﻿E. 
  WILSON 
  ON 
  THE 
  RHAETICS 
  OF 
  NOTTINGHAMSHIRE. 
  455 
  

  

  Avicula-Gontorta 
  shales 
  in 
  Notts 
  comes 
  on 
  the 
  same 
  horizon 
  as 
  the 
  

   middle 
  portion 
  of 
  that 
  series 
  at 
  Gainsboro'. 
  I 
  take 
  that 
  remarkable 
  

   pyritic 
  bone-bed 
  which 
  is 
  identical 
  in 
  character 
  and 
  appearance 
  at 
  

   Gainsboro' 
  and 
  Barnston 
  as 
  fixing 
  an 
  approximately 
  definite 
  horizon 
  

   in 
  the 
  Rhaetic 
  series. 
  From 
  this 
  bone-bed 
  upwards, 
  if 
  we 
  allow 
  

   evanescent 
  seams 
  of 
  sand 
  to 
  thicken 
  ont 
  into 
  thickish 
  beds 
  of 
  sand- 
  

   stone, 
  the 
  Stanton 
  section 
  roughly 
  corresponds 
  with 
  the 
  Gainsboro' 
  

   section. 
  Too 
  much 
  importance 
  must 
  not, 
  however, 
  be 
  ascribed 
  to 
  

   " 
  bone-beds 
  " 
  for 
  the 
  correlation 
  of 
  distant 
  sections. 
  In 
  this 
  in- 
  

   stance 
  the 
  close 
  similarity 
  of 
  these 
  bone-beds 
  is 
  due 
  to 
  such 
  a 
  very 
  

   variable 
  process 
  as 
  the 
  infiltration 
  of 
  mineral 
  matter 
  (bisulphide 
  of 
  

   iron). 
  It 
  must 
  also 
  be 
  remembered 
  that 
  a 
  bone-bed 
  may 
  be 
  in- 
  

   tensely 
  hard 
  and 
  pyritic 
  a 
  few 
  feet 
  below 
  the 
  surface 
  of 
  the 
  ground, 
  

   and 
  yet 
  quite 
  soft 
  and 
  friable 
  at 
  the 
  outcrop, 
  owing 
  to 
  atmospheric 
  

   decomposition 
  of 
  the 
  cementing 
  iron-pyrites. 
  This 
  is, 
  in 
  fact, 
  the 
  

   case 
  at 
  Barnston, 
  and 
  is, 
  no 
  doubt, 
  so 
  elsewhere. 
  Nor 
  is 
  it 
  to 
  be 
  

   supposed 
  that 
  bone-beds 
  in 
  distant 
  sections 
  at 
  about 
  the 
  same 
  hori- 
  

   zon 
  are 
  rigidly 
  homotaxial 
  ; 
  for 
  since 
  these 
  beds 
  were 
  in 
  all 
  proba- 
  

   bility 
  the 
  resulting 
  deposits 
  of 
  migratory 
  shoals, 
  and 
  not 
  of 
  a 
  uni- 
  

   versal 
  swarm 
  of 
  fishes, 
  a 
  certain 
  amount 
  of 
  time 
  must 
  be 
  allowed 
  

   for 
  their 
  transit 
  from 
  one 
  place 
  to 
  another. 
  

  

  Now, 
  as 
  I 
  have 
  already 
  said, 
  I 
  cannot 
  admit 
  that 
  the 
  green 
  marls, 
  

   which 
  in 
  this 
  and 
  the 
  adjoining 
  districts 
  come 
  below 
  the 
  Avicula- 
  

   contorta 
  shales, 
  belong 
  to 
  the 
  Rhaatic 
  series. 
  Eor, 
  whilst 
  there 
  is 
  

   always 
  a 
  sharp 
  stratigraphical 
  line 
  of 
  division, 
  with 
  in 
  some 
  cases 
  

   evidence 
  of 
  erosion, 
  between 
  the 
  green 
  marls 
  and 
  the 
  Paper-shales, 
  

   there 
  is 
  on 
  the 
  other 
  hand 
  every 
  appearance 
  of 
  a 
  gradation 
  between 
  

   the 
  green 
  marls 
  and 
  the 
  underlying 
  red 
  and 
  green 
  marls 
  of 
  the 
  

   Upper 
  Keuper 
  formation. 
  Again, 
  whilst 
  there 
  does 
  not 
  appear 
  to 
  

   be 
  any 
  essential 
  difference 
  in 
  textural 
  character 
  between 
  these 
  green 
  

   marls 
  which 
  come 
  at 
  the 
  top 
  of 
  the 
  Upper 
  Keuper 
  and 
  those 
  lower 
  

   down 
  in 
  that 
  series, 
  there 
  is 
  a 
  very 
  decided 
  textural 
  distinction 
  be- 
  

   tween 
  the 
  green 
  marls 
  and 
  the 
  overlying 
  Rhsetic 
  shales. 
  These 
  

   green 
  marls 
  are, 
  like 
  the 
  rest 
  of 
  the 
  Keuper 
  rocks, 
  practically 
  unfos- 
  

   siliferous 
  ; 
  whereas 
  with 
  the 
  very 
  commencement 
  of 
  the 
  A.-contorta 
  

   beds 
  we 
  get 
  evidence 
  of 
  the 
  incoming 
  of 
  a 
  decidedly 
  marine 
  fauna, 
  

   including 
  not 
  only 
  forms 
  of 
  life 
  that 
  characterize 
  the 
  Rhaetic 
  forma- 
  

   tion 
  of 
  Europe, 
  but 
  also 
  species 
  of 
  mollusca 
  and 
  reptilia 
  which 
  range 
  

   into 
  the 
  overlying 
  Liassic 
  strata. 
  For 
  these 
  reasons, 
  then, 
  I 
  am 
  of 
  

   opinion 
  that 
  in 
  Notts 
  and 
  the 
  adjacent 
  counties, 
  at 
  any 
  rate, 
  the 
  line 
  

   between 
  the 
  Rhaetics 
  and 
  the 
  Trias 
  should 
  be 
  taken 
  at 
  the 
  base, 
  not 
  

   of 
  the 
  green 
  marls, 
  but 
  of 
  the 
  Avieula-contorta 
  beds. 
  

  

  The 
  Rhsetic 
  rocks, 
  as 
  a 
  whole, 
  no 
  doubt, 
  form 
  a 
  stratigraphical 
  as 
  

   well 
  as 
  a 
  palaeontological 
  passage-series 
  between 
  the 
  Keuper 
  aud 
  the 
  

   Lias. 
  This 
  passage 
  is 
  apparent 
  at 
  some 
  places 
  in 
  the 
  West 
  of 
  Eng- 
  

   land, 
  e. 
  g. 
  in 
  the 
  splendid 
  coast-sections 
  at 
  Watchet 
  in 
  the 
  estuary 
  

   of 
  the 
  Severn. 
  There 
  no 
  hard 
  and 
  fast 
  line 
  can 
  be 
  drawn 
  between 
  

   the 
  Upper 
  Keuper 
  beds 
  and 
  the 
  Lower 
  Rhaetics 
  : 
  green 
  and 
  red 
  

   marls 
  may 
  be 
  seen 
  alternating 
  with 
  black 
  shales 
  ; 
  and 
  all 
  are 
  un- 
  

   questionably 
  as 
  much 
  Rhaetic 
  as 
  Keuper. 
  Beneath 
  these 
  " 
  passage- 
  

  

  