﻿440 
  ME. 
  S. 
  S. 
  BECKMAN 
  ON 
  THE 
  

  

  29. 
  On 
  the 
  Cotteswold, 
  Mldfoed, 
  and 
  Yeovil 
  Sands, 
  and 
  the 
  Division 
  

   between 
  Lias 
  and 
  Oolite. 
  By 
  S. 
  S. 
  Beckman, 
  Esq., 
  E.G.S. 
  

   (Eead 
  February 
  20, 
  1889.) 
  

  

  It 
  has 
  been 
  observed 
  that 
  attention 
  to 
  lithology 
  is 
  likely 
  to 
  insure 
  

   success 
  in 
  the 
  matter 
  of 
  correlation. 
  I 
  am 
  bound 
  to 
  confess, 
  how- 
  

   ever, 
  that 
  my 
  experience 
  of 
  Jurassic 
  rocks 
  tells 
  me 
  that 
  in 
  many 
  cases 
  

   this 
  observation 
  is 
  quite 
  incorrect. 
  Within 
  the 
  limits 
  of 
  one 
  basin 
  

   it 
  may 
  happen 
  that 
  the 
  same 
  horizon 
  can 
  often 
  be 
  identified 
  by 
  the 
  

   similarity 
  in 
  lithology 
  ; 
  but 
  even 
  within 
  such 
  limits 
  it 
  certainly 
  will 
  

   not 
  be 
  safe 
  to 
  place 
  much 
  reliance 
  on 
  such 
  a 
  guide 
  ; 
  while 
  in 
  cor- 
  

   relating 
  the 
  strata 
  of 
  one 
  basin 
  with 
  those 
  of 
  another, 
  such 
  an 
  idea 
  

   will 
  probably 
  lead 
  to 
  very 
  decided 
  errors. 
  The 
  strata 
  now 
  to 
  be 
  

   discussed 
  have 
  suffered 
  singularly 
  in 
  the 
  matter 
  of 
  correlation 
  from 
  

   this 
  similarity 
  of 
  lithology. 
  

  

  In 
  the 
  counties 
  of 
  Dorset, 
  Somerset, 
  and 
  Gloucester 
  there 
  occur 
  

   in 
  most 
  places, 
  between 
  clay 
  of 
  Upper 
  Liassic 
  age 
  and 
  limestoue 
  

   of 
  the 
  Inferior-Oolite 
  period, 
  certain 
  yellow 
  micaceous 
  sands, 
  which 
  

   contain, 
  at 
  intervals, 
  in 
  some 
  places 
  regular 
  bands, 
  in 
  others 
  jdnes 
  

   of 
  more 
  or 
  less 
  lenticular 
  masses, 
  of 
  a 
  hard, 
  greyish, 
  sometimes 
  olue- 
  

   hearted, 
  sandstone. 
  Among 
  other 
  local 
  names, 
  these 
  sandy 
  strata 
  

   have 
  been 
  known 
  in 
  the 
  county 
  of 
  Gloucester 
  as 
  Cotteswold 
  Sands, 
  

   in 
  North 
  Somerset 
  as 
  Midford 
  Sands, 
  in 
  the 
  county 
  of 
  Dojset 
  and 
  

   in 
  South 
  Somerset 
  as 
  Yeovil 
  Sands. 
  On 
  account, 
  however, 
  of 
  the 
  

   similar 
  position 
  which 
  they 
  occupy 
  with 
  regard 
  to 
  Lias 
  clay 
  and 
  

   Inferior-Oolite 
  limestone, 
  and 
  also, 
  no 
  doubt, 
  on 
  account 
  of 
  their 
  

   exactly 
  similar 
  lithological 
  appearance, 
  the 
  name 
  " 
  Midforl 
  Sands 
  "* 
  

   (a 
  name 
  first 
  applied 
  by 
  William 
  Smith 
  to 
  the 
  sands 
  ac 
  Midford) 
  

   has 
  been 
  used 
  to 
  designate 
  these 
  sands 
  in 
  the 
  thref 
  counties 
  ; 
  

   under 
  this 
  name 
  they 
  have 
  been 
  mapped 
  by 
  the 
  Geological 
  Survey. 
  

  

  Around 
  the 
  sands 
  which 
  lie 
  between 
  Liassic 
  clay 
  and 
  Oolitic 
  

   limestone 
  a 
  constant 
  discussion 
  has 
  been 
  waged 
  for 
  tie 
  last 
  thirty 
  

   years 
  or 
  more, 
  as 
  to 
  whether 
  they 
  should 
  be 
  classed 
  win 
  the 
  Liassic 
  

   or 
  Oolitic 
  periods. 
  According 
  to 
  the 
  opinion 
  of 
  thos* 
  whom 
  I 
  may 
  

   call 
  the 
  first 
  generation 
  of 
  geologists, 
  whose 
  pionee' 
  was 
  William 
  

   Smith, 
  the 
  sands 
  were 
  " 
  Sands 
  of 
  the 
  Inferior 
  Oolie." 
  The 
  cele- 
  

   brated 
  Dr. 
  Oppel, 
  who 
  visited 
  this 
  country 
  about 
  185-), 
  comprehended 
  

   the 
  positions 
  of 
  these 
  sands 
  with 
  his 
  usual 
  acute 
  perception 
  ; 
  and 
  

   had 
  our 
  English 
  geologists 
  given 
  to 
  his 
  work 
  thf 
  attention 
  which 
  

   it 
  deserves, 
  it 
  ought 
  to 
  have 
  been 
  impossible 
  for 
  the 
  discussion 
  to 
  

   have 
  been 
  maintained. 
  In 
  1856 
  Dr. 
  Oppel, 
  in 
  tie 
  ' 
  Juraformation/ 
  

   p. 
  296, 
  places 
  the 
  Cotteswold 
  Sands 
  of 
  Eroceste 
  Hill 
  in 
  " 
  the 
  zone 
  

   of 
  Posidonomya 
  Bronni," 
  that 
  is, 
  with 
  the 
  UpperLias 
  ; 
  while 
  on 
  the 
  

  

  * 
  In 
  the 
  following 
  paper 
  the 
  term 
  " 
  Midford 
  Sand?" 
  written 
  thus, 
  means 
  

   that 
  it 
  is 
  used 
  in 
  the 
  same 
  sense 
  as 
  by 
  the 
  Officers 
  o 
  the 
  Geological 
  Survey 
  ; 
  

   while 
  Midford 
  Sands 
  refers 
  only 
  to 
  the 
  yellow 
  micacous 
  sands 
  round 
  Bath, 
  

   Midford, 
  &c. 
  

  

  