﻿DEVOXO-STLURIAN 
  FORMATION. 
  203 
  

  

  order 
  to 
  show 
  what 
  a 
  wide 
  interval 
  of 
  time 
  separates 
  the 
  beds 
  

   usually 
  called 
  " 
  Upper 
  " 
  and 
  " 
  Lower 
  " 
  Old 
  Bed 
  Sandstone. 
  The 
  

   grouping 
  together 
  under 
  the 
  same 
  name 
  of 
  two 
  sets 
  of 
  strata 
  actually 
  

   separated 
  by 
  a 
  whole 
  formation 
  of 
  such 
  importance 
  as 
  the 
  Devonian 
  

   has 
  no 
  .parallel 
  in 
  geological 
  nomenclature, 
  and 
  can 
  only 
  be 
  a 
  source 
  

   of 
  confusion 
  to 
  the 
  mind 
  when 
  endeavouring 
  to 
  grasp 
  the 
  order 
  of 
  

   succession 
  of 
  geological 
  periods. 
  It 
  is 
  time, 
  therefore; 
  that 
  we 
  

   should 
  adopt 
  some 
  designation 
  that 
  will 
  in 
  itself 
  exclude 
  the 
  idea 
  of 
  

   association. 
  

  

  I 
  shall 
  now 
  enumerate 
  the 
  localities 
  for 
  these 
  beds 
  in 
  the 
  same 
  

   order 
  as 
  that 
  adopted 
  for 
  the 
  beds 
  of 
  the 
  Old 
  Red 
  Sandstone, 
  com- 
  

   mencing 
  with 
  the 
  Continent. 
  

  

  Localities 
  of 
  the 
  Devono- 
  Silurian 
  Formation. 
  

  

  («) 
  Continental. 
  — 
  Owing 
  to 
  the 
  hiatus, 
  or 
  discordancy, 
  which 
  

   exists 
  in 
  Belgium 
  and 
  France 
  at 
  the 
  base 
  of 
  the 
  Devonian 
  series, 
  

   there 
  are 
  no 
  passage-beds 
  into 
  the 
  Upper 
  Silurian, 
  which 
  is 
  generally 
  

   altogether 
  absent 
  ; 
  and 
  the 
  Devonian 
  beds, 
  with 
  conglomerates 
  at 
  

   different 
  geological 
  horizons, 
  rest 
  on 
  an 
  old 
  shelving 
  shore 
  of 
  Lower 
  

   Silurian 
  or 
  Cambrian 
  grits 
  and 
  schists*. 
  It 
  is 
  probable, 
  however, 
  

   that 
  the 
  Devono-Silurian 
  series 
  may 
  be 
  represented 
  by 
  the 
  lower 
  

   part 
  of 
  the 
  " 
  Systeme 
  gedinnien 
  " 
  (in 
  part) 
  of 
  Dumont, 
  or 
  the 
  

   " 
  Couches 
  de 
  Gedinne 
  " 
  of 
  Gosselet. 
  

  

  (b) 
  Devonshire. 
  — 
  This 
  formation 
  is 
  represented 
  by 
  the 
  Foreland 
  

   grits 
  and 
  slates 
  lying 
  below 
  the 
  Lynton 
  slates 
  and 
  limestones 
  with 
  

   Lower-Devonian 
  fossils, 
  which 
  are 
  largely 
  distinctive. 
  In 
  former 
  

   papers 
  I 
  have 
  assumed, 
  from 
  considerations 
  stated 
  at 
  length, 
  that 
  

   these 
  beds 
  represent 
  both 
  the 
  Glengariff 
  Grits 
  and 
  Slates 
  of 
  Ireland 
  

   and 
  the 
  "passage-beds" 
  of 
  South 
  Wales 
  and 
  Hereford 
  — 
  a 
  view 
  origi- 
  

   nally 
  suggested 
  by 
  Professor 
  Jukes, 
  and 
  supported 
  in 
  his 
  recent 
  

   Presidential 
  Address 
  by 
  Mr. 
  Etheridgef. 
  These 
  beds 
  consist 
  of 
  

   hard, 
  massive, 
  red, 
  purple, 
  and 
  grey 
  grits, 
  sometimes 
  conglomeratic, 
  

   and 
  with 
  irregular 
  bands 
  of 
  slate. 
  Their 
  base 
  is 
  invisible, 
  being- 
  

   covered 
  by 
  the 
  waters 
  of 
  the 
  Severn. 
  They 
  are 
  separated 
  from 
  the 
  

   Old 
  Red 
  Sandstone 
  by 
  several 
  thousand 
  feet 
  of 
  strata, 
  composed 
  of 
  

   the 
  Lynton, 
  Hangman, 
  Ilfracombe, 
  and 
  Morthoe 
  groups. 
  Their 
  

   only 
  fossils 
  are 
  Fucoids 
  and 
  Annelid-markings 
  or 
  burrows 
  ; 
  and 
  the}' 
  

   are 
  laid 
  open 
  in 
  sections 
  of 
  the 
  coast 
  near 
  Lynton 
  and 
  Minehead 
  %. 
  

   From 
  their 
  position 
  below 
  the 
  base 
  of 
  the 
  whole 
  Devonian 
  series, 
  

   as 
  well 
  as 
  on 
  general 
  grounds, 
  we 
  are 
  warranted 
  in 
  assuming 
  that 
  

   these 
  beds 
  form 
  the 
  connecting 
  link 
  between 
  the 
  Devonian 
  and 
  

   Silurian 
  series 
  §. 
  

  

  ward 
  regarding 
  the 
  representative 
  strata 
  of 
  Devonshire 
  and 
  other 
  parts 
  of 
  the 
  

   British 
  Islands, 
  it 
  is 
  scarcely 
  necessary 
  for 
  me 
  any 
  further 
  to 
  insist 
  on 
  them 
  here. 
  

  

  * 
  Mourlon, 
  ' 
  Geol. 
  de 
  la 
  Belgique,' 
  pp. 
  31 
  & 
  51. 
  

  

  t 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxxvii. 
  

  

  \ 
  Ibid. 
  vol. 
  xxxvii. 
  p. 
  196 
  ; 
  also 
  Proc. 
  Roy. 
  Dublin 
  Soc. 
  vol. 
  i. 
  New 
  Series, 
  

   pp. 
  136-38. 
  

  

  § 
  The 
  position 
  of 
  these 
  beds 
  is 
  very 
  well 
  represented 
  on 
  Mr. 
  Ussher's 
  Geo- 
  

   logical 
  Map 
  of 
  Devonshire, 
  which 
  was 
  exhibited 
  at 
  the 
  Meeting 
  of 
  the 
  British 
  

   Association 
  at 
  York 
  (Section 
  C). 
  

  

  