﻿SUBDIVISIONS 
  OF 
  THE 
  SPEETON 
  CLAY. 
  589 
  

  

  waters. 
  It 
  seems 
  as 
  though, 
  during 
  the 
  slow 
  formation 
  of 
  this 
  bed, 
  

   some 
  physical 
  change 
  had 
  taken 
  place 
  which 
  rendered 
  the 
  area 
  unfit 
  

   for 
  its 
  former 
  occupants 
  and 
  permitted 
  a 
  sudden 
  and 
  vigorous 
  inva- 
  

   sion 
  of 
  fresh 
  forms 
  from 
  other 
  waters. 
  

  

  With 
  Belemnites 
  jaculum 
  appears 
  Ammonites 
  noricus 
  — 
  or, 
  rather, 
  

   the 
  Ammonite 
  immediately 
  precedes 
  the 
  Belemnite, 
  for 
  it 
  is 
  found 
  in 
  

   abundance 
  in 
  the 
  Compound 
  Nodules 
  associated 
  with 
  B. 
  lateralis, 
  

   though 
  not 
  lower. 
  Like 
  B. 
  jaculum, 
  it 
  comes 
  in 
  quite 
  suddenly, 
  and 
  

   seems 
  almost 
  immediately 
  to 
  attain 
  its 
  maximum 
  development 
  with 
  

   respect 
  both 
  to 
  size 
  and 
  numbers. 
  About 
  a 
  foot 
  above 
  the 
  nodules 
  

   there 
  is 
  an 
  almost 
  continuous 
  layer 
  of 
  large 
  Ammonites 
  apparently 
  

   of 
  this 
  species, 
  badly 
  preserved 
  as 
  soft 
  impressions 
  in 
  the 
  clay, 
  some 
  

   of 
  them 
  measuring 
  considerably 
  over 
  a 
  foot 
  in 
  diameter. 
  In 
  the 
  

   higher 
  beds 
  of 
  its 
  range 
  it 
  is 
  rare 
  to 
  find 
  Amm. 
  noricus 
  exceeding 
  

   two 
  or 
  three 
  inches. 
  

  

  The 
  Compound 
  Nodular 
  Band 
  is 
  one 
  of 
  the 
  best, 
  if 
  not 
  the 
  best 
  

   horizon 
  for 
  fossils 
  in 
  the 
  whole 
  section. 
  Remains 
  of 
  Saurians 
  

   are 
  comparatively 
  so 
  abundant 
  in 
  it 
  that 
  within 
  the 
  space 
  of 
  the 
  

   short 
  outcrop 
  which 
  can 
  be 
  examined 
  I 
  have 
  thrice 
  found 
  a 
  mass 
  of 
  

   bones 
  indicating 
  the 
  occurrence 
  of 
  a 
  more 
  or 
  less 
  complete 
  skeleton. 
  

  

  Large 
  specimens 
  of 
  Ammonites 
  (other 
  than 
  Amm. 
  noricus, 
  but 
  as 
  

   yet 
  undetermined) 
  and 
  Crioceras 
  also 
  occur 
  in 
  the 
  larger 
  concretions. 
  

   This 
  is 
  the 
  lowest 
  level 
  to 
  which 
  I 
  have 
  traced 
  the 
  last-named 
  

   genus, 
  so 
  plentiful 
  in 
  the 
  overlying 
  beds. 
  

  

  At 
  page 
  591 
  will 
  be 
  found 
  a 
  list 
  of 
  the 
  fossils 
  already 
  recognized 
  

   from 
  the 
  zone 
  of 
  Bel. 
  lateralis 
  (including 
  " 
  the 
  Coprolite-bed"), 
  in 
  

   which 
  also 
  are 
  indicated 
  those 
  found 
  in 
  the 
  Compound 
  Nodular 
  Band 
  

   and 
  the 
  surrounding 
  clay. 
  

  

  That 
  this 
  Compound 
  Nodular 
  Band 
  is 
  the 
  same 
  as 
  Bed 
  No. 
  9 
  

   of 
  Leckenby 
  "s 
  section 
  is 
  placed 
  beyond 
  doubt 
  by 
  the 
  fossils 
  that 
  he 
  

   gives 
  from 
  the 
  beds 
  above 
  and 
  below 
  ; 
  Bel. 
  jaculum 
  and 
  Amm. 
  regalis 
  

   (=Amm. 
  noricus) 
  in 
  the 
  one 
  position, 
  and 
  Gryphcea 
  sinuata 
  (=Exo- 
  

   gyra 
  sinuata) 
  and 
  Astarie 
  sinuata, 
  Bean 
  (evidently 
  a 
  misprint 
  for 
  

   Astarte 
  senecta), 
  are 
  conclusive 
  on 
  this 
  point. 
  And 
  it 
  is 
  equally 
  clear 
  

   that 
  it 
  is 
  to 
  this 
  band, 
  and 
  not 
  to 
  the 
  true 
  Coprolite-bed, 
  that 
  

   Leckenby 
  refers 
  in 
  his 
  note 
  in 
  Dr. 
  T. 
  Wright's 
  ' 
  Monograph 
  ' 
  * 
  as 
  a 
  

   " 
  band 
  of 
  pseudo-coprolites 
  " 
  forming 
  a 
  " 
  line 
  of 
  demarcation 
  " 
  

   " 
  distinct 
  and 
  clear 
  " 
  between 
  the 
  Jurassic 
  and 
  Cretaceous 
  parts 
  of 
  

   the 
  section. 
  

  

  The 
  question 
  therefore 
  now 
  arises, 
  whether 
  the 
  beds 
  in 
  which 
  

   the 
  coronated 
  Ammonites 
  are 
  found 
  should 
  be 
  relegated 
  to 
  the 
  

   Portlandian. 
  If 
  so, 
  we 
  must 
  follow 
  Leckenby 
  in 
  tracing 
  the 
  

   division 
  between 
  the 
  Lower 
  Cretaceous 
  and 
  the 
  Jurassic 
  at 
  the 
  

   Compound 
  Nodular 
  Band. 
  But 
  by 
  so 
  doing 
  we 
  include 
  clays 
  con- 
  

   taining 
  a 
  few 
  species 
  which 
  are 
  not 
  usually 
  recognized 
  as 
  Jurassic, 
  

   such 
  as 
  Belemnites 
  lateralis 
  and 
  Exogyra 
  sinuata 
  f 
  . 
  

  

  * 
  Mon. 
  Brit. 
  Cret. 
  Echinod. 
  pt. 
  i. 
  p. 
  9, 
  Pal. 
  Soc. 
  xxi. 
  

  

  t 
  It 
  will 
  be 
  noticed 
  that 
  most 
  of 
  the 
  Neocomian 
  species 
  given 
  in 
  the 
  list 
  at 
  

   p. 
  591 
  have 
  been 
  found 
  only 
  in 
  the 
  Compound 
  Nodular 
  Band, 
  and 
  not 
  lower. 
  

  

  