﻿586 
  ME. 
  G. 
  W. 
  LAMPLUGH 
  ON 
  THE 
  

  

  markings 
  in 
  various 
  tints 
  of 
  grey, 
  green, 
  blue, 
  and 
  brown, 
  showing 
  

   dark 
  in 
  the 
  paler 
  beds, 
  and 
  pale 
  in 
  the 
  darker. 
  In 
  a 
  thin 
  seam 
  at 
  

   the 
  base 
  of 
  the 
  band 
  this 
  structure 
  is 
  particularly 
  well 
  developed, 
  

   the 
  markings 
  being 
  of 
  a 
  bright 
  blue 
  colour 
  on 
  a 
  dark 
  blue 
  ground. 
  

   Many 
  beds 
  higher 
  in 
  the 
  section 
  show 
  the 
  same 
  peculiarity, 
  

   though 
  not 
  often 
  so 
  definitely. 
  

  

  Small 
  black 
  coprolitic 
  " 
  pebbles 
  " 
  occur 
  sporadically 
  throughout 
  this 
  

   band. 
  Belemnites 
  lateralis 
  abounds, 
  sometimes 
  attaining 
  a 
  large 
  size, 
  

   and 
  both 
  large 
  and 
  small 
  specimens 
  are 
  excellently 
  preserved. 
  The 
  

   other 
  fossils, 
  chiefly 
  bivalves, 
  are, 
  however, 
  in 
  the 
  form 
  of 
  soft 
  crushed 
  

   casts, 
  and 
  though 
  they 
  are 
  by 
  no 
  means 
  rare, 
  there 
  is 
  great 
  difficulty 
  

   in 
  obtaining 
  determinations 
  of 
  them. 
  

  

  Similar 
  though 
  usually 
  somewhat 
  less 
  conspicuous 
  bands 
  of 
  pale 
  

   blue 
  or 
  grey 
  clay 
  constantly 
  recur 
  in 
  all 
  parts 
  of 
  the 
  series 
  at 
  Spee- 
  

   ton, 
  as 
  will 
  be 
  seen 
  from 
  the 
  other 
  sections. 
  These 
  pale 
  clays 
  

   are 
  always 
  tougher 
  than 
  the 
  dark 
  beds, 
  and 
  do 
  not 
  so 
  readily 
  splinter 
  

   or 
  " 
  shale." 
  They 
  probably 
  contain 
  a 
  larger 
  amount 
  of 
  lime, 
  and 
  

   nearly 
  always 
  show 
  a 
  tendency 
  to 
  develop 
  bands 
  of 
  nodules. 
  These 
  

   nodules 
  are 
  sometimes 
  small 
  ovoid 
  or 
  potato-shaped. 
  masses 
  with 
  a 
  

   soft 
  brown 
  exterior 
  but 
  hard 
  and 
  dark 
  within, 
  with 
  crystals 
  of 
  

   selenite 
  and 
  pyrites 
  lining 
  thin 
  septa 
  ; 
  or 
  the}'' 
  form 
  much 
  larger 
  

   irregular 
  masses 
  of 
  hard 
  pale 
  blue 
  or 
  grey 
  limestone, 
  generally 
  

   with 
  strongly 
  marked 
  septa 
  of 
  yellowish 
  calcite. 
  The 
  "potato- 
  

   nodules 
  " 
  do 
  not, 
  as 
  a 
  rule, 
  contain 
  fossils, 
  but 
  the 
  limestone 
  septaria 
  

   at 
  certain 
  horizons 
  often 
  include 
  large 
  but 
  generally 
  imperfectly 
  

   preserved 
  specimens 
  of 
  Crioceras 
  (Ancyloceras) 
  or 
  Ammonites, 
  and 
  

   sometimes 
  other 
  fossils 
  also. 
  

  

  In 
  the 
  dark 
  clays 
  B 
  o, 
  which 
  succeed 
  the 
  pale 
  blue 
  bed, 
  fossils 
  

   are 
  rare, 
  but 
  the 
  horizon 
  is 
  characterized 
  by 
  the 
  relative 
  abundance 
  

   of 
  a 
  Lingula 
  (L. 
  ovalis 
  ?), 
  and 
  we 
  might 
  therefore 
  name 
  it 
  the 
  

   Lingula-hed.. 
  Belemnites 
  lateralis 
  occurs 
  in 
  this 
  bed 
  in 
  a 
  curiously 
  

   decayed 
  state, 
  the 
  exterior 
  being 
  deeply 
  eroded, 
  while 
  the 
  interior, 
  

   instead 
  of 
  showing 
  the 
  usual 
  clear 
  horn-like 
  appearance, 
  is 
  quite 
  

   opaque 
  and 
  white. 
  

  

  A 
  thin 
  pale 
  band 
  separates 
  the 
  Linc/ula-bed 
  from 
  the 
  next 
  division 
  

   of 
  importance. 
  This 
  is 
  a 
  thick 
  bed 
  of 
  splintery 
  brownish 
  clay 
  (B 
  4), 
  

   very 
  full 
  of 
  pyrites 
  disseminated 
  through 
  the 
  mass 
  in 
  minute 
  crystals 
  

   and 
  groups 
  of 
  crystals, 
  which 
  from 
  its 
  thickness 
  and 
  the 
  abundance 
  

   of 
  its 
  fossils 
  is 
  the 
  chief 
  member 
  of 
  the 
  zone. 
  Yet 
  though 
  fossils 
  

   are 
  here 
  so 
  plentiful, 
  especially 
  in 
  the 
  upper 
  part 
  of 
  the 
  bed, 
  it 
  is 
  

   only 
  when 
  the 
  clay 
  is 
  examined 
  in 
  a 
  fresh 
  exposure 
  on 
  the 
  shore 
  or 
  

   at 
  the 
  foot 
  of 
  the 
  cliff 
  that 
  this 
  becomes 
  evident, 
  as 
  the 
  rapid 
  

   decomposition 
  of 
  the 
  pyrites 
  coats 
  the 
  weathered 
  surfaces 
  of 
  the 
  

   bed 
  with 
  a 
  whitish 
  efflorescence, 
  and 
  rapidly 
  destroys 
  all 
  except 
  the 
  

   coarser 
  forms. 
  During 
  the 
  process 
  fine 
  crystals 
  of 
  selenite 
  are 
  

   sometimes 
  produced. 
  

  

  Judd 
  has 
  described 
  these 
  beds 
  as 
  the 
  " 
  zone 
  of 
  Amm. 
  Astierianus^ 
  

   but 
  I 
  have 
  not 
  yet 
  been 
  able 
  to 
  detect 
  any 
  undoubted 
  specimen 
  of 
  

   that 
  species 
  in 
  any 
  bed 
  within 
  the 
  zone 
  of 
  Bel. 
  lateralis. 
  A 
  small 
  

  

  