour 
  is 
  red, 
  and 
  the 
  weight 
  of 
  the 
  fragment 
  in 
  the 
  Geological 
  

   Society's 
  Museum 
  is 
  about 
  45 
  lbs. 
  

  

  In 
  1860 
  Godwin-Austen 
  recorded 
  the 
  occurrence 
  3 
  of 
  a 
  mass 
  of 
  

  

  1 
  ' 
  The 
  Geology 
  of 
  the 
  South-East 
  of 
  England,' 
  p. 
  78. 
  

  

  2 
  ' 
  Geology 
  of 
  Sussex,' 
  p. 
  69. 
  

  

  3 
  Quart. 
  Journ. 
  Geoi. 
  Soc. 
  vol. 
  xvi. 
  p. 
  326. 
  

  

  