﻿COTTESWOLD, 
  MIDFORD, 
  AND 
  YEOVIL 
  SANDS, 
  ETC. 
  467 
  

  

  accompanied 
  by 
  conglomerate 
  and 
  signs 
  of 
  erosion, 
  is 
  also 
  very 
  clearly 
  

   marked 
  in 
  Normandy 
  as 
  indicated 
  in 
  his 
  figure 
  (No. 
  19) 
  p. 
  95. 
  In 
  

   this 
  is 
  shown 
  also 
  the 
  partial 
  extent 
  of 
  the 
  Humphriesianum-zone 
  (the 
  

   dotted 
  stratum). 
  Its 
  absence 
  at 
  Falaise 
  brings 
  the 
  Parkinsoni-zoue 
  

   in 
  contact 
  with 
  the 
  Maliere, 
  which 
  is 
  what 
  we 
  so 
  frequently 
  find 
  in 
  

   this 
  country. 
  In 
  fact, 
  if 
  we 
  omit 
  from 
  the 
  above-mentioned 
  diagram 
  

   the 
  conglomerate 
  and 
  the 
  signs 
  of 
  erosion, 
  if 
  we 
  substitute 
  Con- 
  

   cavum-beds 
  for 
  Maliere, 
  Sherborne 
  for 
  Bayeux, 
  and 
  Bradford 
  Abbas 
  

   for 
  Falaise, 
  and 
  imagine 
  Louse 
  Hill 
  situated 
  a 
  short 
  distance 
  from 
  

   the 
  latter 
  place, 
  we 
  have 
  exactly 
  the 
  position 
  of 
  the 
  Inferior- 
  Oolite 
  

   strata 
  in 
  Dorset, 
  as 
  well 
  as 
  their 
  extent 
  and 
  sequence. 
  It 
  may 
  be 
  

   remarked, 
  however, 
  that 
  in 
  Dorset 
  the 
  absence 
  of 
  any 
  particular 
  beds 
  

   is 
  not 
  necessarily 
  attended 
  with 
  signs 
  of 
  erosion. 
  Lithologically 
  

   there 
  may 
  be 
  little 
  to 
  indicate 
  the 
  absence 
  of 
  even 
  a 
  considerable 
  

   series 
  (page 
  447). 
  

  

  How 
  the 
  matter 
  stands 
  lithologically 
  for 
  the 
  commencement 
  of 
  

   the 
  Toarcian 
  I 
  cannot 
  say, 
  because 
  I 
  have 
  not 
  studied 
  the 
  Liassic 
  

   strata 
  with 
  that 
  minute 
  analysis 
  necessary 
  to 
  grapple 
  with 
  such 
  a 
  

   task; 
  bat 
  in 
  the 
  South-Western 
  counties 
  I 
  know 
  we 
  have 
  a 
  marked 
  

   lithological 
  change 
  from 
  the 
  hard 
  Marlstone 
  of 
  the 
  Middle 
  Lias 
  to 
  the 
  

   clays 
  of 
  the 
  Falciferam-zone 
  ; 
  and 
  this 
  line 
  corresponds 
  with 
  a 
  line 
  of 
  

   division 
  at 
  present 
  in 
  use. 
  In 
  passing 
  1 
  would 
  note 
  that 
  in 
  draw- 
  

   ing 
  dividing-lines 
  we 
  must 
  have 
  regard 
  to 
  what 
  will 
  suit 
  Continental 
  

   strata 
  as 
  well 
  as 
  our 
  own 
  ; 
  that 
  whatever 
  lines 
  we 
  adopt 
  will 
  certainly 
  

   be 
  bridged 
  over 
  more 
  or 
  less 
  in 
  some 
  places 
  ; 
  and 
  that 
  all 
  that 
  we 
  

   can 
  hope 
  is 
  to 
  choose, 
  as 
  the 
  limits 
  of 
  our 
  divisions, 
  lines 
  which 
  can 
  

   be 
  drawn 
  with 
  the 
  most 
  ease 
  over 
  the 
  greatest 
  extent 
  of 
  country. 
  

   Such 
  I 
  claim 
  for 
  the 
  Toarcian. 
  

  

  The 
  following 
  is 
  a 
  general 
  description 
  of 
  the 
  strata 
  for 
  which 
  the 
  

   term 
  " 
  Toarcian 
  " 
  is 
  proposed. 
  

  

  A 
  variable 
  series 
  of 
  clay, 
  sand, 
  and 
  limestone, 
  during 
  the 
  formation 
  

   of 
  which 
  the 
  Ammonite-family 
  Hildoceratidee 
  was 
  dominant, 
  and 
  

   which 
  series, 
  practically 
  speaking, 
  corresponds 
  in 
  its 
  duration 
  with 
  

   the 
  beginning 
  and 
  ending 
  of 
  the 
  majority 
  of 
  members 
  of 
  that 
  family. 
  

  

  The 
  series 
  comprises 
  the 
  period 
  from 
  the 
  Falciferum-zone 
  to 
  the 
  

   Concavum-zone 
  inclusive. 
  

  

  In 
  England 
  the 
  series 
  usually 
  consists 
  of 
  clay 
  at 
  the 
  base, 
  yellow 
  

   sands 
  in 
  the 
  middle, 
  and 
  oolitic 
  limestone 
  at 
  the 
  top 
  ; 
  but 
  the 
  sands 
  

   may 
  be 
  absent 
  ; 
  while 
  clayey 
  or 
  marly 
  conditions 
  may 
  be 
  partially 
  

   reproduced 
  at 
  the 
  very 
  top 
  (Dundry, 
  Corton 
  Downs). 
  

  

  In 
  the 
  south-western 
  parts 
  of 
  the 
  Jurassic 
  development 
  (counties 
  

   of 
  Gloucester, 
  Somerset, 
  and 
  Dorset) 
  the 
  duration 
  of 
  the 
  clay 
  is 
  very 
  

   variable. 
  It 
  may 
  cease, 
  giving 
  place 
  to 
  sands, 
  before 
  the 
  end 
  of 
  the 
  

   Com?7iune-zone, 
  or 
  may 
  last 
  into 
  the 
  middle 
  of 
  the 
  Jurense-zone 
  

   before 
  it 
  gives 
  way. 
  The 
  period 
  of 
  sand-deposit 
  is 
  very 
  variable 
  ; 
  

   it 
  may 
  exist 
  from 
  the 
  middle 
  of 
  the 
  Commune-zone 
  to 
  the 
  middle 
  of 
  

   the 
  Jurense-zone, 
  or 
  from 
  the 
  middle 
  of 
  the 
  latter 
  zone 
  to 
  the 
  middle 
  

   of 
  the 
  Opalinum-zone. 
  The 
  oolitic 
  limestone, 
  too, 
  may 
  begin 
  in 
  the 
  

   middle 
  of 
  the 
  Jurense-zone, 
  or 
  may 
  not 
  begin 
  till 
  nearly 
  the 
  end 
  of 
  

   the 
  Opalinum-zone. 
  Argillaceous 
  marl 
  mixed 
  with 
  some 
  limestone 
  

   may 
  reappear 
  in 
  the 
  Murchisonce- 
  and 
  Concavum-zones. 
  

  

  2l2 
  

  

  