﻿Vol. 
  53.] 
  GEANTTE 
  FROM 
  THE 
  MIDDLE 
  CHALK 
  OE 
  BETCHWOETH. 
  215 
  

  

  We 
  turn 
  now 
  to 
  the 
  main 
  subject 
  of 
  this 
  communication 
  — 
  the 
  

   boulders 
  obtained 
  by 
  me 
  at 
  Betchworth. 
  

  

  According 
  to 
  a 
  tradition 
  which 
  I 
  have 
  been 
  unable 
  to 
  authenticate, 
  

   Betchworth 
  chalk-pit, 
  which 
  is 
  about 
  4 
  miles 
  from 
  Dorking, 
  was 
  

   worked 
  in 
  the 
  time 
  of 
  the 
  Romans. 
  Whether 
  this 
  be 
  true 
  or 
  not, 
  

   there 
  is 
  no 
  doubt 
  that 
  quarrying 
  has 
  been 
  in 
  operation 
  there 
  for 
  a 
  

   very 
  long 
  period. 
  The 
  section 
  exposed 
  in 
  the 
  pit 
  extends 
  from 
  very 
  

   near 
  the 
  base 
  of 
  the 
  Chalk 
  to 
  the 
  top 
  of 
  the 
  zone 
  of 
  Terebrabulina 
  

   gracilis. 
  The 
  two 
  blocks 
  (A 
  and 
  B) 
  which 
  form 
  the 
  subject 
  of 
  

   this 
  communication 
  were 
  obtained 
  last 
  April 
  from 
  one 
  of 
  a 
  gang 
  of 
  

   men 
  working 
  on 
  the 
  western 
  side 
  of 
  the 
  pit, 
  and 
  engaged 
  in 
  clearing 
  

   away 
  the 
  chalk 
  above 
  the 
  zone 
  of 
  Eolaster 
  subglobosus. 
  They 
  came 
  

   from 
  the 
  zone 
  of 
  Terebratulina 
  gracilis, 
  and 
  were 
  found 
  after 
  a 
  

   blast. 
  Unfortunately 
  both 
  of 
  them 
  are 
  broken. 
  It 
  is 
  likely, 
  as 
  

   they 
  are 
  very 
  much 
  decomposed, 
  that 
  they 
  were 
  broken 
  through 
  

   their 
  fall 
  after 
  the 
  blast, 
  or 
  by 
  the 
  blast 
  itself 
  : 
  the 
  boulders 
  may, 
  of 
  

   course, 
  have 
  been 
  broken 
  by 
  the 
  men 
  themselves 
  before 
  they 
  were 
  

   observed; 
  but 
  the 
  workmen 
  assured 
  me 
  that 
  they 
  saw 
  no 
  other 
  

   fragments. 
  

  

  The 
  weight 
  of 
  the 
  larger 
  boulder 
  (A) 
  was 
  7 
  lbs. 
  7 
  oz. 
  when 
  

   it 
  first 
  came 
  into 
  my 
  hands. 
  In 
  shape 
  it 
  is 
  roughly 
  quadran- 
  

   gular, 
  measuring 
  5*8 
  X 
  6'25 
  x 
  4*125 
  inches. 
  It 
  is 
  a 
  fine-grained 
  

   granite, 
  so 
  very 
  much 
  decomposed 
  that 
  it 
  will 
  hardly 
  bear 
  handling, 
  

   and 
  is 
  rotten 
  enough 
  to 
  be 
  rubbed 
  away 
  by 
  the 
  finger. 
  It 
  has 
  the 
  

   remains 
  of 
  several 
  lower 
  valves 
  of 
  Spondylus 
  latus 
  and 
  some 
  

   Serjpulce 
  still 
  attached. 
  On 
  the 
  broken 
  side 
  it 
  is 
  stained 
  with 
  

   streaks 
  and 
  spots 
  of 
  iron 
  oxide. 
  There 
  are 
  also 
  parallel 
  to 
  that 
  side 
  

   one 
  or 
  two 
  small 
  cracks. 
  

  

  The 
  other 
  fragment 
  (B), 
  which 
  seems 
  to 
  be 
  the 
  half 
  of 
  a 
  roughly 
  

   ovoid 
  mass, 
  weighed 
  3 
  lbs. 
  12 
  oz., 
  and 
  measured 
  3*6 
  x 
  5*8 
  x 
  

   4*5 
  inches. 
  This 
  also 
  is 
  a 
  granite 
  ; 
  but 
  it 
  is 
  interesting 
  to 
  observe 
  

   that 
  it 
  is 
  of 
  altogether 
  different 
  character 
  from 
  the 
  other, 
  there 
  

   being 
  large 
  irregular 
  crystals 
  of 
  quartz 
  visible 
  on 
  part 
  of 
  the 
  

   exterior, 
  while 
  on 
  the 
  broken 
  surface 
  mica 
  is 
  very 
  distinct 
  in 
  places. 
  

   It 
  is 
  not 
  nearly 
  so 
  much 
  decomposed 
  as 
  the 
  other 
  specimen. 
  

  

  I 
  am 
  indebted 
  to 
  Prof. 
  Bonney's 
  kindness 
  for 
  the 
  following 
  notes 
  

   on 
  the 
  microscopic 
  structure 
  of 
  the 
  rocks 
  : 
  — 
  

  

  i 
  Boulder 
  A.— 
  Structure 
  granular, 
  with 
  some 
  irregularity 
  in 
  size 
  

   and 
  an 
  occasional 
  slight 
  tendency 
  to 
  clustering 
  of 
  grains 
  which 
  are 
  

   alike 
  in 
  size 
  or 
  nature 
  : 
  seldom 
  any 
  approach 
  to 
  idiomorphism. 
  

   Constituents 
  : 
  quartz 
  (not 
  very 
  abundant), 
  sometimes 
  with 
  slight 
  

   strain-shadowing, 
  occasional 
  microlithic 
  inclusions, 
  and 
  very 
  minute 
  

   cavities. 
  Felspar 
  : 
  ordinary 
  plagioclase, 
  microcline, 
  and 
  probably 
  

   orthoclase 
  : 
  often 
  embedding 
  small 
  grains 
  of 
  quartz 
  ; 
  also 
  some 
  

  

  M. 
  Stirrup, 
  Eep. 
  Brit. 
  Assoc. 
  (Manchester) 
  1887, 
  p. 
  686, 
  and 
  Trans. 
  Manch. 
  

   Geol. 
  Soc. 
  vol. 
  xxi. 
  1891, 
  p. 
  172, 
  etc.; 
  and 
  angular 
  fragments 
  of 
  granite, 
  

   quartzite, 
  etc., 
  in 
  the 
  Carboniferous 
  Limestone, 
  V. 
  Ball, 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  

   vol. 
  xliv. 
  (1888) 
  p. 
  371. 
  To 
  the 
  ice-borne 
  masses 
  of 
  rock 
  of 
  the 
  Glacial 
  Beds 
  it 
  

   is 
  needless 
  to 
  refer. 
  

  

  