﻿444 
  THE 
  MORTE 
  SLATES 
  AND 
  ASSOCIATED 
  BEDS. 
  [Aug. 
  1 
  897, 
  

  

  known 
  to 
  occur 
  in 
  the 
  Devonian, 
  but 
  agree 
  well 
  with 
  fossils 
  which 
  

   occur 
  in 
  the 
  Silurian 
  rocks 
  in 
  other 
  areas, 
  especially 
  in 
  Pembroke- 
  

   shire, 
  on 
  the 
  opposite 
  side 
  of 
  the 
  Bristol 
  Channel. 
  Up 
  to 
  the 
  

   present, 
  four 
  well-marked 
  zones 
  have 
  been 
  made 
  out, 
  two 
  in 
  North 
  

   Devon 
  and 
  two 
  in 
  West 
  Somerset. 
  Few 
  fossils 
  appear 
  to 
  range 
  

   from 
  one 
  zone 
  to 
  the 
  other, 
  and 
  none 
  between 
  the 
  zones 
  in 
  North 
  

   Devon 
  and 
  those 
  in 
  West 
  Somerset, 
  which 
  latter 
  appear 
  to 
  be 
  on 
  

   higher 
  horizons 
  than 
  any 
  as 
  yet 
  discovered 
  in 
  North 
  Devon. 
  In 
  so 
  

   great 
  a 
  thickness 
  of 
  beds, 
  however, 
  there 
  is 
  a 
  possibility 
  that 
  other 
  

   zones 
  may 
  yet 
  be 
  found, 
  as 
  the 
  nature 
  of 
  the 
  sediments 
  would 
  lead 
  

   one 
  to 
  suppose 
  that 
  there 
  is 
  a 
  gradual 
  passage 
  from 
  the 
  lower 
  

   (Silurian) 
  to 
  the 
  higher 
  (Lower 
  Devonian) 
  slates, 
  and 
  that 
  if 
  there 
  

   is 
  a 
  physical 
  break 
  in 
  the 
  succession 
  it 
  must 
  be 
  above 
  these 
  slates. 
  

   The 
  presence 
  of 
  typical 
  Lower 
  Devonian 
  fossils 
  in 
  the 
  slates 
  of 
  

   West 
  Somerset 
  is 
  a 
  fact 
  of 
  great 
  importance, 
  for 
  it 
  shows 
  that 
  there, 
  

   as 
  in 
  North 
  Devon, 
  the 
  oldest 
  beds 
  occur 
  in 
  the 
  centre 
  of 
  the 
  area, 
  

   and 
  that 
  there 
  cannot 
  be 
  a 
  regular 
  upward 
  succession, 
  as 
  has 
  been 
  

   supposed, 
  from 
  north 
  to 
  south. 
  Indeed, 
  there 
  are 
  numerous 
  ex- 
  

   posures 
  which 
  indicate 
  that 
  the 
  beds 
  are 
  thrown 
  off 
  to 
  the 
  north 
  

   and 
  to 
  the 
  south 
  from 
  this 
  central 
  axis. 
  The 
  questions 
  relating 
  to 
  the 
  

   comparative 
  age 
  of 
  the 
  beds 
  north 
  of 
  this 
  axis 
  and 
  that 
  of 
  those 
  on 
  

   the 
  south 
  have 
  not, 
  at 
  present, 
  been 
  completely 
  worked 
  out 
  ; 
  but 
  

   that 
  they 
  are 
  in 
  each 
  case 
  newer 
  than 
  the 
  typical 
  beds 
  of 
  the 
  central 
  

   axis 
  is 
  abundantly 
  clear. 
  In 
  the 
  Ilfracombe 
  Beds 
  on 
  the 
  north 
  and 
  

   the 
  Pilton 
  Beds 
  on 
  the 
  south 
  there 
  appear 
  to 
  be 
  several 
  fossils 
  in 
  

   common, 
  but 
  none 
  between 
  either 
  of 
  these 
  and 
  those 
  of 
  the 
  so-called 
  

