﻿1864.] 
  DAWKINS 
  KELTIC 
  BEDS 
  AND 
  WHITE 
  LIA9. 
  407 
  

  

  2. 
  Palceontological 
  Relations 
  of 
  the 
  White 
  Lias 
  to 
  the 
  Beds 
  above 
  and 
  

   below. 
  — 
  If 
  I 
  have 
  failed 
  to 
  make 
  out 
  distinct 
  zones 
  of 
  Rhsetic 
  life, 
  yet 
  

   the 
  preceding 
  table 
  throws 
  great 
  light 
  upon 
  the 
  mutual 
  relations 
  of 
  

   the 
  beds, 
  and 
  especially 
  with 
  regard 
  to 
  the 
  White 
  Lias. 
  Of 
  the 
  Fishes 
  

   so 
  abundant 
  below, 
  not 
  one 
  passes 
  upwards 
  ; 
  of 
  the 
  Saurians 
  of 
  the 
  

   Ammonites 
  planorbis 
  group 
  above, 
  not 
  one 
  passes 
  downwards. 
  It 
  

   has 
  yielded, 
  so 
  far 
  as 
  I 
  know, 
  neither 
  Vertebrates 
  nor 
  Ammonites*. 
  

   Of 
  its 
  Mollusca, 
  Cardium 
  Rhosticum 
  and 
  Modiola 
  minima, 
  of 
  the 
  

   marlstones 
  below 
  the 
  bone-bed, 
  run 
  side 
  by 
  side 
  into 
  its 
  upper 
  beds, 
  

   where 
  the 
  former 
  becomes 
  extinct, 
  while 
  the 
  latter 
  ranges 
  upwards 
  

   into 
  the 
  zone 
  of 
  Ammonites 
  raricostatus. 
  Mr. 
  Etheridge 
  has 
  iden- 
  

   tified 
  one 
  shell 
  from 
  Long 
  Sutton 
  as 
  Pleurojphorus 
  (sp.), 
  a 
  genus 
  

   peculiarly 
  Rhaetic. 
  Monotis 
  and 
  Ostrea 
  interstriata, 
  on 
  Mr. 
  C. 
  

   Moore's 
  authority, 
  are 
  common 
  to 
  it 
  and 
  the 
  beds 
  below; 
  Ostrea 
  

   liassicaf 
  to 
  the 
  beds 
  below 
  and 
  above. 
  Lima 
  joectinoides 
  and 
  Pecten 
  

   textorius 
  (Saltford), 
  which 
  are 
  unknown 
  below, 
  range 
  into 
  the 
  zone 
  

   of 
  Ammonites 
  Turneri 
  ; 
  Modiola 
  Hillana, 
  Pholadomya 
  glabra, 
  and 
  

   Unicardium 
  cardioides 
  — 
  the 
  two 
  latter 
  found 
  by 
  Mr. 
  Sanders 
  with 
  

   Pinna 
  Hartmanni 
  at 
  Saltford 
  — 
  into 
  that 
  of 
  Ammonites 
  Bucklandi. 
  

   Passing 
  over, 
  therefore, 
  the 
  fossils 
  common 
  alike 
  to 
  the 
  Ammonites 
  

   planorbis 
  group 
  above 
  and 
  the 
  Rhaetic 
  beds 
  below, 
  we 
  have 
  Monotis 
  

   (Moore), 
  Cardium 
  Rhosticum, 
  Pleurojphorus 
  (sp.), 
  and 
  Ostrea 
  inter- 
  

   striata 
  linking 
  it 
  to 
  the 
  former 
  ; 
  Modiola 
  Hillana, 
  Pecten 
  textorius, 
  

   Pholadomya 
  glabra, 
  and 
  Unicardium 
  cardioides 
  to 
  the 
  latter, 
  — 
  a 
  

   mixture 
  of 
  forms 
  which 
  appears 
  to 
  me 
  to 
  indicate 
  a 
  border-land 
  

   between 
  two 
  formations, 
  belonging 
  neither 
  to 
  the 
  one 
  nor 
  the 
  other. 
  

