﻿AND 
  THEIR 
  STRATIGRAPHY. 
  

  

  637 
  

  

  mile 
  N.W., 
  we 
  have 
  110 
  feet 
  Lower 
  Bagshot, 
  and 
  329 
  feet 
  of 
  

   London 
  Clay, 
  well-mouth 
  probably 
  a 
  little 
  above 
  100' 
  O.D., 
  which, 
  

   again, 
  brings 
  the 
  London-Clay 
  surface 
  to 
  about 
  0' 
  O.D. 
  : 
  I 
  can 
  find 
  

   no 
  decisive 
  evidence 
  of 
  these 
  110 
  feet 
  being 
  certainly 
  Lower 
  Bagshot, 
  

   and 
  part 
  may 
  be 
  London-Clay 
  beds. 
  But 
  about 
  midway 
  between 
  

   these 
  two 
  points 
  we 
  have 
  Saint 
  Anne's 
  Hill 
  with 
  the 
  Middle 
  Bagshot 
  

   at 
  least 
  at 
  an 
  altitude 
  of 
  220' 
  ; 
  and 
  taking 
  180 
  feet 
  as 
  given 
  by 
  

   Mr. 
  Hudleston 
  * 
  for 
  the 
  combined 
  thickness 
  of 
  the 
  Middle 
  and 
  

   Lower 
  Bagshot, 
  we 
  have 
  the 
  London-Clay 
  surface 
  at 
  +40' 
  O.D,, 
  that 
  

   is 
  40 
  feet 
  at 
  least 
  above 
  its 
  position 
  at 
  Chertsey, 
  a 
  mile 
  distant 
  ; 
  and 
  

   this 
  line, 
  if 
  produced 
  2000 
  yards 
  further, 
  comes 
  to 
  Woburn 
  Hill, 
  

   where, 
  if 
  this 
  slope 
  has 
  continued, 
  we 
  should 
  expect 
  to 
  find 
  the 
  

   London-Clay 
  surface 
  at 
  —45' 
  or 
  —50' 
  O.D., 
  and 
  Mr. 
  Hudleston 
  f 
  

   says 
  that 
  if 
  the 
  Woburn-Hill 
  brickearth 
  is 
  to 
  be 
  basal 
  Middle 
  Bag- 
  

   shot, 
  the 
  London-Clay 
  surface 
  would 
  be 
  60' 
  below 
  O.D. 
  

  

  The 
  greater 
  part 
  of 
  Egham 
  is 
  at 
  an 
  altitude 
  of 
  50' 
  O.D., 
  and 
  the 
  

   London 
  Clay 
  was 
  reached 
  in 
  the 
  Staines-Waterworks 
  well 
  23 
  feet 
  

   below 
  river-gravel, 
  &c, 
  and 
  was 
  penetrated 
  235 
  feet; 
  so 
  that 
  if 
  we 
  

   restore 
  the 
  London 
  Clay 
  to 
  the 
  same 
  thickness 
  that 
  it 
  attains 
  at 
  

   Thorpe 
  (330 
  feet), 
  the 
  surface 
  of 
  the 
  London 
  Clay 
  will 
  have 
  risen 
  

   to 
  122' 
  O.D., 
  and 
  the 
  top 
  of 
  the 
  Middle 
  Bagshot 
  to 
  302'. 
  

  

  And 
  thus 
  we 
  get 
  a 
  fall 
  in 
  the 
  London-Clay 
  surface 
  of 
  122 
  feet 
  in 
  a 
  

   little 
  over 
  three 
  miles 
  from 
  Egham 
  to 
  Chertsey, 
  which 
  gives 
  40' 
  per 
  

   mile, 
  or 
  the 
  same 
  as 
  we 
  got 
  between 
  St. 
  Anne's 
  Hill 
  and 
  Chertsey; 
  if 
  

   we 
  take 
  the 
  original 
  thickness 
  of 
  the 
  London 
  Clay 
  at 
  386 
  feet, 
  as 
  given 
  

   by 
  the 
  Chertsey-Brewery 
  well, 
  the 
  slope 
  becomes 
  60 
  feet 
  per 
  mile. 
  

  

  Next 
  I 
  have 
  attempted 
  to 
  map, 
  as 
  nearly 
  as 
  I 
  could, 
  the 
  southern 
  

   and 
  eastern 
  limits 
  of 
  the 
  Upper 
  Bagshots 
  (PI. 
  XXI.) 
  J. 
  

  

  It 
  is 
  at 
  the 
  most 
  but 
  an 
  attempt 
  to 
  place 
  the 
  result 
  of 
  my 
  work 
  

   during 
  the 
  last 
  two 
  years 
  at 
  the 
  disposal 
  of 
  others 
  who 
  may 
  be 
  in- 
  

   terested 
  in 
  this 
  district. 
  

  

  The 
  boundary 
  to 
  the 
  !N"."W. 
  is 
  not 
  drawn, 
  as 
  I 
  am 
  not 
  sufficiently 
  

   well 
  acquainted 
  with 
  the 
  ground 
  even 
  to 
  estimate 
  its 
  probable 
  posi- 
  

   tion, 
  which, 
  indeed, 
  is 
  all 
  I 
  claim 
  for 
  the 
  eastern 
  boundary. 
  It 
  will 
  

   be 
  seen 
  at 
  once 
  that 
  a 
  much 
  greater 
  extent 
  is 
  claimed 
  for 
  the 
  Upper 
  

   Bagshot 
  Sands 
  than 
  has 
  been 
  mapped 
  by 
  the 
  Geological 
  Survey, 
  as 
  

   since 
  that 
  was 
  done 
  fresh 
  sections 
  have 
  constantly 
  been 
  available, 
  and 
  

   this 
  area 
  is 
  also 
  even 
  larger 
  than 
  that 
  proposed 
  by 
  Messrs. 
  Gardner, 
  

   Keeping, 
  and 
  Monckton 
  §. 
  

  

  Commencing 
  at 
  Ash, 
  where 
  the 
  pebble-bed 
  is 
  at 
  310' 
  O.D., 
  and 
  

   following 
  the 
  outcrop 
  eastwards 
  round 
  the 
  foot 
  of 
  the 
  hills, 
  it 
  falls 
  

   to 
  300' 
  due 
  north 
  of 
  the 
  head 
  of 
  East 
  Wyke 
  Lane 
  and 
  above 
  the 
  

   brickyard 
  there. 
  Thence 
  it 
  runs 
  behind 
  Normandy 
  Park 
  and 
  again 
  

   appears 
  forming 
  the 
  surface 
  of 
  the 
  ground 
  at 
  Dolleys 
  Hill, 
  250' 
  O.D. 
  ; 
  

   then 
  gradually 
  becoming 
  undistinguishable 
  as 
  it 
  is 
  followed 
  up 
  

   "Whitepatch 
  Bottom, 
  the 
  boundary 
  has 
  to 
  be 
  drawn 
  in 
  from 
  the 
  line 
  

  

  * 
  Ibid. 
  vol. 
  xliii. 
  p. 
  452. 
  t 
  Tom. 
  cit. 
  

  

  X 
  Though 
  the 
  area 
  tinted 
  as 
  Upper 
  Bagshot 
  includes 
  the 
  Blackwater 
  Valley, 
  

   this 
  has 
  only 
  been 
  left 
  thus 
  to 
  avoid 
  complicating 
  the 
  detail 
  by 
  drawing 
  the 
  

   boundaries 
  of 
  the 
  river-deposits. 
  

  

  § 
  Ibid. 
  vol. 
  xliv. 
  p. 
  609. 
  

  

  