   Morte 
  Slates 
  which 
  form 
  the 
  axis. 
  So 
  important 
  a 
  difference 
  in 
  

   the 
  faunas 
  could 
  not 
  have 
  occurred 
  unless 
  the 
  beds 
  were 
  on 
  markedly 
  

   different 
  horizons. 
  The 
  beds, 
  therefore, 
  classed 
  as 
  Morte 
  Slates 
  

   in 
  North 
  Devon 
  and 
  in 
  West 
  Somerset 
  cannot, 
  in 
  future, 
  be 
  placed 
  

   as 
  passage-beds 
  between 
  Middle 
  and 
  Upper 
  Devonian, 
  but 
  must 
  be 
  

   looked 
  upon 
  as 
  older 
  than, 
  and 
  in 
  each 
  area 
  as 
  underlying, 
  the 
  

   Middle 
  Devonian 
  Beds. 
  

  

  If 
  the 
  fossils 
  found 
  at 
  Treborough 
  and 
  at 
  Oakhampton 
  be 
  com- 
  

   pared 
  with' 
  those 
  found 
  in 
  the 
  well-known 
  Lower 
  Devonian 
  in 
  the 
  

   Rhenish 
  area, 
  we 
  find 
  that 
  the 
  Treborough 
  fossils 
  (Chonetes 
  sarci- 
  

   nulata, 
  Ch. 
  plebeia, 
  etc.) 
  occur 
  there 
  in 
  the 
  lowest 
  beds 
  ; 
  and 
  that 
  

   Cryplueus 
  laciniatus, 
  which 
  is 
  a 
  characteristic 
  Oakhampton 
  Quarry 
  

   fossil, 
  occurs 
  in 
  the 
  Rhenish 
  area 
  in 
  higher 
  beds 
  of 
  the 
  Lower 
  

   Devonian. 
  1 
  

  

  I 
  1 
  Since 
  the 
  reading 
  of 
  this 
  paper 
  our 
  attention 
  has 
  been 
  directed 
  to 
  the 
  

   following 
  passage 
  in 
  M. 
  D. 
  P. 
  CEhlert's 
  paper 
  on 
  the 
  ' 
  Devonian 
  Fossils 
  of 
  

   Santa 
  Lucia' 
  (Bull. 
  Soc. 
  geol. 
  France, 
  ser. 
  3, 
  vol. 
  xxiv. 
  1896, 
  p. 
  841) 
  : 
  — 
  

  

  ' 
  If 
  we 
  consider 
  the 
  vertical 
  and 
  horizontal 
  distribution 
  of 
  the 
  genus 
  

   CryphcBus, 
  we 
  are 
  at 
  first 
  eight 
  struck 
  by 
  the 
  fact 
  that 
  it 
  is 
  more 
  especially 
  

   localized 
  in 
  the 
  Coblentzian 
  and 
  the 
  Eifelian. 
  In 
  fact, 
  it 
  is 
  characteristic 
  of 
  

   the 
  strata 
  of 
  that 
  age 
  in 
  the 
  Rhenish 
  area, 
  and 
  is 
  also 
  found 
  in 
  the 
  deposits 
  

   with 
  Hercynian 
  facies 
  of 
  the 
  Harz. 
  On 
  the 
  other 
  hand, 
  it 
  has 
  not 
  been 
  

   recorded 
  in 
  Bohemia 
  in 
  the 
  beds 
  above 
  stage 
  E. 
  In 
  the 
  Ardenne 
  Cryph&us 
  is 
  

   unknown, 
  and 
  in 
  England 
  this 
  group 
  is 
  represented 
  by 
  only 
  one 
  species, 
  quoted 
  

   ;»nd 
  figured 
  by 
  Salter, 
  which 
  moreover 
  appears 
  to 
  be 
  a 
  rarity. 
  In 
  the 
  West 
  of 
  

  

  