   The 
  sudden 
  break 
  in 
  the 
  succession 
  of 
  life 
  between 
  it 
  and 
  the 
  zone 
  

   of 
  Avicula 
  contorta 
  indicates 
  a 
  lacuna, 
  of 
  greater 
  or 
  less 
  magnitude, 
  

   in 
  the 
  succession 
  of 
  the 
  beds. 
  In 
  the 
  absence 
  of 
  arenaceous 
  deposits 
  

   it 
  contrasts 
  with 
  the 
  beds 
  below 
  ; 
  in 
  the 
  great 
  development 
  of 
  the 
  

   calcareous 
  element 
  it 
  resembles 
  the 
  beds 
  above. 
  And, 
  until 
  there 
  be 
  

   further 
  evidence 
  upon 
  the 
  subject, 
  it 
  will 
  be 
  far 
  safer 
  to 
  consider 
  it 
  

   the 
  passage-beds 
  of 
  the 
  Lower 
  Lias 
  than, 
  with 
  Mr. 
  Charles 
  Moore, 
  

   to 
  assign 
  it 
  to 
  the 
  Rhaetic 
  formation, 
  or, 
  with 
  Dr. 
  Wright, 
  putting 
  

   the 
  Saurian 
  zone 
  and 
  the 
  "firestone" 
  beds 
  beneath, 
  to 
  incorporate 
  it 
  

   with 
  the 
  Ammonites 
  planorbis 
  group 
  above. 
  

  

  3. 
  Range 
  of 
  Fossils 
  in 
  Rhcetic 
  Beds. 
  — 
  There 
  are 
  a 
  few 
  points 
  

   worthy 
  of 
  note 
  in 
  the 
  range 
  of 
  the 
  Rhsetic 
  fossils. 
  Of 
  the 
  Fishes 
  

   found 
  below 
  the 
  bone-bed, 
  Acrodus 
  minimus, 
  Sargodon 
  Tomicus, 
  

  

  * 
  Dr. 
  Wright, 
  in 
  his 
  valuable 
  section 
  of 
  the 
  Street 
  quarries 
  (Quart. 
  Journ. 
  

   Geol. 
  Soc. 
  vol. 
  xvi. 
  pp. 
  389-391), 
  considers 
  that 
  the 
  "firestone" 
  and 
  bottom 
  Sau- 
  

   rian-bearing 
  beds 
  he 
  at 
  the 
  base 
  of 
  the 
  group 
  into 
  which 
  he 
  has 
  incorporated 
  the 
  

   White 
  Lias. 
  That 
  he 
  is 
  mistaken 
  in 
  this 
  view 
  I 
  have 
  proved 
  by 
  actual 
  survey. 
  

   The 
  lower 
  Street 
  Saurian 
  beds 
  extend 
  westwards 
  past 
  Woolavington, 
  as 
  far 
  as 
  

   the 
  Dunball 
  Cement 
  Works, 
  where 
  they 
  occupy 
  a 
  position 
  above 
  the 
  White 
  Lias. 
  

   Here, 
  as 
  at 
  King 
  Weston 
  and 
  West 
  Hatch, 
  they 
  contain 
  numerous 
  Saurians, 
  

   associated 
  with 
  Myacites 
  unionoides, 
  the 
  latter 
  of 
  which 
  characterizes 
  the 
  cement- 
  

   shales 
  of 
  the 
  lower 
  zone 
  of 
  the 
  Ammonites 
  planorbis 
  group. 
  On 
  the 
  evidence, 
  

   therefore, 
  of 
  the 
  Street 
  section, 
  and 
  still 
  less 
  of 
  that 
  at 
  Saltford, 
  I 
  cannot 
  admit 
  

   that 
  the 
  fossils 
  of 
  the 
  Saurian 
  zone, 
  or 
  of 
  the 
  beds 
  above 
  it, 
  have 
  been 
  proved 
  to 
  

   belong 
  to 
  the 
  fauna 
  of 
  the 
  White 
  Lias. 
  

  

  t 
  Quart. 
  Journ. 
  Greol. 
  Soc. 
  vol. 
  xvii. 
  p. 
  496. 
  

  

  