﻿1864.] 
  DAWKINS 
  RHJETIC 
  BEDS 
  AND 
  WHITE 
  LIAS. 
  4U5 
  

  

  Avicula 
  and 
  a 
  Pecten. 
  The 
  three 
  upper 
  beds 
  I 
  consider 
  to 
  belong 
  to 
  

   the 
  base 
  of 
  the 
  zone 
  of 
  Ammonites 
  planorbis, 
  which, 
  in 
  a 
  quarry 
  at 
  a 
  

   short 
  distance 
  from 
  the 
  top 
  of 
  the 
  scarp, 
  yields 
  Ostrea 
  liassica 
  and 
  a 
  

   small 
  species 
  of 
  Avicula, 
  and 
  contrasts 
  with 
  the 
  White 
  Lias 
  in 
  the 
  

   dark 
  colour 
  of 
  its 
  beds. 
  The 
  grey 
  marls 
  and 
  black 
  shales 
  of 
  C, 
  non- 
  

   gypsiferous 
  in 
  this 
  section, 
  are 
  highly 
  charged 
  with 
  both 
  the 
  varieties 
  

   of 
  gypsum 
  a 
  little 
  distance 
  to 
  the 
  north 
  ; 
  and 
  a 
  gentleman 
  of 
  

   greater 
  enterprise 
  than 
  prudence, 
  imagining 
  that 
  it 
  occurred 
  in 
  a 
  

   vertical 
  vein, 
  spent 
  .£800 
  in 
  discovering 
  that 
  it 
  runs 
  parallel 
  with 
  

   the 
  bedding 
  underneath 
  his 
  neighbour's 
  land. 
  

  

  From 
  Langport 
  the 
  Avicula 
  contorta 
  zone 
  sweeps 
  southward 
  past 
  

   lied 
  Hill, 
  as 
  far 
  as 
  Hatch 
  Park. 
  Mr. 
  Charles 
  Moore, 
  in 
  his 
  valuable 
  

   paper 
  on 
  the 
  Bhaetic 
  beds 
  of 
  Somerset, 
  has 
  taken 
  away 
  the 
  need 
  of 
  

   my 
  speaking 
  of 
  its 
  occurrence 
  at 
  Beer 
  Crowcombe 
  and 
  North 
  Curry. 
  

   To 
  the 
  extreme 
  accuracy 
  of 
  his 
  sections 
  of 
  the 
  White 
  Lias 
  of 
  Stoke, 
  

   St. 
  May, 
  and 
  Long 
  Sutton, 
  I 
  can 
  bear 
  testimony. 
  No. 
  3 
  of 
  his 
  

   section* 
  at 
  the 
  latter 
  place 
  yielded 
  the 
  only 
  Pleurophorus 
  obtained 
  

   from 
  these 
  beds. 
  

  

  6. 
  Summary 
  of 
  Sections. 
  — 
  A 
  comparison 
  of 
  the 
  Bhaetic 
  sections, 
  

   given 
  above, 
  with 
  those 
  of 
  Dr. 
  Wright 
  f 
  and 
  Mr. 
  Charles 
  Moore, 
  

   shows 
  that, 
  lithologically, 
  hardly 
  any 
  two 
  agree. 
  Sometimes 
  the 
  

   calcareous 
  element 
  is 
  wanting, 
  as 
  at 
  North 
  Curry 
  ; 
  at 
  others 
  it 
  is 
  

   greatly 
  developed, 
  as 
  at 
  Watchet, 
  where 
  the 
  thin 
  beds 
  of 
  limestone 
  

   split 
  up 
  the 
  thick 
  bed 
  of 
  marly 
  shale 
  which 
  generally 
  intervenes 
  

   between 
  the 
  " 
  Pecten-beds 
  " 
  and 
  the 
  " 
  bone-bed." 
  Sometimes 
  the 
  

   sandstones 
  are 
  absent 
  (Bath 
  Easton) 
  or, 
  as 
  is 
  more 
  usually 
  the 
  case, 
  

   are 
  very 
  well 
  represented. 
  This 
  irregularity 
  seems 
  to 
  me 
  to 
  indicate 
  

   a 
  deposit 
  off-shore 
  in 
  comparatively 
  shallow 
  water, 
  affected 
  con- 
  

   siderably 
  by 
  currents. 
  The 
  White 
  Lias, 
  on 
  the 
  contrary, 
  appears 
  to 
  

   have 
  been 
  deposited 
  in 
  a 
  sea 
  of 
  considerable 
  though, 
  as 
  proved 
  by 
  its 
  

   varying 
  thickness, 
  of 
  variable 
  depth, 
  and 
  out 
  of 
  the 
  reach 
  of 
  litoral 
  

   influences. 
  In 
  common 
  with 
  the 
  Lower 
  Lias 
  series 
  it 
  contains 
  no 
  

   arenaceous 
  beds 
  ; 
  as 
  compared 
  with 
  the 
  beds 
  below 
  it, 
  it 
  is 
  remark- 
  

   able 
  for 
  the 
  development 
  of 
  its 
  white, 
  pinkish, 
  and 
  grey 
  limestones. 
  

  

  The 
  sections 
  taken 
  to 
  the 
  east 
  of 
  Watchet, 
  and 
  at 
  Turn 
  Hill, 
  that 
  

   at 
  Saltford 
  given 
  by 
  Dr. 
  Wright, 
  and 
  those 
  of 
  Mr. 
  Charles 
  Moore, 
  

   prove 
  beyond 
  all 
  doubt 
  the 
  true 
  position 
  of 
  the 
  White 
  Lias 
  — 
  below 
  

   the 
  Saurian 
  zone 
  of 
  the 
  Ammonites 
  planorbis 
  group, 
  and 
  immediately 
  

   above 
  the 
  Avicula 
  contorta 
  series. 
  

  

  § 
  III. 
  Palaeontology. 
  

  

  In 
  the 
  preceding 
  sections 
  I 
  have 
  paid 
  particular 
  attention 
  to 
  each 
  

   Bhaetic 
  bed, 
  to 
  see 
  whether, 
  as 
  on 
  the 
  Continent, 
  well-defined 
  zones 
  

   of 
  life 
  are 
  traceable. 
  The 
  following 
  table, 
  showing 
  the 
  range 
  of 
  

   each 
  species, 
  as 
  far 
  as 
  the 
  A. 
  'planorbis 
  zone, 
  is 
  the 
  result 
  of 
  the 
  

   endeavour. 
  It 
  is 
  by 
  no 
  means 
  an 
  exhaustive 
  list, 
  and 
  represents 
  

   merely 
  the 
  fossils 
  that 
  I 
  have 
  found 
  myself. 
  

  

  * 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xvii. 
  p. 
  491. 
  

   t 
  Ibid. 
  vol. 
  xvi. 
  pp. 
  378 
  ct 
  seq. 
  

  

  